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/*--------------------------------------------------------------------
* bgworker.h
* POSTGRES pluggable background workers interface
*
* A background worker is a process able to run arbitrary, user-supplied code,
* including normal transactions.
*
* Any external module loaded via shared_preload_libraries can register a
* worker. Workers can also be registered dynamically at runtime. In either
* case, the worker process is forked from the postmaster and runs the
* user-supplied "main" function. This code may connect to a database and
* run transactions. Workers can remain active indefinitely, but will be
* terminated if a shutdown or crash occurs.
*
* If the fork() call fails in the postmaster, it will try again later. Note
* that the failure can only be transient (fork failure due to high load,
* memory pressure, too many processes, etc); more permanent problems, like
* failure to connect to a database, are detected later in the worker and dealt
* with just by having the worker exit normally. A worker which exits with
* a return code of 0 will never be restarted and will be removed from worker
* list. A worker which exits with a return code of 1 will be restarted after
* the configured restart interval (unless that interval is BGW_NEVER_RESTART).
* The TerminateBackgroundWorker() function can be used to terminate a
* dynamically registered background worker; the worker will be sent a SIGTERM
* and will not be restarted after it exits. Whenever the postmaster knows
* that a worker will not be restarted, it unregisters the worker, freeing up
* that worker's slot for use by a new worker.
*
* Note that there might be more than one worker in a database concurrently,
* and the same module may request more than one worker running the same (or
* different) code.
*
*
* Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* src/include/postmaster/bgworker.h
*--------------------------------------------------------------------
*/
#ifndef BGWORKER_H
#define BGWORKER_H
/*---------------------------------------------------------------------
* External module API.
*---------------------------------------------------------------------
*/
/*
* Pass this flag to have your worker be able to connect to shared memory.
*/
#define BGWORKER_SHMEM_ACCESS 0x0001
/*
* This flag means the bgworker requires a database connection. The connection
* is not established automatically; the worker must establish it later.
* It requires that BGWORKER_SHMEM_ACCESS was passed too.
*/
#define BGWORKER_BACKEND_DATABASE_CONNECTION 0x0002
/*
* This class is used internally for parallel queries, to keep track of the
* number of active parallel workers and make sure we never launch more than
* max_parallel_workers parallel workers at the same time. Third party
* background workers should not use this class.
*/
#define BGWORKER_CLASS_PARALLEL 0x0010
/* add additional bgworker classes here */
typedef void (*bgworker_main_type) (Datum main_arg);
/*
* Points in time at which a bgworker can request to be started
*/
typedef enum
{
BgWorkerStart_PostmasterStart,
BgWorkerStart_ConsistentState,
BgWorkerStart_RecoveryFinished
} BgWorkerStartTime;
#define BGW_DEFAULT_RESTART_INTERVAL 60
#define BGW_NEVER_RESTART -1
#define BGW_MAXLEN 96
#define BGW_EXTRALEN 128
typedef struct BackgroundWorker
{
char bgw_name[BGW_MAXLEN];
char bgw_type[BGW_MAXLEN];
int bgw_flags;
BgWorkerStartTime bgw_start_time;
int bgw_restart_time; /* in seconds, or BGW_NEVER_RESTART */
char bgw_library_name[BGW_MAXLEN];
char bgw_function_name[BGW_MAXLEN];
Datum bgw_main_arg;
char bgw_extra[BGW_EXTRALEN];
pid_t bgw_notify_pid; /* SIGUSR1 this backend on start/stop */
} BackgroundWorker;
typedef enum BgwHandleStatus
{
BGWH_STARTED, /* worker is running */
BGWH_NOT_YET_STARTED, /* worker hasn't been started yet */
BGWH_STOPPED, /* worker has exited */
BGWH_POSTMASTER_DIED /* postmaster died; worker status unclear */
} BgwHandleStatus;
struct BackgroundWorkerHandle;
typedef struct BackgroundWorkerHandle BackgroundWorkerHandle;
/* Register a new bgworker during shared_preload_libraries */
extern void RegisterBackgroundWorker(BackgroundWorker *worker);
/* Register a new bgworker from a regular backend */
extern bool RegisterDynamicBackgroundWorker(BackgroundWorker *worker,
BackgroundWorkerHandle **handle);
/* Query the status of a bgworker */
extern BgwHandleStatus GetBackgroundWorkerPid(BackgroundWorkerHandle *handle,
pid_t *pidp);
extern BgwHandleStatus WaitForBackgroundWorkerStartup(BackgroundWorkerHandle *handle, pid_t *pid);
extern BgwHandleStatus
WaitForBackgroundWorkerShutdown(BackgroundWorkerHandle *);
extern const char *GetBackgroundWorkerTypeByPid(pid_t pid);
/* Terminate a bgworker */
extern void TerminateBackgroundWorker(BackgroundWorkerHandle *handle);
/* This is valid in a running worker */
extern PGDLLIMPORT BackgroundWorker *MyBgworkerEntry;
/*
* Connect to the specified database, as the specified user. Only a worker
* that passed BGWORKER_BACKEND_DATABASE_CONNECTION during registration may
* call this.
*
* If username is NULL, bootstrapping superuser is used.
* If dbname is NULL, connection is made to no specific database;
* only shared catalogs can be accessed.
*/
extern void BackgroundWorkerInitializeConnection(const char *dbname, const char *username, uint32 flags);
/* Just like the above, but specifying database and user by OID. */
extern void BackgroundWorkerInitializeConnectionByOid(Oid dboid, Oid useroid, uint32 flags);
/*
* Flags to BackgroundWorkerInitializeConnection et al
*
*
* Allow bypassing datallowconn restrictions when connecting to database
*/
#define BGWORKER_BYPASS_ALLOWCONN 1
/* Block/unblock signals in a background worker process */
extern void BackgroundWorkerBlockSignals(void);
extern void BackgroundWorkerUnblockSignals(void);
#endif /* BGWORKER_H */
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