path: root/src/sentinel.c

/* Redis Sentinel implementation
 *
 * Copyright (c) 2009-2012, Salvatore Sanfilippo <antirez at gmail dot com>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   * Redistributions of source code must retain the above copyright notice,
 *     this list of conditions and the following disclaimer.
 *   * Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *   * Neither the name of Redis nor the names of its contributors may be used
 *     to endorse or promote products derived from this software without
 *     specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include "server.h"
#include "hiredis.h"
#ifdef USE_OPENSSL
#include "openssl/ssl.h"
#include "hiredis_ssl.h"
#endif
#include "async.h"

#include <ctype.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <fcntl.h>

extern char **environ;

#ifdef USE_OPENSSL
extern SSL_CTX *redis_tls_ctx;
extern SSL_CTX *redis_tls_client_ctx;
#endif

#define REDIS_SENTINEL_PORT 26379

/* ======================== Sentinel global state =========================== */

/* Address object, used to describe an ip:port pair. */
typedef struct sentinelAddr {
    char *hostname;         /* Hostname OR address, as specified */
    char *ip;               /* Always a resolved address */
    int port;
} sentinelAddr;

/* A Sentinel Redis Instance object is monitoring. */
#define SRI_MASTER  (1<<0)
#define SRI_SLAVE   (1<<1)
#define SRI_SENTINEL (1<<2)
#define SRI_S_DOWN (1<<3)   /* Subjectively down (no quorum). */
#define SRI_O_DOWN (1<<4)   /* Objectively down (confirmed by others). */
#define SRI_MASTER_DOWN (1<<5) /* A Sentinel with this flag set thinks that
                                   its master is down. */
#define SRI_FAILOVER_IN_PROGRESS (1<<6) /* Failover is in progress for
                                           this master. */
#define SRI_PROMOTED (1<<7)            /* Slave selected for promotion. */
#define SRI_RECONF_SENT (1<<8)     /* SLAVEOF <newmaster> sent. */
#define SRI_RECONF_INPROG (1<<9)   /* Slave synchronization in progress. */
#define SRI_RECONF_DONE (1<<10)     /* Slave synchronized with new master. */
#define SRI_FORCE_FAILOVER (1<<11)  /* Force failover with master up. */
#define SRI_SCRIPT_KILL_SENT (1<<12) /* SCRIPT KILL already sent on -BUSY */
#define SRI_MASTER_REBOOT  (1<<13)   /* Master was detected as rebooting */

/* Note: times are in milliseconds. */
#define SENTINEL_PING_PERIOD 1000

static mstime_t sentinel_info_period = 10000;
static mstime_t sentinel_ping_period = SENTINEL_PING_PERIOD;
static mstime_t sentinel_ask_period = 1000;
static mstime_t sentinel_publish_period = 2000;
static mstime_t sentinel_default_down_after = 30000;
static mstime_t sentinel_tilt_trigger = 2000;
static mstime_t sentinel_tilt_period = SENTINEL_PING_PERIOD * 30;
static mstime_t sentinel_slave_reconf_timeout = 10000;
static mstime_t sentinel_min_link_reconnect_period = 15000;
static mstime_t sentinel_election_timeout = 10000;
static mstime_t sentinel_script_max_runtime = 60000;  /* 60 seconds max exec time. */
static mstime_t sentinel_script_retry_delay = 30000;  /* 30 seconds between retries. */
static mstime_t sentinel_default_failover_timeout = 60*3*1000;

#define SENTINEL_HELLO_CHANNEL "__sentinel__:hello"
#define SENTINEL_DEFAULT_SLAVE_PRIORITY 100
#define SENTINEL_DEFAULT_PARALLEL_SYNCS 1
#define SENTINEL_MAX_PENDING_COMMANDS 100

#define SENTINEL_MAX_DESYNC 1000
#define SENTINEL_DEFAULT_DENY_SCRIPTS_RECONFIG 1
#define SENTINEL_DEFAULT_RESOLVE_HOSTNAMES 0
#define SENTINEL_DEFAULT_ANNOUNCE_HOSTNAMES 0

/* Failover machine different states. */
#define SENTINEL_FAILOVER_STATE_NONE 0  /* No failover in progress. */
#define SENTINEL_FAILOVER_STATE_WAIT_START 1  /* Wait for failover_start_time*/
#define SENTINEL_FAILOVER_STATE_SELECT_SLAVE 2 /* Select slave to promote */
#define SENTINEL_FAILOVER_STATE_SEND_SLAVEOF_NOONE 3 /* Slave -> Master */
#define SENTINEL_FAILOVER_STATE_WAIT_PROMOTION 4 /* Wait slave to change role */
#define SENTINEL_FAILOVER_STATE_RECONF_SLAVES 5 /* SLAVEOF newmaster */
#define SENTINEL_FAILOVER_STATE_UPDATE_CONFIG 6 /* Monitor promoted slave. */

#define SENTINEL_MASTER_LINK_STATUS_UP 0
#define SENTINEL_MASTER_LINK_STATUS_DOWN 1

/* Generic flags that can be used with different functions.
 * They use higher bits to avoid colliding with the function specific
 * flags. */
#define SENTINEL_NO_FLAGS 0
#define SENTINEL_GENERATE_EVENT (1<<16)
#define SENTINEL_LEADER (1<<17)
#define SENTINEL_OBSERVER (1<<18)

/* Script execution flags and limits. */
#define SENTINEL_SCRIPT_NONE 0
#define SENTINEL_SCRIPT_RUNNING 1
#define SENTINEL_SCRIPT_MAX_QUEUE 256
#define SENTINEL_SCRIPT_MAX_RUNNING 16
#define SENTINEL_SCRIPT_MAX_RETRY 10

/* SENTINEL SIMULATE-FAILURE command flags. */
#define SENTINEL_SIMFAILURE_NONE 0
#define SENTINEL_SIMFAILURE_CRASH_AFTER_ELECTION (1<<0)
#define SENTINEL_SIMFAILURE_CRASH_AFTER_PROMOTION (1<<1)

/* The link to a sentinelRedisInstance. When we have the same set of Sentinels
 * monitoring many masters, we have different instances representing the
 * same Sentinels, one per master, and we need to share the hiredis connections
 * among them. Otherwise if 5 Sentinels are monitoring 100 masters we create
 * 500 outgoing connections instead of 5.
 *
 * So this structure represents a reference counted link in terms of the two
 * hiredis connections for commands and Pub/Sub, and the fields needed for
 * failure detection, since the ping/pong time are now local to the link: if
 * the link is available, the instance is available. This way we don't just
 * have 5 connections instead of 500, we also send 5 pings instead of 500.
 *
 * Links are shared only for Sentinels: master and slave instances have
 * a link with refcount = 1, always. */
typedef struct instanceLink {
    int refcount;          /* Number of sentinelRedisInstance owners. */
    int disconnected;      /* Non-zero if we need to reconnect cc or pc. */
    int pending_commands;  /* Number of commands sent waiting for a reply. */
    redisAsyncContext *cc; /* Hiredis context for commands. */
    redisAsyncContext *pc; /* Hiredis context for Pub / Sub. */
    mstime_t cc_conn_time; /* cc connection time. */
    mstime_t pc_conn_time; /* pc connection time. */
    mstime_t pc_last_activity; /* Last time we received any message. */
    mstime_t last_avail_time; /* Last time the instance replied to ping with
                                 a reply we consider valid. */
    mstime_t act_ping_time;   /* Time at which the last pending ping (no pong
                                 received after it) was sent. This field is
                                 set to 0 when a pong is received, and set again
                                 to the current time if the value is 0 and a new
                                 ping is sent. */
    mstime_t last_ping_time;  /* Time at which we sent the last ping. This is
                                 only used to avoid sending too many pings
                                 during failure. Idle time is computed using
                                 the act_ping_time field. */
    mstime_t last_pong_time;  /* Last time the instance replied to ping,
                                 whatever the reply was. That's used to check
                                 if the link is idle and must be reconnected. */
    mstime_t last_reconn_time;  /* Last reconnection attempt performed when
                                   the link was down. */
} instanceLink;

typedef struct sentinelRedisInstance {
    int flags;      /* See SRI_... defines */
    char *name;     /* Master name from the point of view of this sentinel. */
    char *runid;    /* Run ID of this instance, or unique ID if is a Sentinel.*/
    uint64_t config_epoch;  /* Configuration epoch. */
    sentinelAddr *addr; /* Master host. */
    instanceLink *link; /* Link to the instance, may be shared for Sentinels. */
    mstime_t last_pub_time;   /* Last time we sent hello via Pub/Sub. */
    mstime_t last_hello_time; /* Only used if SRI_SENTINEL is set. Last time
                                 we received a hello from this Sentinel
                                 via Pub/Sub. */
    mstime_t last_master_down_reply_time; /* Time of last reply to
                                             SENTINEL is-master-down command. */
    mstime_t s_down_since_time; /* Subjectively down since time. */
    mstime_t o_down_since_time; /* Objectively down since time. */
    mstime_t down_after_period; /* Consider it down after that period. */
    mstime_t master_reboot_down_after_period; /* Consider master down after that period. */
    mstime_t master_reboot_since_time; /* master reboot time since time. */
    mstime_t info_refresh;  /* Time at which we received INFO output from it. */
    dict *renamed_commands;     /* Commands renamed in this instance:
                                   Sentinel will use the alternative commands
                                   mapped on this table to send things like
                                   SLAVEOF, CONFING, INFO, ... */

    /* Role and the first time we observed it.
     * This is useful in order to delay replacing what the instance reports
     * with our own configuration. We need to always wait some time in order
     * to give a chance to the leader to report the new configuration before
     * we do silly things. */
    int role_reported;
    mstime_t role_reported_time;
    mstime_t slave_conf_change_time; /* Last time slave master addr changed. */

    /* Master specific. */
    dict *sentinels;    /* Other sentinels monitoring the same master. */
    dict *slaves;       /* Slaves for this master instance. */
    unsigned int quorum;/* Number of sentinels that need to agree on failure. */
    int parallel_syncs; /* How many slaves to reconfigure at same time. */
    char *auth_pass;    /* Password to use for AUTH against master & replica. */
    char *auth_user;    /* Username for ACLs AUTH against master & replica. */

    /* Slave specific. */
    mstime_t master_link_down_time; /* Slave replication link down time. */
    int slave_priority; /* Slave priority according to its INFO output. */
    int replica_announced; /* Replica announcing according to its INFO output. */
    mstime_t slave_reconf_sent_time; /* Time at which we sent SLAVE OF <new> */
    struct sentinelRedisInstance *master; /* Master instance if it's slave. */
    char *slave_master_host;    /* Master host as reported by INFO */
    int slave_master_port;      /* Master port as reported by INFO */
    int slave_master_link_status; /* Master link status as reported by INFO */
    unsigned long long slave_repl_offset; /* Slave replication offset. */
    /* Failover */
    char *leader;       /* If this is a master instance, this is the runid of
                           the Sentinel that should perform the failover. If
                           this is a Sentinel, this is the runid of the Sentinel
                           that this Sentinel voted as leader. */
    uint64_t leader_epoch; /* Epoch of the 'leader' field. */
    uint64_t failover_epoch; /* Epoch of the currently started failover. */
    int failover_state; /* See SENTINEL_FAILOVER_STATE_* defines. */
    mstime_t failover_state_change_time;
    mstime_t failover_start_time;   /* Last failover attempt start time. */
    mstime_t failover_timeout;      /* Max time to refresh failover state. */
    mstime_t failover_delay_logged; /* For what failover_start_time value we
                                       logged the failover delay. */
    struct sentinelRedisInstance *promoted_slave; /* Promoted slave instance. */
    /* Scripts executed to notify admin or reconfigure clients: when they
     * are set to NULL no script is executed. */
    char *notification_script;
    char *client_reconfig_script;
    sds info; /* cached INFO output */
} sentinelRedisInstance;

/* Main state. */
struct sentinelState {
    char myid[CONFIG_RUN_ID_SIZE+1]; /* This sentinel ID. */
    uint64_t current_epoch;         /* Current epoch. */
    dict *masters;      /* Dictionary of master sentinelRedisInstances.
                           Key is the instance name, value is the
                           sentinelRedisInstance structure pointer. */
    int tilt;           /* Are we in TILT mode? */
    int running_scripts;    /* Number of scripts in execution right now. */
    mstime_t tilt_start_time;       /* When TITL started. */
    mstime_t previous_time;         /* Last time we ran the time handler. */
    list *scripts_queue;            /* Queue of user scripts to execute. */
    char *announce_ip;  /* IP addr that is gossiped to other sentinels if
                           not NULL. */
    int announce_port;  /* Port that is gossiped to other sentinels if
                           non zero. */
    unsigned long simfailure_flags; /* Failures simulation. */
    int deny_scripts_reconfig; /* Allow SENTINEL SET ... to change script
                                  paths at runtime? */
    char *sentinel_auth_pass;    /* Password to use for AUTH against other sentinel */
    char *sentinel_auth_user;    /* Username for ACLs AUTH against other sentinel. */
    int resolve_hostnames;       /* Support use of hostnames, assuming DNS is well configured. */
    int announce_hostnames;      /* Announce hostnames instead of IPs when we have them. */
} sentinel;

/* A script execution job. */
typedef struct sentinelScriptJob {
    int flags;              /* Script job flags: SENTINEL_SCRIPT_* */
    int retry_num;          /* Number of times we tried to execute it. */
    char **argv;            /* Arguments to call the script. */
    mstime_t start_time;    /* Script execution time if the script is running,
                               otherwise 0 if we are allowed to retry the
                               execution at any time. If the script is not
                               running and it's not 0, it means: do not run
                               before the specified time. */
    pid_t pid;              /* Script execution pid. */
} sentinelScriptJob;

/* ======================= hiredis ae.c adapters =============================
 * Note: this implementation is taken from hiredis/adapters/ae.h, however
 * we have our modified copy for Sentinel in order to use our allocator
 * and to have full control over how the adapter works. */

typedef struct redisAeEvents {
    redisAsyncContext *context;
    aeEventLoop *loop;
    int fd;
    int reading, writing;
} redisAeEvents;

static void redisAeReadEvent(aeEventLoop *el, int fd, void *privdata, int mask) {
    ((void)el); ((void)fd); ((void)mask);

    redisAeEvents *e = (redisAeEvents*)privdata;
    redisAsyncHandleRead(e->context);
}

static void redisAeWriteEvent(aeEventLoop *el, int fd, void *privdata, int mask) {
    ((void)el); ((void)fd); ((void)mask);

    redisAeEvents *e = (redisAeEvents*)privdata;
    redisAsyncHandleWrite(e->context);
}

static void redisAeAddRead(void *privdata) {
    redisAeEvents *e = (redisAeEvents*)privdata;
    aeEventLoop *loop = e->loop;
    if (!e->reading) {
        e->reading = 1;
        aeCreateFileEvent(loop,e->fd,AE_READABLE,redisAeReadEvent,e);
    }
}

static void redisAeDelRead(void *privdata) {
    redisAeEvents *e = (redisAeEvents*)privdata;
    aeEventLoop *loop = e->loop;
    if (e->reading) {
        e->reading = 0;
        aeDeleteFileEvent(loop,e->fd,AE_READABLE);
    }
}

static void redisAeAddWrite(void *privdata) {
    redisAeEvents *e = (redisAeEvents*)privdata;
    aeEventLoop *loop = e->loop;
    if (!e->writing) {
        e->writing = 1;
        aeCreateFileEvent(loop,e->fd,AE_WRITABLE,redisAeWriteEvent,e);
    }
}

static void redisAeDelWrite(void *privdata) {
    redisAeEvents *e = (redisAeEvents*)privdata;
    aeEventLoop *loop = e->loop;
    if (e->writing) {
        e->writing = 0;
        aeDeleteFileEvent(loop,e->fd,AE_WRITABLE);
    }
}

static void redisAeCleanup(void *privdata) {
    redisAeEvents *e = (redisAeEvents*)privdata;
    redisAeDelRead(privdata);
    redisAeDelWrite(privdata);
    zfree(e);
}

static int redisAeAttach(aeEventLoop *loop, redisAsyncContext *ac) {
    redisContext *c = &(ac->c);
    redisAeEvents *e;

    /* Nothing should be attached when something is already attached */
    if (ac->ev.data != NULL)
        return C_ERR;

    /* Create container for context and r/w events */
    e = (redisAeEvents*)zmalloc(sizeof(*e));
    e->context = ac;
    e->loop = loop;
    e->fd = c->fd;
    e->reading = e->writing = 0;

    /* Register functions to start/stop listening for events */
    ac->ev.addRead = redisAeAddRead;
    ac->ev.delRead = redisAeDelRead;
    ac->ev.addWrite = redisAeAddWrite;
    ac->ev.delWrite = redisAeDelWrite;
    ac->ev.cleanup = redisAeCleanup;
    ac->ev.data = e;

    return C_OK;
}

/* ============================= Prototypes ================================= */

void sentinelLinkEstablishedCallback(const redisAsyncContext *c, int status);
void sentinelDisconnectCallback(const redisAsyncContext *c, int status);
void sentinelReceiveHelloMessages(redisAsyncContext *c, void *reply, void *privdata);
sentinelRedisInstance *sentinelGetMasterByName(char *name);
char *sentinelGetSubjectiveLeader(sentinelRedisInstance *master);
char *sentinelGetObjectiveLeader(sentinelRedisInstance *master);
void instanceLinkConnectionError(const redisAsyncContext *c);
const char *sentinelRedisInstanceTypeStr(sentinelRedisInstance *ri);
void sentinelAbortFailover(sentinelRedisInstance *ri);
void sentinelEvent(int level, char *type, sentinelRedisInstance *ri, const char *fmt, ...);
sentinelRedisInstance *sentinelSelectSlave(sentinelRedisInstance *master);
void sentinelScheduleScriptExecution(char *path, ...);
void sentinelStartFailover(sentinelRedisInstance *master);
void sentinelDiscardReplyCallback(redisAsyncContext *c, void *reply, void *privdata);
int sentinelSendSlaveOf(sentinelRedisInstance *ri, const sentinelAddr *addr);
char *sentinelVoteLeader(sentinelRedisInstance *master, uint64_t req_epoch, char *req_runid, uint64_t *leader_epoch);
int sentinelFlushConfig(void);
void sentinelGenerateInitialMonitorEvents(void);
int sentinelSendPing(sentinelRedisInstance *ri);
int sentinelForceHelloUpdateForMaster(sentinelRedisInstance *master);
sentinelRedisInstance *getSentinelRedisInstanceByAddrAndRunID(dict *instances, char *ip, int port, char *runid);
void sentinelSimFailureCrash(void);

/* ========================= Dictionary types =============================== */

void releaseSentinelRedisInstance(sentinelRedisInstance *ri);

void dictInstancesValDestructor (dict *d, void *obj) {
    UNUSED(d);
    releaseSentinelRedisInstance(obj);
}

/* Instance name (sds) -> instance (sentinelRedisInstance pointer)
 *
 * also used for: sentinelRedisInstance->sentinels dictionary that maps
 * sentinels ip:port to last seen time in Pub/Sub hello message. */
dictType instancesDictType = {
    dictSdsHash,               /* hash function */
    NULL,                      /* key dup */
    NULL,                      /* val dup */
    dictSdsKeyCompare,         /* key compare */
    NULL,                      /* key destructor */
    dictInstancesValDestructor,/* val destructor */
    NULL                       /* allow to expand */
};

/* Instance runid (sds) -> votes (long casted to void*)
 *
 * This is useful into sentinelGetObjectiveLeader() function in order to
 * count the votes and understand who is the leader. */
dictType leaderVotesDictType = {
    dictSdsHash,               /* hash function */
    NULL,                      /* key dup */
    NULL,                      /* val dup */
    dictSdsKeyCompare,         /* key compare */
    NULL,                      /* key destructor */
    NULL,                      /* val destructor */
    NULL                       /* allow to expand */
};

/* Instance renamed commands table. */
dictType renamedCommandsDictType = {
    dictSdsCaseHash,           /* hash function */
    NULL,                      /* key dup */
    NULL,                      /* val dup */
    dictSdsKeyCaseCompare,     /* key compare */
    dictSdsDestructor,         /* key destructor */
    dictSdsDestructor,         /* val destructor */
    NULL                       /* allow to expand */
};

/* =========================== Initialization =============================== */

void sentinelSetCommand(client *c);
void sentinelConfigGetCommand(client *c);
void sentinelConfigSetCommand(client *c);

/* this array is used for sentinel config lookup, which need to be loaded
 * before monitoring masters config to avoid dependency issues */
const char *preMonitorCfgName[] = { 
    "announce-ip",
    "announce-port",
    "deny-scripts-reconfig",
    "sentinel-user",
    "sentinel-pass",
    "current-epoch",
    "myid",
    "resolve-hostnames",
    "announce-hostnames"
};

/* This function overwrites a few normal Redis config default with Sentinel
 * specific defaults. */
void initSentinelConfig(void) {
    server.port = REDIS_SENTINEL_PORT;
    server.protected_mode = 0; /* Sentinel must be exposed. */
}

void freeSentinelLoadQueueEntry(void *item);

/* Perform the Sentinel mode initialization. */
void initSentinel(void) {
    /* Initialize various data structures. */
    sentinel.current_epoch = 0;
    sentinel.masters = dictCreate(&instancesDictType);
    sentinel.tilt = 0;
    sentinel.tilt_start_time = 0;
    sentinel.previous_time = mstime();
    sentinel.running_scripts = 0;
    sentinel.scripts_queue = listCreate();
    sentinel.announce_ip = NULL;
    sentinel.announce_port = 0;
    sentinel.simfailure_flags = SENTINEL_SIMFAILURE_NONE;
    sentinel.deny_scripts_reconfig = SENTINEL_DEFAULT_DENY_SCRIPTS_RECONFIG;
    sentinel.sentinel_auth_pass = NULL;
    sentinel.sentinel_auth_user = NULL;
    sentinel.resolve_hostnames = SENTINEL_DEFAULT_RESOLVE_HOSTNAMES;
    sentinel.announce_hostnames = SENTINEL_DEFAULT_ANNOUNCE_HOSTNAMES;
    memset(sentinel.myid,0,sizeof(sentinel.myid));
    server.sentinel_config = NULL;
}

/* This function is for checking whether sentinel config file has been set,
 * also checking whether we have write permissions. */
void sentinelCheckConfigFile(void) {
    if (server.configfile == NULL) {
        serverLog(LL_WARNING,
            "Sentinel needs config file on disk to save state. Exiting...");
        exit(1);
    } else if (access(server.configfile,W_OK) == -1) {
        serverLog(LL_WARNING,
            "Sentinel config file %s is not writable: %s. Exiting...",
            server.configfile,strerror(errno));
        exit(1);
    }
}

/* This function gets called when the server is in Sentinel mode, started,
 * loaded the configuration, and is ready for normal operations. */
void sentinelIsRunning(void) {
    int j;

    /* If this Sentinel has yet no ID set in the configuration file, we
     * pick a random one and persist the config on disk. From now on this
     * will be this Sentinel ID across restarts. */
    for (j = 0; j < CONFIG_RUN_ID_SIZE; j++)
        if (sentinel.myid[j] != 0) break;

    if (j == CONFIG_RUN_ID_SIZE) {
        /* Pick ID and persist the config. */
        getRandomHexChars(sentinel.myid,CONFIG_RUN_ID_SIZE);
        sentinelFlushConfig();
    }

    /* Log its ID to make debugging of issues simpler. */
    serverLog(LL_WARNING,"Sentinel ID is %s", sentinel.myid);

    /* We want to generate a +monitor event for every configured master
     * at startup. */
    sentinelGenerateInitialMonitorEvents();
}

/* ============================== sentinelAddr ============================== */

/* Create a sentinelAddr object and return it on success.
 * On error NULL is returned and errno is set to:
 *  ENOENT: Can't resolve the hostname, unless accept_unresolved is non-zero.
 *  EINVAL: Invalid port number.
 */
sentinelAddr *createSentinelAddr(char *hostname, int port, int is_accept_unresolved) {
    char ip[NET_IP_STR_LEN];
    sentinelAddr *sa;

    if (port < 0 || port > 65535) {
        errno = EINVAL;
        return NULL;
    }
    if (anetResolve(NULL,hostname,ip,sizeof(ip),
                    sentinel.resolve_hostnames ? ANET_NONE : ANET_IP_ONLY) == ANET_ERR) {
        serverLog(LL_WARNING, "Failed to resolve hostname '%s'", hostname);
        if (sentinel.resolve_hostnames && is_accept_unresolved) {
            ip[0] = '\0';
        }
        else {
            errno = ENOENT;
            return NULL;
        }
    }
    sa = zmalloc(sizeof(*sa));
    sa->hostname = sdsnew(hostname);
    sa->ip = sdsnew(ip);
    sa->port = port;
    return sa;
}

/* Return a duplicate of the source address. */
sentinelAddr *dupSentinelAddr(sentinelAddr *src) {
    sentinelAddr *sa;

    sa = zmalloc(sizeof(*sa));
    sa->hostname = sdsnew(src->hostname);
    sa->ip = sdsnew(src->ip);
    sa->port = src->port;
    return sa;
}

/* Free a Sentinel address. Can't fail. */
void releaseSentinelAddr(sentinelAddr *sa) {
    sdsfree(sa->hostname);
    sdsfree(sa->ip);
    zfree(sa);
}

/* Return non-zero if the two addresses are equal, either by address
 * or by hostname if they could not have been resolved.
 */
int sentinelAddrOrHostnameEqual(sentinelAddr *a, sentinelAddr *b) {
    return a->port == b->port &&
            (!strcmp(a->ip, b->ip)  ||
            !strcasecmp(a->hostname, b->hostname));
}

/* Return non-zero if a hostname matches an address. */
int sentinelAddrEqualsHostname(sentinelAddr *a, char *hostname) {
    char ip[NET_IP_STR_LEN];

    /* Try resolve the hostname and compare it to the address */
    if (anetResolve(NULL, hostname, ip, sizeof(ip),
                    sentinel.resolve_hostnames ? ANET_NONE : ANET_IP_ONLY) == ANET_ERR) {

        /* If failed resolve then compare based on hostnames. That is our best effort as
         * long as the server is unavailable for some reason. It is fine since Redis 
         * instance cannot have multiple hostnames for a given setup */
        return !strcasecmp(sentinel.resolve_hostnames ? a->hostname : a->ip, hostname);
    }
    /* Compare based on address */
    return !strcasecmp(a->ip, ip);
}

const char *announceSentinelAddr(const sentinelAddr *a) {
    return sentinel.announce_hostnames ? a->hostname : a->ip;
}

/* Return an allocated sds with hostname/address:port. IPv6
 * addresses are bracketed the same way anetFormatAddr() does.
 */
sds announceSentinelAddrAndPort(const sentinelAddr *a) {
    const char *addr = announceSentinelAddr(a);
    if (strchr(addr, ':') != NULL)
        return sdscatprintf(sdsempty(), "[%s]:%d", addr, a->port);
    else
        return sdscatprintf(sdsempty(), "%s:%d", addr, a->port);
}

/* =========================== Events notification ========================== */

/* Send an event to log, pub/sub, user notification script.
 *
 * 'level' is the log level for logging. Only LL_WARNING events will trigger
 * the execution of the user notification script.
 *
 * 'type' is the message type, also used as a pub/sub channel name.
 *
 * 'ri', is the redis instance target of this event if applicable, and is
 * used to obtain the path of the notification script to execute.
 *
 * The remaining arguments are printf-alike.
 * If the format specifier starts with the two characters "%@" then ri is
 * not NULL, and the message is prefixed with an instance identifier in the
 * following format:
 *
 *  <instance type> <instance name> <ip> <port>
 *
 *  If the instance type is not master, than the additional string is
 *  added to specify the originating master:
 *
 *  @ <master name> <master ip> <master port>
 *
 *  Any other specifier after "%@" is processed by printf itself.
 */
void sentinelEvent(int level, char *type, sentinelRedisInstance *ri,
                   const char *fmt, ...) {
    va_list ap;
    char msg[LOG_MAX_LEN];
    robj *channel, *payload;

    /* Handle %@ */
    if (fmt[0] == '%' && fmt[1] == '@') {
        sentinelRedisInstance *master = (ri->flags & SRI_MASTER) ?
                                         NULL : ri->master;

        if (master) {
            snprintf(msg, sizeof(msg), "%s %s %s %d @ %s %s %d",
                sentinelRedisInstanceTypeStr(ri),
                ri->name, announceSentinelAddr(ri->addr), ri->addr->port,
                master->name, announceSentinelAddr(master->addr), master->addr->port);
        } else {
            snprintf(msg, sizeof(msg), "%s %s %s %d",
                sentinelRedisInstanceTypeStr(ri),
                ri->name, announceSentinelAddr(ri->addr), ri->addr->port);
        }
        fmt += 2;
    } else {
        msg[0] = '\0';
    }

    /* Use vsprintf for the rest of the formatting if any. */
    if (fmt[0] != '\0') {
        va_start(ap, fmt);
        vsnprintf(msg+strlen(msg), sizeof(msg)-strlen(msg), fmt, ap);
        va_end(ap);
    }

    /* Log the message if the log level allows it to be logged. */
    if (level >= server.verbosity)
        serverLog(level,"%s %s",type,msg);

    /* Publish the message via Pub/Sub if it's not a debugging one. */
    if (level != LL_DEBUG) {
        channel = createStringObject(type,strlen(type));
        payload = createStringObject(msg,strlen(msg));
        pubsubPublishMessage(channel,payload,0);
        decrRefCount(channel);
        decrRefCount(payload);
    }

    /* Call the notification script if applicable. */
    if (level == LL_WARNING && ri != NULL) {
        sentinelRedisInstance *master = (ri->flags & SRI_MASTER) ?
                                         ri : ri->master;
        if (master && master->notification_script) {
            sentinelScheduleScriptExecution(master->notification_script,
                type,msg,NULL);
        }
    }
}

/* This function is called only at startup and is used to generate a
 * +monitor event for every configured master. The same events are also
 * generated when a master to monitor is added at runtime via the
 * SENTINEL MONITOR command. */
void sentinelGenerateInitialMonitorEvents(void) {
    dictIterator *di;
    dictEntry *de;

    di = dictGetIterator(sentinel.masters);
    while((de = dictNext(di)) != NULL) {
        sentinelRedisInstance *ri = dictGetVal(de);
        sentinelEvent(LL_WARNING,"+monitor",ri,"%@ quorum %d",ri->quorum);
    }
    dictReleaseIterator(di);
}

/* ============================ script execution ============================ */

/* Release a script job structure and all the associated data. */
void sentinelReleaseScriptJob(sentinelScriptJob *sj) {
    int j = 0;

    while(sj->argv[j]) sdsfree(sj->argv[j++]);
    zfree(sj->argv);
    zfree(sj);
}

#define SENTINEL_SCRIPT_MAX_ARGS 16
void sentinelScheduleScriptExecution(char *path, ...) {
    va_list ap;
    char *argv[SENTINEL_SCRIPT_MAX_ARGS+1];
    int argc = 1;
    sentinelScriptJob *sj;

    va_start(ap, path);
    while(argc < SENTINEL_SCRIPT_MAX_ARGS) {
        argv[argc] = va_arg(ap,char*);
        if (!argv[argc]) break;
        argv[argc] = sdsnew(argv[argc]); /* Copy the string. */
        argc++;
    }
    va_end(ap);
    argv[0] = sdsnew(path);

    sj = zmalloc(sizeof(*sj));
    sj->flags = SENTINEL_SCRIPT_NONE;
    sj->retry_num = 0;
    sj->argv = zmalloc(sizeof(char*)*(argc+1));
    sj->start_time = 0;
    sj->pid = 0;
    memcpy(sj->argv,argv,sizeof(char*)*(argc+1));

    listAddNodeTail(sentinel.scripts_queue,sj);

    /* Remove the oldest non running script if we already hit the limit. */
    if (listLength(sentinel.scripts_queue) > SENTINEL_SCRIPT_MAX_QUEUE) {
        listNode *ln;
        listIter li;

        listRewind(sentinel.scripts_queue,&li);
        while ((ln = listNext(&li)) != NULL) {
            sj = ln->value;

            if (sj->flags & SENTINEL_SCRIPT_RUNNING) continue;
            /* The first node is the oldest as we add on tail. */
            listDelNode(sentinel.scripts_queue,ln);
            sentinelReleaseScriptJob(sj);
            break;
        }
        serverAssert(listLength(sentinel.scripts_queue) <=
                    SENTINEL_SCRIPT_MAX_QUEUE);
    }
}

/* Lookup a script in the scripts queue via pid, and returns the list node
 * (so that we can easily remove it from the queue if needed). */
listNode *sentinelGetScriptListNodeByPid(pid_t pid) {
    listNode *ln;
    listIter li;

    listRewind(sentinel.scripts_queue,&li);
    while ((ln = listNext(&li)) != NULL) {
        sentinelScriptJob *sj = ln->value;

        if ((sj->flags & SENTINEL_SCRIPT_RUNNING) && sj->pid == pid)
            return ln;
    }
    return NULL;
}

/* Run pending scripts if we are not already at max number of running
 * scripts. */
void sentinelRunPendingScripts(void) {
    listNode *ln;
    listIter li;
    mstime_t now = mstime();

    /* Find jobs that are not running and run them, from the top to the
     * tail of the queue, so we run older jobs first. */
    listRewind(sentinel.scripts_queue,&li);
    while (sentinel.running_scripts < SENTINEL_SCRIPT_MAX_RUNNING &&
           (ln = listNext(&li)) != NULL)
    {
        sentinelScriptJob *sj = ln->value;
        pid_t pid;

        /* Skip if already running. */
        if (sj->flags & SENTINEL_SCRIPT_RUNNING) continue;

        /* Skip if it's a retry, but not enough time has elapsed. */
        if (sj->start_time && sj->start_time > now) continue;

        sj->flags |= SENTINEL_SCRIPT_RUNNING;
        sj->start_time = mstime();
        sj->retry_num++;
        pid = fork();

        if (pid == -1) {
            /* Parent (fork error).
             * We report fork errors as signal 99, in order to unify the
             * reporting with other kind of errors. */
            sentinelEvent(LL_WARNING,"-script-error",NULL,
                          "%s %d %d", sj->argv[0], 99, 0);
            sj->flags &= ~SENTINEL_SCRIPT_RUNNING;
            sj->pid = 0;
        } else if (pid == 0) {
            /* Child */
            tlsCleanup();
            execve(sj->argv[0],sj->argv,environ);
            /* If we are here an error occurred. */
            _exit(2); /* Don't retry execution. */
        } else {
            sentinel.running_scripts++;
            sj->pid = pid;
            sentinelEvent(LL_DEBUG,"+script-child",NULL,"%ld",(long)pid);
        }
    }
}

/* How much to delay the execution of a script that we need to retry after
 * an error?
 *
 * We double the retry delay for every further retry we do. So for instance
 * if RETRY_DELAY is set to 30 seconds and the max number of retries is 10
 * starting from the second attempt to execute the script the delays are:
 * 30 sec, 60 sec, 2 min, 4 min, 8 min, 16 min, 32 min, 64 min, 128 min. */
mstime_t sentinelScriptRetryDelay(int retry_num) {
    mstime_t delay = sentinel_script_retry_delay;

    while (retry_num-- > 1) delay *= 2;
    return delay;
}

/* Check for scripts that terminated, and remove them from the queue if the
 * script terminated successfully. If instead the script was terminated by
 * a signal, or returned exit code "1", it is scheduled to run again if
 * the max number of retries did not already elapsed. */
void sentinelCollectTerminatedScripts(void) {
    int statloc;
    pid_t pid;

    while ((pid = waitpid(-1, &statloc, WNOHANG)) > 0) {
        int exitcode = WEXITSTATUS(statloc);
        int bysignal = 0;
        listNode *ln;
        sentinelScriptJob *sj;

        if (WIFSIGNALED(statloc)) bysignal = WTERMSIG(statloc);
        sentinelEvent(LL_DEBUG,"-script-child",NULL,"%ld %d %d",
            (long)pid, exitcode, bysignal);

        ln = sentinelGetScriptListNodeByPid(pid);
        if (ln == NULL) {
            serverLog(LL_WARNING,"waitpid() returned a pid (%ld) we can't find in our scripts execution queue!", (long)pid);
            continue;
        }
        sj = ln->value;

        /* If the script was terminated by a signal or returns an
         * exit code of "1" (that means: please retry), we reschedule it
         * if the max number of retries is not already reached. */
        if ((bysignal || exitcode == 1) &&
            sj->retry_num != SENTINEL_SCRIPT_MAX_RETRY)
        {
            sj->flags &= ~SENTINEL_SCRIPT_RUNNING;
            sj->pid = 0;
            sj->start_time = mstime() +
                             sentinelScriptRetryDelay(sj->retry_num);
        } else {
            /* Otherwise let's remove the script, but log the event if the
             * execution did not terminated in the best of the ways. */
            if (bysignal || exitcode != 0) {
                sentinelEvent(LL_WARNING,"-script-error",NULL,
                              "%s %d %d", sj->argv[0], bysignal, exitcode);
            }
            listDelNode(sentinel.scripts_queue,ln);
            sentinelReleaseScriptJob(sj);
        }
        sentinel.running_scripts--;
    }
}

/* Kill scripts in timeout, they'll be collected by the
 * sentinelCollectTerminatedScripts() function. */
void sentinelKillTimedoutScripts(void) {
    listNode *ln;
    listIter li;
    mstime_t now = mstime();

    listRewind(sentinel.scripts_queue,&li);
    while ((ln = listNext(&li)) != NULL) {
        sentinelScriptJob *sj = ln->value;

        if (sj->flags & SENTINEL_SCRIPT_RUNNING &&
            (now - sj->start_time) > sentinel_script_max_runtime)
        {
            sentinelEvent(LL_WARNING,"-script-timeout",NULL,"%s %ld",
                sj->argv[0], (long)sj->pid);
            kill(sj->pid,SIGKILL);
        }
    }
}

/* Implements SENTINEL PENDING-SCRIPTS command. */
void sentinelPendingScriptsCommand(client *c) {
    listNode *ln;
    listIter li;

    addReplyArrayLen(c,listLength(sentinel.scripts_queue));
    listRewind(sentinel.scripts_queue,&li);
    while ((ln = listNext(&li)) != NULL) {
        sentinelScriptJob *sj = ln->value;
        int j = 0;

        addReplyMapLen(c,5);

        addReplyBulkCString(c,"argv");
        while (sj->argv[j]) j++;
        addReplyArrayLen(c,j);
        j = 0;
        while (sj->argv[j]) addReplyBulkCString(c,sj->argv[j++]);

        addReplyBulkCString(c,"flags");
        addReplyBulkCString(c,
            (sj->flags & SENTINEL_SCRIPT_RUNNING) ? "running" : "scheduled");

        addReplyBulkCString(c,"pid");
        addReplyBulkLongLong(c,sj->pid);

        if (sj->flags & SENTINEL_SCRIPT_RUNNING) {
            addReplyBulkCString(c,"run-time");
            addReplyBulkLongLong(c,mstime() - sj->start_time);
        } else {
            mstime_t delay = sj->start_time ? (sj->start_time-mstime()) : 0;
            if (delay < 0) delay = 0;
            addReplyBulkCString(c,"run-delay");
            addReplyBulkLongLong(c,delay);
        }

        addReplyBulkCString(c,"retry-num");
        addReplyBulkLongLong(c,sj->retry_num);
    }
}

/* This function calls, if any, the client reconfiguration script with the
 * following parameters:
 *
 * <master-name> <role> <state> <from-ip> <from-port> <to-ip> <to-port>
 *
 * It is called every time a failover is performed.
 *
 * <state> is currently always "start".
 * <role> is either "leader" or "observer".
 *
 * from/to fields are respectively master -> promoted slave addresses for
 * "start" and "end". */
void sentinelCallClientReconfScript(sentinelRedisInstance *master, int role, char *state, sentinelAddr *from, sentinelAddr *to) {
    char fromport[32], toport[32];

    if (master->client_reconfig_script == NULL) return;
    ll2string(fromport,sizeof(fromport),from->port);
    ll2string(toport,sizeof(toport),to->port);
    sentinelScheduleScriptExecution(master->client_reconfig_script,
        master->name,
        (role == SENTINEL_LEADER) ? "leader" : "observer",
        state, announceSentinelAddr(from), fromport,
        announceSentinelAddr(to), toport, NULL);
}

/* =============================== instanceLink ============================= */

/* Create a not yet connected link object. */
instanceLink *createInstanceLink(void) {
    instanceLink *link = zmalloc(sizeof(*link));

    link->refcount = 1;
    link->disconnected = 1;
    link->pending_commands = 0;
    link->cc = NULL;
    link->pc = NULL;
    link->cc_conn_time = 0;
    link->pc_conn_time = 0;
    link->last_reconn_time = 0;
    link->pc_last_activity = 0;
    /* We set the act_ping_time to "now" even if we actually don't have yet
     * a connection with the node, nor we sent a ping.
     * This is useful to detect a timeout in case we'll not be able to connect
     * with the node at all. */
    link->act_ping_time = mstime();
    link->last_ping_time = 0;
    link->last_avail_time = mstime();
    link->last_pong_time = mstime();
    return link;
}

/* Disconnect a hiredis connection in the context of an instance link. */
void instanceLinkCloseConnection(instanceLink *link, redisAsyncContext *c) {
    if (c == NULL) return;

    if (link->cc == c) {
        link->cc = NULL;
        link->pending_commands = 0;
    }
    if (link->pc == c) link->pc = NULL;
    c->data = NULL;
    link->disconnected = 1;
    redisAsyncFree(c);
}

/* Decrement the refcount of a link object, if it drops to zero, actually
 * free it and return NULL. Otherwise don't do anything and return the pointer
 * to the object.
 *
 * If we are not going to free the link and ri is not NULL, we rebind all the
 * pending requests in link->cc (hiredis connection for commands) to a
 * callback that will just ignore them. This is useful to avoid processing
 * replies for an instance that no longer exists. */
instanceLink *releaseInstanceLink(instanceLink *link, sentinelRedisInstance *ri)
{
    serverAssert(link->refcount > 0);
    link->refcount--;
    if (link->refcount != 0) {
        if (ri && ri->link->cc) {
            /* This instance may have pending callbacks in the hiredis async
             * context, having as 'privdata' the instance that we are going to
             * free. Let's rewrite the callback list, directly exploiting
             * hiredis internal data structures, in order to bind them with
             * a callback that will ignore the reply at all. */
            redisCallback *cb;
            redisCallbackList *callbacks = &link->cc->replies;

            cb = callbacks->head;
            while(cb) {
                if (cb->privdata == ri) {
                    cb->fn = sentinelDiscardReplyCallback;
                    cb->privdata = NULL; /* Not strictly needed. */
                }
                cb = cb->next;
            }
        }
        return link; /* Other active users. */
    }

    instanceLinkCloseConnection(link,link->cc);
    instanceLinkCloseConnection(link,link->pc);
    zfree(link);
    return NULL;
}

/* This function will attempt to share the instance link we already have
 * for the same Sentinel in the context of a different master, with the
 * instance we are passing as argument.
 *
 * This way multiple Sentinel objects that refer all to the same physical
 * Sentinel instance but in the context of different masters will use
 * a single connection, will send a single PING per second for failure
 * detection and so forth.
 *
 * Return C_OK if a matching Sentinel was found in the context of a
 * different master and sharing was performed. Otherwise C_ERR
 * is returned. */
int sentinelTryConnectionSharing(sentinelRedisInstance *ri) {
    serverAssert(ri->flags & SRI_SENTINEL);
    dictIterator *di;
    dictEntry *de;

    if (ri->runid == NULL) return C_ERR; /* No way to identify it. */
    if (ri->link->refcount > 1) return C_ERR; /* Already shared. */

    di = dictGetIterator(sentinel.masters);
    while((de = dictNext(di)) != NULL) {
        sentinelRedisInstance *master = dictGetVal(de), *match;
        /* We want to share with the same physical Sentinel referenced
         * in other masters, so skip our master. */
        if (master == ri->master) continue;
        match = getSentinelRedisInstanceByAddrAndRunID(master->sentinels,
                                                       NULL,0,ri->runid);
        if (match == NULL) continue; /* No match. */
        if (match == ri) continue; /* Should never happen but... safer. */

        /* We identified a matching Sentinel, great! Let's free our link
         * and use the one of the matching Sentinel. */
        releaseInstanceLink(ri->link,NULL);
        ri->link = match->link;
        match->link->refcount++;
        dictReleaseIterator(di);
        return C_OK;
    }
    dictReleaseIterator(di);
    return C_ERR;
}

/* Disconnect the relevant master and its replicas. */
void dropInstanceConnections(sentinelRedisInstance *ri) {
    serverAssert(ri->flags & SRI_MASTER);

    /* Disconnect with the master. */
    instanceLinkCloseConnection(ri->link, ri->link->cc);
    instanceLinkCloseConnection(ri->link, ri->link->pc);
    
    /* Disconnect with all replicas. */
    dictIterator *di;
    dictEntry *de;
    sentinelRedisInstance *repl_ri;
    di = dictGetIterator(ri->slaves);
    while ((de = dictNext(di)) != NULL) {
        repl_ri = dictGetVal(de);
        instanceLinkCloseConnection(repl_ri->link, repl_ri->link->cc);
        instanceLinkCloseConnection(repl_ri->link, repl_ri->link->pc);
    }
    dictReleaseIterator(di);
}

/* Drop all connections to other sentinels. Returns the number of connections
 * dropped.*/
int sentinelDropConnections(void) {
    dictIterator *di;
    dictEntry *de;
    int dropped = 0;

    di = dictGetIterator(sentinel.masters);
    while ((de = dictNext(di)) != NULL) {
        dictIterator *sdi;
        dictEntry *sde;

        sentinelRedisInstance *ri = dictGetVal(de);
        sdi = dictGetIterator(ri->sentinels);
        while ((sde = dictNext(sdi)) != NULL) {
            sentinelRedisInstance *si = dictGetVal(sde);
            if (!si->link->disconnected) {
                instanceLinkCloseConnection(si->link, si->link->pc);
                instanceLinkCloseConnection(si->link, si->link->cc);
                dropped++;
            }
        }
        dictReleaseIterator(sdi);
    }
    dictReleaseIterator(di);

    return dropped;
}

/* When we detect a Sentinel to switch address (reporting a different IP/port
 * pair in Hello messages), let's update all the matching Sentinels in the
 * context of other masters as well and disconnect the links, so that everybody
 * will be updated.
 *
 * Return the number of updated Sentinel addresses. */
int sentinelUpdateSentinelAddressInAllMasters(sentinelRedisInstance *ri) {
    serverAssert(ri->flags & SRI_SENTINEL);
    dictIterator *di;
    dictEntry *de;
    int reconfigured = 0;

    di = dictGetIterator(sentinel.masters);
    while((de = dictNext(di)) != NULL) {
        sentinelRedisInstance *master = dictGetVal(de), *match;
        match = getSentinelRedisInstanceByAddrAndRunID(master->sentinels,
                                                       NULL,0,ri->runid);
        /* If there is no match, this master does not know about this
         * Sentinel, try with the next one. */
        if (match == NULL) continue;

        /* Disconnect the old links if connected. */
        if (match->link->cc != NULL)
            instanceLinkCloseConnection(match->link,match->link->cc);
        if (match->link->pc != NULL)
            instanceLinkCloseConnection(match->link,match->link->pc);

        if (match == ri) continue; /* Address already updated for it. */

        /* Update the address of the matching Sentinel by copying the address
         * of the Sentinel object that received the address update. */
        releaseSentinelAddr(match->addr);
        match->addr = dupSentinelAddr(ri->addr);
        reconfigured++;
    }
    dictReleaseIterator(di);
    if (reconfigured)
        sentinelEvent(LL_NOTICE,"+sentinel-address-update", ri,
                    "%@ %d additional matching instances", reconfigured);
    return reconfigured;
}

/* This function is called when a hiredis connection reported an error.
 * We set it to NULL and mark the link as disconnected so that it will be
 * reconnected again.
 *
 * Note: we don't free the hiredis context as hiredis will do it for us
 * for async connections. */
void instanceLinkConnectionError(const redisAsyncContext *c) {
    instanceLink *link = c->data;
    int pubsub;

    if (!link) return;

    pubsub = (link->pc == c);
    if (pubsub)
        link->pc = NULL;
    else
        link->cc = NULL;
    link->disconnected = 1;
}

/* Hiredis connection established / disconnected callbacks. We need them
 * just to cleanup our link state. */
void sentinelLinkEstablishedCallback(const redisAsyncContext *c, int status) {
    if (status != C_OK) instanceLinkConnectionError(c);
}

void sentinelDisconnectCallback(const redisAsyncContext *c, int status) {
    UNUSED(status);
    instanceLinkConnectionError(c);
}

/* ========================== sentinelRedisInstance ========================= */

/* Create a redis instance, the following fields must be populated by the
 * caller if needed:
 * runid: set to NULL but will be populated once INFO output is received.
 * info_refresh: is set to 0 to mean that we never received INFO so far.
 *
 * If SRI_MASTER is set into initial flags the instance is added to
 * sentinel.masters table.
 *
 * if SRI_SLAVE or SRI_SENTINEL is set then 'master' must be not NULL and the
 * instance is added into master->slaves or master->sentinels table.
 *
 * If the instance is a slave, the name parameter is ignored and is created
 * automatically as ip/hostname:port.
 *
 * The function fails if hostname can't be resolved or port is out of range.
 * When this happens NULL is returned and errno is set accordingly to the
 * createSentinelAddr() function.
 *
 * The function may also fail and return NULL with errno set to EBUSY if
 * a master with the same name, a slave with the same address, or a sentinel
 * with the same ID already exists. */

sentinelRedisInstance *createSentinelRedisInstance(char *name, int flags, char *hostname, int port, int quorum, sentinelRedisInstance *master) {
    sentinelRedisInstance *ri;
    sentinelAddr *addr;
    dict *table = NULL;
    sds sdsname;

    serverAssert(flags & (SRI_MASTER|SRI_SLAVE|SRI_SENTINEL));
    serverAssert((flags & SRI_MASTER) || master != NULL);

    /* Check address validity. */
    addr = createSentinelAddr(hostname,port,1);
    if (addr == NULL) return NULL;

    /* For slaves use ip/host:port as name. */
    if (flags & SRI_SLAVE)
        sdsname = announceSentinelAddrAndPort(addr);
    else
        sdsname = sdsnew(name);

    /* Make sure the entry is not duplicated. This may happen when the same
     * name for a master is used multiple times inside the configuration or
     * if we try to add multiple times a slave or sentinel with same ip/port
     * to a master. */
    if (flags & SRI_MASTER) table = sentinel.masters;
    else if (flags & SRI_SLAVE) table = master->slaves;
    else if (flags & SRI_SENTINEL) table = master->sentinels;
    if (dictFind(table,sdsname)) {
        releaseSentinelAddr(addr);
        sdsfree(sdsname);
        errno = EBUSY;
        return NULL;
    }

    /* Create the instance object. */
    ri = zmalloc(sizeof(*ri));
    /* Note that all the instances are started in the disconnected state,
     * the event loop will take care of connecting them. */
    ri->flags = flags;
    ri->name = sdsname;
    ri->runid = NULL;
    ri->config_epoch = 0;
    ri->addr = addr;
    ri->link = createInstanceLink();
    ri->last_pub_time = mstime();
    ri->last_hello_time = mstime();
    ri->last_master_down_reply_time = mstime();
    ri->s_down_since_time = 0;
    ri->o_down_since_time = 0;
    ri->down_after_period = master ? master->down_after_period : sentinel_default_down_after;
    ri->master_reboot_down_after_period = 0;
    ri->master_link_down_time = 0;
    ri->auth_pass = NULL;
    ri->auth_user = NULL;
    ri->slave_priority = SENTINEL_DEFAULT_SLAVE_PRIORITY;
    ri->replica_announced = 1;
    ri->slave_reconf_sent_time = 0;
    ri->slave_master_host = NULL;
    ri->slave_master_port = 0;
    ri->slave_master_link_status = SENTINEL_MASTER_LINK_STATUS_DOWN;
    ri->slave_repl_offset = 0;
    ri->sentinels = dictCreate(&instancesDictType);
    ri->quorum = quorum;
    ri->parallel_syncs = SENTINEL_DEFAULT_PARALLEL_SYNCS;
    ri->master = master;
    ri->slaves = dictCreate(&instancesDictType);
    ri->info_refresh = 0;
    ri->renamed_commands = dictCreate(&renamedCommandsDictType);

    /* Failover state. */
    ri->leader = NULL;
    ri->leader_epoch = 0;
    ri->failover_epoch = 0;
    ri->failover_state = SENTINEL_FAILOVER_STATE_NONE;
    ri->failover_state_change_time = 0;
    ri->failover_start_time = 0;
    ri->failover_timeout = sentinel_default_failover_timeout;
    ri->failover_delay_logged = 0;
    ri->promoted_slave = NULL;
    ri->notification_script = NULL;
    ri->client_reconfig_script = NULL;
    ri->info = NULL;

    /* Role */
    ri->role_reported = ri->flags & (SRI_MASTER|SRI_SLAVE);
    ri->role_reported_time = mstime();
    ri->slave_conf_change_time = mstime();

    /* Add into the right table. */
    dictAdd(table, ri->name, ri);
    return ri;
}

/* Release this instance and all its slaves, sentinels, hiredis connections.
 * This function does not take care of unlinking the instance from the main
 * masters table (if it is a master) or from its master sentinels/slaves table
 * if it is a slave or sentinel. */
void releaseSentinelRedisInstance(sentinelRedisInstance *ri) {
    /* Release all its slaves or sentinels if any. */
    dictRelease(ri->sentinels);
    dictRelease(ri->slaves);

    /* Disconnect the instance. */
    releaseInstanceLink(ri->link,ri);

    /* Free other resources. */
    sdsfree(ri->name);
    sdsfree(ri->runid);
    sdsfree(ri->notification_script);
    sdsfree(ri->client_reconfig_script);
    sdsfree(ri->slave_master_host);
    sdsfree(ri->leader);
    sdsfree(ri->auth_pass);
    sdsfree(ri->auth_user);
    sdsfree(ri->info);
    releaseSentinelAddr(ri->addr);
    dictRelease(ri->renamed_commands);

    /* Clear state into the master if needed. */
    if ((ri->flags & SRI_SLAVE) && (ri->flags & SRI_PROMOTED) && ri->master)
        ri->master->promoted_slave = NULL;

    zfree(ri);
}

/* Lookup a slave in a master Redis instance, by ip and port. */
sentinelRedisInstance *sentinelRedisInstanceLookupSlave(
                sentinelRedisInstance *ri, char *slave_addr, int port)
{
    sds key;
    sentinelRedisInstance *slave;
    sentinelAddr *addr;

    serverAssert(ri->flags & SRI_MASTER);

    /* We need to handle a slave_addr that is potentially a hostname.
     * If that is the case, depending on configuration we either resolve
     * it and use the IP address or fail.
     */
    addr = createSentinelAddr(slave_addr, port, 0);
    if (!addr) return NULL;
    key = announceSentinelAddrAndPort(addr);
    releaseSentinelAddr(addr);

    slave = dictFetchValue(ri->slaves,key);
    sdsfree(key);
    return slave;
}

/* Return the name of the type of the instance as a string. */
const char *sentinelRedisInstanceTypeStr(sentinelRedisInstance *ri) {
    if (ri->flags & SRI_MASTER) return "master";
    else if (ri->flags & SRI_SLAVE) return "slave";
    else if (ri->flags & SRI_SENTINEL) return "sentinel";
    else return "unknown";
}

/* This function remove the Sentinel with the specified ID from the
 * specified master.
 *
 * If "runid" is NULL the function returns ASAP.
 *
 * This function is useful because on Sentinels address switch, we want to
 * remove our old entry and add a new one for the same ID but with the new
 * address.
 *
 * The function returns 1 if the matching Sentinel was removed, otherwise
 * 0 if there was no Sentinel with this ID. */
int removeMatchingSentinelFromMaster(sentinelRedisInstance *master, char *runid) {
    dictIterator *di;
    dictEntry *de;
    int removed = 0;

    if (runid == NULL) return 0;

    di = dictGetSafeIterator(master->sentinels);
    while((de = dictNext(di)) != NULL) {
        sentinelRedisInstance *ri = dictGetVal(de);

        if (ri->runid && strcmp(ri->runid,runid) == 0) {
            dictDelete(master->sentinels,ri->name);
            removed++;
        }
    }
    dictReleaseIterator(di);
    return removed;
}

/* Search an instance with the same runid, ip and port into a dictionary
 * of instances. Return NULL if not found, otherwise return the instance
 * pointer.
 *
 * runid or addr can be NULL. In such a case the search is performed only
 * by the non-NULL field. */
sentinelRedisInstance *getSentinelRedisInstanceByAddrAndRunID(dict *instances, char *addr, int port, char *runid) {
    dictIterator *di;
    dictEntry *de;
    sentinelRedisInstance *instance = NULL;
    sentinelAddr *ri_addr = NULL;

    serverAssert(addr || runid);   /* User must pass at least one search param. */
    if (addr != NULL) {
        /* Try to resolve addr. If hostnames are used, we're accepting an ri_addr
         * that contains an hostname only and can still be matched based on that.
         */
        ri_addr = createSentinelAddr(addr,port,1);
        if (!ri_addr) return NULL;
    }
    di = dictGetIterator(instances);
    while((de = dictNext(di)) != NULL) {
        sentinelRedisInstance *ri = dictGetVal(de);

        if (runid && !ri->runid) continue;
        if ((runid == NULL || strcmp(ri->runid, runid) == 0) &&
            (addr == NULL || sentinelAddrOrHostnameEqual(ri->addr, ri_addr)))
        {
            instance = ri;
            break;
        }
    }
    dictReleaseIterator(di);
    if (ri_addr != NULL)
        releaseSentinelAddr(ri_addr);

    return instance;
}

/* Master lookup by name */
sentinelRedisInstance *sentinelGetMasterByName(char *name) {
    sentinelRedisInstance *ri;
    sds sdsname = sdsnew(name);

    ri = dictFetchValue(sentinel.masters,sdsname);
    sdsfree(sdsname);
    return ri;
}

/* Reset the state of a monitored master:
 * 1) Remove all slaves.
 * 2) Remove all sentinels.
 * 3) Remove most of the flags resulting from runtime operations.
 * 4) Reset timers to their default value. For example after a reset it will be
 *    possible to failover again the same master ASAP, without waiting the
 *    failover timeout delay.
 * 5) In the process of doing this undo the failover if in progress.
 * 6) Disconnect the connections with the master (will reconnect automatically).
 */

#define SENTINEL_RESET_NO_SENTINELS (1<<0)
void sentinelResetMaster(sentinelRedisInstance *ri, int flags) {
    serverAssert(ri->flags & SRI_MASTER);
    dictRelease(ri->slaves);
    ri->slaves = dictCreate(&instancesDictType);
    if (!(flags & SENTINEL_RESET_NO_SENTINELS)) {
        dictRelease(ri->sentinels);
        ri->sentinels = dictCreate(&instancesDictType);
    }
    instanceLinkCloseConnection(ri->link,ri->link->cc);
    instanceLinkCloseConnection(ri->link,ri->link->pc);
    ri->flags &= SRI_MASTER;
    if (ri->leader) {
        sdsfree(ri->leader);
        ri->leader = NULL;
    }
    ri->failover_state = SENTINEL_FAILOVER_STATE_NONE;
    ri->failover_state_change_time = 0;
    ri->failover_start_time = 0; /* We can failover again ASAP. */
    ri->promoted_slave = NULL;
    sdsfree(ri->runid);
    sdsfree(ri->slave_master_host);
    ri->runid = NULL;
    ri->slave_master_host = NULL;
    ri->link->act_ping_time = mstime();
    ri->link->last_ping_time = 0;
    ri->link->last_avail_time = mstime();
    ri->link->last_pong_time = mstime();
    ri->role_reported_time = mstime();
    ri->role_reported = SRI_MASTER;
    if (flags & SENTINEL_GENERATE_EVENT)
        sentinelEvent(LL_WARNING,"+reset-master",ri,"%@");
}

/* Call sentinelResetMaster() on every master with a name matching the specified
 * pattern. */
int sentinelResetMastersByPattern(char *pattern, int flags) {
    dictIterator *di;
    dictEntry *de;
    int reset = 0;

    di = dictGetIterator(sentinel.masters);
    while((de = dictNext(di)) != NULL) {
        sentinelRedisInstance *ri = dictGetVal(de);

        if (ri->name) {
            if (stringmatch(pattern,ri->name,0)) {
                sentinelResetMaster(ri,flags);
                reset++;
            }
        }
    }
    dictReleaseIterator(di);
    return reset;
}

/* Reset the specified master with sentinelResetMaster(), and also change
 * the ip:port address, but take the name of the instance unmodified.
 *
 * This is used to handle the +switch-master event.
 *
 * The function returns C_ERR if the address can't be resolved for some
 * reason. Otherwise C_OK is returned.  */
int sentinelResetMasterAndChangeAddress(sentinelRedisInstance *master, char *hostname, int port) {
    sentinelAddr *oldaddr, *newaddr;
    sentinelAddr **slaves = NULL;
    int numslaves = 0, j;
    dictIterator *di;
    dictEntry *de;

    newaddr = createSentinelAddr(hostname,port,0);
    if (newaddr == NULL) return C_ERR;

    /* There can be only 0 or 1 slave that has the newaddr.
     * and It can add old master 1 more slave. 
     * so It allocates dictSize(master->slaves) + 1          */
    slaves = zmalloc(sizeof(sentinelAddr*)*(dictSize(master->slaves) + 1));
    
    /* Don't include the one having the address we are switching to. */
    di = dictGetIterator(master->slaves);
    while((de = dictNext(di)) != NULL) {
        sentinelRedisInstance *slave = dictGetVal(de);

        if (sentinelAddrOrHostnameEqual(slave->addr,newaddr)) continue;
        slaves[numslaves++] = dupSentinelAddr(slave->addr);
    }
    dictReleaseIterator(di);

    /* If we are switching to a different address, include the old address
     * as a slave as well, so that we'll be able to sense / reconfigure
     * the old master. */
    if (!sentinelAddrOrHostnameEqual(newaddr,master->addr)) {
        slaves[numslaves++] = dupSentinelAddr(master->addr);
    }

    /* Reset and switch address. */
    sentinelResetMaster(master,SENTINEL_RESET_NO_SENTINELS);
    oldaddr = master->addr;
    master->addr = newaddr;
    master->o_down_since_time = 0;
    master->s_down_since_time = 0;

    /* Add slaves back. */
    for (j = 0; j < numslaves; j++) {
        sentinelRedisInstance *slave;

        slave = createSentinelRedisInstance(NULL,SRI_SLAVE,slaves[j]->hostname,
                    slaves[j]->port, master->quorum, master);
        releaseSentinelAddr(slaves[j]);
        if (slave) sentinelEvent(LL_NOTICE,"+slave",slave,"%@");
    }
    zfree(slaves);

    /* Release the old address at the end so we are safe even if the function
     * gets the master->addr->ip and master->addr->port as arguments. */
    releaseSentinelAddr(oldaddr);
    sentinelFlushConfig();
    return C_OK;
}

/* Return non-zero if there was no SDOWN or ODOWN error associated to this
 * instance in the latest 'ms' milliseconds. */
int sentinelRedisInstanceNoDownFor(sentinelRedisInstance *ri, mstime_t ms) {
    mstime_t most_recent;

    most_recent = ri->s_down_since_time;
    if (ri->o_down_since_time > most_recent)
        most_recent = ri->o_down_since_time;
    return most_recent == 0 || (mstime() - most_recent) > ms;
}

/* Return the current master address, that is, its address or the address
 * of the promoted slave if already operational. */
sentinelAddr *sentinelGetCurrentMasterAddress(sentinelRedisInstance *master) {
    /* If we are failing over the master, and the state is already
     * SENTINEL_FAILOVER_STATE_RECONF_SLAVES or greater, it means that we
     * already have the new configuration epoch in the master, and the
     * slave acknowledged the configuration switch. Advertise the new
     * address. */
    if ((master->flags & SRI_FAILOVER_IN_PROGRESS) &&
        master->promoted_slave &&
        master->failover_state >= SENTINEL_FAILOVER_STATE_RECONF_SLAVES)
    {
        return master->promoted_slave->addr;
    } else {
        return master->addr;
    }
}

/* This function sets the down_after_period field value in 'master' to all
 * the slaves and sentinel instances connected to this master. */
void sentinelPropagateDownAfterPeriod(sentinelRedisInstance *master) {
    dictIterator *di;
    dictEntry *de;
    int j;
    dict *d[] = {master->slaves, master->sentinels, NULL};

    for (j = 0; d[j]; j++) {
        di = dictGetIterator(d[j]);
        while((de = dictNext(di)) != NULL) {
            sentinelRedisInstance *ri = dictGetVal(de);
            ri->down_after_period = master->down_after_period;
        }
        dictReleaseIterator(di);
    }
}

/* This function is used in order to send commands to Redis instances: the
 * commands we send from Sentinel may be renamed, a common case is a master
 * with CONFIG and SLAVEOF commands renamed for security concerns. In that
 * case we check the ri->renamed_command table (or if the instance is a slave,
 * we check the one of the master), and map the command that we should send
 * to the set of renamed commands. However, if the command was not renamed,
 * we just return "command" itself. */
char *sentinelInstanceMapCommand(sentinelRedisInstance *ri, char *command) {
    sds sc = sdsnew(command);
    if (ri->master) ri = ri->master;
    char *retval = dictFetchValue(ri->renamed_commands, sc);
    sdsfree(sc);
    return retval ? retval : command;
}

/* ============================ Config handling ============================= */

/* Generalise handling create instance error. Use SRI_MASTER, SRI_SLAVE or
 * SRI_SENTINEL as a role value. */
const char *sentinelCheckCreateInstanceErrors(int role) {
    switch(errno) {
    case EBUSY:
        switch (role) {
        case SRI_MASTER:
            return "Duplicate master name.";
        case SRI_SLAVE:
            return "Duplicate hostname and port for replica.";
        case SRI_SENTINEL:
            return "Duplicate runid for sentinel.";
        default:
            serverAssert(0);
            break;
        }
        break;
    case ENOENT:
        return "Can't resolve instance hostname.";
    case EINVAL:
        return "Invalid port number.";
    default:
        return "Unknown Error for creating instances.";
    }
}

/* init function for server.sentinel_config */
void initializeSentinelConfig() {
    server.sentinel_config = zmalloc(sizeof(struct sentinelConfig));
    server.sentinel_config->monitor_cfg = listCreate();
    server.sentinel_config->pre_monitor_cfg = listCreate();
    server.sentinel_config->post_monitor_cfg = listCreate();
    listSetFreeMethod(server.sentinel_config->monitor_cfg,freeSentinelLoadQueueEntry);
    listSetFreeMethod(server.sentinel_config->pre_monitor_cfg,freeSentinelLoadQueueEntry);
    listSetFreeMethod(server.sentinel_config->post_monitor_cfg,freeSentinelLoadQueueEntry);
}

/* destroy function for server.sentinel_config */
void freeSentinelConfig() {
    /* release these three config queues since we will not use it anymore */
    listRelease(server.sentinel_config->pre_monitor_cfg);
    listRelease(server.sentinel_config->monitor_cfg);
    listRelease(server.sentinel_config->post_monitor_cfg);
    zfree(server.sentinel_config);
    server.sentinel_config = NULL;
}

/* Search config name in pre monitor config name array, return 1 if found,
 * 0 if not found. */
int searchPreMonitorCfgName(const char *name) {
    for (unsigned int i = 0; i < sizeof(preMonitorCfgName)/sizeof(preMonitorCfgName[0]); i++) {
        if (!strcasecmp(preMonitorCfgName[i],name)) return 1;
    }
    return 0;
}

/* free method for sentinelLoadQueueEntry when release the list */
void freeSentinelLoadQueueEntry(void *item) {
    struct sentinelLoadQueueEntry *entry = item;
    sdsfreesplitres(entry->argv,entry->argc);
    sdsfree(entry->line);
    zfree(entry);
}

/* This function is used for queuing sentinel configuration, the main
 * purpose of this function is to delay parsing the sentinel config option
 * in order to avoid the order dependent issue from the config. */
void queueSentinelConfig(sds *argv, int argc, int linenum, sds line) {
    int i;
    struct sentinelLoadQueueEntry *entry;

    /* initialize sentinel_config for the first call */
    if (server.sentinel_config == NULL) initializeSentinelConfig();

    entry = zmalloc(sizeof(struct sentinelLoadQueueEntry));
    entry->argv = zmalloc(sizeof(char*)*argc);
    entry->argc = argc;
    entry->linenum = linenum;
    entry->line = sdsdup(line);
    for (i = 0; i < argc; i++) {
        entry->argv[i] = sdsdup(argv[i]);
    }
    /*  Separate config lines with pre monitor config, monitor config and
     *  post monitor config, in order to parsing config dependencies
     *  correctly. */
    if (!strcasecmp(argv[0],"monitor")) {
        listAddNodeTail(server.sentinel_config->monitor_cfg,entry);
    } else if (searchPreMonitorCfgName(argv[0])) {
        listAddNodeTail(server.sentinel_config->pre_monitor_cfg,entry);
    } else{
        listAddNodeTail(server.sentinel_config->post_monitor_cfg,entry);
    }
}

/* This function is used for loading the sentinel configuration from
 * pre_monitor_cfg, monitor_cfg and post_monitor_cfg list */
void loadSentinelConfigFromQueue(void) {
    const char *err = NULL;
    listIter li;
    listNode *ln;
    int linenum = 0;
    sds line = NULL;
    unsigned int j;

    /* if there is no sentinel_config entry, we can return immediately */
    if (server.sentinel_config == NULL) return;

    list *sentinel_configs[3] = {
        server.sentinel_config->pre_monitor_cfg,
        server.sentinel_config->monitor_cfg,
        server.sentinel_config->post_monitor_cfg
    };
    /* loading from pre monitor config queue first to avoid dependency issues
     * loading from monitor config queue
     * loading from the post monitor config queue */
    for (j = 0; j < sizeof(sentinel_configs) / sizeof(sentinel_configs[0]); j++) {
        listRewind(sentinel_configs[j],&li);
        while((ln = listNext(&li))) {
            struct sentinelLoadQueueEntry *entry = ln->value;
            err = sentinelHandleConfiguration(entry->argv,entry->argc);
            if (err) {
                linenum = entry->linenum;
                line = entry->line;
                goto loaderr;
            }
        }
    }

    /* free sentinel_config when config loading is finished */
    freeSentinelConfig();
    return;

loaderr:
    fprintf(stderr, "\n*** FATAL CONFIG FILE ERROR (Redis %s) ***\n",
        REDIS_VERSION);
    fprintf(stderr, "Reading the configuration file, at line %d\n", linenum);
    fprintf(stderr, ">>> '%s'\n", line);
    fprintf(stderr, "%s\n", err);
    exit(1);
}

const char *sentinelHandleConfiguration(char **argv, int argc) {

    sentinelRedisInstance *ri;

    if (!strcasecmp(argv[0],"monitor") && argc == 5) {
        /* monitor <name> <host> <port> <quorum> */
        int quorum = atoi(argv[4]);

        if (quorum <= 0) return "Quorum must be 1 or greater.";
        if (createSentinelRedisInstance(argv[1],SRI_MASTER,argv[2],
                                        atoi(argv[3]),quorum,NULL) == NULL)
        {
            return sentinelCheckCreateInstanceErrors(SRI_MASTER);
        }
    } else if (!strcasecmp(argv[0],"down-after-milliseconds") && argc == 3) {
        /* down-after-milliseconds <name> <milliseconds> */
        ri = sentinelGetMasterByName(argv[1]);
        if (!ri) return "No such master with specified name.";
        ri->down_after_period = atoi(argv[2]);
        if (ri->down_after_period <= 0)
            return "negative or zero time parameter.";
        sentinelPropagateDownAfterPeriod(ri);
    } else if (!strcasecmp(argv[0],"failover-timeout") && argc == 3) {
        /* failover-timeout <name> <milliseconds> */
        ri = sentinelGetMasterByName(argv[1]);
        if (!ri) return "No such master with specified name.";
        ri->failover_timeout = atoi(argv[2]);
        if (ri->failover_timeout <= 0)
            return "negative or zero time parameter.";
    } else if (!strcasecmp(argv[0],"parallel-syncs") && argc == 3) {
        /* parallel-syncs <name> <milliseconds> */
        ri = sentinelGetMasterByName(argv[1]);
        if (!ri) return "No such master with specified name.";
        ri->parallel_syncs = atoi(argv[2]);
    } else if (!strcasecmp(argv[0],"notification-script") && argc == 3) {
        /* notification-script <name> <path> */
        ri = sentinelGetMasterByName(argv[1]);
        if (!ri) return "No such master with specified name.";
        if (access(argv[2],X_OK) == -1)
            return "Notification script seems non existing or non executable.";
        ri->notification_script = sdsnew(argv[2]);
    } else if (!strcasecmp(argv[0],"client-reconfig-script") && argc == 3) {
        /* client-reconfig-script <name> <path> */
        ri = sentinelGetMasterByName(argv[1]);
        if (!ri) return "No such master with specified name.";
        if (access(argv[2],X_OK) == -1)
            return "Client reconfiguration script seems non existing or "
                   "non executable.";
        ri->client_reconfig_script = sdsnew(argv[2]);
    } else if (!strcasecmp(argv[0],"auth-pass") && argc == 3) {
        /* auth-pass <name> <password> */
        ri = sentinelGetMasterByName(argv[1]);
        if (!ri) return "No such master with specified name.";
        ri->auth_pass = sdsnew(argv[2]);
    } else if (!strcasecmp(argv[0],"auth-user") && argc == 3) {
        /* auth-user <name> <username> */
        ri = sentinelGetMasterByName(argv[1]);
        if (!ri) return "No such master with specified name.";
        ri->auth_user = sdsnew(argv[2]);
    } else if (!strcasecmp(argv[0],"current-epoch") && argc == 2) {
        /* current-epoch <epoch> */
        unsigned long long current_epoch = strtoull(argv[1],NULL,10);
        if (current_epoch > sentinel.current_epoch)
            sentinel.current_epoch = current_epoch;
    } else if (!strcasecmp(argv[0],"myid") && argc == 2) {
        if (strlen(argv[1]) != CONFIG_RUN_ID_SIZE)
            return "Malformed Sentinel id in myid option.";
        memcpy(sentinel.myid,argv[1],CONFIG_RUN_ID_SIZE);
    } else if (!strcasecmp(argv[0],"config-epoch") && argc == 3) {
        /* config-epoch <name> <epoch> */
        ri = sentinelGetMasterByName(argv[1]);
        if (!ri) return "No such master with specified name.";
        ri->config_epoch = strtoull(argv[2],NULL,10);
        /* The following update of current_epoch is not really useful as
         * now the current epoch is persisted on the config file, but
         * we leave this check here for redundancy. */
        if (ri->config_epoch > sentinel.current_epoch)
            sentinel.current_epoch = ri->config_epoch;
    } else if (!strcasecmp(argv[0],"leader-epoch") && argc == 3) {
        /* leader-epoch <name> <epoch> */
        ri = sentinelGetMasterByName(argv[1]);
        if (!ri) return "No such master with specified name.";
        ri->leader_epoch = strtoull(argv[2],NULL,10);
    } else if ((!strcasecmp(argv[0],"known-slave") ||
                !strcasecmp(argv[0],"known-replica")) && argc == 4)
    {
        sentinelRedisInstance *slave;

        /* known-replica <name> <ip> <port> */
        ri = sentinelGetMasterByName(argv[1]);
        if (!ri) return "No such master with specified name.";
        if ((slave = createSentinelRedisInstance(NULL,SRI_SLAVE,argv[2],
                    atoi(argv[3]), ri->quorum, ri)) == NULL)
        {
            return sentinelCheckCreateInstanceErrors(SRI_SLAVE);
        }
    } else if (!strcasecmp(argv[0],"known-sentinel") &&
               (argc == 4 || argc == 5)) {
        sentinelRedisInstance *si;

        if (argc == 5) { /* Ignore the old form without runid. */
            /* known-sentinel <name> <ip> <port> [runid] */
            ri = sentinelGetMasterByName(argv[1]);
            if (!ri) return "No such master with specified name.";
            if ((si = createSentinelRedisInstance(argv[4],SRI_SENTINEL,argv[2],
                        atoi(argv[3]), ri->quorum, ri)) == NULL)
            {
                return sentinelCheckCreateInstanceErrors(SRI_SENTINEL);
            }
            si->runid = sdsnew(argv[4]);
            sentinelTryConnectionSharing(si);
        }
    } else if (!strcasecmp(argv[0],"rename-command") && argc == 4) {
        /* rename-command <name> <command> <renamed-command> */
        ri = sentinelGetMasterByName(argv[1]);
        if (!ri) return "No such master with specified name.";
        sds oldcmd = sdsnew(argv[2]);
        sds newcmd = sdsnew(argv[3]);
        if (dictAdd(ri->renamed_commands,oldcmd,newcmd) != DICT_OK) {
            sdsfree(oldcmd);
            sdsfree(newcmd);
            return "Same command renamed multiple times with rename-command.";
        }
    } else if (!strcasecmp(argv[0],"announce-ip") && argc == 2) {
        /* announce-ip <ip-address> */
        if (strlen(argv[1]))
            sentinel.announce_ip = sdsnew(argv[1]);
    } else if (!strcasecmp(argv[0],"announce-port") && argc == 2) {
        /* announce-port <port> */
        sentinel.announce_port = atoi(argv[1]);
    } else if (!strcasecmp(argv[0],"deny-scripts-reconfig") && argc == 2) {
        /* deny-scripts-reconfig <yes|no> */
        if ((sentinel.deny_scripts_reconfig = yesnotoi(argv[1])) == -1) {
            return "Please specify yes or no for the "
                   "deny-scripts-reconfig options.";
        }
    } else if (!strcasecmp(argv[0],"sentinel-user") && argc == 2) {
        /* sentinel-user <user-name> */
        if (strlen(argv[1]))
            sentinel.sentinel_auth_user = sdsnew(argv[1]);
    } else if (!strcasecmp(argv[0],"sentinel-pass") && argc == 2) {
        /* sentinel-pass <password> */
        if (strlen(argv[1]))
            sentinel.sentinel_auth_pass = sdsnew(argv[1]);
    } else if (!strcasecmp(argv[0],"resolve-hostnames") && argc == 2) {
        /* resolve-hostnames <yes|no> */
        if ((sentinel.resolve_hostnames = yesnotoi(argv[1])) == -1) {
            return "Please specify yes or no for the resolve-hostnames option.";
        }
    } else if (!strcasecmp(argv[0],"announce-hostnames") && argc == 2) {
        /* announce-hostnames <yes|no> */
        if ((sentinel.announce_hostnames = yesnotoi(argv[1])) == -1) {
            return "Please specify yes or no for the announce-hostnames option.";
        }
    } else if (!strcasecmp(argv[0],"master-reboot-down-after-period") && argc == 3) {
        /* master-reboot-down-after-period <name> <milliseconds> */
        ri = sentinelGetMasterByName(argv[1]);
        if (!ri) return "No such master with specified name.";
        ri->master_reboot_down_after_period = atoi(argv[2]);
        if (ri->master_reboot_down_after_period < 0)
            return "negative time parameter.";
    } else {
        return "Unrecognized sentinel configuration statement.";
    }
    return NULL;
}

/* Implements CONFIG REWRITE for "sentinel" option.
 * This is used not just to rewrite the configuration given by the user
 * (the configured masters) but also in order to retain the state of
 * Sentinel across restarts: config epoch of masters, associated slaves
 * and sentinel instances, and so forth. */
void rewriteConfigSentinelOption(struct rewriteConfigState *state) {
    dictIterator *di, *di2;
    dictEntry *de;
    sds line;

    /* sentinel unique ID. */
    line = sdscatprintf(sdsempty(), "sentinel myid %s", sentinel.myid);
    rewriteConfigRewriteLine(state,"sentinel myid",line,1);

    /* sentinel deny-scripts-reconfig. */
    line = sdscatprintf(sdsempty(), "sentinel deny-scripts-reconfig %s",
        sentinel.deny_scripts_reconfig ? "yes" : "no");
    rewriteConfigRewriteLine(state,"sentinel deny-scripts-reconfig",line,
        sentinel.deny_scripts_reconfig != SENTINEL_DEFAULT_DENY_SCRIPTS_RECONFIG);

    /* sentinel resolve-hostnames.
     * This must be included early in the file so it is already in effect
     * when reading the file.
     */
    line = sdscatprintf(sdsempty(), "sentinel resolve-hostnames %s",
                        sentinel.resolve_hostnames ? "yes" : "no");
    rewriteConfigRewriteLine(state,"sentinel resolve-hostnames",line,
                             sentinel.resolve_hostnames != SENTINEL_DEFAULT_RESOLVE_HOSTNAMES);

    /* sentinel announce-hostnames. */
    line = sdscatprintf(sdsempty(), "sentinel announce-hostnames %s",
                        sentinel.announce_hostnames ? "yes" : "no");
    rewriteConfigRewriteLine(state,"sentinel announce-hostnames",line,
                             sentinel.announce_hostnames != SENTINEL_DEFAULT_ANNOUNCE_HOSTNAMES);

    /* For every master emit a "sentinel monitor" config entry. */
    di = dictGetIterator(sentinel.masters);
    while((de = dictNext(di)) != NULL) {
        sentinelRedisInstance *master, *ri;
        sentinelAddr *master_addr;

        /* sentinel monitor */
        master = dictGetVal(de);
        master_addr = sentinelGetCurrentMasterAddress(master);
        line = sdscatprintf(sdsempty(),"sentinel monitor %s %s %d %d",
            master->name, announceSentinelAddr(master_addr), master_addr->port,
            master->quorum);
        rewriteConfigRewriteLine(state,"sentinel monitor",line,1);
        /* rewriteConfigMarkAsProcessed is handled after the loop */

        /* sentinel down-after-milliseconds */
        if (master->down_after_period != sentinel_default_down_after) {
            line = sdscatprintf(sdsempty(),
                "sentinel down-after-milliseconds %s %ld",
                master->name, (long) master->down_after_period);
            rewriteConfigRewriteLine(state,"sentinel down-after-milliseconds",line,1);
            /* rewriteConfigMarkAsProcessed is handled after the loop */
        }

        /* sentinel failover-timeout */
        if (master->failover_timeout != sentinel_default_failover_timeout) {
            line = sdscatprintf(sdsempty(),
                "sentinel failover-timeout %s %ld",
                master->name, (long) master->failover_timeout);
            rewriteConfigRewriteLine(state,"sentinel failover-timeout",line,1);
            /* rewriteConfigMarkAsProcessed is handled after the loop */

        }

        /* sentinel parallel-syncs */
        if (master->parallel_syncs != SENTINEL_DEFAULT_PARALLEL_SYNCS) {
            line = sdscatprintf(sdsempty(),
                "sentinel parallel-syncs %s %d",
                master->name, master->parallel_syncs);
            rewriteConfigRewriteLine(state,"sentinel parallel-syncs",line,1);
            /* rewriteConfigMarkAsProcessed is handled after the loop */
        }

        /* sentinel notification-script */
        if (master->notification_script) {
            line = sdscatprintf(sdsempty(),
                "sentinel notification-script %s %s",
                master->name, master->notification_script);
            rewriteConfigRewriteLine(state,"sentinel notification-script",line,1);
            /* rewriteConfigMarkAsProcessed is handled after the loop */
        }

        /* sentinel client-reconfig-script */
        if (master->client_reconfig_script) {
            line = sdscatprintf(sdsempty(),
                "sentinel client-reconfig-script %s %s",
                master->name, master->client_reconfig_script);
            rewriteConfigRewriteLine(state,"sentinel client-reconfig-script",line,1);
            /* rewriteConfigMarkAsProcessed is handled after the loop */
        }

        /* sentinel auth-pass & auth-user */
        if (master->auth_pass) {
            line = sdscatprintf(sdsempty(),
                "sentinel auth-pass %s %s",
                master->name, master->auth_pass);
            rewriteConfigRewriteLine(state,"sentinel auth-pass",line,1);
            /* rewriteConfigMarkAsProcessed is handled after the loop */
        }

        if (master->auth_user) {
            line = sdscatprintf(sdsempty(),
                "sentinel auth-user %s %s",
                master->name, master->auth_user);
            rewriteConfigRewriteLine(state,"sentinel auth-user",line,1);
            /* rewriteConfigMarkAsProcessed is handled after the loop */
        }

        /* sentinel master-reboot-down-after-period */
        if (master->master_reboot_down_after_period != 0) {
            line = sdscatprintf(sdsempty(),
                "sentinel master-reboot-down-after-period %s %ld",
                master->name, (long) master->master_reboot_down_after_period);
            rewriteConfigRewriteLine(state,"sentinel master-reboot-down-after-period",line,1);
            /* rewriteConfigMarkAsProcessed is handled after the loop */
        }

        /* sentinel config-epoch */
        line = sdscatprintf(sdsempty(),
            "sentinel config-epoch %s %llu",
            master->name, (unsigned long long) master->config_epoch);
        rewriteConfigRewriteLine(state,"sentinel config-epoch",line,1);
        /* rewriteConfigMarkAsProcessed is handled after the loop */


        /* sentinel leader-epoch */
        line = sdscatprintf(sdsempty(),
            "sentinel leader-epoch %s %llu",
            master->name, (unsigned long long) master->leader_epoch);
        rewriteConfigRewriteLine(state,"sentinel leader-epoch",line,1);
        /* rewriteConfigMarkAsProcessed is handled after the loop */

        /* sentinel known-slave */
        di2 = dictGetIterator(master->slaves);
        while((de = dictNext(di2)) != NULL) {
            sentinelAddr *slave_addr;

            ri = dictGetVal(de);
            slave_addr = ri->addr;

            /* If master_addr (obtained using sentinelGetCurrentMasterAddress()
             * so it may be the address of the promoted slave) is equal to this
             * slave's address, a failover is in progress and the slave was
             * already successfully promoted. So as the address of this slave
             * we use the old master address instead. */
            if (sentinelAddrOrHostnameEqual(slave_addr,master_addr))
                slave_addr = master->addr;
            line = sdscatprintf(sdsempty(),
                "sentinel known-replica %s %s %d",
                master->name, announceSentinelAddr(slave_addr), slave_addr->port);
            rewriteConfigRewriteLine(state,"sentinel known-replica",line,1);
            /* rewriteConfigMarkAsProcessed is handled after the loop */
        }
        dictReleaseIterator(di2);

        /* sentinel known-sentinel */
        di2 = dictGetIterator(master->sentinels);
        while((de = dictNext(di2)) != NULL) {
            ri = dictGetVal(de);
            if (ri->runid == NULL) continue;
            line = sdscatprintf(sdsempty(),
                "sentinel known-sentinel %s %s %d %s",
                master->name, announceSentinelAddr(ri->addr), ri->addr->port, ri->runid);
            rewriteConfigRewriteLine(state,"sentinel known-sentinel",line,1);
            /* rewriteConfigMarkAsProcessed is handled after the loop */
        }
        dictReleaseIterator(di2);

        /* sentinel rename-command */
        di2 = dictGetIterator(master->renamed_commands);
        while((de = dictNext(di2)) != NULL) {
            sds oldname = dictGetKey(de);
            sds newname = dictGetVal(de);
            line = sdscatprintf(sdsempty(),
                "sentinel rename-command %s %s %s",
                master->name, oldname, newname);
            rewriteConfigRewriteLine(state,"sentinel rename-command",line,1);
            /* rewriteConfigMarkAsProcessed is handled after the loop */
        }
        dictReleaseIterator(di2);
    }

    /* sentinel current-epoch is a global state valid for all the masters. */
    line = sdscatprintf(sdsempty(),
        "sentinel current-epoch %llu", (unsigned long long) sentinel.current_epoch);
    rewriteConfigRewriteLine(state,"sentinel current-epoch",line,1);

    /* sentinel announce-ip. */
    if (sentinel.announce_ip) {
        line = sdsnew("sentinel announce-ip ");
        line = sdscatrepr(line, sentinel.announce_ip, sdslen(sentinel.announce_ip));
        rewriteConfigRewriteLine(state,"sentinel announce-ip",line,1);
    } else {
        rewriteConfigMarkAsProcessed(state,"sentinel announce-ip");
    }

    /* sentinel announce-port. */
    if (sentinel.announce_port) {
        line = sdscatprintf(sdsempty(),"sentinel announce-port %d",
                            sentinel.announce_port);
        rewriteConfigRewriteLine(state,"sentinel announce-port",line,1);
    } else {
        rewriteConfigMarkAsProcessed(state,"sentinel announce-port");
    }

    /* sentinel sentinel-user. */
    if (sentinel.sentinel_auth_user) {
        line = sdscatprintf(sdsempty(), "sentinel sentinel-user %s", sentinel.sentinel_auth_user);
        rewriteConfigRewriteLine(state,"sentinel sentinel-user",line,1);
    } else {
        rewriteConfigMarkAsProcessed(state,"sentinel sentinel-user");
    }

    /* sentinel sentinel-pass. */
    if (sentinel.sentinel_auth_pass) {
        line = sdscatprintf(sdsempty(), "sentinel sentinel-pass %s", sentinel.sentinel_auth_pass);
        rewriteConfigRewriteLine(state,"sentinel sentinel-pass",line,1);
    } else {
        rewriteConfigMarkAsProcessed(state,"sentinel sentinel-pass");  
    }

    dictReleaseIterator(di);

    /* NOTE: the purpose here is in case due to the state change, the config rewrite 
     does not handle the configs, however, previously the config was set in the config file, 
     rewriteConfigMarkAsProcessed should be put here to mark it as processed in order to 
     delete the old config entry.
    */
    rewriteConfigMarkAsProcessed(state,"sentinel monitor");
    rewriteConfigMarkAsProcessed(state,"sentinel down-after-milliseconds");
    rewriteConfigMarkAsProcessed(state,"sentinel failover-timeout");
    rewriteConfigMarkAsProcessed(state,"sentinel parallel-syncs");
    rewriteConfigMarkAsProcessed(state,"sentinel notification-script");
    rewriteConfigMarkAsProcessed(state,"sentinel client-reconfig-script");
    rewriteConfigMarkAsProcessed(state,"sentinel auth-pass");
    rewriteConfigMarkAsProcessed(state,"sentinel auth-user");
    rewriteConfigMarkAsProcessed(state,"sentinel config-epoch");
    rewriteConfigMarkAsProcessed(state,"sentinel leader-epoch");
    rewriteConfigMarkAsProcessed(state,"sentinel known-replica");
    rewriteConfigMarkAsProcessed(state,"sentinel known-sentinel");
    rewriteConfigMarkAsProcessed(state,"sentinel rename-command");
    rewriteConfigMarkAsProcessed(state,"sentinel master-reboot-down-after-period");
}

/* This function uses the config rewriting Redis engine in order to persist
 * the state of the Sentinel in the current configuration file.
 *
 * Before returning the function calls fsync() against the generated
 * configuration file to make sure changes are committed to disk.
 *
 * On failure the function logs a warning on the Redis log. */
int sentinelFlushConfig(void) {
    int fd = -1;
    int saved_hz = server.hz;
    int rewrite_status;

    server.hz = CONFIG_DEFAULT_HZ;
    rewrite_status = rewriteConfig(server.configfile, 0);
    server.hz = saved_hz;

    if (rewrite_status == -1) goto werr;
    if ((fd = open(server.configfile,O_RDONLY)) == -1) goto werr;
    if (fsync(fd) == -1) goto werr;
    if (close(fd) == EOF) goto werr;
    serverLog(LL_NOTICE,"Sentinel new configuration saved on disk");
    return C_OK;

werr:
    serverLog(LL_WARNING,"WARNING: Sentinel was not able to save the new configuration on disk!!!: %s", strerror(errno));
    if (fd != -1) close(fd);
    return C_ERR;
}

/* Call sentinelFlushConfig() produce a success/error reply to the
 * calling client.
 */
static void sentinelFlushConfigAndReply(client *c) {
    if (sentinelFlushConfig() == C_ERR)
        addReplyError(c, "Failed to save config file. Check server logs.");
    else
        addReply(c, shared.ok);
}

/* ====================== hiredis connection handling ======================= */

/* Send the AUTH command with the specified master password if needed.
 * Note that for slaves the password set for the master is used.
 *
 * In case this Sentinel requires a password as well, via the "requirepass"
 * configuration directive, we assume we should use the local password in
 * order to authenticate when connecting with the other Sentinels as well.
 * So basically all the Sentinels share the same password and use it to
 * authenticate reciprocally.
 *
 * We don't check at all if the command was successfully transmitted
 * to the instance as if it fails Sentinel will detect the instance down,
 * will disconnect and reconnect the link and so forth. */
void sentinelSendAuthIfNeeded(sentinelRedisInstance *ri, redisAsyncContext *c) {
    char *auth_pass = NULL;
    char *auth_user = NULL;

    if (ri->flags & SRI_MASTER) {
        auth_pass = ri->auth_pass;
        auth_user = ri->auth_user;
    } else if (ri->flags & SRI_SLAVE) {
        auth_pass = ri->master->auth_pass;
        auth_user = ri->master->auth_user;
    } else if (ri->flags & SRI_SENTINEL) {
        /* If sentinel_auth_user is NULL, AUTH will use default user
           with sentinel_auth_pass to authenticate */
        if (sentinel.sentinel_auth_pass) {
            auth_pass = sentinel.sentinel_auth_pass;
            auth_user = sentinel.sentinel_auth_user;
        } else {
            /* Compatibility with old configs. requirepass is used
             * for both incoming and outgoing authentication. */
            auth_pass = server.requirepass;
            auth_user = NULL;
        }
    }

    if (auth_pass && auth_user == NULL) {
        if (redisAsyncCommand(c, sentinelDiscardReplyCallback, ri, "%s %s",
            sentinelInstanceMapCommand(ri,"AUTH"),
            auth_pass) == C_OK) ri->link->pending_commands++;
    } else if (auth_pass && auth_user) {
        /* If we also have an username, use the ACL-style AUTH command
         * with two arguments, username and password. */
        if (redisAsyncCommand(c, sentinelDiscardReplyCallback, ri, "%s %s %s",
            sentinelInstanceMapCommand(ri,"AUTH"),
            auth_user, auth_pass) == C_OK) ri->link->pending_commands++;
    }
}

/* Use CLIENT SETNAME to name the connection in the Redis instance as
 * sentinel-<first_8_chars_of_runid>-<connection_type>
 * The connection type is "cmd" or "pubsub" as specified by 'type'.
 *
 * This makes it possible to list all the sentinel instances connected
 * to a Redis server with CLIENT LIST, grepping for a specific name format. */
void sentinelSetClientName(sentinelRedisInstance *ri, redisAsyncContext *c, char *type) {
    char name[64];

    snprintf(name,sizeof(name),"sentinel-%.8s-%s",sentinel.myid,type);
    if (redisAsyncCommand(c, sentinelDiscardReplyCallback, ri,
        "%s SETNAME %s",
        sentinelInstanceMapCommand(ri,"CLIENT"),
        name) == C_OK)
    {
        ri->link->pending_commands++;
    }
}

static int instanceLinkNegotiateTLS(redisAsyncContext *context) {
#ifndef USE_OPENSSL
    (void) context;
#else
    if (!redis_tls_ctx) return C_ERR;
    SSL *ssl = SSL_new(redis_tls_client_ctx ? redis_tls_client_ctx : redis_tls_ctx);
    if (!ssl) return C_ERR;

    if (redisInitiateSSL(&context->c, ssl) == REDIS_ERR) {
        SSL_free(ssl);
        return C_ERR;
    }
#endif
    return C_OK;
}

/* Create the async connections for the instance link if the link
 * is disconnected. Note that link->disconnected is true even if just
 * one of the two links (commands and pub/sub) is missing. */
void sentinelReconnectInstance(sentinelRedisInstance *ri) {

    if (ri->link->disconnected == 0) return;
    if (ri->addr->port == 0) return; /* port == 0 means invalid address. */
    instanceLink *link = ri->link;
    mstime_t now = mstime();

    if (now - ri->link->last_reconn_time < sentinel_ping_period) return;
    ri->link->last_reconn_time = now;

    /* Commands connection. */
    if (link->cc == NULL) {

        /* It might be that the instance is disconnected because it wasn't available earlier when the instance
         * allocated, say during failover, and therefore we failed to resolve its ip.
         * Another scenario is that the instance restarted with new ip, and we should resolve its new ip based on
         * its hostname */
        if (sentinel.resolve_hostnames) {
            sentinelAddr *tryResolveAddr = createSentinelAddr(ri->addr->hostname, ri->addr->port, 0);
            if (tryResolveAddr != NULL) {
                releaseSentinelAddr(ri->addr);
                ri->addr = tryResolveAddr;
            }
        }

        link->cc = redisAsyncConnectBind(ri->addr->ip,ri->addr->port,server.bind_source_addr);

        if (link->cc && !link->cc->err) anetCloexec(link->cc->c.fd);
        if (!link->cc) {
            sentinelEvent(LL_DEBUG,"-cmd-link-reconnection",ri,"%@ #Failed to establish connection");
        } else if (!link->cc->err && server.tls_replication &&
                (instanceLinkNegotiateTLS(link->cc) == C_ERR)) {
            sentinelEvent(LL_DEBUG,"-cmd-link-reconnection",ri,"%@ #Failed to initialize TLS");
            instanceLinkCloseConnection(link,link->cc);
        } else if (link->cc->err) {
            sentinelEvent(LL_DEBUG,"-cmd-link-reconnection",ri,"%@ #%s",
                link->cc->errstr);
            instanceLinkCloseConnection(link,link->cc);
        } else {
            link->pending_commands = 0;
            link->cc_conn_time = mstime();
            link->cc->data = link;
            redisAeAttach(server.el,link->cc);
            redisAsyncSetConnectCallback(link->cc,
                    sentinelLinkEstablishedCallback);
            redisAsyncSetDisconnectCallback(link->cc,
                    sentinelDisconnectCallback);
            sentinelSendAuthIfNeeded(ri,link->cc);
            sentinelSetClientName(ri,link->cc,"cmd");

            /* Send a PING ASAP when reconnecting. */
            sentinelSendPing(ri);
        }
    }
    /* Pub / Sub */
    if ((ri->flags & (SRI_MASTER|SRI_SLAVE)) && link->pc == NULL) {
        link->pc = redisAsyncConnectBind(ri->addr->ip,ri->addr->port,server.bind_source_addr);
        if (link->pc && !link->pc->err) anetCloexec(link->pc->c.fd);
        if (!link->pc) {
            sentinelEvent(LL_DEBUG,"-pubsub-link-reconnection",ri,"%@ #Failed to establish connection");
        } else if (!link->pc->err && server.tls_replication &&
                (instanceLinkNegotiateTLS(link->pc) == C_ERR)) {
            sentinelEvent(LL_DEBUG,"-pubsub-link-reconnection",ri,"%@ #Failed to initialize TLS");
        } else if (link->pc->err) {
            sentinelEvent(LL_DEBUG,"-pubsub-link-reconnection",ri,"%@ #%s",
                link->pc->errstr);
            instanceLinkCloseConnection(link,link->pc);
        } else {
            int retval;
            link->pc_conn_time = mstime();
            link->pc->data = link;
            redisAeAttach(server.el,link->pc);
            redisAsyncSetConnectCallback(link->pc,
                    sentinelLinkEstablishedCallback);
            redisAsyncSetDisconnectCallback(link->pc,
                    sentinelDisconnectCallback);
            sentinelSendAuthIfNeeded(ri,link->pc);
            sentinelSetClientName(ri,link->pc,"pubsub");
            /* Now we subscribe to the Sentinels "Hello" channel. */
            retval = redisAsyncCommand(link->pc,
                sentinelReceiveHelloMessages, ri, "%s %s",
                sentinelInstanceMapCommand(ri,"SUBSCRIBE"),
                SENTINEL_HELLO_CHANNEL);
            if (retval != C_OK) {
                /* If we can't subscribe, the Pub/Sub connection is useless
                 * and we can simply disconnect it and try again. */
                instanceLinkCloseConnection(link,link->pc);
                return;
            }
        }
    }
    /* Clear the disconnected status only if we have both the connections
     * (or just the commands connection if this is a sentinel instance). */
    if (link->cc && (ri->flags & SRI_SENTINEL || link->pc))
        link->disconnected = 0;
}

/* ======================== Redis instances pinging  ======================== */

/* Return true if master looks "sane", that is:
 * 1) It is actually a master in the current configuration.
 * 2) It reports itself as a master.
 * 3) It is not SDOWN or ODOWN.
 * 4) We obtained last INFO no more than two times the INFO period time ago. */
int sentinelMasterLooksSane(sentinelRedisInstance *master) {
    return
        master->flags & SRI_MASTER &&
        master->role_reported == SRI_MASTER &&
        (master->flags & (SRI_S_DOWN|SRI_O_DOWN)) == 0 &&
        (mstime() - master->info_refresh) < sentinel_info_period*2;
}

/* Process the INFO output from masters. */
void sentinelRefreshInstanceInfo(sentinelRedisInstance *ri, const char *info) {
    sds *lines;
    int numlines, j;
    int role = 0;

    /* cache full INFO output for instance */
    sdsfree(ri->info);
    ri->info = sdsnew(info);

    /* The following fields must be reset to a given value in the case they
     * are not found at all in the INFO output. */
    ri->master_link_down_time = 0;

    /* Process line by line. */
    lines = sdssplitlen(info,strlen(info),"\r\n",2,&numlines);
    for (j = 0; j < numlines; j++) {
        sentinelRedisInstance *slave;
        sds l = lines[j];

        /* run_id:<40 hex chars>*/
        if (sdslen(l) >= 47 && !memcmp(l,"run_id:",7)) {
            if (ri->runid == NULL) {
                ri->runid = sdsnewlen(l+7,40);
            } else {
                if (strncmp(ri->runid,l+7,40) != 0) {
                    sentinelEvent(LL_NOTICE,"+reboot",ri,"%@");

                    if (ri->flags & SRI_MASTER && ri->master_reboot_down_after_period != 0) {
                        ri->flags |= SRI_MASTER_REBOOT;
                        ri->master_reboot_since_time = mstime();
                    }

                    sdsfree(ri->runid);
                    ri->runid = sdsnewlen(l+7,40);
                }
            }
        }

        /* old versions: slave0:<ip>,<port>,<state>
         * new versions: slave0:ip=127.0.0.1,port=9999,... */
        if ((ri->flags & SRI_MASTER) &&
            sdslen(l) >= 7 &&
            !memcmp(l,"slave",5) && isdigit(l[5]))
        {
            char *ip, *port, *end;

            if (strstr(l,"ip=") == NULL) {
                /* Old format. */
                ip = strchr(l,':'); if (!ip) continue;
                ip++; /* Now ip points to start of ip address. */
                port = strchr(ip,','); if (!port) continue;
                *port = '\0'; /* nul term for easy access. */
                port++; /* Now port points to start of port number. */
                end = strchr(port,','); if (!end) continue;
                *end = '\0'; /* nul term for easy access. */
            } else {
                /* New format. */
                ip = strstr(l,"ip="); if (!ip) continue;
                ip += 3; /* Now ip points to start of ip address. */
                port = strstr(l,"port="); if (!port) continue;
                port += 5; /* Now port points to start of port number. */
                /* Nul term both fields for easy access. */
                end = strchr(ip,','); if (end) *end = '\0';
                end = strchr(port,','); if (end) *end = '\0';
            }

            /* Check if we already have this slave into our table,
             * otherwise add it. */
            if (sentinelRedisInstanceLookupSlave(ri,ip,atoi(port)) == NULL) {
                if ((slave = createSentinelRedisInstance(NULL,SRI_SLAVE,ip,
                            atoi(port), ri->quorum, ri)) != NULL)
                {
                    sentinelEvent(LL_NOTICE,"+slave",slave,"%@");
                    sentinelFlushConfig();
                }
            }
        }

        /* master_link_down_since_seconds:<seconds> */
        if (sdslen(l) >= 32 &&
            !memcmp(l,"master_link_down_since_seconds",30))
        {
            ri->master_link_down_time = strtoll(l+31,NULL,10)*1000;
        }

        /* role:<role> */
        if (sdslen(l) >= 11 && !memcmp(l,"role:master",11)) role = SRI_MASTER;
        else if (sdslen(l) >= 10 && !memcmp(l,"role:slave",10)) role = SRI_SLAVE;

        if (role == SRI_SLAVE) {
            /* master_host:<host> */
            if (sdslen(l) >= 12 && !memcmp(l,"master_host:",12)) {
                if (ri->slave_master_host == NULL ||
                    strcasecmp(l+12,ri->slave_master_host))
                {
                    sdsfree(ri->slave_master_host);
                    ri->slave_master_host = sdsnew(l+12);
                    ri->slave_conf_change_time = mstime();
                }
            }

            /* master_port:<port> */
            if (sdslen(l) >= 12 && !memcmp(l,"master_port:",12)) {
                int slave_master_port = atoi(l+12);

                if (ri->slave_master_port != slave_master_port) {
                    ri->slave_master_port = slave_master_port;
                    ri->slave_conf_change_time = mstime();
                }
            }

            /* master_link_status:<status> */
            if (sdslen(l) >= 19 && !memcmp(l,"master_link_status:",19)) {
                ri->slave_master_link_status =
                    (strcasecmp(l+19,"up") == 0) ?
                    SENTINEL_MASTER_LINK_STATUS_UP :
                    SENTINEL_MASTER_LINK_STATUS_DOWN;
            }

            /* slave_priority:<priority> */
            if (sdslen(l) >= 15 && !memcmp(l,"slave_priority:",15))
                ri->slave_priority = atoi(l+15);

            /* slave_repl_offset:<offset> */
            if (sdslen(l) >= 18 && !memcmp(l,"slave_repl_offset:",18))
                ri->slave_repl_offset = strtoull(l+18,NULL,10);

            /* replica_announced:<announcement> */
            if (sdslen(l) >= 18 && !memcmp(l,"replica_announced:",18))
                ri->replica_announced = atoi(l+18);
        }
    }
    ri->info_refresh = mstime();
    sdsfreesplitres(lines,numlines);

    /* ---------------------------- Acting half -----------------------------
     * Some things will not happen if sentinel.tilt is true, but some will
     * still be processed. */

    /* Remember when the role changed. */
    if (role != ri->role_reported) {
        ri->role_reported_time = mstime();
        ri->role_reported = role;
        if (role == SRI_SLAVE) ri->slave_conf_change_time = mstime();
        /* Log the event with +role-change if the new role is coherent or
         * with -role-change if there is a mismatch with the current config. */
        sentinelEvent(LL_VERBOSE,
            ((ri->flags & (SRI_MASTER|SRI_SLAVE)) == role) ?
            "+role-change" : "-role-change",
            ri, "%@ new reported role is %s",
            role == SRI_MASTER ? "master" : "slave");
    }

    /* None of the following conditions are processed when in tilt mode, so
     * return asap. */
    if (sentinel.tilt) return;

    /* Handle master -> slave role switch. */
    if ((ri->flags & SRI_MASTER) && role == SRI_SLAVE) {
        /* Nothing to do, but masters claiming to be slaves are
         * considered to be unreachable by Sentinel, so eventually
         * a failover will be triggered. */
    }

    /* Handle slave -> master role switch. */
    if ((ri->flags & SRI_SLAVE) && role == SRI_MASTER) {
        /* If this is a promoted slave we can change state to the
         * failover state machine. */
        if ((ri->flags & SRI_PROMOTED) &&
            (ri->master->flags & SRI_FAILOVER_IN_PROGRESS) &&
            (ri->master->failover_state ==
                SENTINEL_FAILOVER_STATE_WAIT_PROMOTION))
        {
            /* Now that we are sure the slave was reconfigured as a master
             * set the master configuration epoch to the epoch we won the
             * election to perform this failover. This will force the other
             * Sentinels to update their config (assuming there is not
             * a newer one already available). */
            ri->master->config_epoch = ri->master->failover_epoch;
            ri->master->failover_state = SENTINEL_FAILOVER_STATE_RECONF_SLAVES;
            ri->master->failover_state_change_time = mstime();
            sentinelFlushConfig();
            sentinelEvent(LL_WARNING,"+promoted-slave",ri,"%@");
            if (sentinel.simfailure_flags &
                SENTINEL_SIMFAILURE_CRASH_AFTER_PROMOTION)
                sentinelSimFailureCrash();
            sentinelEvent(LL_WARNING,"+failover-state-reconf-slaves",
                ri->master,"%@");
            sentinelCallClientReconfScript(ri->master,SENTINEL_LEADER,
                "start",ri->master->addr,ri->addr);
            sentinelForceHelloUpdateForMaster(ri->master);
        } else {
            /* A slave turned into a master. We want to force our view and
             * reconfigure as slave. Wait some time after the change before
             * going forward, to receive new configs if any. */
            mstime_t wait_time = sentinel_publish_period*4;

            if (!(ri->flags & SRI_PROMOTED) &&
                 sentinelMasterLooksSane(ri->master) &&
                 sentinelRedisInstanceNoDownFor(ri,wait_time) &&
                 mstime() - ri->role_reported_time > wait_time)
            {
                int retval = sentinelSendSlaveOf(ri,ri->master->addr);
                if (retval == C_OK)
                    sentinelEvent(LL_NOTICE,"+convert-to-slave",ri,"%@");
            }
        }
    }

    /* Handle slaves replicating to a different master address. */
    if ((ri->flags & SRI_SLAVE) &&
        role == SRI_SLAVE &&
        (ri->slave_master_port != ri->master->addr->port ||
         !sentinelAddrEqualsHostname(ri->master->addr, ri->slave_master_host)))
    {
        mstime_t wait_time = ri->master->failover_timeout;

        /* Make sure the master is sane before reconfiguring this instance
         * into a slave. */
        if (sentinelMasterLooksSane(ri->master) &&
            sentinelRedisInstanceNoDownFor(ri,wait_time) &&
            mstime() - ri->slave_conf_change_time > wait_time)
        {
            int retval = sentinelSendSlaveOf(ri,ri->master->addr);
            if (retval == C_OK)
                sentinelEvent(LL_NOTICE,"+fix-slave-config",ri,"%@");
        }
    }

    /* Detect if the slave that is in the process of being reconfigured
     * changed state. */
    if ((ri->flags & SRI_SLAVE) && role == SRI_SLAVE &&
        (ri->flags & (SRI_RECONF_SENT|SRI_RECONF_INPROG)))
    {
        /* SRI_RECONF_SENT -> SRI_RECONF_INPROG. */
        if ((ri->flags & SRI_RECONF_SENT) &&
            ri->slave_master_host &&
            sentinelAddrEqualsHostname(ri->master->promoted_slave->addr,
                ri->slave_master_host) &&
            ri->slave_master_port == ri->master->promoted_slave->addr->port)
        {
            ri->flags &= ~SRI_RECONF_SENT;
            ri->flags |= SRI_RECONF_INPROG;
            sentinelEvent(LL_NOTICE,"+slave-reconf-inprog",ri,"%@");
        }

        /* SRI_RECONF_INPROG -> SRI_RECONF_DONE */
        if ((ri->flags & SRI_RECONF_INPROG) &&
            ri->slave_master_link_status == SENTINEL_MASTER_LINK_STATUS_UP)
        {
            ri->flags &= ~SRI_RECONF_INPROG;
            ri->flags |= SRI_RECONF_DONE;
            sentinelEvent(LL_NOTICE,"+slave-reconf-done",ri,"%@");
        }
    }
}

void sentinelInfoReplyCallback(redisAsyncContext *c, void *reply, void *privdata) {
    sentinelRedisInstance *ri = privdata;
    instanceLink *link = c->data;
    redisReply *r;

    if (!reply || !link) return;
    link->pending_commands--;
    r = reply;

    if (r->type == REDIS_REPLY_STRING)
        sentinelRefreshInstanceInfo(ri,r->str);
}

/* Just discard the reply. We use this when we are not monitoring the return
 * value of the command but its effects directly. */
void sentinelDiscardReplyCallback(redisAsyncContext *c, void *reply, void *privdata) {
    instanceLink *link = c->data;
    UNUSED(reply);
    UNUSED(privdata);

    if (link) link->pending_commands--;
}

void sentinelPingReplyCallback(redisAsyncContext *c, void *reply, void *privdata) {
    sentinelRedisInstance *ri = privdata;
    instanceLink *link = c->data;
    redisReply *r;

    if (!reply || !link) return;
    link->pending_commands--;
    r = reply;

    if (r->type == REDIS_REPLY_STATUS ||
        r->type == REDIS_REPLY_ERROR) {
        /* Update the "instance available" field only if this is an
         * acceptable reply. */
        if (strncmp(r->str,"PONG",4) == 0 ||
            strncmp(r->str,"LOADING",7) == 0 ||
            strncmp(r->str,"MASTERDOWN",10) == 0)
        {
            link->last_avail_time = mstime();
            link->act_ping_time = 0; /* Flag the pong as received. */

            if (ri->flags & SRI_MASTER_REBOOT && strncmp(r->str,"PONG",4) == 0)
                ri->flags &= ~SRI_MASTER_REBOOT;

        } else {
            /* Send a SCRIPT KILL command if the instance appears to be
             * down because of a busy script. */
            if (strncmp(r->str,"BUSY",4) == 0 &&
                (ri->flags & SRI_S_DOWN) &&
                !(ri->flags & SRI_SCRIPT_KILL_SENT))
            {
                if (redisAsyncCommand(ri->link->cc,
                        sentinelDiscardReplyCallback, ri,
                        "%s KILL",
                        sentinelInstanceMapCommand(ri,"SCRIPT")) == C_OK)
                {
                    ri->link->pending_commands++;
                }
                ri->flags |= SRI_SCRIPT_KILL_SENT;
            }
        }
    }
    link->last_pong_time = mstime();
}

/* This is called when we get the reply about the PUBLISH command we send
 * to the master to advertise this sentinel. */
void sentinelPublishReplyCallback(redisAsyncContext *c, void *reply, void *privdata) {
    sentinelRedisInstance *ri = privdata;
    instanceLink *link = c->data;
    redisReply *r;

    if (!reply || !link) return;
    link->pending_commands--;
    r = reply;

    /* Only update pub_time if we actually published our message. Otherwise
     * we'll retry again in 100 milliseconds. */
    if (r->type != REDIS_REPLY_ERROR)
        ri->last_pub_time = mstime();
}

/* Process a hello message received via Pub/Sub in master or slave instance,
 * or sent directly to this sentinel via the (fake) PUBLISH command of Sentinel.
 *
 * If the master name specified in the message is not known, the message is
 * discarded. */
void sentinelProcessHelloMessage(char *hello, int hello_len) {
    /* Format is composed of 8 tokens:
     * 0=ip,1=port,2=runid,3=current_epoch,4=master_name,
     * 5=master_ip,6=master_port,7=master_config_epoch. */
    int numtokens, port, removed, master_port;
    uint64_t current_epoch, master_config_epoch;
    char **token = sdssplitlen(hello, hello_len, ",", 1, &numtokens);
    sentinelRedisInstance *si, *master;

    if (numtokens == 8) {
        /* Obtain a reference to the master this hello message is about */
        master = sentinelGetMasterByName(token[4]);
        if (!master) goto cleanup; /* Unknown master, skip the message. */

        /* First, try to see if we already have this sentinel. */
        port = atoi(token[1]);
        master_port = atoi(token[6]);
        si = getSentinelRedisInstanceByAddrAndRunID(
                        master->sentinels,token[0],port,token[2]);
        current_epoch = strtoull(token[3],NULL,10);
        master_config_epoch = strtoull(token[7],NULL,10);

        if (!si) {
            /* If not, remove all the sentinels that have the same runid
             * because there was an address change, and add the same Sentinel
             * with the new address back. */
            removed = removeMatchingSentinelFromMaster(master,token[2]);
            if (removed) {
                sentinelEvent(LL_NOTICE,"+sentinel-address-switch",master,
                    "%@ ip %s port %d for %s", token[0],port,token[2]);
            } else {
                /* Check if there is another Sentinel with the same address this
                 * new one is reporting. What we do if this happens is to set its
                 * port to 0, to signal the address is invalid. We'll update it
                 * later if we get an HELLO message. */
                sentinelRedisInstance *other =
                    getSentinelRedisInstanceByAddrAndRunID(
                        master->sentinels, token[0],port,NULL);
                if (other) {
                    /* If there is already other sentinel with same address (but
                     * different runid) then remove the old one across all masters */
                    sentinelEvent(LL_NOTICE,"+sentinel-invalid-addr",other,"%@");
                    dictIterator *di;
                    dictEntry *de;

                    /* Keep a copy of runid. 'other' about to be deleted in loop. */
                    sds runid_obsolete = sdsnew(other->runid);

                    di = dictGetIterator(sentinel.masters);
                    while((de = dictNext(di)) != NULL) {
                        sentinelRedisInstance *master = dictGetVal(de);
                        removeMatchingSentinelFromMaster(master, runid_obsolete);
                    }
                    dictReleaseIterator(di);
                    sdsfree(runid_obsolete);
                }
            }

            /* Add the new sentinel. */
            si = createSentinelRedisInstance(token[2],SRI_SENTINEL,
                            token[0],port,master->quorum,master);

            if (si) {
                if (!removed) sentinelEvent(LL_NOTICE,"+sentinel",si,"%@");
                /* The runid is NULL after a new instance creation and
                 * for Sentinels we don't have a later chance to fill it,
                 * so do it now. */
                si->runid = sdsnew(token[2]);
                sentinelTryConnectionSharing(si);
                if (removed) sentinelUpdateSentinelAddressInAllMasters(si);
                sentinelFlushConfig();
            }
        }

        /* Update local current_epoch if received current_epoch is greater.*/
        if (current_epoch > sentinel.current_epoch) {
            sentinel.current_epoch = current_epoch;
            sentinelFlushConfig();
            sentinelEvent(LL_WARNING,"+new-epoch",master,"%llu",
                (unsigned long long) sentinel.current_epoch);
        }

        /* Update master info if received configuration is newer. */
        if (si && master->config_epoch < master_config_epoch) {
            master->config_epoch = master_config_epoch;
            if (master_port != master->addr->port ||
                !sentinelAddrEqualsHostname(master->addr, token[5]))
            {
                sentinelAddr *old_addr;

                sentinelEvent(LL_WARNING,"+config-update-from",si,"%@");
                sentinelEvent(LL_WARNING,"+switch-master",
                    master,"%s %s %d %s %d",
                    master->name,
                    announceSentinelAddr(master->addr), master->addr->port,
                    token[5], master_port);

                old_addr = dupSentinelAddr(master->addr);
                sentinelResetMasterAndChangeAddress(master, token[5], master_port);
                sentinelCallClientReconfScript(master,
                    SENTINEL_OBSERVER,"start",
                    old_addr,master->addr);
                releaseSentinelAddr(old_addr);
            }
        }

        /* Update the state of the Sentinel. */
        if (si) si->last_hello_time = mstime();
    }

cleanup:
    sdsfreesplitres(token,numtokens);
}


/* This is our Pub/Sub callback for the Hello channel. It's useful in order
 * to discover other sentinels attached at the same master. */
void sentinelReceiveHelloMessages(redisAsyncContext *c, void *reply, void *privdata) {
    sentinelRedisInstance *ri = privdata;
    redisReply *r;
    UNUSED(c);

    if (!reply || !ri) return;
    r = reply;

    /* Update the last activity in the pubsub channel. Note that since we
     * receive our messages as well this timestamp can be used to detect
     * if the link is probably disconnected even if it seems otherwise. */
    ri->link->pc_last_activity = mstime();

    /* Sanity check in the reply we expect, so that the code that follows
     * can avoid to check for details. */
    if (r->type != REDIS_REPLY_ARRAY ||
        r->elements != 3 ||
        r->element[0]->type != REDIS_REPLY_STRING ||
        r->element[1]->type != REDIS_REPLY_STRING ||
        r->element[2]->type != REDIS_REPLY_STRING ||
        strcmp(r->element[0]->str,"message") != 0) return;

    /* We are not interested in meeting ourselves */
    if (strstr(r->element[2]->str,sentinel.myid) != NULL) return;

    sentinelProcessHelloMessage(r->element[2]->str, r->element[2]->len);
}

/* Send a "Hello" message via Pub/Sub to the specified 'ri' Redis
 * instance in order to broadcast the current configuration for this
 * master, and to advertise the existence of this Sentinel at the same time.
 *
 * The message has the following format:
 *
 * sentinel_ip,sentinel_port,sentinel_runid,current_epoch,
 * master_name,master_ip,master_port,master_config_epoch.
 *
 * Returns C_OK if the PUBLISH was queued correctly, otherwise
 * C_ERR is returned. */
int sentinelSendHello(sentinelRedisInstance *ri) {
    char ip[NET_IP_STR_LEN];
    char payload[NET_IP_STR_LEN+1024];
    int retval;
    char *announce_ip;
    int announce_port;
    sentinelRedisInstance *master = (ri->flags & SRI_MASTER) ? ri : ri->master;
    sentinelAddr *master_addr = sentinelGetCurrentMasterAddress(master);

    if (ri->link->disconnected) return C_ERR;

    /* Use the specified announce address if specified, otherwise try to
     * obtain our own IP address. */
    if (sentinel.announce_ip) {
        announce_ip = sentinel.announce_ip;
    } else {
        if (anetFdToString(ri->link->cc->c.fd,ip,sizeof(ip),NULL,FD_TO_SOCK_NAME) == -1)
            return C_ERR;
        announce_ip = ip;
    }
    if (sentinel.announce_port) announce_port = sentinel.announce_port;
    else if (server.tls_replication && server.tls_port) announce_port = server.tls_port;
    else announce_port = server.port;

    /* Format and send the Hello message. */
    snprintf(payload,sizeof(payload),
        "%s,%d,%s,%llu," /* Info about this sentinel. */
        "%s,%s,%d,%llu", /* Info about current master. */
        announce_ip, announce_port, sentinel.myid,
        (unsigned long long) sentinel.current_epoch,
        /* --- */
        master->name,announceSentinelAddr(master_addr),master_addr->port,
        (unsigned long long) master->config_epoch);
    retval = redisAsyncCommand(ri->link->cc,
        sentinelPublishReplyCallback, ri, "%s %s %s",
        sentinelInstanceMapCommand(ri,"PUBLISH"),
        SENTINEL_HELLO_CHANNEL,payload);
    if (retval != C_OK) return C_ERR;
    ri->link->pending_commands++;
    return C_OK;
}

/* Reset last_pub_time in all the instances in the specified dictionary
 * in order to force the delivery of a Hello update ASAP. */
void sentinelForceHelloUpdateDictOfRedisInstances(dict *instances) {
    dictIterator *di;
    dictEntry *de;

    di = dictGetSafeIterator(instances);
    while((de = dictNext(di)) != NULL) {
        sentinelRedisInstance *ri = dictGetVal(de);
        if (ri->last_pub_time >= (sentinel_publish_period+1))
            ri->last_pub_time -= (sentinel_publish_period+1);
    }
    dictReleaseIterator(di);
}

/* This function forces the delivery of a "Hello" message (see
 * sentinelSendHello() top comment for further information) to all the Redis
 * and Sentinel instances related to the specified 'master'.
 *
 * It is technically not needed since we send an update to every instance
 * with a period of SENTINEL_PUBLISH_PERIOD milliseconds, however when a
 * Sentinel upgrades a configuration it is a good idea to deliver an update
 * to the other Sentinels ASAP. */
int sentinelForceHelloUpdateForMaster(sentinelRedisInstance *master) {
    if (!(master->flags & SRI_MASTER)) return C_ERR;
    if (master->last_pub_time >= (sentinel_publish_period+1))
        master->last_pub_time -= (sentinel_publish_period+1);
    sentinelForceHelloUpdateDictOfRedisInstances(master->sentinels);
    sentinelForceHelloUpdateDictOfRedisInstances(master->slaves);
    return C_OK;
}

/* Send a PING to the specified instance and refresh the act_ping_time
 * if it is zero (that is, if we received a pong for the previous ping).
 *
 * On error zero is returned, and we can't consider the PING command
 * queued in the connection. */
int sentinelSendPing(sentinelRedisInstance *ri) {
    int retval = redisAsyncCommand(ri->link->cc,
        sentinelPingReplyCallback, ri, "%s",
        sentinelInstanceMapCommand(ri,"PING"));
    if (retval == C_OK) {
        ri->link->pending_commands++;
        ri->link->last_ping_time = mstime();
        /* We update the active ping time only if we received the pong for
         * the previous ping, otherwise we are technically waiting since the
         * first ping that did not receive a reply. */
        if (ri->link->act_ping_time == 0)
            ri->link->act_ping_time = ri->link->last_ping_time;
        return 1;
    } else {
        return 0;
    }
}

/* Send periodic PING, INFO, and PUBLISH to the Hello channel to
 * the specified master or slave instance. */
void sentinelSendPeriodicCommands(sentinelRedisInstance *ri) {
    mstime_t now = mstime();
    mstime_t info_period, ping_period;
    int retval;

    /* Return ASAP if we have already a PING or INFO already pending, or
     * in the case the instance is not properly connected. */
    if (ri->link->disconnected) return;

    /* For INFO, PING, PUBLISH that are not critical commands to send we
     * also have a limit of SENTINEL_MAX_PENDING_COMMANDS. We don't
     * want to use a lot of memory just because a link is not working
     * properly (note that anyway there is a redundant protection about this,
     * that is, the link will be disconnected and reconnected if a long
     * timeout condition is detected. */
    if (ri->link->pending_commands >=
        SENTINEL_MAX_PENDING_COMMANDS * ri->link->refcount) return;

    /* If this is a slave of a master in O_DOWN condition we start sending
     * it INFO every second, instead of the usual SENTINEL_INFO_PERIOD
     * period. In this state we want to closely monitor slaves in case they
     * are turned into masters by another Sentinel, or by the sysadmin.
     *
     * Similarly we monitor the INFO output more often if the slave reports
     * to be disconnected from the master, so that we can have a fresh
     * disconnection time figure. */
    if ((ri->flags & SRI_SLAVE) &&
        ((ri->master->flags & (SRI_O_DOWN|SRI_FAILOVER_IN_PROGRESS)) ||
         (ri->master_link_down_time != 0)))
    {
        info_period = 1000;
    } else {
        info_period = sentinel_info_period;
    }

    /* We ping instances every time the last received pong is older than
     * the configured 'down-after-milliseconds' time, but every second
     * anyway if 'down-after-milliseconds' is greater than 1 second. */
    ping_period = ri->down_after_period;
    if (ping_period > sentinel_ping_period) ping_period = sentinel_ping_period;

    /* Send INFO to masters and slaves, not sentinels. */
    if ((ri->flags & SRI_SENTINEL) == 0 &&
        (ri->info_refresh == 0 ||
        (now - ri->info_refresh) > info_period))
    {
        retval = redisAsyncCommand(ri->link->cc,
            sentinelInfoReplyCallback, ri, "%s",
            sentinelInstanceMapCommand(ri,"INFO"));
        if (retval == C_OK) ri->link->pending_commands++;
    }

    /* Send PING to all the three kinds of instances. */
    if ((now - ri->link->last_pong_time) > ping_period &&
               (now - ri->link->last_ping_time) > ping_period/2) {
        sentinelSendPing(ri);
    }

    /* PUBLISH hello messages to all the three kinds of instances. */
    if ((now - ri->last_pub_time) > sentinel_publish_period) {
        sentinelSendHello(ri);
    }
}

/* =========================== SENTINEL command ============================= */

/* SENTINEL CONFIG SET <option> */
void sentinelConfigSetCommand(client *c) {
    robj *o = c->argv[3];
    robj *val = c->argv[4];
    long long numval;
    int drop_conns = 0;

    if (!strcasecmp(o->ptr, "resolve-hostnames")) {
        if ((numval = yesnotoi(val->ptr)) == -1) goto badfmt;
        sentinel.resolve_hostnames = numval;
    } else if (!strcasecmp(o->ptr, "announce-hostnames")) {
        if ((numval = yesnotoi(val->ptr)) == -1) goto badfmt;
        sentinel.announce_hostnames = numval;
    } else if (!strcasecmp(o->ptr, "announce-ip")) {
        if (sentinel.announce_ip) sdsfree(sentinel.announce_ip);
        sentinel.announce_ip = sdsnew(val->ptr);
    } else if (!strcasecmp(o->ptr, "announce-port")) {
        if (getLongLongFromObject(val, &numval) == C_ERR ||
            numval < 0 || numval > 65535)
            goto badfmt;
        sentinel.announce_port = numval;
    } else if (!strcasecmp(o->ptr, "sentinel-user")) {
        sdsfree(sentinel.sentinel_auth_user);
        sentinel.sentinel_auth_user = sdslen(val->ptr) == 0 ?
            NULL : sdsdup(val->ptr);
        drop_conns = 1;
    } else if (!strcasecmp(o->ptr, "sentinel-pass")) {
        sdsfree(sentinel.sentinel_auth_pass);
        sentinel.sentinel_auth_pass = sdslen(val->ptr) == 0 ?
            NULL : sdsdup(val->ptr);
        drop_conns = 1;
    } else {
        addReplyErrorFormat(c, "Invalid argument '%s' to SENTINEL CONFIG SET",
                            (char *) o->ptr);
        return;
    }

    sentinelFlushConfigAndReply(c);

    /* Drop Sentinel connections to initiate a reconnect if needed. */
    if (drop_conns)
        sentinelDropConnections();

    return;

badfmt:
    addReplyErrorFormat(c, "Invalid value '%s' to SENTINEL CONFIG SET '%s'",
                        (char *) val->ptr, (char *) o->ptr);
}

/* SENTINEL CONFIG GET <option> */
void sentinelConfigGetCommand(client *c) {
    robj *o = c->argv[3];
    const char *pattern = o->ptr;
    void *replylen = addReplyDeferredLen(c);
    int matches = 0;

    if (stringmatch(pattern,"resolve-hostnames",1)) {
        addReplyBulkCString(c,"resolve-hostnames");
        addReplyBulkCString(c,sentinel.resolve_hostnames ? "yes" : "no");
        matches++;
    }

    if (stringmatch(pattern, "announce-hostnames", 1)) {
        addReplyBulkCString(c,"announce-hostnames");
        addReplyBulkCString(c,sentinel.announce_hostnames ? "yes" : "no");
        matches++;
    }

    if (stringmatch(pattern, "announce-ip", 1)) {
        addReplyBulkCString(c,"announce-ip");
        addReplyBulkCString(c,sentinel.announce_ip ? sentinel.announce_ip : "");
        matches++;
    }

    if (stringmatch(pattern, "announce-port", 1)) {
        addReplyBulkCString(c, "announce-port");
        addReplyBulkLongLong(c, sentinel.announce_port);
        matches++;
    }

    if (stringmatch(pattern, "sentinel-user", 1)) {
        addReplyBulkCString(c, "sentinel-user");
        addReplyBulkCString(c, sentinel.sentinel_auth_user ? sentinel.sentinel_auth_user : "");
        matches++;
    }

    if (stringmatch(pattern, "sentinel-pass", 1)) {
        addReplyBulkCString(c, "sentinel-pass");
        addReplyBulkCString(c, sentinel.sentinel_auth_pass ? sentinel.sentinel_auth_pass : "");
        matches++;
    }

    setDeferredMapLen(c, replylen, matches);
}

const char *sentinelFailoverStateStr(int state) {
    switch(state) {
    case SENTINEL_FAILOVER_STATE_NONE: return "none";
    case SENTINEL_FAILOVER_STATE_WAIT_START: return "wait_start";
    case SENTINEL_FAILOVER_STATE_SELECT_SLAVE: return "select_slave";
    case SENTINEL_FAILOVER_STATE_SEND_SLAVEOF_NOONE: return "send_slaveof_noone";
    case SENTINEL_FAILOVER_STATE_WAIT_PROMOTION: return "wait_promotion";
    case SENTINEL_FAILOVER_STATE_RECONF_SLAVES: return "reconf_slaves";
    case SENTINEL_FAILOVER_STATE_UPDATE_CONFIG: return "update_config";
    default: return "unknown";
    }
}

/* Redis instance to Redis protocol representation. */
void addReplySentinelRedisInstance(client *c, sentinelRedisInstance *ri) {
    char *flags = sdsempty();
    void *mbl;
    int fields = 0;

    mbl = addReplyDeferredLen(c);

    addReplyBulkCString(c,"name");
    addReplyBulkCString(c,ri->name);
    fields++;

    addReplyBulkCString(c,"ip");
    addReplyBulkCString(c,announceSentinelAddr(ri->addr));
    fields++;

    addReplyBulkCString(c,"port");
    addReplyBulkLongLong(c,ri->addr->port);
    fields++;

    addReplyBulkCString(c,"runid");
    addReplyBulkCString(c,ri->runid ? ri->runid : "");
    fields++;

    addReplyBulkCString(c,"flags");
    if (ri->flags & SRI_S_DOWN) flags = sdscat(flags,"s_down,");
    if (ri->flags & SRI_O_DOWN) flags = sdscat(flags,"o_down,");
    if (ri->flags & SRI_MASTER) flags = sdscat(flags,"master,");
    if (ri->flags & SRI_SLAVE) flags = sdscat(flags,"slave,");
    if (ri->flags & SRI_SENTINEL) flags = sdscat(flags,"sentinel,");
    if (ri->link->disconnected) flags = sdscat(flags,"disconnected,");
    if (ri->flags & SRI_MASTER_DOWN) flags = sdscat(flags,"master_down,");
    if (ri->flags & SRI_FAILOVER_IN_PROGRESS)
        flags = sdscat(flags,"failover_in_progress,");
    if (ri->flags & SRI_PROMOTED) flags = sdscat(flags,"promoted,");
    if (ri->flags & SRI_RECONF_SENT) flags = sdscat(flags,"reconf_sent,");
    if (ri->flags & SRI_RECONF_INPROG) flags = sdscat(flags,"reconf_inprog,");
    if (ri->flags & SRI_RECONF_DONE) flags = sdscat(flags,"reconf_done,");
    if (ri->flags & SRI_FORCE_FAILOVER) flags = sdscat(flags,"force_failover,");
    if (ri->flags & SRI_SCRIPT_KILL_SENT) flags = sdscat(flags,"script_kill_sent,");

    if (sdslen(flags) != 0) sdsrange(flags,0,-2); /* remove last "," */
    addReplyBulkCString(c,flags);
    sdsfree(flags);
    fields++;

    addReplyBulkCString(c,"link-pending-commands");
    addReplyBulkLongLong(c,ri->link->pending_commands);
    fields++;

    addReplyBulkCString(c,"link-refcount");
    addReplyBulkLongLong(c,ri->link->refcount);
    fields++;

    if (ri->flags & SRI_FAILOVER_IN_PROGRESS) {
        addReplyBulkCString(c,"failover-state");
        addReplyBulkCString(c,(char*)sentinelFailoverStateStr(ri->failover_state));
        fields++;
    }

    addReplyBulkCString(c,"last-ping-sent");
    addReplyBulkLongLong(c,
        ri->link->act_ping_time ? (mstime() - ri->link->act_ping_time) : 0);
    fields++;

    addReplyBulkCString(c,"last-ok-ping-reply");
    addReplyBulkLongLong(c,mstime() - ri->link->last_avail_time);
    fields++;

    addReplyBulkCString(c,"last-ping-reply");
    addReplyBulkLongLong(c,mstime() - ri->link->last_pong_time);
    fields++;

    if (ri->flags & SRI_S_DOWN) {
        addReplyBulkCString(c,"s-down-time");
        addReplyBulkLongLong(c,mstime()-ri->s_down_since_time);
        fields++;
    }

    if (ri->flags & SRI_O_DOWN) {
        addReplyBulkCString(c,"o-down-time");
        addReplyBulkLongLong(c,mstime()-ri->o_down_since_time);
        fields++;
    }

    addReplyBulkCString(c,"down-after-milliseconds");
    addReplyBulkLongLong(c,ri->down_after_period);
    fields++;

    /* Masters and Slaves */
    if (ri->flags & (SRI_MASTER|SRI_SLAVE)) {
        addReplyBulkCString(c,"info-refresh");
        addReplyBulkLongLong(c,
            ri->info_refresh ? (mstime() - ri->info_refresh) : 0);
        fields++;

        addReplyBulkCString(c,"role-reported");
        addReplyBulkCString(c, (ri->role_reported == SRI_MASTER) ? "master" :
                                                                   "slave");
        fields++;

        addReplyBulkCString(c,"role-reported-time");
        addReplyBulkLongLong(c,mstime() - ri->role_reported_time);
        fields++;
    }

    /* Only masters */
    if (ri->flags & SRI_MASTER) {
        addReplyBulkCString(c,"config-epoch");
        addReplyBulkLongLong(c,ri->config_epoch);
        fields++;

        addReplyBulkCString(c,"num-slaves");
        addReplyBulkLongLong(c,dictSize(ri->slaves));
        fields++;

        addReplyBulkCString(c,"num-other-sentinels");
        addReplyBulkLongLong(c,dictSize(ri->sentinels));
        fields++;

        addReplyBulkCString(c,"quorum");
        addReplyBulkLongLong(c,ri->quorum);
        fields++;

        addReplyBulkCString(c,"failover-timeout");
        addReplyBulkLongLong(c,ri->failover_timeout);
        fields++;

        addReplyBulkCString(c,"parallel-syncs");
        addReplyBulkLongLong(c,ri->parallel_syncs);
        fields++;

        if (ri->notification_script) {
            addReplyBulkCString(c,"notification-script");
            addReplyBulkCString(c,ri->notification_script);
            fields++;
        }

        if (ri->client_reconfig_script) {
            addReplyBulkCString(c,"client-reconfig-script");
            addReplyBulkCString(c,ri->client_reconfig_script);
            fields++;
        }
    }

    /* Only slaves */
    if (ri->flags & SRI_SLAVE) {
        addReplyBulkCString(c,"master-link-down-time");
        addReplyBulkLongLong(c,ri->master_link_down_time);
        fields++;

        addReplyBulkCString(c,"master-link-status");
        addReplyBulkCString(c,
            (ri->slave_master_link_status == SENTINEL_MASTER_LINK_STATUS_UP) ?
            "ok" : "err");
        fields++;

        addReplyBulkCString(c,"master-host");
        addReplyBulkCString(c,
            ri->slave_master_host ? ri->slave_master_host : "?");
        fields++;

        addReplyBulkCString(c,"master-port");
        addReplyBulkLongLong(c,ri->slave_master_port);
        fields++;

        addReplyBulkCString(c,"slave-priority");
        addReplyBulkLongLong(c,ri->slave_priority);
        fields++;

        addReplyBulkCString(c,"slave-repl-offset");
        addReplyBulkLongLong(c,ri->slave_repl_offset);
        fields++;

        addReplyBulkCString(c,"replica-announced");
        addReplyBulkLongLong(c,ri->replica_announced);
        fields++;
    }

    /* Only sentinels */
    if (ri->flags & SRI_SENTINEL) {
        addReplyBulkCString(c,"last-hello-message");
        addReplyBulkLongLong(c,mstime() - ri->last_hello_time);
        fields++;

        addReplyBulkCString(c,"voted-leader");
        addReplyBulkCString(c,ri->leader ? ri->leader : "?");
        fields++;

        addReplyBulkCString(c,"voted-leader-epoch");
        addReplyBulkLongLong(c,ri->leader_epoch);
        fields++;
    }

    setDeferredMapLen(c,mbl,fields);
}

void sentinelSetDebugConfigParameters(client *c){
    int j;
    int badarg = 0; /* Bad argument position for error reporting. */
    char *option;

    /* Process option - value pairs. */
    for (j = 2; j < c->argc; j++) {
        int moreargs = (c->argc-1) - j;
        option = c->argv[j]->ptr;
        long long ll;

        if (!strcasecmp(option,"info-period") && moreargs > 0) {
            /* info-period <milliseconds> */
            robj *o = c->argv[++j];
            if (getLongLongFromObject(o,&ll) == C_ERR || ll <= 0) {
                badarg = j;
                goto badfmt;
            }
            sentinel_info_period = ll;

        } else if (!strcasecmp(option,"ping-period") && moreargs > 0) {
            /* ping-period <milliseconds> */
            robj *o = c->argv[++j];
            if (getLongLongFromObject(o,&ll) == C_ERR || ll <= 0) {
                badarg = j;
                goto badfmt;
            }
            sentinel_ping_period = ll;

        } else if (!strcasecmp(option,"ask-period") && moreargs > 0) {
            /* ask-period <milliseconds> */
            robj *o = c->argv[++j];
            if (getLongLongFromObject(o,&ll) == C_ERR || ll <= 0) {
                badarg = j;
                goto badfmt;
            }
            sentinel_ask_period = ll;

        } else if (!strcasecmp(option,"publish-period") && moreargs > 0) {
            /* publish-period <milliseconds> */
            robj *o = c->argv[++j];
            if (getLongLongFromObject(o,&ll) == C_ERR || ll <= 0) {
                badarg = j;
                goto badfmt;
            }
            sentinel_publish_period = ll;

        } else if (!strcasecmp(option,"default-down-after") && moreargs > 0) {
            /* default-down-after <milliseconds> */
            robj *o = c->argv[++j];
            if (getLongLongFromObject(o,&ll) == C_ERR || ll <= 0) {
                badarg = j;
                goto badfmt;
            }
            sentinel_default_down_after = ll;

        } else if (!strcasecmp(option,"tilt-trigger") && moreargs > 0) {
            /* tilt-trigger <milliseconds> */
            robj *o = c->argv[++j];
            if (getLongLongFromObject(o,&ll) == C_ERR || ll <= 0) {
                badarg = j;
                goto badfmt;
            }
            sentinel_tilt_trigger = ll;

        } else if (!strcasecmp(option,"tilt-period") && moreargs > 0) {
            /* tilt-period <milliseconds> */
            robj *o = c->argv[++j];
            if (getLongLongFromObject(o,&ll) == C_ERR || ll <= 0) {
                badarg = j;
                goto badfmt;
            }
            sentinel_tilt_period = ll;

        } else if (!strcasecmp(option,"slave-reconf-timeout") && moreargs > 0) {
            /* slave-reconf-timeout <milliseconds> */
            robj *o = c->argv[++j];
            if (getLongLongFromObject(o,&ll) == C_ERR || ll <= 0) {
                badarg = j;
                goto badfmt;
            }
            sentinel_slave_reconf_timeout = ll;

        } else if (!strcasecmp(option,"min-link-reconnect-period") && moreargs > 0) {
            /* min-link-reconnect-period <milliseconds> */
            robj *o = c->argv[++j];
            if (getLongLongFromObject(o,&ll) == C_ERR || ll <= 0) {
                badarg = j;
                goto badfmt;
            }
            sentinel_min_link_reconnect_period = ll;

        } else if (!strcasecmp(option,"default-failover-timeout") && moreargs > 0) {
            /* default-failover-timeout <milliseconds> */
            robj *o = c->argv[++j];
            if (getLongLongFromObject(o,&ll) == C_ERR || ll <= 0) {
                badarg = j;
                goto badfmt;
            }
            sentinel_default_failover_timeout = ll;

        } else if (!strcasecmp(option,"election-timeout") && moreargs > 0) {
            /* election-timeout <milliseconds> */
            robj *o = c->argv[++j];
            if (getLongLongFromObject(o,&ll) == C_ERR || ll <= 0) {
                badarg = j;
                goto badfmt;
            }
            sentinel_election_timeout = ll;

        } else if (!strcasecmp(option,"script-max-runtime") && moreargs > 0) {
            /* script-max-runtime <milliseconds> */
            robj *o = c->argv[++j];
            if (getLongLongFromObject(o,&ll) == C_ERR || ll <= 0) {
                badarg = j;
                goto badfmt;
            }
            sentinel_script_max_runtime = ll;

        } else if (!strcasecmp(option,"script-retry-delay") && moreargs > 0) {
            /* script-retry-delay <milliseconds> */
            robj *o = c->argv[++j];
            if (getLongLongFromObject(o,&ll) == C_ERR || ll <= 0) {
                badarg = j;
                goto badfmt;
            }
            sentinel_script_retry_delay = ll;

        } else {
            addReplyErrorFormat(c,"Unknown option or number of arguments for "
                                  "SENTINEL DEBUG '%s'", option);
            return;
        }
    }

    addReply(c,shared.ok);
    return;

badfmt: /* Bad format errors */
    addReplyErrorFormat(c,"Invalid argument '%s' for SENTINEL DEBUG '%s'",
        (char*)c->argv[badarg]->ptr,option);

    return;
}

void addReplySentinelDebugInfo(client *c) {
    void *mbl;
    int fields = 0;

    mbl = addReplyDeferredLen(c);

    addReplyBulkCString(c,"INFO-PERIOD");
    addReplyBulkLongLong(c,sentinel_info_period);
    fields++;

    addReplyBulkCString(c,"PING-PERIOD");
    addReplyBulkLongLong(c,sentinel_ping_period);
    fields++;

    addReplyBulkCString(c,"ASK-PERIOD");
    addReplyBulkLongLong(c,sentinel_ask_period);
    fields++;

    addReplyBulkCString(c,"PUBLISH-PERIOD");
    addReplyBulkLongLong(c,sentinel_publish_period);
    fields++;

    addReplyBulkCString(c,"DEFAULT-DOWN-AFTER");
    addReplyBulkLongLong(c,sentinel_default_down_after);
    fields++;

    addReplyBulkCString(c,"DEFAULT-FAILOVER-TIMEOUT");
    addReplyBulkLongLong(c,sentinel_default_failover_timeout);
    fields++;

    addReplyBulkCString(c,"TILT-TRIGGER");
    addReplyBulkLongLong(c,sentinel_tilt_trigger);
    fields++;

    addReplyBulkCString(c,"TILT-PERIOD");
    addReplyBulkLongLong(c,sentinel_tilt_period);
    fields++;

    addReplyBulkCString(c,"SLAVE-RECONF-TIMEOUT");
    addReplyBulkLongLong(c,sentinel_slave_reconf_timeout);
    fields++;

    addReplyBulkCString(c,"MIN-LINK-RECONNECT-PERIOD");
    addReplyBulkLongLong(c,sentinel_min_link_reconnect_period);
    fields++;

    addReplyBulkCString(c,"ELECTION-TIMEOUT");
    addReplyBulkLongLong(c,sentinel_election_timeout);
    fields++;

    addReplyBulkCString(c,"SCRIPT-MAX-RUNTIME");
    addReplyBulkLongLong(c,sentinel_script_max_runtime);
    fields++;

    addReplyBulkCString(c,"SCRIPT-RETRY-DELAY");
    addReplyBulkLongLong(c,sentinel_script_retry_delay);
    fields++;

    setDeferredMapLen(c,mbl,fields);
}

/* Output a number of instances contained inside a dictionary as
 * Redis protocol. */
void addReplyDictOfRedisInstances(client *c, dict *instances) {
    dictIterator *di;
    dictEntry *de;
    long slaves = 0;
    void *replylen = addReplyDeferredLen(c);

    di = dictGetIterator(instances);
    while((de = dictNext(di)) != NULL) {
        sentinelRedisInstance *ri = dictGetVal(de);

        /* don't announce unannounced replicas */
        if (ri->flags & SRI_SLAVE && !ri->replica_announced) continue;
        addReplySentinelRedisInstance(c,ri);
        slaves++;
    }
    dictReleaseIterator(di);
    setDeferredArrayLen(c, replylen, slaves);
}

/* Lookup the named master into sentinel.masters.
 * If the master is not found reply to the client with an error and returns
 * NULL. */
sentinelRedisInstance *sentinelGetMasterByNameOrReplyError(client *c,
                        robj *name)
{
    sentinelRedisInstance *ri;

    ri = dictFetchValue(sentinel.masters,name->ptr);
    if (!ri) {
        addReplyError(c,"No such master with that name");
        return NULL;
    }
    return ri;
}

#define SENTINEL_ISQR_OK 0
#define SENTINEL_ISQR_NOQUORUM (1<<0)
#define SENTINEL_ISQR_NOAUTH (1<<1)
int sentinelIsQuorumReachable(sentinelRedisInstance *master, int *usableptr) {
    dictIterator *di;
    dictEntry *de;
    int usable = 1; /* Number of usable Sentinels. Init to 1 to count myself. */
    int result = SENTINEL_ISQR_OK;
    int voters = dictSize(master->sentinels)+1; /* Known Sentinels + myself. */

    di = dictGetIterator(master->sentinels);
    while((de = dictNext(di)) != NULL) {
        sentinelRedisInstance *ri = dictGetVal(de);

        if (ri->flags & (SRI_S_DOWN|SRI_O_DOWN)) continue;
        usable++;
    }
    dictReleaseIterator(di);

    if (usable < (int)master->quorum) result |= SENTINEL_ISQR_NOQUORUM;
    if (usable < voters/2+1) result |= SENTINEL_ISQR_NOAUTH;
    if (usableptr) *usableptr = usable;
    return result;
}

void sentinelCommand(client *c) {
    if (c->argc == 2 && !strcasecmp(c->argv[1]->ptr,"help")) {
        const char *help[] = {
"CKQUORUM <master-name>",
"    Check if the current Sentinel configuration is able to reach the quorum",
"    needed to failover a master and the majority needed to authorize the",
"    failover.",
"CONFIG SET <param> <value>",
"    Set a global Sentinel configuration parameter.",
"CONFIG GET <param>",
"    Get global Sentinel configuration parameter.",
"DEBUG [<param> <value> ...]",
"    Show a list of configurable time parameters and their values (milliseconds).",
"    Or update current configurable parameters values (one or more).",
"GET-MASTER-ADDR-BY-NAME <master-name>",
"    Return the ip and port number of the master with that name.",
"FAILOVER <master-name>",
"    Manually failover a master node without asking for agreement from other",
"    Sentinels",
"FLUSHCONFIG",
"    Force Sentinel to rewrite its configuration on disk, including the current",
"    Sentinel state.",
"INFO-CACHE <master-name>",
"    Return last cached INFO output from masters and all its replicas.",
"IS-MASTER-DOWN-BY-ADDR <ip> <port> <current-epoch> <runid>",
"    Check if the master specified by ip:port is down from current Sentinel's",
"    point of view.",
"MASTER <master-name>",
"    Show the state and info of the specified master.",
"MASTERS",
"    Show a list of monitored masters and their state.",
"MONITOR <name> <ip> <port> <quorum>",
"    Start monitoring a new master with the specified name, ip, port and quorum.",
"MYID",
"    Return the ID of the Sentinel instance.",
"PENDING-SCRIPTS",
"    Get pending scripts information.",
"REMOVE <master-name>",
"    Remove master from Sentinel's monitor list.",
"REPLICAS <master-name>",
"    Show a list of replicas for this master and their state.",
"RESET <pattern>",
"    Reset masters for specific master name matching this pattern.",
"SENTINELS <master-name>",
"    Show a list of Sentinel instances for this master and their state.",
"SET <master-name> <option> <value> [<option> <value> ...]",
"    Set configuration parameters for certain masters.",
"SIMULATE-FAILURE [CRASH-AFTER-ELECTION] [CRASH-AFTER-PROMOTION] [HELP]",
"    Simulate a Sentinel crash.",
NULL
        };
        addReplyHelp(c, help);
    } else if (!strcasecmp(c->argv[1]->ptr,"masters")) {
        /* SENTINEL MASTERS */
        if (c->argc != 2) goto numargserr;
        addReplyDictOfRedisInstances(c,sentinel.masters);
    } else if (!strcasecmp(c->argv[1]->ptr,"master")) {
        /* SENTINEL MASTER <name> */
        sentinelRedisInstance *ri;

        if (c->argc != 3) goto numargserr;
        if ((ri = sentinelGetMasterByNameOrReplyError(c,c->argv[2]))
            == NULL) return;
        addReplySentinelRedisInstance(c,ri);
    } else if (!strcasecmp(c->argv[1]->ptr,"slaves") ||
               !strcasecmp(c->argv[1]->ptr,"replicas"))
    {
        /* SENTINEL REPLICAS <master-name> */
        sentinelRedisInstance *ri;

        if (c->argc != 3) goto numargserr;
        if ((ri = sentinelGetMasterByNameOrReplyError(c,c->argv[2])) == NULL)
            return;
        addReplyDictOfRedisInstances(c,ri->slaves);
    } else if (!strcasecmp(c->argv[1]->ptr,"sentinels")) {
        /* SENTINEL SENTINELS <master-name> */
        sentinelRedisInstance *ri;

        if (c->argc != 3) goto numargserr;
        if ((ri = sentinelGetMasterByNameOrReplyError(c,c->argv[2])) == NULL)
            return;
        addReplyDictOfRedisInstances(c,ri->sentinels);
    } else if (!strcasecmp(c->argv[1]->ptr,"myid") && c->argc == 2) {
        /* SENTINEL MYID */
        addReplyBulkCBuffer(c,sentinel.myid,CONFIG_RUN_ID_SIZE);
    } else if (!strcasecmp(c->argv[1]->ptr,"is-master-down-by-addr")) {
        /* SENTINEL IS-MASTER-DOWN-BY-ADDR <ip> <port> <current-epoch> <runid>
         *
         * Arguments:
         *
         * ip and port are the ip and port of the master we want to be
         * checked by Sentinel. Note that the command will not check by
         * name but just by master, in theory different Sentinels may monitor
         * different masters with the same name.
         *
         * current-epoch is needed in order to understand if we are allowed
         * to vote for a failover leader or not. Each Sentinel can vote just
         * one time per epoch.
         *
         * runid is "*" if we are not seeking for a vote from the Sentinel
         * in order to elect the failover leader. Otherwise it is set to the
         * runid we want the Sentinel to vote if it did not already voted.
         */
        sentinelRedisInstance *ri;
        long long req_epoch;
        uint64_t leader_epoch = 0;
        char *leader = NULL;
        long port;
        int isdown = 0;

        if (c->argc != 6) goto numargserr;
        if (getLongFromObjectOrReply(c,c->argv[3],&port,NULL) != C_OK ||
            getLongLongFromObjectOrReply(c,c->argv[4],&req_epoch,NULL)
                                                              != C_OK)
            return;
        ri = getSentinelRedisInstanceByAddrAndRunID(sentinel.masters,
            c->argv[2]->ptr,port,NULL);

        /* It exists? Is actually a master? Is subjectively down? It's down.
         * Note: if we are in tilt mode we always reply with "0". */
        if (!sentinel.tilt && ri && (ri->flags & SRI_S_DOWN) &&
                                    (ri->flags & SRI_MASTER))
            isdown = 1;

        /* Vote for the master (or fetch the previous vote) if the request
         * includes a runid, otherwise the sender is not seeking for a vote. */
        if (ri && ri->flags & SRI_MASTER && strcasecmp(c->argv[5]->ptr,"*")) {
            leader = sentinelVoteLeader(ri,(uint64_t)req_epoch,
                                            c->argv[5]->ptr,
                                            &leader_epoch);
        }

        /* Reply with a three-elements multi-bulk reply:
         * down state, leader, vote epoch. */
        addReplyArrayLen(c,3);
        addReply(c, isdown ? shared.cone : shared.czero);
        addReplyBulkCString(c, leader ? leader : "*");
        addReplyLongLong(c, (long long)leader_epoch);
        if (leader) sdsfree(leader);
    } else if (!strcasecmp(c->argv[1]->ptr,"reset")) {
        /* SENTINEL RESET <pattern> */
        if (c->argc != 3) goto numargserr;
        addReplyLongLong(c,sentinelResetMastersByPattern(c->argv[2]->ptr,SENTINEL_GENERATE_EVENT));
    } else if (!strcasecmp(c->argv[1]->ptr,"get-master-addr-by-name")) {
        /* SENTINEL GET-MASTER-ADDR-BY-NAME <master-name> */
        sentinelRedisInstance *ri;

        if (c->argc != 3) goto numargserr;
        ri = sentinelGetMasterByName(c->argv[2]->ptr);
        if (ri == NULL) {
            addReplyNullArray(c);
        } else {
            sentinelAddr *addr = sentinelGetCurrentMasterAddress(ri);

            addReplyArrayLen(c,2);
            addReplyBulkCString(c,announceSentinelAddr(addr));
            addReplyBulkLongLong(c,addr->port);
        }
    } else if (!strcasecmp(c->argv[1]->ptr,"failover")) {
        /* SENTINEL FAILOVER <master-name> */
        sentinelRedisInstance *ri;

        if (c->argc != 3) goto numargserr;
        if ((ri = sentinelGetMasterByNameOrReplyError(c,c->argv[2])) == NULL)
            return;
        if (ri->flags & SRI_FAILOVER_IN_PROGRESS) {
            addReplyError(c,"-INPROG Failover already in progress");
            return;
        }
        if (sentinelSelectSlave(ri) == NULL) {
            addReplyError(c,"-NOGOODSLAVE No suitable replica to promote");
            return;
        }
        serverLog(LL_WARNING,"Executing user requested FAILOVER of '%s'",
            ri->name);
        sentinelStartFailover(ri);
        ri->flags |= SRI_FORCE_FAILOVER;
        addReply(c,shared.ok);
    } else if (!strcasecmp(c->argv[1]->ptr,"pending-scripts")) {
        /* SENTINEL PENDING-SCRIPTS */

        if (c->argc != 2) goto numargserr;
        sentinelPendingScriptsCommand(c);
    } else if (!strcasecmp(c->argv[1]->ptr,"monitor")) {
        /* SENTINEL MONITOR <name> <ip> <port> <quorum> */
        sentinelRedisInstance *ri;
        long quorum, port;
        char ip[NET_IP_STR_LEN];

        if (c->argc != 6) goto numargserr;
        if (getLongFromObjectOrReply(c,c->argv[5],&quorum,"Invalid quorum")
            != C_OK) return;
        if (getLongFromObjectOrReply(c,c->argv[4],&port,"Invalid port")
            != C_OK) return;

        if (quorum <= 0) {
            addReplyError(c, "Quorum must be 1 or greater.");
            return;
        }

        /* If resolve-hostnames is used, actual DNS resolution may take place.
         * Otherwise just validate address.
         */
        if (anetResolve(NULL,c->argv[3]->ptr,ip,sizeof(ip),
                        sentinel.resolve_hostnames ? ANET_NONE : ANET_IP_ONLY) == ANET_ERR) {
            addReplyError(c, "Invalid IP address or hostname specified");
            return;
        }

        /* Parameters are valid. Try to create the master instance. */
        ri = createSentinelRedisInstance(c->argv[2]->ptr,SRI_MASTER,
                c->argv[3]->ptr,port,quorum,NULL);
        if (ri == NULL) {
            addReplyError(c,sentinelCheckCreateInstanceErrors(SRI_MASTER));
        } else {
            sentinelFlushConfigAndReply(c);
            sentinelEvent(LL_WARNING,"+monitor",ri,"%@ quorum %d",ri->quorum);
        }
    } else if (!strcasecmp(c->argv[1]->ptr,"flushconfig")) {
        if (c->argc != 2) goto numargserr;
        sentinelFlushConfigAndReply(c);
        return;
    } else if (!strcasecmp(c->argv[1]->ptr,"remove")) {
        /* SENTINEL REMOVE <name> */
        sentinelRedisInstance *ri;

        if (c->argc != 3) goto numargserr;
        if ((ri = sentinelGetMasterByNameOrReplyError(c,c->argv[2]))
            == NULL) return;
        sentinelEvent(LL_WARNING,"-monitor",ri,"%@");
        dictDelete(sentinel.masters,c->argv[2]->ptr);
        sentinelFlushConfigAndReply(c);
    } else if (!strcasecmp(c->argv[1]->ptr,"ckquorum")) {
        /* SENTINEL CKQUORUM <name> */
        sentinelRedisInstance *ri;
        int usable;

        if (c->argc != 3) goto numargserr;
        if ((ri = sentinelGetMasterByNameOrReplyError(c,c->argv[2]))
            == NULL) return;
        int result = sentinelIsQuorumReachable(ri,&usable);
        if (result == SENTINEL_ISQR_OK) {
            addReplySds(c, sdscatfmt(sdsempty(),
                "+OK %i usable Sentinels. Quorum and failover authorization "
                "can be reached\r\n",usable));
        } else {
            sds e = sdscatfmt(sdsempty(),
                "-NOQUORUM %i usable Sentinels. ",usable);
            if (result & SENTINEL_ISQR_NOQUORUM)
                e = sdscat(e,"Not enough available Sentinels to reach the"
                             " specified quorum for this master");
            if (result & SENTINEL_ISQR_NOAUTH) {
                if (result & SENTINEL_ISQR_NOQUORUM) e = sdscat(e,". ");
                e = sdscat(e, "Not enough available Sentinels to reach the"
                              " majority and authorize a failover");
            }
            addReplyErrorSds(c,e);
        }
    } else if (!strcasecmp(c->argv[1]->ptr,"set")) {
        sentinelSetCommand(c);
    } else if (!strcasecmp(c->argv[1]->ptr,"config")) {
        if (c->argc < 3) goto numargserr;
        if (!strcasecmp(c->argv[2]->ptr,"set") && c->argc == 5)
            sentinelConfigSetCommand(c);
        else if (!strcasecmp(c->argv[2]->ptr,"get") && c->argc == 4)
            sentinelConfigGetCommand(c);
        else
            addReplyError(c, "Only SENTINEL CONFIG GET <option> / SET <option> <value> are supported.");
    } else if (!strcasecmp(c->argv[1]->ptr,"info-cache")) {
        /* SENTINEL INFO-CACHE <name> */
        if (c->argc < 2) goto numargserr;
        mstime_t now = mstime();

        /* Create an ad-hoc dictionary type so that we can iterate
         * a dictionary composed of just the master groups the user
         * requested. */
        dictType copy_keeper = instancesDictType;
        copy_keeper.valDestructor = NULL;
        dict *masters_local = sentinel.masters;
        if (c->argc > 2) {
            masters_local = dictCreate(&copy_keeper);

            for (int i = 2; i < c->argc; i++) {
                sentinelRedisInstance *ri;
                ri = sentinelGetMasterByName(c->argv[i]->ptr);
                if (!ri) continue; /* ignore non-existing names */
                dictAdd(masters_local, ri->name, ri);
            }
        }

        /* Reply format:
         *   1.) master name
         *   2.) 1.) info from master
         *       2.) info from replica
         *       ...
         *   3.) other master name
         *   ...
         */
        addReplyArrayLen(c,dictSize(masters_local) * 2);

        dictIterator  *di;
        dictEntry *de;
        di = dictGetIterator(masters_local);
        while ((de = dictNext(di)) != NULL) {
            sentinelRedisInstance *ri = dictGetVal(de);
            addReplyBulkCBuffer(c,ri->name,strlen(ri->name));
            addReplyArrayLen(c,dictSize(ri->slaves) + 1); /* +1 for self */
            addReplyArrayLen(c,2);
            addReplyLongLong(c,
                ri->info_refresh ? (now - ri->info_refresh) : 0);
            if (ri->info)
                addReplyBulkCBuffer(c,ri->info,sdslen(ri->info));
            else
                addReplyNull(c);

            dictIterator *sdi;
            dictEntry *sde;
            sdi = dictGetIterator(ri->slaves);
            while ((sde = dictNext(sdi)) != NULL) {
                sentinelRedisInstance *sri = dictGetVal(sde);
                addReplyArrayLen(c,2);
                addReplyLongLong(c,
                    ri->info_refresh ? (now - sri->info_refresh) : 0);
                if (sri->info)
                    addReplyBulkCBuffer(c,sri->info,sdslen(sri->info));
                else
                    addReplyNull(c);
            }
            dictReleaseIterator(sdi);
        }
        dictReleaseIterator(di);
        if (masters_local != sentinel.masters) dictRelease(masters_local);
    } else if (!strcasecmp(c->argv[1]->ptr,"simulate-failure")) {
        /* SENTINEL SIMULATE-FAILURE [CRASH-AFTER-ELECTION] [CRASH-AFTER-PROMOTION] [HELP] */
        int j;

        sentinel.simfailure_flags = SENTINEL_SIMFAILURE_NONE;
        for (j = 2; j < c->argc; j++) {
            if (!strcasecmp(c->argv[j]->ptr,"crash-after-election")) {
                sentinel.simfailure_flags |=
                    SENTINEL_SIMFAILURE_CRASH_AFTER_ELECTION;
                serverLog(LL_WARNING,"Failure simulation: this Sentinel "
                    "will crash after being successfully elected as failover "
                    "leader");
            } else if (!strcasecmp(c->argv[j]->ptr,"crash-after-promotion")) {
                sentinel.simfailure_flags |=
                    SENTINEL_SIMFAILURE_CRASH_AFTER_PROMOTION;
                serverLog(LL_WARNING,"Failure simulation: this Sentinel "
                    "will crash after promoting the selected replica to master");
            } else if (!strcasecmp(c->argv[j]->ptr,"help")) {
                addReplyArrayLen(c,2);
                addReplyBulkCString(c,"crash-after-election");
                addReplyBulkCString(c,"crash-after-promotion");
                return;
            } else {
                addReplyError(c,"Unknown failure simulation specified");
                return;
            }
        }
        addReply(c,shared.ok);
    } else if (!strcasecmp(c->argv[1]->ptr,"debug")) {
        if(c->argc == 2)
            addReplySentinelDebugInfo(c);
        else
            sentinelSetDebugConfigParameters(c);
    } 
    else {
        addReplySubcommandSyntaxError(c);
    }
    return;

numargserr:
    addReplyErrorArity(c);
}

void addInfoSectionsToDict(dict *section_dict, char **sections);

/* INFO [<section> [<section> ...]] */
void sentinelInfoCommand(client *c) {
    char *sentinel_sections[] = {"server", "clients", "cpu", "stats", "sentinel", NULL};
    int sec_all = 0, sec_everything = 0;
    static dict *cached_all_info_sections = NULL;

    /* Get requested section list. */
    dict *sections_dict = genInfoSectionDict(c->argv+1, c->argc-1, sentinel_sections, &sec_all, &sec_everything);

    /* Purge unsupported sections from the requested ones. */
    dictEntry *de;
    dictIterator *di = dictGetSafeIterator(sections_dict);
    while((de = dictNext(di)) != NULL) {
        int i;
        sds sec = dictGetKey(de);
        for (i=0; sentinel_sections[i]; i++)
            if (!strcasecmp(sentinel_sections[i], sec))
                break;
        /* section not found? remove it */
        if (!sentinel_sections[i])
            dictDelete(sections_dict, sec);
    }
    dictReleaseIterator(di);

    /* Insert explicit all sections (don't pass these vars to genRedisInfoString) */
    if (sec_all || sec_everything) {
        releaseInfoSectionDict(sections_dict);
        /* We cache this dict as an optimization. */
        if (!cached_all_info_sections) {
            cached_all_info_sections = dictCreate(&stringSetDictType);
            addInfoSectionsToDict(cached_all_info_sections, sentinel_sections);
        }
        sections_dict = cached_all_info_sections;
    }

    sds info = genRedisInfoString(sections_dict, 0, 0);
    if (sec_all || (dictFind(sections_dict, "sentinel") != NULL)) {
        dictIterator *di;
        dictEntry *de;
        int master_id = 0;

        if (sdslen(info) != 0)
            info = sdscat(info,"\r\n");
        info = sdscatprintf(info,
            "# Sentinel\r\n"
            "sentinel_masters:%lu\r\n"
            "sentinel_tilt:%d\r\n"
            "sentinel_tilt_since_seconds:%jd\r\n"
            "sentinel_running_scripts:%d\r\n"
            "sentinel_scripts_queue_length:%ld\r\n"
            "sentinel_simulate_failure_flags:%lu\r\n",
            dictSize(sentinel.masters),
            sentinel.tilt,
            sentinel.tilt ? (intmax_t)((mstime()-sentinel.tilt_start_time)/1000) : -1,
            sentinel.running_scripts,
            listLength(sentinel.scripts_queue),
            sentinel.simfailure_flags);

        di = dictGetIterator(sentinel.masters);
        while((de = dictNext(di)) != NULL) {
            sentinelRedisInstance *ri = dictGetVal(de);
            char *status = "ok";

            if (ri->flags & SRI_O_DOWN) status = "odown";
            else if (ri->flags & SRI_S_DOWN) status = "sdown";
            info = sdscatprintf(info,
                "master%d:name=%s,status=%s,address=%s:%d,"
                "slaves=%lu,sentinels=%lu\r\n",
                master_id++, ri->name, status,
                announceSentinelAddr(ri->addr), ri->addr->port,
                dictSize(ri->slaves),
                dictSize(ri->sentinels)+1);
        }
        dictReleaseIterator(di);
    }
    if (sections_dict != cached_all_info_sections)
        releaseInfoSectionDict(sections_dict);
    addReplyBulkSds(c, info);
}

/* Implements Sentinel version of the ROLE command. The output is
 * "sentinel" and the list of currently monitored master names. */
void sentinelRoleCommand(client *c) {
    dictIterator *di;
    dictEntry *de;

    addReplyArrayLen(c,2);
    addReplyBulkCBuffer(c,"sentinel",8);
    addReplyArrayLen(c,dictSize(sentinel.masters));

    di = dictGetIterator(sentinel.masters);
    while((de = dictNext(di)) != NULL) {
        sentinelRedisInstance *ri = dictGetVal(de);

        addReplyBulkCString(c,ri->name);
    }
    dictReleaseIterator(di);
}

/* SENTINEL SET <mastername> [<option> <value> ...] */
void sentinelSetCommand(client *c) {
    sentinelRedisInstance *ri;
    int j, changes = 0;
    int badarg = 0; /* Bad argument position for error reporting. */
    char *option;
    int redacted;

    if ((ri = sentinelGetMasterByNameOrReplyError(c,c->argv[2]))
        == NULL) return;

    /* Process option - value pairs. */
    for (j = 3; j < c->argc; j++) {
        int moreargs = (c->argc-1) - j;
        option = c->argv[j]->ptr;
        long long ll;
        int old_j = j; /* Used to know what to log as an event. */
        redacted = 0;

        if (!strcasecmp(option,"down-after-milliseconds") && moreargs > 0) {
            /* down-after-milliseconds <milliseconds> */
            robj *o = c->argv[++j];
            if (getLongLongFromObject(o,&ll) == C_ERR || ll <= 0) {
                badarg = j;
                goto badfmt;
            }
            ri->down_after_period = ll;
            sentinelPropagateDownAfterPeriod(ri);
            changes++;
        } else if (!strcasecmp(option,"failover-timeout") && moreargs > 0) {
            /* failover-timeout <milliseconds> */
            robj *o = c->argv[++j];
            if (getLongLongFromObject(o,&ll) == C_ERR || ll <= 0) {
                badarg = j;
                goto badfmt;
            }
            ri->failover_timeout = ll;
            changes++;
        } else if (!strcasecmp(option,"parallel-syncs") && moreargs > 0) {
            /* parallel-syncs <milliseconds> */
            robj *o = c->argv[++j];
            if (getLongLongFromObject(o,&ll) == C_ERR || ll <= 0) {
                badarg = j;
                goto badfmt;
            }
            ri->parallel_syncs = ll;
            changes++;
        } else if (!strcasecmp(option,"notification-script") && moreargs > 0) {
            /* notification-script <path> */
            char *value = c->argv[++j]->ptr;
            if (sentinel.deny_scripts_reconfig) {
                addReplyError(c,
                    "Reconfiguration of scripts path is denied for "
                    "security reasons. Check the deny-scripts-reconfig "
                    "configuration directive in your Sentinel configuration");
                goto seterr;
            }

            if (strlen(value) && access(value,X_OK) == -1) {
                addReplyError(c,
                    "Notification script seems non existing or non executable");
                goto seterr;
            }
            sdsfree(ri->notification_script);
            ri->notification_script = strlen(value) ? sdsnew(value) : NULL;
            changes++;
        } else if (!strcasecmp(option,"client-reconfig-script") && moreargs > 0) {
            /* client-reconfig-script <path> */
            char *value = c->argv[++j]->ptr;
            if (sentinel.deny_scripts_reconfig) {
                addReplyError(c,
                    "Reconfiguration of scripts path is denied for "
                    "security reasons. Check the deny-scripts-reconfig "
                    "configuration directive in your Sentinel configuration");
                goto seterr;
            }

            if (strlen(value) && access(value,X_OK) == -1) {
                addReplyError(c,
                    "Client reconfiguration script seems non existing or "
                    "non executable");
                goto seterr;
            }
            sdsfree(ri->client_reconfig_script);
            ri->client_reconfig_script = strlen(value) ? sdsnew(value) : NULL;
            changes++;
        } else if (!strcasecmp(option,"auth-pass") && moreargs > 0) {
            /* auth-pass <password> */
            char *value = c->argv[++j]->ptr;
            sdsfree(ri->auth_pass);
            ri->auth_pass = strlen(value) ? sdsnew(value) : NULL;
            dropInstanceConnections(ri);
            changes++;
            redacted = 1;
        } else if (!strcasecmp(option,"auth-user") && moreargs > 0) {
            /* auth-user <username> */
            char *value = c->argv[++j]->ptr;
            sdsfree(ri->auth_user);
            ri->auth_user = strlen(value) ? sdsnew(value) : NULL;
            dropInstanceConnections(ri);
            changes++;
        } else if (!strcasecmp(option,"quorum") && moreargs > 0) {
            /* quorum <count> */
            robj *o = c->argv[++j];
            if (getLongLongFromObject(o,&ll) == C_ERR || ll <= 0) {
                badarg = j;
                goto badfmt;
            }
            ri->quorum = ll;
            changes++;
        } else if (!strcasecmp(option,"rename-command") && moreargs > 1) {
            /* rename-command <oldname> <newname> */
            sds oldname = c->argv[++j]->ptr;
            sds newname = c->argv[++j]->ptr;

            if ((sdslen(oldname) == 0) || (sdslen(newname) == 0)) {
                badarg = sdslen(newname) ? j-1 : j;
                goto badfmt;
            }

            /* Remove any older renaming for this command. */
            dictDelete(ri->renamed_commands,oldname);

            /* If the target name is the same as the source name there
             * is no need to add an entry mapping to itself. */
            if (!dictSdsKeyCaseCompare(ri->renamed_commands,oldname,newname)) {
                oldname = sdsdup(oldname);
                newname = sdsdup(newname);
                dictAdd(ri->renamed_commands,oldname,newname);
            }
            changes++;
        } else if (!strcasecmp(option,"master-reboot-down-after-period") && moreargs > 0) {
            /* master-reboot-down-after-period <milliseconds> */
            robj *o = c->argv[++j];
            if (getLongLongFromObject(o,&ll) == C_ERR || ll < 0) {
                badarg = j;
                goto badfmt;
            }
            ri->master_reboot_down_after_period = ll;
            changes++;
        } else {
            addReplyErrorFormat(c,"Unknown option or number of arguments for "
                                  "SENTINEL SET '%s'", option);
            goto seterr;
        }

        /* Log the event. */
        int numargs = j-old_j+1;
        switch(numargs) {
        case 2:
            sentinelEvent(LL_WARNING,"+set",ri,"%@ %s %s",(char*)c->argv[old_j]->ptr,
                                                          redacted ? "******" : (char*)c->argv[old_j+1]->ptr);
            break;
        case 3:
            sentinelEvent(LL_WARNING,"+set",ri,"%@ %s %s %s",(char*)c->argv[old_j]->ptr,
                                                             (char*)c->argv[old_j+1]->ptr,
                                                             (char*)c->argv[old_j+2]->ptr);
            break;
        default:
            sentinelEvent(LL_WARNING,"+set",ri,"%@ %s",(char*)c->argv[old_j]->ptr);
            break;
        }
    }
    if (changes) sentinelFlushConfigAndReply(c);
    return;

badfmt: /* Bad format errors */
    addReplyErrorFormat(c,"Invalid argument '%s' for SENTINEL SET '%s'",
        (char*)c->argv[badarg]->ptr,option);
seterr:
    /* TODO: Handle the case of both bad input and save error, possibly handling
     * SENTINEL SET atomically. */
    if (changes) sentinelFlushConfig();
}

/* Our fake PUBLISH command: it is actually useful only to receive hello messages
 * from the other sentinel instances, and publishing to a channel other than
 * SENTINEL_HELLO_CHANNEL is forbidden.
 *
 * Because we have a Sentinel PUBLISH, the code to send hello messages is the same
 * for all the three kind of instances: masters, slaves, sentinels. */
void sentinelPublishCommand(client *c) {
    if (strcmp(c->argv[1]->ptr,SENTINEL_HELLO_CHANNEL)) {
        addReplyError(c, "Only HELLO messages are accepted by Sentinel instances.");
        return;
    }
    sentinelProcessHelloMessage(c->argv[2]->ptr,sdslen(c->argv[2]->ptr));
    addReplyLongLong(c,1);
}

/* ===================== SENTINEL availability checks ======================= */

/* Is this instance down from our point of view? */
void sentinelCheckSubjectivelyDown(sentinelRedisInstance *ri) {
    mstime_t elapsed = 0;

    if (ri->link->act_ping_time)
        elapsed = mstime() - ri->link->act_ping_time;
    else if (ri->link->disconnected)
        elapsed = mstime() - ri->link->last_avail_time;

    /* Check if we are in need for a reconnection of one of the
     * links, because we are detecting low activity.
     *
     * 1) Check if the command link seems connected, was connected not less
     *    than SENTINEL_MIN_LINK_RECONNECT_PERIOD, but still we have a
     *    pending ping for more than half the timeout. */
    if (ri->link->cc &&
        (mstime() - ri->link->cc_conn_time) >
        sentinel_min_link_reconnect_period &&
        ri->link->act_ping_time != 0 && /* There is a pending ping... */
        /* The pending ping is delayed, and we did not receive
         * error replies as well. */
        (mstime() - ri->link->act_ping_time) > (ri->down_after_period/2) &&
        (mstime() - ri->link->last_pong_time) > (ri->down_after_period/2))
    {
        instanceLinkCloseConnection(ri->link,ri->link->cc);
    }

    /* 2) Check if the pubsub link seems connected, was connected not less
     *    than SENTINEL_MIN_LINK_RECONNECT_PERIOD, but still we have no
     *    activity in the Pub/Sub channel for more than
     *    SENTINEL_PUBLISH_PERIOD * 3.
     */
    if (ri->link->pc &&
        (mstime() - ri->link->pc_conn_time) >
         sentinel_min_link_reconnect_period &&
        (mstime() - ri->link->pc_last_activity) > (sentinel_publish_period*3))
    {
        instanceLinkCloseConnection(ri->link,ri->link->pc);
    }

    /* Update the SDOWN flag. We believe the instance is SDOWN if:
     *
     * 1) It is not replying.
     * 2) We believe it is a master, it reports to be a slave for enough time
     *    to meet the down_after_period, plus enough time to get two times
     *    INFO report from the instance. */
    if (elapsed > ri->down_after_period ||
        (ri->flags & SRI_MASTER &&
         ri->role_reported == SRI_SLAVE &&
         mstime() - ri->role_reported_time >
          (ri->down_after_period+sentinel_info_period*2)) ||
          (ri->flags & SRI_MASTER_REBOOT && 
           mstime()-ri->master_reboot_since_time > ri->master_reboot_down_after_period))
    {
        /* Is subjectively down */
        if ((ri->flags & SRI_S_DOWN) == 0) {
            sentinelEvent(LL_WARNING,"+sdown",ri,"%@");
            ri->s_down_since_time = mstime();
            ri->flags |= SRI_S_DOWN;
        }
    } else {
        /* Is subjectively up */
        if (ri->flags & SRI_S_DOWN) {
            sentinelEvent(LL_WARNING,"-sdown",ri,"%@");
            ri->flags &= ~(SRI_S_DOWN|SRI_SCRIPT_KILL_SENT);
        }
    }
}

/* Is this instance down according to the configured quorum?
 *
 * Note that ODOWN is a weak quorum, it only means that enough Sentinels
 * reported in a given time range that the instance was not reachable.
 * However messages can be delayed so there are no strong guarantees about
 * N instances agreeing at the same time about the down state. */
void sentinelCheckObjectivelyDown(sentinelRedisInstance *master) {
    dictIterator *di;
    dictEntry *de;
    unsigned int quorum = 0, odown = 0;

    if (master->flags & SRI_S_DOWN) {
        /* Is down for enough sentinels? */
        quorum = 1; /* the current sentinel. */
        /* Count all the other sentinels. */
        di = dictGetIterator(master->sentinels);
        while((de = dictNext(di)) != NULL) {
            sentinelRedisInstance *ri = dictGetVal(de);

            if (ri->flags & SRI_MASTER_DOWN) quorum++;
        }
        dictReleaseIterator(di);
        if (quorum >= master->quorum) odown = 1;
    }

    /* Set the flag accordingly to the outcome. */
    if (odown) {
        if ((master->flags & SRI_O_DOWN) == 0) {
            sentinelEvent(LL_WARNING,"+odown",master,"%@ #quorum %d/%d",
                quorum, master->quorum);
            master->flags |= SRI_O_DOWN;
            master->o_down_since_time = mstime();
        }
    } else {
        if (master->flags & SRI_O_DOWN) {
            sentinelEvent(LL_WARNING,"-odown",master,"%@");
            master->flags &= ~SRI_O_DOWN;
        }
    }
}

/* Receive the SENTINEL is-master-down-by-addr reply, see the
 * sentinelAskMasterStateToOtherSentinels() function for more information. */
void sentinelReceiveIsMasterDownReply(redisAsyncContext *c, void *reply, void *privdata) {
    sentinelRedisInstance *ri = privdata;
    instanceLink *link = c->data;
    redisReply *r;

    if (!reply || !link) return;
    link->pending_commands--;
    r = reply;

    /* Ignore every error or unexpected reply.
     * Note that if the command returns an error for any reason we'll
     * end clearing the SRI_MASTER_DOWN flag for timeout anyway. */
    if (r->type == REDIS_REPLY_ARRAY && r->elements == 3 &&
        r->element[0]->type == REDIS_REPLY_INTEGER &&
        r->element[1]->type == REDIS_REPLY_STRING &&
        r->element[2]->type == REDIS_REPLY_INTEGER)
    {
        ri->last_master_down_reply_time = mstime();
        if (r->element[0]->integer == 1) {
            ri->flags |= SRI_MASTER_DOWN;
        } else {
            ri->flags &= ~SRI_MASTER_DOWN;
        }
        if (strcmp(r->element[1]->str,"*")) {
            /* If the runid in the reply is not "*" the Sentinel actually
             * replied with a vote. */
            sdsfree(ri->leader);
            if ((long long)ri->leader_epoch != r->element[2]->integer)
                serverLog(LL_WARNING,
                    "%s voted for %s %llu", ri->name,
                    r->element[1]->str,
                    (unsigned long long) r->element[2]->integer);
            ri->leader = sdsnew(r->element[1]->str);
            ri->leader_epoch = r->element[2]->integer;
        }
    }
}

/* If we think the master is down, we start sending
 * SENTINEL IS-MASTER-DOWN-BY-ADDR requests to other sentinels
 * in order to get the replies that allow to reach the quorum
 * needed to mark the master in ODOWN state and trigger a failover. */
#define SENTINEL_ASK_FORCED (1<<0)
void sentinelAskMasterStateToOtherSentinels(sentinelRedisInstance *master, int flags) {
    dictIterator *di;
    dictEntry *de;

    di = dictGetIterator(master->sentinels);
    while((de = dictNext(di)) != NULL) {
        sentinelRedisInstance *ri = dictGetVal(de);
        mstime_t elapsed = mstime() - ri->last_master_down_reply_time;
        char port[32];
        int retval;

        /* If the master state from other sentinel is too old, we clear it. */
        if (elapsed > sentinel_ask_period*5) {
            ri->flags &= ~SRI_MASTER_DOWN;
            sdsfree(ri->leader);
            ri->leader = NULL;
        }

        /* Only ask if master is down to other sentinels if:
         *
         * 1) We believe it is down, or there is a failover in progress.
         * 2) Sentinel is connected.
         * 3) We did not receive the info within SENTINEL_ASK_PERIOD ms. */
        if ((master->flags & SRI_S_DOWN) == 0) continue;
        if (ri->link->disconnected) continue;
        if (!(flags & SENTINEL_ASK_FORCED) &&
            mstime() - ri->last_master_down_reply_time < sentinel_ask_period)
            continue;

        /* Ask */
        ll2string(port,sizeof(port),master->addr->port);
        retval = redisAsyncCommand(ri->link->cc,
                    sentinelReceiveIsMasterDownReply, ri,
                    "%s is-master-down-by-addr %s %s %llu %s",
                    sentinelInstanceMapCommand(ri,"SENTINEL"),
                    announceSentinelAddr(master->addr), port,
                    sentinel.current_epoch,
                    (master->failover_state > SENTINEL_FAILOVER_STATE_NONE) ?
                    sentinel.myid : "*");
        if (retval == C_OK) ri->link->pending_commands++;
    }
    dictReleaseIterator(di);
}

/* =============================== FAILOVER ================================= */

/* Crash because of user request via SENTINEL simulate-failure command. */
void sentinelSimFailureCrash(void) {
    serverLog(LL_WARNING,
        "Sentinel CRASH because of SENTINEL simulate-failure");
    exit(99);
}

/* Vote for the sentinel with 'req_runid' or return the old vote if already
 * voted for the specified 'req_epoch' or one greater.
 *
 * If a vote is not available returns NULL, otherwise return the Sentinel
 * runid and populate the leader_epoch with the epoch of the vote. */
char *sentinelVoteLeader(sentinelRedisInstance *master, uint64_t req_epoch, char *req_runid, uint64_t *leader_epoch) {
    if (req_epoch > sentinel.current_epoch) {
        sentinel.current_epoch = req_epoch;
        sentinelFlushConfig();
        sentinelEvent(LL_WARNING,"+new-epoch",master,"%llu",
            (unsigned long long) sentinel.current_epoch);
    }

    if (master->leader_epoch < req_epoch && sentinel.current_epoch <= req_epoch)
    {
        sdsfree(master->leader);
        master->leader = sdsnew(req_runid);
        master->leader_epoch = sentinel.current_epoch;
        sentinelFlushConfig();
        sentinelEvent(LL_WARNING,"+vote-for-leader",master,"%s %llu",
            master->leader, (unsigned long long) master->leader_epoch);
        /* If we did not voted for ourselves, set the master failover start
         * time to now, in order to force a delay before we can start a
         * failover for the same master. */
        if (strcasecmp(master->leader,sentinel.myid))
            master->failover_start_time = mstime()+rand()%SENTINEL_MAX_DESYNC;
    }

    *leader_epoch = master->leader_epoch;
    return master->leader ? sdsnew(master->leader) : NULL;
}

struct sentinelLeader {
    char *runid;
    unsigned long votes;
};

/* Helper function for sentinelGetLeader, increment the counter
 * relative to the specified runid. */
int sentinelLeaderIncr(dict *counters, char *runid) {
    dictEntry *existing, *de;
    uint64_t oldval;

    de = dictAddRaw(counters,runid,&existing);
    if (existing) {
        oldval = dictGetUnsignedIntegerVal(existing);
        dictSetUnsignedIntegerVal(existing,oldval+1);
        return oldval+1;
    } else {
        serverAssert(de != NULL);
        dictSetUnsignedIntegerVal(de,1);
        return 1;
    }
}

/* Scan all the Sentinels attached to this master to check if there
 * is a leader for the specified epoch.
 *
 * To be a leader for a given epoch, we should have the majority of
 * the Sentinels we know (ever seen since the last SENTINEL RESET) that
 * reported the same instance as leader for the same epoch. */
char *sentinelGetLeader(sentinelRedisInstance *master, uint64_t epoch) {
    dict *counters;
    dictIterator *di;
    dictEntry *de;
    unsigned int voters = 0, voters_quorum;
    char *myvote;
    char *winner = NULL;
    uint64_t leader_epoch;
    uint64_t max_votes = 0;

    serverAssert(master->flags & (SRI_O_DOWN|SRI_FAILOVER_IN_PROGRESS));
    counters = dictCreate(&leaderVotesDictType);

    voters = dictSize(master->sentinels)+1; /* All the other sentinels and me.*/

    /* Count other sentinels votes */
    di = dictGetIterator(master->sentinels);
    while((de = dictNext(di)) != NULL) {
        sentinelRedisInstance *ri = dictGetVal(de);
        if (ri->leader != NULL && ri->leader_epoch == sentinel.current_epoch)
            sentinelLeaderIncr(counters,ri->leader);
    }
    dictReleaseIterator(di);

    /* Check what's the winner. For the winner to win, it needs two conditions:
     * 1) Absolute majority between voters (50% + 1).
     * 2) And anyway at least master->quorum votes. */
    di = dictGetIterator(counters);
    while((de = dictNext(di)) != NULL) {
        uint64_t votes = dictGetUnsignedIntegerVal(de);

        if (votes > max_votes) {
            max_votes = votes;
            winner = dictGetKey(de);
        }
    }
    dictReleaseIterator(di);

    /* Count this Sentinel vote:
     * if this Sentinel did not voted yet, either vote for the most
     * common voted sentinel, or for itself if no vote exists at all. */
    if (winner)
        myvote = sentinelVoteLeader(master,epoch,winner,&leader_epoch);
    else
        myvote = sentinelVoteLeader(master,epoch,sentinel.myid,&leader_epoch);

    if (myvote && leader_epoch == epoch) {
        uint64_t votes = sentinelLeaderIncr(counters,myvote);

        if (votes > max_votes) {
            max_votes = votes;
            winner = myvote;
        }
    }

    voters_quorum = voters/2+1;
    if (winner && (max_votes < voters_quorum || max_votes < master->quorum))
        winner = NULL;

    winner = winner ? sdsnew(winner) : NULL;
    sdsfree(myvote);
    dictRelease(counters);
    return winner;
}

/* Send SLAVEOF to the specified instance, always followed by a
 * CONFIG REWRITE command in order to store the new configuration on disk
 * when possible (that is, if the Redis instance is recent enough to support
 * config rewriting, and if the server was started with a configuration file).
 *
 * If Host is NULL the function sends "SLAVEOF NO ONE".
 *
 * The command returns C_OK if the SLAVEOF command was accepted for
 * (later) delivery otherwise C_ERR. The command replies are just
 * discarded. */
int sentinelSendSlaveOf(sentinelRedisInstance *ri, const sentinelAddr *addr) {
    char portstr[32];
    const char *host;
    int retval;

    /* If host is NULL we send SLAVEOF NO ONE that will turn the instance
    * into a master. */
    if (!addr) {
        host = "NO";
        memcpy(portstr,"ONE",4);
    } else {
        host = announceSentinelAddr(addr);
        ll2string(portstr,sizeof(portstr),addr->port);
    }

    /* In order to send SLAVEOF in a safe way, we send a transaction performing
     * the following tasks:
     * 1) Reconfigure the instance according to the specified host/port params.
     * 2) Rewrite the configuration.
     * 3) Disconnect all clients (but this one sending the command) in order
     *    to trigger the ask-master-on-reconnection protocol for connected
     *    clients.
     *
     * Note that we don't check the replies returned by commands, since we
     * will observe instead the effects in the next INFO output. */
    retval = redisAsyncCommand(ri->link->cc,
        sentinelDiscardReplyCallback, ri, "%s",
        sentinelInstanceMapCommand(ri,"MULTI"));
    if (retval == C_ERR) return retval;
    ri->link->pending_commands++;

    retval = redisAsyncCommand(ri->link->cc,
        sentinelDiscardReplyCallback, ri, "%s %s %s",
        sentinelInstanceMapCommand(ri,"SLAVEOF"),
        host, portstr);
    if (retval == C_ERR) return retval;
    ri->link->pending_commands++;

    retval = redisAsyncCommand(ri->link->cc,
        sentinelDiscardReplyCallback, ri, "%s REWRITE",
        sentinelInstanceMapCommand(ri,"CONFIG"));
    if (retval == C_ERR) return retval;
    ri->link->pending_commands++;

    /* CLIENT KILL TYPE <type> is only supported starting from Redis 2.8.12,
     * however sending it to an instance not understanding this command is not
     * an issue because CLIENT is variadic command, so Redis will not
     * recognized as a syntax error, and the transaction will not fail (but
     * only the unsupported command will fail). */
    for (int type = 0; type < 2; type++) {
        retval = redisAsyncCommand(ri->link->cc,
            sentinelDiscardReplyCallback, ri, "%s KILL TYPE %s",
            sentinelInstanceMapCommand(ri,"CLIENT"),
            type == 0 ? "normal" : "pubsub");
        if (retval == C_ERR) return retval;
        ri->link->pending_commands++;
    }

    retval = redisAsyncCommand(ri->link->cc,
        sentinelDiscardReplyCallback, ri, "%s",
        sentinelInstanceMapCommand(ri,"EXEC"));
    if (retval == C_ERR) return retval;
    ri->link->pending_commands++;

    return C_OK;
}

/* Setup the master state to start a failover. */
void sentinelStartFailover(sentinelRedisInstance *master) {
    serverAssert(master->flags & SRI_MASTER);

    master->failover_state = SENTINEL_FAILOVER_STATE_WAIT_START;
    master->flags |= SRI_FAILOVER_IN_PROGRESS;
    master->failover_epoch = ++sentinel.current_epoch;
    sentinelEvent(LL_WARNING,"+new-epoch",master,"%llu",
        (unsigned long long) sentinel.current_epoch);
    sentinelEvent(LL_WARNING,"+try-failover",master,"%@");
    master->failover_start_time = mstime()+rand()%SENTINEL_MAX_DESYNC;
    master->failover_state_change_time = mstime();
}

/* This function checks if there are the conditions to start the failover,
 * that is:
 *
 * 1) Master must be in ODOWN condition.
 * 2) No failover already in progress.
 * 3) No failover already attempted recently.
 *
 * We still don't know if we'll win the election so it is possible that we
 * start the failover but that we'll not be able to act.
 *
 * Return non-zero if a failover was started. */
int sentinelStartFailoverIfNeeded(sentinelRedisInstance *master) {
    /* We can't failover if the master is not in O_DOWN state. */
    if (!(master->flags & SRI_O_DOWN)) return 0;

    /* Failover already in progress? */
    if (master->flags & SRI_FAILOVER_IN_PROGRESS) return 0;

    /* Last failover attempt started too little time ago? */
    if (mstime() - master->failover_start_time <
        master->failover_timeout*2)
    {
        if (master->failover_delay_logged != master->failover_start_time) {
            time_t clock = (master->failover_start_time +
                            master->failover_timeout*2) / 1000;
            char ctimebuf[26];

            ctime_r(&clock,ctimebuf);
            ctimebuf[24] = '\0'; /* Remove newline. */
            master->failover_delay_logged = master->failover_start_time;
            serverLog(LL_WARNING,
                "Next failover delay: I will not start a failover before %s",
                ctimebuf);
        }
        return 0;
    }

    sentinelStartFailover(master);
    return 1;
}

/* Select a suitable slave to promote. The current algorithm only uses
 * the following parameters:
 *
 * 1) None of the following conditions: S_DOWN, O_DOWN, DISCONNECTED.
 * 2) Last time the slave replied to ping no more than 5 times the PING period.
 * 3) info_refresh not older than 3 times the INFO refresh period.
 * 4) master_link_down_time no more than:
 *     (now - master->s_down_since_time) + (master->down_after_period * 10).
 *    Basically since the master is down from our POV, the slave reports
 *    to be disconnected no more than 10 times the configured down-after-period.
 *    This is pretty much black magic but the idea is, the master was not
 *    available so the slave may be lagging, but not over a certain time.
 *    Anyway we'll select the best slave according to replication offset.
 * 5) Slave priority can't be zero, otherwise the slave is discarded.
 *
 * Among all the slaves matching the above conditions we select the slave
 * with, in order of sorting key:
 *
 * - lower slave_priority.
 * - bigger processed replication offset.
 * - lexicographically smaller runid.
 *
 * Basically if runid is the same, the slave that processed more commands
 * from the master is selected.
 *
 * The function returns the pointer to the selected slave, otherwise
 * NULL if no suitable slave was found.
 */

/* Helper for sentinelSelectSlave(). This is used by qsort() in order to
 * sort suitable slaves in a "better first" order, to take the first of
 * the list. */
int compareSlavesForPromotion(const void *a, const void *b) {
    sentinelRedisInstance **sa = (sentinelRedisInstance **)a,
                          **sb = (sentinelRedisInstance **)b;
    char *sa_runid, *sb_runid;

    if ((*sa)->slave_priority != (*sb)->slave_priority)
        return (*sa)->slave_priority - (*sb)->slave_priority;

    /* If priority is the same, select the slave with greater replication
     * offset (processed more data from the master). */
    if ((*sa)->slave_repl_offset > (*sb)->slave_repl_offset) {
        return -1; /* a < b */
    } else if ((*sa)->slave_repl_offset < (*sb)->slave_repl_offset) {
        return 1; /* a > b */
    }

    /* If the replication offset is the same select the slave with that has
     * the lexicographically smaller runid. Note that we try to handle runid
     * == NULL as there are old Redis versions that don't publish runid in
     * INFO. A NULL runid is considered bigger than any other runid. */
    sa_runid = (*sa)->runid;
    sb_runid = (*sb)->runid;
    if (sa_runid == NULL && sb_runid == NULL) return 0;
    else if (sa_runid == NULL) return 1;  /* a > b */
    else if (sb_runid == NULL) return -1; /* a < b */
    return strcasecmp(sa_runid, sb_runid);
}

sentinelRedisInstance *sentinelSelectSlave(sentinelRedisInstance *master) {
    sentinelRedisInstance **instance =
        zmalloc(sizeof(instance[0])*dictSize(master->slaves));
    sentinelRedisInstance *selected = NULL;
    int instances = 0;
    dictIterator *di;
    dictEntry *de;
    mstime_t max_master_down_time = 0;

    if (master->flags & SRI_S_DOWN)
        max_master_down_time += mstime() - master->s_down_since_time;
    max_master_down_time += master->down_after_period * 10;

    di = dictGetIterator(master->slaves);

    while((de = dictNext(di)) != NULL) {
        sentinelRedisInstance *slave = dictGetVal(de);
        mstime_t info_validity_time;

        if (slave->flags & (SRI_S_DOWN|SRI_O_DOWN)) continue;
        if (slave->link->disconnected) continue;
        if (mstime() - slave->link->last_avail_time > sentinel_ping_period*5) continue;
        if (slave->slave_priority == 0) continue;

        /* If the master is in SDOWN state we get INFO for slaves every second.
         * Otherwise we get it with the usual period so we need to account for
         * a larger delay. */
        if (master->flags & SRI_S_DOWN)
            info_validity_time = sentinel_ping_period*5;
        else
            info_validity_time = sentinel_info_period*3;
        if (mstime() - slave->info_refresh > info_validity_time) continue;
        if (slave->master_link_down_time > max_master_down_time) continue;
        instance[instances++] = slave;
    }
    dictReleaseIterator(di);
    if (instances) {
        qsort(instance,instances,sizeof(sentinelRedisInstance*),
            compareSlavesForPromotion);
        selected = instance[0];
    }
    zfree(instance);
    return selected;
}

/* ---------------- Failover state machine implementation ------------------- */
void sentinelFailoverWaitStart(sentinelRedisInstance *ri) {
    char *leader;
    int isleader;

    /* Check if we are the leader for the failover epoch. */
    leader = sentinelGetLeader(ri, ri->failover_epoch);
    isleader = leader && strcasecmp(leader,sentinel.myid) == 0;
    sdsfree(leader);

    /* If I'm not the leader, and it is not a forced failover via
     * SENTINEL FAILOVER, then I can't continue with the failover. */
    if (!isleader && !(ri->flags & SRI_FORCE_FAILOVER)) {
        mstime_t election_timeout = sentinel_election_timeout;

        /* The election timeout is the MIN between SENTINEL_ELECTION_TIMEOUT
         * and the configured failover timeout. */
        if (election_timeout > ri->failover_timeout)
            election_timeout = ri->failover_timeout;
        /* Abort the failover if I'm not the leader after some time. */
        if (mstime() - ri->failover_start_time > election_timeout) {
            sentinelEvent(LL_WARNING,"-failover-abort-not-elected",ri,"%@");
            sentinelAbortFailover(ri);
        }
        return;
    }
    sentinelEvent(LL_WARNING,"+elected-leader",ri,"%@");
    if (sentinel.simfailure_flags & SENTINEL_SIMFAILURE_CRASH_AFTER_ELECTION)
        sentinelSimFailureCrash();
    ri->failover_state = SENTINEL_FAILOVER_STATE_SELECT_SLAVE;
    ri->failover_state_change_time = mstime();
    sentinelEvent(LL_WARNING,"+failover-state-select-slave",ri,"%@");
}

void sentinelFailoverSelectSlave(sentinelRedisInstance *ri) {
    sentinelRedisInstance *slave = sentinelSelectSlave(ri);

    /* We don't handle the timeout in this state as the function aborts
     * the failover or go forward in the next state. */
    if (slave == NULL) {
        sentinelEvent(LL_WARNING,"-failover-abort-no-good-slave",ri,"%@");
        sentinelAbortFailover(ri);
    } else {
        sentinelEvent(LL_WARNING,"+selected-slave",slave,"%@");
        slave->flags |= SRI_PROMOTED;
        ri->promoted_slave = slave;
        ri->failover_state = SENTINEL_FAILOVER_STATE_SEND_SLAVEOF_NOONE;
        ri->failover_state_change_time = mstime();
        sentinelEvent(LL_NOTICE,"+failover-state-send-slaveof-noone",
            slave, "%@");
    }
}

void sentinelFailoverSendSlaveOfNoOne(sentinelRedisInstance *ri) {
    int retval;

    /* We can't send the command to the promoted slave if it is now
     * disconnected. Retry again and again with this state until the timeout
     * is reached, then abort the failover. */
    if (ri->promoted_slave->link->disconnected) {
        if (mstime() - ri->failover_state_change_time > ri->failover_timeout) {
            sentinelEvent(LL_WARNING,"-failover-abort-slave-timeout",ri,"%@");
            sentinelAbortFailover(ri);
        }
        return;
    }

    /* Send SLAVEOF NO ONE command to turn the slave into a master.
     * We actually register a generic callback for this command as we don't
     * really care about the reply. We check if it worked indirectly observing
     * if INFO returns a different role (master instead of slave). */
    retval = sentinelSendSlaveOf(ri->promoted_slave,NULL);
    if (retval != C_OK) return;
    sentinelEvent(LL_NOTICE, "+failover-state-wait-promotion",
        ri->promoted_slave,"%@");
    ri->failover_state = SENTINEL_FAILOVER_STATE_WAIT_PROMOTION;
    ri->failover_state_change_time = mstime();
}

/* We actually wait for promotion indirectly checking with INFO when the
 * slave turns into a master. */
void sentinelFailoverWaitPromotion(sentinelRedisInstance *ri) {
    /* Just handle the timeout. Switching to the next state is handled
     * by the function parsing the INFO command of the promoted slave. */
    if (mstime() - ri->failover_state_change_time > ri->failover_timeout) {
        sentinelEvent(LL_WARNING,"-failover-abort-slave-timeout",ri,"%@");
        sentinelAbortFailover(ri);
    }
}

void sentinelFailoverDetectEnd(sentinelRedisInstance *master) {
    int not_reconfigured = 0, timeout = 0;
    dictIterator *di;
    dictEntry *de;
    mstime_t elapsed = mstime() - master->failover_state_change_time;

    /* We can't consider failover finished if the promoted slave is
     * not reachable. */
    if (master->promoted_slave == NULL ||
        master->promoted_slave->flags & SRI_S_DOWN) return;

    /* The failover terminates once all the reachable slaves are properly
     * configured. */
    di = dictGetIterator(master->slaves);
    while((de = dictNext(di)) != NULL) {
        sentinelRedisInstance *slave = dictGetVal(de);

        if (slave->flags & (SRI_PROMOTED|SRI_RECONF_DONE)) continue;
        if (slave->flags & SRI_S_DOWN) continue;
        not_reconfigured++;
    }
    dictReleaseIterator(di);

    /* Force end of failover on timeout. */
    if (elapsed > master->failover_timeout) {
        not_reconfigured = 0;
        timeout = 1;
        sentinelEvent(LL_WARNING,"+failover-end-for-timeout",master,"%@");
    }

    if (not_reconfigured == 0) {
        sentinelEvent(LL_WARNING,"+failover-end",master,"%@");
        master->failover_state = SENTINEL_FAILOVER_STATE_UPDATE_CONFIG;
        master->failover_state_change_time = mstime();
    }

    /* If I'm the leader it is a good idea to send a best effort SLAVEOF
     * command to all the slaves still not reconfigured to replicate with
     * the new master. */
    if (timeout) {
        dictIterator *di;
        dictEntry *de;

        di = dictGetIterator(master->slaves);
        while((de = dictNext(di)) != NULL) {
            sentinelRedisInstance *slave = dictGetVal(de);
            int retval;

            if (slave->flags & (SRI_PROMOTED|SRI_RECONF_DONE|SRI_RECONF_SENT)) continue;
            if (slave->link->disconnected) continue;

            retval = sentinelSendSlaveOf(slave,master->promoted_slave->addr);
            if (retval == C_OK) {
                sentinelEvent(LL_NOTICE,"+slave-reconf-sent-be",slave,"%@");
                slave->flags |= SRI_RECONF_SENT;
            }
        }
        dictReleaseIterator(di);
    }
}

/* Send SLAVE OF <new master address> to all the remaining slaves that
 * still don't appear to have the configuration updated. */
void sentinelFailoverReconfNextSlave(sentinelRedisInstance *master) {
    dictIterator *di;
    dictEntry *de;
    int in_progress = 0;

    di = dictGetIterator(master->slaves);
    while((de = dictNext(di)) != NULL) {
        sentinelRedisInstance *slave = dictGetVal(de);

        if (slave->flags & (SRI_RECONF_SENT|SRI_RECONF_INPROG))
            in_progress++;
    }
    dictReleaseIterator(di);

    di = dictGetIterator(master->slaves);
    while(in_progress < master->parallel_syncs &&
          (de = dictNext(di)) != NULL)
    {
        sentinelRedisInstance *slave = dictGetVal(de);
        int retval;

        /* Skip the promoted slave, and already configured slaves. */
        if (slave->flags & (SRI_PROMOTED|SRI_RECONF_DONE)) continue;

        /* If too much time elapsed without the slave moving forward to
         * the next state, consider it reconfigured even if it is not.
         * Sentinels will detect the slave as misconfigured and fix its
         * configuration later. */
        if ((slave->flags & SRI_RECONF_SENT) &&
            (mstime() - slave->slave_reconf_sent_time) >
            sentinel_slave_reconf_timeout)
        {
            sentinelEvent(LL_NOTICE,"-slave-reconf-sent-timeout",slave,"%@");
            slave->flags &= ~SRI_RECONF_SENT;
            slave->flags |= SRI_RECONF_DONE;
        }

        /* Nothing to do for instances that are disconnected or already
         * in RECONF_SENT state. */
        if (slave->flags & (SRI_RECONF_SENT|SRI_RECONF_INPROG)) continue;
        if (slave->link->disconnected) continue;

        /* Send SLAVEOF <new master>. */
        retval = sentinelSendSlaveOf(slave,master->promoted_slave->addr);
        if (retval == C_OK) {
            slave->flags |= SRI_RECONF_SENT;
            slave->slave_reconf_sent_time = mstime();
            sentinelEvent(LL_NOTICE,"+slave-reconf-sent",slave,"%@");
            in_progress++;
        }
    }
    dictReleaseIterator(di);

    /* Check if all the slaves are reconfigured and handle timeout. */
    sentinelFailoverDetectEnd(master);
}

/* This function is called when the slave is in
 * SENTINEL_FAILOVER_STATE_UPDATE_CONFIG state. In this state we need
 * to remove it from the master table and add the promoted slave instead. */
void sentinelFailoverSwitchToPromotedSlave(sentinelRedisInstance *master) {
    sentinelRedisInstance *ref = master->promoted_slave ?
                                 master->promoted_slave : master;

    sentinelEvent(LL_WARNING,"+switch-master",master,"%s %s %d %s %d",
        master->name, announceSentinelAddr(master->addr), master->addr->port,
        announceSentinelAddr(ref->addr), ref->addr->port);

    sentinelResetMasterAndChangeAddress(master,ref->addr->hostname,ref->addr->port);
}

void sentinelFailoverStateMachine(sentinelRedisInstance *ri) {
    serverAssert(ri->flags & SRI_MASTER);

    if (!(ri->flags & SRI_FAILOVER_IN_PROGRESS)) return;

    switch(ri->failover_state) {
        case SENTINEL_FAILOVER_STATE_WAIT_START:
            sentinelFailoverWaitStart(ri);
            break;
        case SENTINEL_FAILOVER_STATE_SELECT_SLAVE:
            sentinelFailoverSelectSlave(ri);
            break;
        case SENTINEL_FAILOVER_STATE_SEND_SLAVEOF_NOONE:
            sentinelFailoverSendSlaveOfNoOne(ri);
            break;
        case SENTINEL_FAILOVER_STATE_WAIT_PROMOTION:
            sentinelFailoverWaitPromotion(ri);
            break;
        case SENTINEL_FAILOVER_STATE_RECONF_SLAVES:
            sentinelFailoverReconfNextSlave(ri);
            break;
    }
}

/* Abort a failover in progress:
 *
 * This function can only be called before the promoted slave acknowledged
 * the slave -> master switch. Otherwise the failover can't be aborted and
 * will reach its end (possibly by timeout). */
void sentinelAbortFailover(sentinelRedisInstance *ri) {
    serverAssert(ri->flags & SRI_FAILOVER_IN_PROGRESS);
    serverAssert(ri->failover_state <= SENTINEL_FAILOVER_STATE_WAIT_PROMOTION);

    ri->flags &= ~(SRI_FAILOVER_IN_PROGRESS|SRI_FORCE_FAILOVER);
    ri->failover_state = SENTINEL_FAILOVER_STATE_NONE;
    ri->failover_state_change_time = mstime();
    if (ri->promoted_slave) {
        ri->promoted_slave->flags &= ~SRI_PROMOTED;
        ri->promoted_slave = NULL;
    }
}

/* ======================== SENTINEL timer handler ==========================
 * This is the "main" our Sentinel, being sentinel completely non blocking
 * in design.
 * -------------------------------------------------------------------------- */

/* Perform scheduled operations for the specified Redis instance. */
void sentinelHandleRedisInstance(sentinelRedisInstance *ri) {
    /* ========== MONITORING HALF ============ */
    /* Every kind of instance */
    sentinelReconnectInstance(ri);
    sentinelSendPeriodicCommands(ri);

    /* ============== ACTING HALF ============= */
    /* We don't proceed with the acting half if we are in TILT mode.
     * TILT happens when we find something odd with the time, like a
     * sudden change in the clock. */
    if (sentinel.tilt) {
        if (mstime()-sentinel.tilt_start_time < sentinel_tilt_period) return;
        sentinel.tilt = 0;
        sentinelEvent(LL_WARNING,"-tilt",NULL,"#tilt mode exited");
    }

    /* Every kind of instance */
    sentinelCheckSubjectivelyDown(ri);

    /* Masters and slaves */
    if (ri->flags & (SRI_MASTER|SRI_SLAVE)) {
        /* Nothing so far. */
    }

    /* Only masters */
    if (ri->flags & SRI_MASTER) {
        sentinelCheckObjectivelyDown(ri);
        if (sentinelStartFailoverIfNeeded(ri))
            sentinelAskMasterStateToOtherSentinels(ri,SENTINEL_ASK_FORCED);
        sentinelFailoverStateMachine(ri);
        sentinelAskMasterStateToOtherSentinels(ri,SENTINEL_NO_FLAGS);
    }
}

/* Perform scheduled operations for all the instances in the dictionary.
 * Recursively call the function against dictionaries of slaves. */
void sentinelHandleDictOfRedisInstances(dict *instances) {
    dictIterator *di;
    dictEntry *de;
    sentinelRedisInstance *switch_to_promoted = NULL;

    /* There are a number of things we need to perform against every master. */
    di = dictGetIterator(instances);
    while((de = dictNext(di)) != NULL) {
        sentinelRedisInstance *ri = dictGetVal(de);

        sentinelHandleRedisInstance(ri);
        if (ri->flags & SRI_MASTER) {
            sentinelHandleDictOfRedisInstances(ri->slaves);
            sentinelHandleDictOfRedisInstances(ri->sentinels);
            if (ri->failover_state == SENTINEL_FAILOVER_STATE_UPDATE_CONFIG) {
                switch_to_promoted = ri;
            }
        }
    }
    if (switch_to_promoted)
        sentinelFailoverSwitchToPromotedSlave(switch_to_promoted);
    dictReleaseIterator(di);
}

/* This function checks if we need to enter the TILT mode.
 *
 * The TILT mode is entered if we detect that between two invocations of the
 * timer interrupt, a negative amount of time, or too much time has passed.
 * Note that we expect that more or less just 100 milliseconds will pass
 * if everything is fine. However we'll see a negative number or a
 * difference bigger than SENTINEL_TILT_TRIGGER milliseconds if one of the
 * following conditions happen:
 *
 * 1) The Sentinel process for some time is blocked, for every kind of
 * random reason: the load is huge, the computer was frozen for some time
 * in I/O or alike, the process was stopped by a signal. Everything.
 * 2) The system clock was altered significantly.
 *
 * Under both this conditions we'll see everything as timed out and failing
 * without good reasons. Instead we enter the TILT mode and wait
 * for SENTINEL_TILT_PERIOD to elapse before starting to act again.
 *
 * During TILT time we still collect information, we just do not act. */
void sentinelCheckTiltCondition(void) {
    mstime_t now = mstime();
    mstime_t delta = now - sentinel.previous_time;

    if (delta < 0 || delta > sentinel_tilt_trigger) {
        sentinel.tilt = 1;
        sentinel.tilt_start_time = mstime();
        sentinelEvent(LL_WARNING,"+tilt",NULL,"#tilt mode entered");
    }
    sentinel.previous_time = mstime();
}

void sentinelTimer(void) {
    sentinelCheckTiltCondition();
    sentinelHandleDictOfRedisInstances(sentinel.masters);
    sentinelRunPendingScripts();
    sentinelCollectTerminatedScripts();
    sentinelKillTimedoutScripts();

    /* We continuously change the frequency of the Redis "timer interrupt"
     * in order to desynchronize every Sentinel from every other.
     * This non-determinism avoids that Sentinels started at the same time
     * exactly continue to stay synchronized asking to be voted at the
     * same time again and again (resulting in nobody likely winning the
     * election because of split brain voting). */
    server.hz = CONFIG_DEFAULT_HZ + rand() % CONFIG_DEFAULT_HZ;
}