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Diffstat (limited to 'sql/mdl.cc')
| -rw-r--r-- | sql/mdl.cc | 3341 |
1 files changed, 3341 insertions, 0 deletions
diff --git a/sql/mdl.cc b/sql/mdl.cc new file mode 100644 index 00000000..32374415 --- /dev/null +++ b/sql/mdl.cc @@ -0,0 +1,3341 @@ +/* Copyright (c) 2007, 2012, Oracle and/or its affiliates. + Copyright (c) 2020, 2022, MariaDB + + This program is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; version 2 of the License. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program; if not, write to the Free Software Foundation, + 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA */ + + +#include "mariadb.h" +#include "sql_class.h" +#include "debug_sync.h" +#include "sql_array.h" +#include "rpl_rli.h" +#include <lf.h> +#include "unireg.h" +#include <mysql/plugin.h> +#include <mysql/service_thd_wait.h> +#include <mysql/psi/mysql_stage.h> +#include <tpool.h> +#include <pfs_metadata_provider.h> +#include <mysql/psi/mysql_mdl.h> +#include <algorithm> +#include <array> +#ifdef WITH_WSREP +#include "wsrep_mysqld.h" +#endif + +static PSI_memory_key key_memory_MDL_context_acquire_locks; + +#ifdef HAVE_PSI_INTERFACE +static PSI_mutex_key key_MDL_wait_LOCK_wait_status; + +static PSI_mutex_info all_mdl_mutexes[]= +{ + { &key_MDL_wait_LOCK_wait_status, "MDL_wait::LOCK_wait_status", 0} +}; + +static PSI_rwlock_key key_MDL_lock_rwlock; +static PSI_rwlock_key key_MDL_context_LOCK_waiting_for; + +static PSI_rwlock_info all_mdl_rwlocks[]= +{ + { &key_MDL_lock_rwlock, "MDL_lock::rwlock", 0}, + { &key_MDL_context_LOCK_waiting_for, "MDL_context::LOCK_waiting_for", 0} +}; + +static PSI_cond_key key_MDL_wait_COND_wait_status; + +static PSI_cond_info all_mdl_conds[]= +{ + { &key_MDL_wait_COND_wait_status, "MDL_context::COND_wait_status", 0} +}; + +static PSI_memory_info all_mdl_memory[]= +{ + { &key_memory_MDL_context_acquire_locks, "MDL_context::acquire_locks", 0} +}; + +/** + Initialise all the performance schema instrumentation points + used by the MDL subsystem. +*/ +static void init_mdl_psi_keys(void) +{ + int count; + + count= array_elements(all_mdl_mutexes); + mysql_mutex_register("sql", all_mdl_mutexes, count); + + count= array_elements(all_mdl_rwlocks); + mysql_rwlock_register("sql", all_mdl_rwlocks, count); + + count= array_elements(all_mdl_conds); + mysql_cond_register("sql", all_mdl_conds, count); + + count= array_elements(all_mdl_memory); + mysql_memory_register("sql", all_mdl_memory, count); + + MDL_key::init_psi_keys(); +} +#endif /* HAVE_PSI_INTERFACE */ + + +/** + Thread state names to be used in case when we have to wait on resource + belonging to certain namespace. +*/ + +PSI_stage_info MDL_key::m_namespace_to_wait_state_name[NAMESPACE_END]= +{ + {0, "Waiting for backup lock", 0}, + {0, "Waiting for schema metadata lock", 0}, + {0, "Waiting for table metadata lock", 0}, + {0, "Waiting for stored function metadata lock", 0}, + {0, "Waiting for stored procedure metadata lock", 0}, + {0, "Waiting for stored package body metadata lock", 0}, + {0, "Waiting for trigger metadata lock", 0}, + {0, "Waiting for event metadata lock", 0}, + {0, "User lock", 0} /* Be compatible with old status. */ +}; + + +static const LEX_STRING lock_types[]= +{ + { C_STRING_WITH_LEN("MDL_INTENTION_EXCLUSIVE") }, + { C_STRING_WITH_LEN("MDL_SHARED") }, + { C_STRING_WITH_LEN("MDL_SHARED_HIGH_PRIO") }, + { C_STRING_WITH_LEN("MDL_SHARED_READ") }, + { C_STRING_WITH_LEN("MDL_SHARED_WRITE") }, + { C_STRING_WITH_LEN("MDL_SHARED_UPGRADABLE") }, + { C_STRING_WITH_LEN("MDL_SHARED_READ_ONLY") }, + { C_STRING_WITH_LEN("MDL_SHARED_NO_WRITE") }, + { C_STRING_WITH_LEN("MDL_SHARED_NO_READ_WRITE") }, + { C_STRING_WITH_LEN("MDL_EXCLUSIVE") }, +}; + + +static const LEX_STRING backup_lock_types[]= +{ + { C_STRING_WITH_LEN("MDL_BACKUP_START") }, + { C_STRING_WITH_LEN("MDL_BACKUP_FLUSH") }, + { C_STRING_WITH_LEN("MDL_BACKUP_WAIT_FLUSH") }, + { C_STRING_WITH_LEN("MDL_BACKUP_WAIT_DDL") }, + { C_STRING_WITH_LEN("MDL_BACKUP_WAIT_COMMIT") }, + { C_STRING_WITH_LEN("MDL_BACKUP_FTWRL1") }, + { C_STRING_WITH_LEN("MDL_BACKUP_FTWRL2") }, + { C_STRING_WITH_LEN("MDL_BACKUP_DML") }, + { C_STRING_WITH_LEN("MDL_BACKUP_TRANS_DML") }, + { C_STRING_WITH_LEN("MDL_BACKUP_SYS_DML") }, + { C_STRING_WITH_LEN("MDL_BACKUP_DDL") }, + { C_STRING_WITH_LEN("MDL_BACKUP_BLOCK_DDL") }, + { C_STRING_WITH_LEN("MDL_BACKUP_ALTER_COPY") }, + { C_STRING_WITH_LEN("MDL_BACKUP_COMMIT") } +}; + + +#ifdef HAVE_PSI_INTERFACE +void MDL_key::init_psi_keys() +{ + int i; + int count; + PSI_stage_info *info __attribute__((unused)); + + count= array_elements(MDL_key::m_namespace_to_wait_state_name); + for (i= 0; i<count; i++) + { + /* mysql_stage_register wants an array of pointers, registering 1 by 1. */ + info= & MDL_key::m_namespace_to_wait_state_name[i]; + mysql_stage_register("sql", &info, 1); + } +} +#endif + +static bool mdl_initialized= 0; + + +/** + A collection of all MDL locks. A singleton, + there is only one instance of the map in the server. +*/ + +class MDL_map +{ +public: + void init(); + void destroy(); + MDL_lock *find_or_insert(LF_PINS *pins, const MDL_key *key); + unsigned long get_lock_owner(LF_PINS *pins, const MDL_key *key); + void remove(LF_PINS *pins, MDL_lock *lock); + LF_PINS *get_pins() { return lf_hash_get_pins(&m_locks); } +private: + LF_HASH m_locks; /**< All acquired locks in the server. */ + /** Pre-allocated MDL_lock object for BACKUP namespace. */ + MDL_lock *m_backup_lock; + friend int mdl_iterate(mdl_iterator_callback, void *); +}; + + +/** + A context of the recursive traversal through all contexts + in all sessions in search for deadlock. +*/ + +class Deadlock_detection_visitor: public MDL_wait_for_graph_visitor +{ +public: + Deadlock_detection_visitor(MDL_context *start_node_arg) + : m_start_node(start_node_arg), + m_victim(NULL), + m_current_search_depth(0), + m_found_deadlock(FALSE) + {} + virtual bool enter_node(MDL_context *node); + virtual void leave_node(MDL_context *node); + + virtual bool inspect_edge(MDL_context *dest); + + MDL_context *get_victim() const { return m_victim; } +private: + /** + Change the deadlock victim to a new one if it has lower deadlock + weight. + */ + void opt_change_victim_to(MDL_context *new_victim); +private: + /** + The context which has initiated the search. There + can be multiple searches happening in parallel at the same time. + */ + MDL_context *m_start_node; + /** If a deadlock is found, the context that identifies the victim. */ + MDL_context *m_victim; + /** Set to the 0 at start. Increased whenever + we descend into another MDL context (aka traverse to the next + wait-for graph node). When MAX_SEARCH_DEPTH is reached, we + assume that a deadlock is found, even if we have not found a + loop. + */ + uint m_current_search_depth; + /** TRUE if we found a deadlock. */ + bool m_found_deadlock; + /** + Maximum depth for deadlock searches. After this depth is + achieved we will unconditionally declare that there is a + deadlock. + + @note This depth should be small enough to avoid stack + being exhausted by recursive search algorithm. + + TODO: Find out what is the optimal value for this parameter. + Current value is safe, but probably sub-optimal, + as there is an anecdotal evidence that real-life + deadlocks are even shorter typically. + */ + static const uint MAX_SEARCH_DEPTH= 32; +}; + +#ifndef DBUG_OFF + +/* + Print a list of all locks to DBUG trace to help with debugging +*/ + +const char *dbug_print_mdl(MDL_ticket *mdl_ticket) +{ + thread_local char buffer[256]; + MDL_key *mdl_key= mdl_ticket->get_key(); + my_snprintf(buffer, sizeof(buffer) - 1, "%.*s/%.*s (%s)", + (int) mdl_key->db_name_length(), mdl_key->db_name(), + (int) mdl_key->name_length(), mdl_key->name(), + mdl_ticket->get_type_name()->str); + return buffer; +} + + +const char *dbug_print(MDL_ticket *mdl_ticket) +{ + return dbug_print_mdl(mdl_ticket); +} + + +static int mdl_dbug_print_lock(MDL_ticket *mdl_ticket, void *arg, bool granted) +{ + String *tmp= (String*) arg; + char buffer[256]; + size_t length= my_snprintf(buffer, sizeof(buffer) - 1, + "\n %s (%s)", dbug_print_mdl(mdl_ticket), + granted ? "granted" : "waiting"); + tmp->append(buffer, length); + return 0; +} + +const char *mdl_dbug_print_locks() +{ + thread_local String tmp; + tmp.length(0); + mdl_iterate(mdl_dbug_print_lock, (void*) &tmp); + return tmp.c_ptr(); +} +#endif /* DBUG_OFF */ + +/** + Enter a node of a wait-for graph. After + a node is entered, inspect_edge() will be called + for all wait-for destinations of this node. Then + leave_node() will be called. + We call "enter_node()" for all nodes we inspect, + including the starting node. + + @retval TRUE Maximum search depth exceeded. + @retval FALSE OK. +*/ + +bool Deadlock_detection_visitor::enter_node(MDL_context *node) +{ + m_found_deadlock= ++m_current_search_depth >= MAX_SEARCH_DEPTH; + if (m_found_deadlock) + { + DBUG_ASSERT(! m_victim); + opt_change_victim_to(node); + } + return m_found_deadlock; +} + + +/** + Done inspecting this node. Decrease the search + depth. If a deadlock is found, and we are + backtracking to the start node, optionally + change the deadlock victim to one with lower + deadlock weight. +*/ + +void Deadlock_detection_visitor::leave_node(MDL_context *node) +{ + --m_current_search_depth; + if (m_found_deadlock) + opt_change_victim_to(node); +} + + +/** + Inspect a wait-for graph edge from one MDL context to another. + + @retval TRUE A loop is found. + @retval FALSE No loop is found. +*/ + +bool Deadlock_detection_visitor::inspect_edge(MDL_context *node) +{ + m_found_deadlock= node == m_start_node; + return m_found_deadlock; +} + + +/** + Change the deadlock victim to a new one if it has lower deadlock + weight. + + @retval new_victim Victim is not changed. + @retval !new_victim New victim became the current. +*/ + +void +Deadlock_detection_visitor::opt_change_victim_to(MDL_context *new_victim) +{ + if (m_victim == NULL || + m_victim->get_deadlock_weight() >= new_victim->get_deadlock_weight()) + { + /* Swap victims, unlock the old one. */ + MDL_context *tmp= m_victim; + m_victim= new_victim; + m_victim->lock_deadlock_victim(); + if (tmp) + tmp->unlock_deadlock_victim(); + } +} + + +/** + Get a bit corresponding to enum_mdl_type value in a granted/waiting bitmaps + and compatibility matrices. +*/ + +/** + The lock context. Created internally for an acquired lock. + For a given name, there exists only one MDL_lock instance, + and it exists only when the lock has been granted. + Can be seen as an MDL subsystem's version of TABLE_SHARE. + + This is an abstract class which lacks information about + compatibility rules for lock types. They should be specified + in its descendants. +*/ + +class MDL_lock +{ +public: + typedef mdl_bitmap_t bitmap_t; + + class Ticket_list + { + using List= ilist<MDL_ticket>; + public: + Ticket_list() :m_bitmap(0) { m_type_counters.fill(0); } + + void add_ticket(MDL_ticket *ticket); + void remove_ticket(MDL_ticket *ticket); + bool is_empty() const { return m_list.empty(); } + bitmap_t bitmap() const { return m_bitmap; } + List::const_iterator begin() const { return m_list.begin(); } + List::const_iterator end() const { return m_list.end(); } + private: + /** List of tickets. */ + List m_list; + /** Bitmap of types of tickets in this list. */ + bitmap_t m_bitmap; + std::array<uint32_t, MDL_BACKUP_END> m_type_counters; // hash table + }; + + + /** + Helper struct which defines how different types of locks are handled + for a specific MDL_lock. In practice we use only three strategies: + "backup" lock strategy for locks in BACKUP namespace, "scoped" lock + strategy for locks in SCHEMA namespace and "object" lock strategy for + all other namespaces. + */ + struct MDL_lock_strategy + { + virtual const bitmap_t *incompatible_granted_types_bitmap() const = 0; + virtual const bitmap_t *incompatible_waiting_types_bitmap() const = 0; + virtual bool needs_notification(const MDL_ticket *ticket) const = 0; + virtual bool conflicting_locks(const MDL_ticket *ticket) const = 0; + virtual bitmap_t hog_lock_types_bitmap() const = 0; + virtual ~MDL_lock_strategy() = default; + }; + + + /** + An implementation of the scoped metadata lock. The only locking modes + which are supported at the moment are SHARED and INTENTION EXCLUSIVE + and EXCLUSIVE + */ + struct MDL_scoped_lock : public MDL_lock_strategy + { + MDL_scoped_lock() = default; + virtual const bitmap_t *incompatible_granted_types_bitmap() const + { return m_granted_incompatible; } + virtual const bitmap_t *incompatible_waiting_types_bitmap() const + { return m_waiting_incompatible; } + virtual bool needs_notification(const MDL_ticket *ticket) const + { return (ticket->get_type() == MDL_SHARED); } + + /** + Notify threads holding scoped IX locks which conflict with a pending + S lock. + + Thread which holds global IX lock can be a handler thread for + insert delayed. We need to kill such threads in order to get + global shared lock. We do this my calling code outside of MDL. + */ + virtual bool conflicting_locks(const MDL_ticket *ticket) const + { return ticket->get_type() == MDL_INTENTION_EXCLUSIVE; } + + /* + In scoped locks, only IX lock request would starve because of X/S. But that + is practically very rare case. So just return 0 from this function. + */ + virtual bitmap_t hog_lock_types_bitmap() const + { return 0; } + private: + static const bitmap_t m_granted_incompatible[MDL_TYPE_END]; + static const bitmap_t m_waiting_incompatible[MDL_TYPE_END]; + }; + + + /** + An implementation of a per-object lock. Supports SHARED, SHARED_UPGRADABLE, + SHARED HIGH PRIORITY and EXCLUSIVE locks. + */ + struct MDL_object_lock : public MDL_lock_strategy + { + MDL_object_lock() = default; + virtual const bitmap_t *incompatible_granted_types_bitmap() const + { return m_granted_incompatible; } + virtual const bitmap_t *incompatible_waiting_types_bitmap() const + { return m_waiting_incompatible; } + virtual bool needs_notification(const MDL_ticket *ticket) const + { + return (MDL_BIT(ticket->get_type()) & + (MDL_BIT(MDL_SHARED_NO_WRITE) | + MDL_BIT(MDL_SHARED_NO_READ_WRITE) | + MDL_BIT(MDL_EXCLUSIVE))); + } + + /** + Notify threads holding a shared metadata locks on object which + conflict with a pending X, SNW or SNRW lock. + + If thread which holds conflicting lock is waiting on table-level + lock or some other non-MDL resource we might need to wake it up + by calling code outside of MDL. + */ + virtual bool conflicting_locks(const MDL_ticket *ticket) const + { return ticket->get_type() < MDL_SHARED_UPGRADABLE; } + + /* + To prevent starvation, these lock types that are only granted + max_write_lock_count times in a row while other lock types are + waiting. + */ + virtual bitmap_t hog_lock_types_bitmap() const + { + return (MDL_BIT(MDL_SHARED_NO_WRITE) | + MDL_BIT(MDL_SHARED_NO_READ_WRITE) | + MDL_BIT(MDL_EXCLUSIVE)); + } + + private: + static const bitmap_t m_granted_incompatible[MDL_TYPE_END]; + static const bitmap_t m_waiting_incompatible[MDL_TYPE_END]; + }; + + + struct MDL_backup_lock: public MDL_lock_strategy + { + MDL_backup_lock() = default; + virtual const bitmap_t *incompatible_granted_types_bitmap() const + { return m_granted_incompatible; } + virtual const bitmap_t *incompatible_waiting_types_bitmap() const + { return m_waiting_incompatible; } + virtual bool needs_notification(const MDL_ticket *ticket) const + { + return (MDL_BIT(ticket->get_type()) & MDL_BIT(MDL_BACKUP_FTWRL1)); + } + + /** + Insert delayed threads may hold DML or TRANS_DML lock. + We need to kill such threads in order to get lock for FTWRL statements. + We do this by calling code outside of MDL. + */ + virtual bool conflicting_locks(const MDL_ticket *ticket) const + { + return (MDL_BIT(ticket->get_type()) & + (MDL_BIT(MDL_BACKUP_DML) | + MDL_BIT(MDL_BACKUP_TRANS_DML))); + } + + /* + In backup namespace DML/DDL may starve because of concurrent FTWRL or + BACKUP statements. This scenario is partically useless in real world, + so we just return 0 here. + */ + virtual bitmap_t hog_lock_types_bitmap() const + { return 0; } + private: + static const bitmap_t m_granted_incompatible[MDL_BACKUP_END]; + static const bitmap_t m_waiting_incompatible[MDL_BACKUP_END]; + }; + +public: + /** The key of the object (data) being protected. */ + MDL_key key; + /** + Read-write lock protecting this lock context. + + @note The fact that we use read-write lock prefers readers here is + important as deadlock detector won't work correctly otherwise. + + For example, imagine that we have following waiters graph: + + ctxA -> obj1 -> ctxB -> obj1 -| + ^ | + |----------------------------| + + and both ctxA and ctxB start deadlock detection process: + + ctxA read-locks obj1 ctxB read-locks obj2 + ctxA goes deeper ctxB goes deeper + + Now ctxC comes in who wants to start waiting on obj1, also + ctxD comes in who wants to start waiting on obj2. + + ctxC tries to write-lock obj1 ctxD tries to write-lock obj2 + ctxC is blocked ctxD is blocked + + Now ctxA and ctxB resume their search: + + ctxA tries to read-lock obj2 ctxB tries to read-lock obj1 + + If m_rwlock prefers writes (or fair) both ctxA and ctxB would be + blocked because of pending write locks from ctxD and ctxC + correspondingly. Thus we will get a deadlock in deadlock detector. + If m_wrlock prefers readers (actually ignoring pending writers is + enough) ctxA and ctxB will continue and no deadlock will occur. + */ + mysql_prlock_t m_rwlock; + + bool is_empty() const + { + return (m_granted.is_empty() && m_waiting.is_empty()); + } + + const bitmap_t *incompatible_granted_types_bitmap() const + { return m_strategy->incompatible_granted_types_bitmap(); } + const bitmap_t *incompatible_waiting_types_bitmap() const + { return m_strategy->incompatible_waiting_types_bitmap(); } + + bool has_pending_conflicting_lock(enum_mdl_type type); + + bool can_grant_lock(enum_mdl_type type, MDL_context *requstor_ctx, + bool ignore_lock_priority) const; + + inline unsigned long get_lock_owner() const; + + void reschedule_waiters(); + + void remove_ticket(LF_PINS *pins, Ticket_list MDL_lock::*queue, + MDL_ticket *ticket); + + bool visit_subgraph(MDL_ticket *waiting_ticket, + MDL_wait_for_graph_visitor *gvisitor); + + bool needs_notification(const MDL_ticket *ticket) const + { return m_strategy->needs_notification(ticket); } + void notify_conflicting_locks(MDL_context *ctx) + { + for (const auto &conflicting_ticket : m_granted) + { + if (conflicting_ticket.get_ctx() != ctx && + m_strategy->conflicting_locks(&conflicting_ticket)) + { + MDL_context *conflicting_ctx= conflicting_ticket.get_ctx(); + + ctx->get_owner()-> + notify_shared_lock(conflicting_ctx->get_owner(), + conflicting_ctx->get_needs_thr_lock_abort()); + } + } + } + + bitmap_t hog_lock_types_bitmap() const + { return m_strategy->hog_lock_types_bitmap(); } + +#ifndef DBUG_OFF + bool check_if_conflicting_replication_locks(MDL_context *ctx); +#endif + + /** List of granted tickets for this lock. */ + Ticket_list m_granted; + /** Tickets for contexts waiting to acquire a lock. */ + Ticket_list m_waiting; + + /** + Number of times high priority lock requests have been granted while + low priority lock requests were waiting. + */ + ulong m_hog_lock_count; + +public: + + MDL_lock() + : m_hog_lock_count(0), + m_strategy(0) + { mysql_prlock_init(key_MDL_lock_rwlock, &m_rwlock); } + + MDL_lock(const MDL_key *key_arg) + : key(key_arg), + m_hog_lock_count(0), + m_strategy(&m_backup_lock_strategy) + { + DBUG_ASSERT(key_arg->mdl_namespace() == MDL_key::BACKUP); + mysql_prlock_init(key_MDL_lock_rwlock, &m_rwlock); + } + + ~MDL_lock() + { mysql_prlock_destroy(&m_rwlock); } + + static void lf_alloc_constructor(uchar *arg) + { new (arg + LF_HASH_OVERHEAD) MDL_lock(); } + + static void lf_alloc_destructor(uchar *arg) + { ((MDL_lock*)(arg + LF_HASH_OVERHEAD))->~MDL_lock(); } + + static void lf_hash_initializer(LF_HASH *hash __attribute__((unused)), + MDL_lock *lock, MDL_key *key_arg) + { + DBUG_ASSERT(key_arg->mdl_namespace() != MDL_key::BACKUP); + new (&lock->key) MDL_key(key_arg); + if (key_arg->mdl_namespace() == MDL_key::SCHEMA) + lock->m_strategy= &m_scoped_lock_strategy; + else + lock->m_strategy= &m_object_lock_strategy; + } + + const MDL_lock_strategy *m_strategy; +private: + static const MDL_backup_lock m_backup_lock_strategy; + static const MDL_scoped_lock m_scoped_lock_strategy; + static const MDL_object_lock m_object_lock_strategy; +}; + + +const MDL_lock::MDL_backup_lock MDL_lock::m_backup_lock_strategy; +const MDL_lock::MDL_scoped_lock MDL_lock::m_scoped_lock_strategy; +const MDL_lock::MDL_object_lock MDL_lock::m_object_lock_strategy; + + +static MDL_map mdl_locks; + + +extern "C" +{ +static uchar * +mdl_locks_key(const uchar *record, size_t *length, + my_bool not_used __attribute__((unused))) +{ + MDL_lock *lock=(MDL_lock*) record; + *length= lock->key.length(); + return (uchar*) lock->key.ptr(); +} +} /* extern "C" */ + + +/** + Initialize the metadata locking subsystem. + + This function is called at server startup. + + In particular, initializes the new global mutex and + the associated condition variable: LOCK_mdl and COND_mdl. + These locking primitives are implementation details of the MDL + subsystem and are private to it. +*/ + +void mdl_init() +{ + DBUG_ASSERT(! mdl_initialized); + mdl_initialized= TRUE; + +#ifdef HAVE_PSI_INTERFACE + init_mdl_psi_keys(); +#endif + + mdl_locks.init(); +} + + +/** + Release resources of metadata locking subsystem. + + Destroys the global mutex and the condition variable. + Called at server shutdown. +*/ + +void mdl_destroy() +{ + if (mdl_initialized) + { + mdl_initialized= FALSE; + mdl_locks.destroy(); + } +} + + +struct mdl_iterate_arg +{ + mdl_iterator_callback callback; + void *argument; +}; + + +static my_bool mdl_iterate_lock(MDL_lock *lock, mdl_iterate_arg *arg) +{ + /* + We can skip check for m_strategy here, becase m_granted + must be empty for such locks anyway. + */ + mysql_prlock_rdlock(&lock->m_rwlock); + bool res= std::any_of(lock->m_granted.begin(), lock->m_granted.end(), + [arg](MDL_ticket &ticket) { + return arg->callback(&ticket, arg->argument, true); + }); + res= std::any_of(lock->m_waiting.begin(), lock->m_waiting.end(), + [arg](MDL_ticket &ticket) { + return arg->callback(&ticket, arg->argument, false); + }); + mysql_prlock_unlock(&lock->m_rwlock); + return res; +} + + +int mdl_iterate(mdl_iterator_callback callback, void *arg) +{ + DBUG_ENTER("mdl_iterate"); + mdl_iterate_arg argument= { callback, arg }; + LF_PINS *pins= mdl_locks.get_pins(); + int res= 1; + + if (pins) + { + res= mdl_iterate_lock(mdl_locks.m_backup_lock, &argument) || + lf_hash_iterate(&mdl_locks.m_locks, pins, + (my_hash_walk_action) mdl_iterate_lock, &argument); + lf_hash_put_pins(pins); + } + DBUG_RETURN(res); +} + + +my_hash_value_type mdl_hash_function(CHARSET_INFO *cs, + const uchar *key, size_t length) +{ + MDL_key *mdl_key= (MDL_key*) (key - offsetof(MDL_key, m_ptr)); + return mdl_key->hash_value(); +} + + +/** Initialize the container for all MDL locks. */ + +void MDL_map::init() +{ + MDL_key backup_lock_key(MDL_key::BACKUP, "", ""); + + m_backup_lock= new (std::nothrow) MDL_lock(&backup_lock_key); + + lf_hash_init(&m_locks, sizeof(MDL_lock), LF_HASH_UNIQUE, 0, 0, + mdl_locks_key, &my_charset_bin); + m_locks.alloc.constructor= MDL_lock::lf_alloc_constructor; + m_locks.alloc.destructor= MDL_lock::lf_alloc_destructor; + m_locks.initializer= (lf_hash_initializer) MDL_lock::lf_hash_initializer; + m_locks.hash_function= mdl_hash_function; +} + + +/** + Destroy the container for all MDL locks. + @pre It must be empty. +*/ + +void MDL_map::destroy() +{ + delete m_backup_lock; + + DBUG_ASSERT(!lf_hash_size(&m_locks)); + lf_hash_destroy(&m_locks); +} + + +/** + Find MDL_lock object corresponding to the key, create it + if it does not exist. + + @retval non-NULL - Success. MDL_lock instance for the key with + locked MDL_lock::m_rwlock. + @retval NULL - Failure (OOM). +*/ + +MDL_lock* MDL_map::find_or_insert(LF_PINS *pins, const MDL_key *mdl_key) +{ + MDL_lock *lock; + + if (mdl_key->mdl_namespace() == MDL_key::BACKUP) + { + /* + Return pointer to pre-allocated MDL_lock instance. Such an optimization + allows to save one hash lookup for any statement changing data. + + It works since this namespace contains only one element so keys + for them look like '<namespace-id>\0\0'. + */ + DBUG_ASSERT(mdl_key->length() == 3); + mysql_prlock_wrlock(&m_backup_lock->m_rwlock); + return m_backup_lock; + } + +retry: + while (!(lock= (MDL_lock*) lf_hash_search(&m_locks, pins, mdl_key->ptr(), + mdl_key->length()))) + if (lf_hash_insert(&m_locks, pins, (uchar*) mdl_key) == -1) + return NULL; + + mysql_prlock_wrlock(&lock->m_rwlock); + if (unlikely(!lock->m_strategy)) + { + mysql_prlock_unlock(&lock->m_rwlock); + lf_hash_search_unpin(pins); + goto retry; + } + lf_hash_search_unpin(pins); + + return lock; +} + + +/** + * Return thread id of the owner of the lock, if it is owned. + */ + +unsigned long +MDL_map::get_lock_owner(LF_PINS *pins, const MDL_key *mdl_key) +{ + unsigned long res= 0; + + if (mdl_key->mdl_namespace() == MDL_key::BACKUP) + { + mysql_prlock_rdlock(&m_backup_lock->m_rwlock); + res= m_backup_lock->get_lock_owner(); + mysql_prlock_unlock(&m_backup_lock->m_rwlock); + } + else + { + MDL_lock *lock= (MDL_lock*) lf_hash_search(&m_locks, pins, mdl_key->ptr(), + mdl_key->length()); + if (lock) + { + /* + We can skip check for m_strategy here, becase m_granted + must be empty for such locks anyway. + */ + mysql_prlock_rdlock(&lock->m_rwlock); + res= lock->get_lock_owner(); + mysql_prlock_unlock(&lock->m_rwlock); + lf_hash_search_unpin(pins); + } + } + return res; +} + + +/** + Destroy MDL_lock object or delegate this responsibility to + whatever thread that holds the last outstanding reference to + it. +*/ + +void MDL_map::remove(LF_PINS *pins, MDL_lock *lock) +{ + if (lock->key.mdl_namespace() == MDL_key::BACKUP) + { + /* Never destroy pre-allocated MDL_lock object in BACKUP namespace. */ + mysql_prlock_unlock(&lock->m_rwlock); + return; + } + + lock->m_strategy= 0; + mysql_prlock_unlock(&lock->m_rwlock); + lf_hash_delete(&m_locks, pins, lock->key.ptr(), lock->key.length()); +} + + +/** + Initialize a metadata locking context. + + This is to be called when a new server connection is created. +*/ + +MDL_context::MDL_context() + : + m_owner(NULL), + m_needs_thr_lock_abort(FALSE), + m_waiting_for(NULL), + m_pins(NULL) +{ + mysql_prlock_init(key_MDL_context_LOCK_waiting_for, &m_LOCK_waiting_for); +} + + +/** + Destroy metadata locking context. + + Assumes and asserts that there are no active or pending locks + associated with this context at the time of the destruction. + + Currently does nothing. Asserts that there are no pending + or satisfied lock requests. The pending locks must be released + prior to destruction. This is a new way to express the assertion + that all tables are closed before a connection is destroyed. +*/ + +void MDL_context::destroy() +{ + DBUG_ASSERT(m_tickets[MDL_STATEMENT].is_empty()); + DBUG_ASSERT(m_tickets[MDL_TRANSACTION].is_empty()); + DBUG_ASSERT(m_tickets[MDL_EXPLICIT].is_empty()); + + mysql_prlock_destroy(&m_LOCK_waiting_for); + if (m_pins) + lf_hash_put_pins(m_pins); +} + + +bool MDL_context::fix_pins() +{ + return m_pins ? false : (m_pins= mdl_locks.get_pins()) == 0; +} + + +/** + Initialize a lock request. + + This is to be used for every lock request. + + Note that initialization and allocation are split into two + calls. This is to allow flexible memory management of lock + requests. Normally a lock request is stored in statement memory + (e.g. is a member of struct TABLE_LIST), but we would also like + to allow allocation of lock requests in other memory roots, + for example in the grant subsystem, to lock privilege tables. + + The MDL subsystem does not own or manage memory of lock requests. + + @param mdl_namespace Id of namespace of object to be locked + @param db Name of database to which the object belongs + @param name Name of of the object + @param mdl_type The MDL lock type for the request. +*/ + +void MDL_request::init_with_source(MDL_key::enum_mdl_namespace mdl_namespace, + const char *db_arg, + const char *name_arg, + enum_mdl_type mdl_type_arg, + enum_mdl_duration mdl_duration_arg, + const char *src_file, + uint src_line) +{ + key.mdl_key_init(mdl_namespace, db_arg, name_arg); + type= mdl_type_arg; + duration= mdl_duration_arg; + ticket= NULL; + m_src_file= src_file; + m_src_line= src_line; +} + + +/** + Initialize a lock request using pre-built MDL_key. + + @sa MDL_request::init(namespace, db, name, type). + + @param key_arg The pre-built MDL key for the request. + @param mdl_type_arg The MDL lock type for the request. +*/ + +void MDL_request::init_by_key_with_source(const MDL_key *key_arg, + enum_mdl_type mdl_type_arg, + enum_mdl_duration mdl_duration_arg, + const char *src_file, + uint src_line) +{ + key.mdl_key_init(key_arg); + type= mdl_type_arg; + duration= mdl_duration_arg; + ticket= NULL; + m_src_file= src_file; + m_src_line= src_line; +} + + +/** + Auxiliary functions needed for creation/destruction of MDL_ticket + objects. + + @todo This naive implementation should be replaced with one that saves + on memory allocation by reusing released objects. +*/ + +MDL_ticket *MDL_ticket::create(MDL_context *ctx_arg, enum_mdl_type type_arg +#ifndef DBUG_OFF + , enum_mdl_duration duration_arg +#endif + ) +{ + return new (std::nothrow) + MDL_ticket(ctx_arg, type_arg +#ifndef DBUG_OFF + , duration_arg +#endif + ); +} + + +void MDL_ticket::destroy(MDL_ticket *ticket) +{ + mysql_mdl_destroy(ticket->m_psi); + ticket->m_psi= NULL; + + delete ticket; +} + + +/** + Return the 'weight' of this ticket for the + victim selection algorithm. Requests with + lower weight are preferred to requests + with higher weight when choosing a victim. +*/ + +uint MDL_ticket::get_deadlock_weight() const +{ + if (m_lock->key.mdl_namespace() == MDL_key::BACKUP) + { + if (m_type == MDL_BACKUP_FTWRL1) + return DEADLOCK_WEIGHT_FTWRL1; + return DEADLOCK_WEIGHT_DDL; + } + return m_type >= MDL_SHARED_UPGRADABLE ? + DEADLOCK_WEIGHT_DDL : DEADLOCK_WEIGHT_DML; +} + + +/** Construct an empty wait slot. */ + +MDL_wait::MDL_wait() + :m_wait_status(EMPTY) +{ + mysql_mutex_init(key_MDL_wait_LOCK_wait_status, &m_LOCK_wait_status, NULL); + mysql_cond_init(key_MDL_wait_COND_wait_status, &m_COND_wait_status, NULL); +} + + +/** Destroy system resources. */ + +MDL_wait::~MDL_wait() +{ + mysql_mutex_destroy(&m_LOCK_wait_status); + mysql_cond_destroy(&m_COND_wait_status); +} + + +/** + Set the status unless it's already set. Return FALSE if set, + TRUE otherwise. +*/ + +bool MDL_wait::set_status(enum_wait_status status_arg) +{ + bool was_occupied= TRUE; + mysql_mutex_lock(&m_LOCK_wait_status); + if (m_wait_status == EMPTY) + { + was_occupied= FALSE; + m_wait_status= status_arg; + mysql_cond_signal(&m_COND_wait_status); + } + mysql_mutex_unlock(&m_LOCK_wait_status); + return was_occupied; +} + + +/** Query the current value of the wait slot. */ + +MDL_wait::enum_wait_status MDL_wait::get_status() +{ + enum_wait_status result; + mysql_mutex_lock(&m_LOCK_wait_status); + result= m_wait_status; + mysql_mutex_unlock(&m_LOCK_wait_status); + return result; +} + + +/** Clear the current value of the wait slot. */ + +void MDL_wait::reset_status() +{ + mysql_mutex_lock(&m_LOCK_wait_status); + m_wait_status= EMPTY; + mysql_mutex_unlock(&m_LOCK_wait_status); +} + + +/** + Wait for the status to be assigned to this wait slot. + + @param owner MDL context owner. + @param abs_timeout Absolute time after which waiting should stop. + @param set_status_on_timeout TRUE - If in case of timeout waiting + context should close the wait slot by + sending TIMEOUT to itself. + FALSE - Otherwise. + @param wait_state_name Thread state name to be set for duration of wait. + + @returns Signal posted. +*/ + +MDL_wait::enum_wait_status +MDL_wait::timed_wait(MDL_context_owner *owner, struct timespec *abs_timeout, + bool set_status_on_timeout, + const PSI_stage_info *wait_state_name) +{ + PSI_stage_info old_stage; + enum_wait_status result; + int wait_result= 0; + DBUG_ENTER("MDL_wait::timed_wait"); + + mysql_mutex_lock(&m_LOCK_wait_status); + + owner->ENTER_COND(&m_COND_wait_status, &m_LOCK_wait_status, + wait_state_name, & old_stage); + thd_wait_begin(NULL, THD_WAIT_META_DATA_LOCK); + tpool::tpool_wait_begin(); + while (!m_wait_status && !owner->is_killed() && + wait_result != ETIMEDOUT && wait_result != ETIME) + { +#ifdef WITH_WSREP +# ifdef ENABLED_DEBUG_SYNC + // Allow tests to block the applier thread using the DBUG facilities + DBUG_EXECUTE_IF("sync.wsrep_before_mdl_wait", + { + const char act[]= + "now " + "wait_for signal.wsrep_before_mdl_wait"; + DBUG_ASSERT(!debug_sync_set_action((owner->get_thd()), + STRING_WITH_LEN(act))); + };); +# endif + if (WSREP_ON && wsrep_thd_is_BF(owner->get_thd(), false)) + { + wait_result= mysql_cond_wait(&m_COND_wait_status, &m_LOCK_wait_status); + } + else +#endif /* WITH_WSREP */ + wait_result= mysql_cond_timedwait(&m_COND_wait_status, &m_LOCK_wait_status, + abs_timeout); + } + tpool::tpool_wait_end(); + thd_wait_end(NULL); + + if (m_wait_status == EMPTY) + { + /* + Wait has ended not due to a status being set from another + thread but due to this connection/statement being killed or a + time out. + To avoid races, which may occur if another thread sets + GRANTED status before the code which calls this method + processes the abort/timeout, we assign the status under + protection of the m_LOCK_wait_status, within the critical + section. An exception is when set_status_on_timeout is + false, which means that the caller intends to restart the + wait. + */ + if (owner->is_killed()) + m_wait_status= KILLED; + else if (set_status_on_timeout) + m_wait_status= TIMEOUT; + } + result= m_wait_status; + + owner->EXIT_COND(& old_stage); + + DBUG_RETURN(result); +} + + +/** + Add ticket to MDL_lock's list of waiting requests and + update corresponding bitmap of lock types. +*/ + +void MDL_lock::Ticket_list::add_ticket(MDL_ticket *ticket) +{ + /* + Ticket being added to the list must have MDL_ticket::m_lock set, + since for such tickets methods accessing this member might be + called by other threads. + */ + DBUG_ASSERT(ticket->get_lock()); +#ifdef WITH_WSREP + if (WSREP_ON && (this == &(ticket->get_lock()->m_waiting)) && + wsrep_thd_is_BF(ticket->get_ctx()->get_thd(), false)) + { + DBUG_ASSERT(WSREP(ticket->get_ctx()->get_thd())); + + m_list.insert(std::find_if(ticket->get_lock()->m_waiting.begin(), + ticket->get_lock()->m_waiting.end(), + [](const MDL_ticket &waiting) { + return !wsrep_thd_is_BF( + waiting.get_ctx()->get_thd(), true); + }), + *ticket); + } + else +#endif /* WITH_WSREP */ + { + /* + Add ticket to the *back* of the queue to ensure fairness + among requests with the same priority. + */ + m_list.push_back(*ticket); + } + m_bitmap|= MDL_BIT(ticket->get_type()); + m_type_counters[ticket->get_type()]++; +} + + +/** + Remove ticket from MDL_lock's list of requests and + update corresponding bitmap of lock types. +*/ + +void MDL_lock::Ticket_list::remove_ticket(MDL_ticket *ticket) +{ + m_list.remove(*ticket); + /* + Check if waiting queue has another ticket with the same type as + one which was removed. If there is no such ticket, i.e. we have + removed last ticket of particular type, then we need to update + bitmap of waiting ticket's types. + */ + if (--m_type_counters[ticket->get_type()] == 0) + m_bitmap&= ~MDL_BIT(ticket->get_type()); +} + + +/** + Determine waiting contexts which requests for the lock can be + satisfied, grant lock to them and wake them up. + + @note Together with MDL_lock::add_ticket() this method implements + fair scheduling among requests with the same priority. + It tries to grant lock from the head of waiters list, while + add_ticket() adds new requests to the back of this list. + +*/ + +void MDL_lock::reschedule_waiters() +{ + bool skip_high_priority= false; + bitmap_t hog_lock_types= hog_lock_types_bitmap(); + + if (m_hog_lock_count >= max_write_lock_count) + { + /* + If number of successively granted high-prio, strong locks has exceeded + max_write_lock_count give a way to low-prio, weak locks to avoid their + starvation. + */ + + if ((m_waiting.bitmap() & ~hog_lock_types) != 0) + { + /* + Even though normally when m_hog_lock_count is non-0 there is + some pending low-prio lock, we still can encounter situation + when m_hog_lock_count is non-0 and there are no pending low-prio + locks. This, for example, can happen when a ticket for pending + low-prio lock was removed from waiters list due to timeout, + and reschedule_waiters() is called after that to update the + waiters queue. m_hog_lock_count will be reset to 0 at the + end of this call in such case. + + Note that it is not an issue if we fail to wake up any pending + waiters for weak locks in the loop below. This would mean that + all of them are either killed, timed out or chosen as a victim + by deadlock resolver, but have not managed to remove ticket + from the waiters list yet. After tickets will be removed from + the waiters queue there will be another call to + reschedule_waiters() with pending bitmap updated to reflect new + state of waiters queue. + */ + skip_high_priority= true; + } + } + + /* + Find the first (and hence the oldest) waiting request which + can be satisfied (taking into account priority). Grant lock to it. + Repeat the process for the remainder of waiters. + Note we don't need to re-start iteration from the head of the + list after satisfying the first suitable request as in our case + all compatible types of requests have the same priority. + + TODO/FIXME: We should: + - Either switch to scheduling without priorities + which will allow to stop iteration through the + list of waiters once we found the first ticket + which can't be satisfied + - Or implement some check using bitmaps which will + allow to stop iteration in cases when, e.g., we + grant SNRW lock and there are no pending S or + SH locks. + */ + for (auto it= m_waiting.begin(); it != m_waiting.end(); ++it) + { + /* + Skip high-prio, strong locks if earlier we have decided to give way to + low-prio, weaker locks. + */ + if (skip_high_priority && + ((MDL_BIT(it->get_type()) & hog_lock_types) != 0)) + continue; + + if (can_grant_lock(it->get_type(), it->get_ctx(), + skip_high_priority)) + { + if (!it->get_ctx()->m_wait.set_status(MDL_wait::GRANTED)) + { + /* + Satisfy the found request by updating lock structures. + It is OK to do so even after waking up the waiter since any + session which tries to get any information about the state of + this lock has to acquire MDL_lock::m_rwlock first and thus, + when manages to do so, already sees an updated state of the + MDL_lock object. + */ + auto prev_it= std::prev(it); // this might be begin()-- but the hack + // works because list is circular + m_waiting.remove_ticket(&*it); + m_granted.add_ticket(&*it); + + /* + Increase counter of successively granted high-priority strong locks, + if we have granted one. + */ + if ((MDL_BIT(it->get_type()) & hog_lock_types) != 0) + m_hog_lock_count++; + + it= prev_it; + } + /* + If we could not update the wait slot of the waiter, + it can be due to fact that its connection/statement was + killed or it has timed out (i.e. the slot is not empty). + Since in all such cases the waiter assumes that the lock was + not been granted, we should keep the request in the waiting + queue and look for another request to reschedule. + */ + } + } + + if ((m_waiting.bitmap() & ~hog_lock_types) == 0) + { + /* + Reset number of successively granted high-prio, strong locks + if there are no pending low-prio, weak locks. + This ensures: + - That m_hog_lock_count is correctly reset after strong lock + is released and weak locks are granted (or there are no + other lock requests). + - That situation when SNW lock is granted along with some SR + locks, but SW locks are still blocked are handled correctly. + - That m_hog_lock_count is zero in most cases when there are no pending + weak locks (see comment at the start of this method for example of + exception). This allows to save on checks at the start of this method. + */ + m_hog_lock_count= 0; + } +} + + +/** + Compatibility (or rather "incompatibility") matrices for scoped metadata + lock. + Scoped locks are database (or schema) locks. + Arrays of bitmaps which elements specify which granted/waiting locks + are incompatible with type of lock being requested. + + The first array specifies if particular type of request can be satisfied + if there is granted scoped lock of certain type. + + (*) Since intention shared scoped locks (IS) are compatible with all other + type of locks, they don't need to be implemented and there is no code + for them. + + | Type of active | + Request | scoped lock | + type | IS(*) IX S X | + ---------+------------------+ + IS(*) | + + + + | + IX | + + - - | + S | + - + - | + X | + - - - | + + The second array specifies if particular type of request can be satisfied + if there is already waiting request for the scoped lock of certain type. + I.e. it specifies what is the priority of different lock types. + + | Pending | + Request | scoped lock | + type | IS(*) IX S X | + ---------+-----------------+ + IS(*) | + + + + | + IX | + + - - | + S | + + + - | + X | + + + + | + + Here: "+" -- means that request can be satisfied + "-" -- means that request can't be satisfied and should wait + + Note that relation between scoped locks and objects locks requested + by statement is not straightforward and is therefore fully defined + by SQL-layer. + For example, in order to support global read lock implementation + SQL-layer acquires IX lock in GLOBAL namespace for each statement + that can modify metadata or data (i.e. for each statement that + needs SW, SU, SNW, SNRW or X object locks). OTOH, to ensure that + DROP DATABASE works correctly with concurrent DDL, IX metadata locks + in SCHEMA namespace are acquired for DDL statements which can update + metadata in the schema (i.e. which acquire SU, SNW, SNRW and X locks + on schema objects) and aren't acquired for DML. +*/ + +const MDL_lock::bitmap_t +MDL_lock::MDL_scoped_lock::m_granted_incompatible[MDL_TYPE_END]= +{ + MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED), + MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_INTENTION_EXCLUSIVE), + 0, 0, 0, 0, 0, 0, 0, + MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED) | MDL_BIT(MDL_INTENTION_EXCLUSIVE) +}; + +const MDL_lock::bitmap_t +MDL_lock::MDL_scoped_lock::m_waiting_incompatible[MDL_TYPE_END]= +{ + MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED), + MDL_BIT(MDL_EXCLUSIVE), 0, 0, 0, 0, 0, 0, 0, 0 +}; + + +/** + Compatibility (or rather "incompatibility") matrices for per-object + metadata lock. Arrays of bitmaps which elements specify which granted/ + waiting locks are incompatible with type of lock being requested. + + The first array specifies if particular type of request can be satisfied + if there is granted lock of certain type. + + Request | Granted requests for lock | + type | S SH SR SW SU SRO SNW SNRW X | + ----------+------------------------------------+ + S | + + + + + + + + - | + SH | + + + + + + + + - | + SR | + + + + + + + - - | + SW | + + + + + - - - - | + SU | + + + + - + - - - | + SRO | + + + - + + + - - | + SNW | + + + - - + - - - | + SNRW | + + - - - - - - - | + X | - - - - - - - - - | + SU -> X | - - - - 0 - 0 0 0 | + SNW -> X | - - - 0 0 - 0 0 0 | + SNRW -> X | - - 0 0 0 0 0 0 0 | + + The second array specifies if particular type of request can be satisfied + if there is waiting request for the same lock of certain type. In other + words it specifies what is the priority of different lock types. + + Request | Pending requests for lock | + type | S SH SR SW SU SRO SNW SNRW X | + ----------+-----------------------------------+ + S | + + + + + + + + - | + SH | + + + + + + + + + | + SR | + + + + + + + - - | + SW | + + + + + + - - - | + SU | + + + + + + + + - | + SRO | + + + - + + + - - | + SNW | + + + + + + + + - | + SNRW | + + + + + + + + - | + X | + + + + + + + + + | + SU -> X | + + + + + + + + + | + SNW -> X | + + + + + + + + + | + SNRW -> X | + + + + + + + + + | + + Here: "+" -- means that request can be satisfied + "-" -- means that request can't be satisfied and should wait + "0" -- means impossible situation which will trigger assert + + @note In cases then current context already has "stronger" type + of lock on the object it will be automatically granted + thanks to usage of the MDL_context::find_ticket() method. + + @note IX locks are excluded since they are not used for per-object + metadata locks. +*/ + +const MDL_lock::bitmap_t +MDL_lock::MDL_object_lock::m_granted_incompatible[MDL_TYPE_END]= +{ + 0, + MDL_BIT(MDL_EXCLUSIVE), + MDL_BIT(MDL_EXCLUSIVE), + MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED_NO_READ_WRITE), + MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED_NO_READ_WRITE) | + MDL_BIT(MDL_SHARED_NO_WRITE) | MDL_BIT(MDL_SHARED_READ_ONLY), + MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED_NO_READ_WRITE) | + MDL_BIT(MDL_SHARED_NO_WRITE) | MDL_BIT(MDL_SHARED_UPGRADABLE), + MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED_NO_READ_WRITE) | + MDL_BIT(MDL_SHARED_WRITE), + MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED_NO_READ_WRITE) | + MDL_BIT(MDL_SHARED_NO_WRITE) | MDL_BIT(MDL_SHARED_UPGRADABLE) | + MDL_BIT(MDL_SHARED_WRITE), + MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED_NO_READ_WRITE) | + MDL_BIT(MDL_SHARED_NO_WRITE) | MDL_BIT(MDL_SHARED_READ_ONLY) | + MDL_BIT(MDL_SHARED_UPGRADABLE) | MDL_BIT(MDL_SHARED_WRITE) | + MDL_BIT(MDL_SHARED_READ), + MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED_NO_READ_WRITE) | + MDL_BIT(MDL_SHARED_NO_WRITE) | MDL_BIT(MDL_SHARED_READ_ONLY) | + MDL_BIT(MDL_SHARED_UPGRADABLE) | MDL_BIT(MDL_SHARED_WRITE) | + MDL_BIT(MDL_SHARED_READ) | MDL_BIT(MDL_SHARED_HIGH_PRIO) | + MDL_BIT(MDL_SHARED) +}; + + +const MDL_lock::bitmap_t +MDL_lock::MDL_object_lock::m_waiting_incompatible[MDL_TYPE_END]= +{ + 0, + MDL_BIT(MDL_EXCLUSIVE), + 0, + MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED_NO_READ_WRITE), + MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED_NO_READ_WRITE) | + MDL_BIT(MDL_SHARED_NO_WRITE), + MDL_BIT(MDL_EXCLUSIVE), + MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED_NO_READ_WRITE) | + MDL_BIT(MDL_SHARED_WRITE), + MDL_BIT(MDL_EXCLUSIVE), + MDL_BIT(MDL_EXCLUSIVE), + 0 +}; + + +/** + Compatibility (or rather "incompatibility") matrices for backup metadata + lock. Arrays of bitmaps which elements specify which granted/waiting locks + are incompatible with type of lock being requested. + + The first array specifies if particular type of request can be satisfied + if there is granted backup lock of certain type. + + Request | Type of active backup lock | + type | S0 S1 S2 S3 S4 F1 F2 D TD SD DD BL AC C | + ----------+---------------------------------------------------------+ + S0 | - - - - - + + + + + + + + + | + S1 | - + + + + + + + + + + + + + | + S2 | - + + + + + + - + + + + + + | + S3 | - + + + + + + - + + - + + + | + S4 | - + + + + + + - + - - + + - | + FTWRL1 | + + + + + + + - - - - + - + | + FTWRL2 | + + + + + + + - - - - + - - | + D | + - - - - - - + + + + + + + | + TD | + + + + + - - + + + + + + + | + SD | + + + + - - - + + + + + + + | + DDL | + + + - - - - + + + + - + + | + BLOCK_DDL | - + + + + + + + + + - + + + | + ALTER_COP | + + + + + - - + + + + + + + | + COMMIT | + + + + - + - + + + + + + + | + + The second array specifies if particular type of request can be satisfied + if there is already waiting request for the backup lock of certain type. + I.e. it specifies what is the priority of different lock types. + + Request | Pending backup lock | + type | S0 S1 S2 S3 S4 F1 F2 D TD SD DD BL AC C | + ----------+---------------------------------------------------------+ + S0 | + - - - - + + + + + + + + + | + S1 | + + + + + + + + + + + + + + | + S2 | + + + + + + + + + + + + + + | + S3 | + + + + + + + + + + + + + + | + S4 | + + + + + + + + + + + + + + | + FTWRL1 | + + + + + + + + + + + + + + | + FTWRL2 | + + + + + + + + + + + + + + | + D | + - - - - - - + + + + + + + | + TD | + + + + + - - + + + + + + + | + SD | + + + + - - - + + + + + + + | + DDL | + + + - - - - + + + + - + + | + BLOCK_DDL | + + + + + + + + + + + + + + | + ALTER_COP | + + + + + - - + + + + + + + | + COMMIT | + + + + - + - + + + + + + + | + + Here: "+" -- means that request can be satisfied + "-" -- means that request can't be satisfied and should wait +*/ + +/* + NOTE: If you add a new MDL_BACKUP_XXX level lock, you have to also add it + to MDL_BACKUP_START in the two arrays below! +*/ + +const MDL_lock::bitmap_t +MDL_lock::MDL_backup_lock::m_granted_incompatible[MDL_BACKUP_END]= +{ + /* MDL_BACKUP_START */ + MDL_BIT(MDL_BACKUP_START) | MDL_BIT(MDL_BACKUP_FLUSH) | MDL_BIT(MDL_BACKUP_WAIT_FLUSH) | MDL_BIT(MDL_BACKUP_WAIT_DDL) | MDL_BIT(MDL_BACKUP_WAIT_COMMIT) | MDL_BIT(MDL_BACKUP_BLOCK_DDL), + MDL_BIT(MDL_BACKUP_START), + MDL_BIT(MDL_BACKUP_START) | MDL_BIT(MDL_BACKUP_DML), + MDL_BIT(MDL_BACKUP_START) | MDL_BIT(MDL_BACKUP_DML) | MDL_BIT(MDL_BACKUP_DDL), + MDL_BIT(MDL_BACKUP_START) | MDL_BIT(MDL_BACKUP_DML) | MDL_BIT(MDL_BACKUP_SYS_DML) | MDL_BIT(MDL_BACKUP_DDL) | MDL_BIT(MDL_BACKUP_COMMIT), + + /* MDL_BACKUP_FTWRL1 */ + MDL_BIT(MDL_BACKUP_DML) | MDL_BIT(MDL_BACKUP_TRANS_DML) | MDL_BIT(MDL_BACKUP_SYS_DML) | MDL_BIT(MDL_BACKUP_DDL) | MDL_BIT(MDL_BACKUP_ALTER_COPY), + MDL_BIT(MDL_BACKUP_DML) | MDL_BIT(MDL_BACKUP_TRANS_DML) | MDL_BIT(MDL_BACKUP_SYS_DML) | MDL_BIT(MDL_BACKUP_DDL) | MDL_BIT(MDL_BACKUP_ALTER_COPY) | MDL_BIT(MDL_BACKUP_COMMIT), + /* MDL_BACKUP_DML */ + MDL_BIT(MDL_BACKUP_FLUSH) | MDL_BIT(MDL_BACKUP_WAIT_FLUSH) | MDL_BIT(MDL_BACKUP_WAIT_DDL) | MDL_BIT(MDL_BACKUP_WAIT_COMMIT) | MDL_BIT(MDL_BACKUP_FTWRL1) | MDL_BIT(MDL_BACKUP_FTWRL2), + MDL_BIT(MDL_BACKUP_FTWRL1) | MDL_BIT(MDL_BACKUP_FTWRL2), + MDL_BIT(MDL_BACKUP_WAIT_COMMIT) | MDL_BIT(MDL_BACKUP_FTWRL1) | MDL_BIT(MDL_BACKUP_FTWRL2), + /* MDL_BACKUP_DDL */ + MDL_BIT(MDL_BACKUP_WAIT_DDL) | MDL_BIT(MDL_BACKUP_WAIT_COMMIT) | MDL_BIT(MDL_BACKUP_FTWRL1) | MDL_BIT(MDL_BACKUP_FTWRL2) | MDL_BIT(MDL_BACKUP_BLOCK_DDL), + /* MDL_BACKUP_BLOCK_DDL */ + MDL_BIT(MDL_BACKUP_START) | MDL_BIT(MDL_BACKUP_FLUSH) | MDL_BIT(MDL_BACKUP_WAIT_FLUSH) | MDL_BIT(MDL_BACKUP_WAIT_DDL) | MDL_BIT(MDL_BACKUP_WAIT_COMMIT) | MDL_BIT(MDL_BACKUP_BLOCK_DDL) | MDL_BIT(MDL_BACKUP_DDL), + MDL_BIT(MDL_BACKUP_FTWRL1) | MDL_BIT(MDL_BACKUP_FTWRL2), + /* MDL_BACKUP_COMMIT */ + MDL_BIT(MDL_BACKUP_WAIT_COMMIT) | MDL_BIT(MDL_BACKUP_FTWRL2) +}; + + +const MDL_lock::bitmap_t +MDL_lock::MDL_backup_lock::m_waiting_incompatible[MDL_BACKUP_END]= +{ + /* MDL_BACKUP_START */ + MDL_BIT(MDL_BACKUP_FLUSH) | MDL_BIT(MDL_BACKUP_WAIT_FLUSH) | MDL_BIT(MDL_BACKUP_WAIT_DDL) | MDL_BIT(MDL_BACKUP_WAIT_COMMIT) | MDL_BIT(MDL_BACKUP_BLOCK_DDL), + 0, + 0, + 0, + 0, + /* MDL_BACKUP_FTWRL1 */ + 0, + 0, + + /* MDL_BACKUP_DML */ + MDL_BIT(MDL_BACKUP_FLUSH) | MDL_BIT(MDL_BACKUP_WAIT_FLUSH) | MDL_BIT(MDL_BACKUP_WAIT_DDL) | MDL_BIT(MDL_BACKUP_WAIT_COMMIT) | MDL_BIT(MDL_BACKUP_FTWRL1) | MDL_BIT(MDL_BACKUP_FTWRL2), + MDL_BIT(MDL_BACKUP_FTWRL1) | MDL_BIT(MDL_BACKUP_FTWRL2), + MDL_BIT(MDL_BACKUP_WAIT_COMMIT) | MDL_BIT(MDL_BACKUP_FTWRL1) | MDL_BIT(MDL_BACKUP_FTWRL2), + /* MDL_BACKUP_DDL */ + MDL_BIT(MDL_BACKUP_WAIT_DDL) | MDL_BIT(MDL_BACKUP_WAIT_COMMIT) | MDL_BIT(MDL_BACKUP_FTWRL1) | MDL_BIT(MDL_BACKUP_FTWRL2) | MDL_BIT(MDL_BACKUP_BLOCK_DDL), + /* MDL_BACKUP_BLOCK_DDL */ + MDL_BIT(MDL_BACKUP_START), + MDL_BIT(MDL_BACKUP_FTWRL1) | MDL_BIT(MDL_BACKUP_FTWRL2), + /* MDL_BACKUP_COMMIT */ + MDL_BIT(MDL_BACKUP_WAIT_COMMIT) | MDL_BIT(MDL_BACKUP_FTWRL2) +}; + + +/** + Check if request for the metadata lock can be satisfied given its + current state. + + New lock request can be satisfied iff: + - There are no incompatible types of satisfied requests + in other contexts + - There are no waiting requests which have higher priority + than this request when priority was not ignored. + + @param type_arg The requested lock type. + @param requestor_ctx The MDL context of the requestor. + @param ignore_lock_priority Ignore lock priority. + + @retval TRUE Lock request can be satisfied + @retval FALSE There is some conflicting lock. + + @note In cases then current context already has "stronger" type + of lock on the object it will be automatically granted + thanks to usage of the MDL_context::find_ticket() method. +*/ + +bool +MDL_lock::can_grant_lock(enum_mdl_type type_arg, + MDL_context *requestor_ctx, + bool ignore_lock_priority) const +{ + bitmap_t waiting_incompat_map= incompatible_waiting_types_bitmap()[type_arg]; + bitmap_t granted_incompat_map= incompatible_granted_types_bitmap()[type_arg]; + +#ifdef WITH_WSREP + /* + Approve lock request in BACKUP namespace for BF threads. + */ + if (!wsrep_check_mode(WSREP_MODE_BF_MARIABACKUP) && + (wsrep_thd_is_toi(requestor_ctx->get_thd()) || + wsrep_thd_is_applying(requestor_ctx->get_thd())) && + key.mdl_namespace() == MDL_key::BACKUP) + { + bool waiting_incompatible= m_waiting.bitmap() & waiting_incompat_map; + bool granted_incompatible= m_granted.bitmap() & granted_incompat_map; + if (waiting_incompatible || granted_incompatible) + { + WSREP_DEBUG("global lock granted for BF%s: %lu %s", + waiting_incompatible ? " (waiting queue)" : "", + thd_get_thread_id(requestor_ctx->get_thd()), + wsrep_thd_query(requestor_ctx->get_thd())); + } + return true; + } +#endif /* WITH_WSREP */ + + if (!ignore_lock_priority && (m_waiting.bitmap() & waiting_incompat_map)) + return false; + + if (m_granted.bitmap() & granted_incompat_map) + { + bool can_grant= true; + + /* Check that the incompatible lock belongs to some other context. */ + for (const auto &ticket : m_granted) + { + if (ticket.get_ctx() != requestor_ctx && + ticket.is_incompatible_when_granted(type_arg)) + { + can_grant= false; +#ifdef WITH_WSREP + /* + non WSREP threads must report conflict immediately + note: RSU processing wsrep threads, have wsrep_on==OFF + */ + if (WSREP(requestor_ctx->get_thd()) || + requestor_ctx->get_thd()->wsrep_cs().mode() == + wsrep::client_state::m_rsu) + { + wsrep_handle_mdl_conflict(requestor_ctx, &ticket, &key); + if (wsrep_log_conflicts) + { + auto key= ticket.get_key(); + WSREP_INFO("MDL conflict db=%s table=%s ticket=%d solved by abort", + key->db_name(), key->name(), ticket.get_type()); + } + continue; + } +#endif /* WITH_WSREP */ + break; + } + } + return can_grant; + } + return true; +} + + +/** + Return thread id of the thread to which the first ticket was + granted. +*/ + +inline unsigned long +MDL_lock::get_lock_owner() const +{ + if (m_granted.is_empty()) + return 0; + + return m_granted.begin()->get_ctx()->get_thread_id(); +} + + +/** Remove a ticket from waiting or pending queue and wakeup up waiters. */ + +void MDL_lock::remove_ticket(LF_PINS *pins, Ticket_list MDL_lock::*list, + MDL_ticket *ticket) +{ + mysql_prlock_wrlock(&m_rwlock); + (this->*list).remove_ticket(ticket); + if (is_empty()) + mdl_locks.remove(pins, this); + else + { + /* + There can be some contexts waiting to acquire a lock + which now might be able to do it. Grant the lock to + them and wake them up! + + We always try to reschedule locks, since there is no easy way + (i.e. by looking at the bitmaps) to find out whether it is + required or not. + In a general case, even when the queue's bitmap is not changed + after removal of the ticket, there is a chance that some request + can be satisfied (due to the fact that a granted request + reflected in the bitmap might belong to the same context as a + pending request). + */ + reschedule_waiters(); + mysql_prlock_unlock(&m_rwlock); + } +} + + +/** + Check if we have any pending locks which conflict with existing + shared lock. + + @pre The ticket must match an acquired lock. + + @return TRUE if there is a conflicting lock request, FALSE otherwise. +*/ + +bool MDL_lock::has_pending_conflicting_lock(enum_mdl_type type) +{ + bool result; + + mysql_prlock_rdlock(&m_rwlock); + result= (m_waiting.bitmap() & incompatible_granted_types_bitmap()[type]); + mysql_prlock_unlock(&m_rwlock); + return result; +} + + +MDL_wait_for_graph_visitor::~MDL_wait_for_graph_visitor() += default; + + +MDL_wait_for_subgraph::~MDL_wait_for_subgraph() += default; + +/** + Check if ticket represents metadata lock of "stronger" or equal type + than specified one. I.e. if metadata lock represented by ticket won't + allow any of locks which are not allowed by specified type of lock. + + @return TRUE if ticket has stronger or equal type + FALSE otherwise. +*/ + +bool MDL_ticket::has_stronger_or_equal_type(enum_mdl_type type) const +{ + const MDL_lock::bitmap_t * + granted_incompat_map= m_lock->incompatible_granted_types_bitmap(); + + return ! (granted_incompat_map[type] & ~(granted_incompat_map[m_type])); +} + + +bool MDL_ticket::is_incompatible_when_granted(enum_mdl_type type) const +{ + return (MDL_BIT(m_type) & + m_lock->incompatible_granted_types_bitmap()[type]); +} + + +bool MDL_ticket::is_incompatible_when_waiting(enum_mdl_type type) const +{ + return (MDL_BIT(m_type) & + m_lock->incompatible_waiting_types_bitmap()[type]); +} + + +static const LEX_STRING +*get_mdl_lock_name(MDL_key::enum_mdl_namespace mdl_namespace, + enum_mdl_type type) +{ + return mdl_namespace == MDL_key::BACKUP ? + &backup_lock_types[type] : + &lock_types[type]; +} + + +const LEX_STRING *MDL_ticket::get_type_name() const +{ + return get_mdl_lock_name(get_key()->mdl_namespace(), m_type); +} + +const LEX_STRING *MDL_ticket::get_type_name(enum_mdl_type type) const +{ + return get_mdl_lock_name(get_key()->mdl_namespace(), type); +} + + +/** + Check whether the context already holds a compatible lock ticket + on an object. + Start searching from list of locks for the same duration as lock + being requested. If not look at lists for other durations. + + @param mdl_request Lock request object for lock to be acquired + @param[out] result_duration Duration of lock which was found. + + @note Tickets which correspond to lock types "stronger" than one + being requested are also considered compatible. + + @return A pointer to the lock ticket for the object or NULL otherwise. +*/ + +MDL_ticket * +MDL_context::find_ticket(MDL_request *mdl_request, + enum_mdl_duration *result_duration) +{ + MDL_ticket *ticket; + int i; + + for (i= 0; i < MDL_DURATION_END; i++) + { + enum_mdl_duration duration= (enum_mdl_duration)((mdl_request->duration+i) % + MDL_DURATION_END); + Ticket_iterator it(m_tickets[duration]); + + while ((ticket= it++)) + { + if (mdl_request->key.is_equal(&ticket->m_lock->key) && + ticket->has_stronger_or_equal_type(mdl_request->type)) + { + DBUG_PRINT("info", ("Adding mdl lock %s to %s", + get_mdl_lock_name(mdl_request->key.mdl_namespace(), + mdl_request->type)->str, + ticket->get_type_name()->str)); + *result_duration= duration; + return ticket; + } + } + } + return NULL; +} + + +/** + Try to acquire one lock. + + Unlike exclusive locks, shared locks are acquired one by + one. This is interface is chosen to simplify introduction of + the new locking API to the system. MDL_context::try_acquire_lock() + is currently used from open_table(), and there we have only one + table to work with. + + This function may also be used to try to acquire an exclusive + lock on a destination table, by ALTER TABLE ... RENAME. + + Returns immediately without any side effect if encounters a lock + conflict. Otherwise takes the lock. + + FIXME: Compared to lock_table_name_if_not_cached() (from 5.1) + it gives slightly more false negatives. + + @param mdl_request [in/out] Lock request object for lock to be acquired + + @retval FALSE Success. The lock may have not been acquired. + Check the ticket, if it's NULL, a conflicting lock + exists. + @retval TRUE Out of resources, an error has been reported. +*/ + +bool +MDL_context::try_acquire_lock(MDL_request *mdl_request) +{ + MDL_ticket *ticket; + + if (try_acquire_lock_impl(mdl_request, &ticket)) + return TRUE; + + if (! mdl_request->ticket) + { + /* + Our attempt to acquire lock without waiting has failed. + Let us release resources which were acquired in the process. + We can't get here if we allocated a new lock object so there + is no need to release it. + */ + DBUG_ASSERT(! ticket->m_lock->is_empty()); + mysql_prlock_unlock(&ticket->m_lock->m_rwlock); + MDL_ticket::destroy(ticket); + } + + return FALSE; +} + + +/** + Auxiliary method for acquiring lock without waiting. + + @param mdl_request [in/out] Lock request object for lock to be acquired + @param out_ticket [out] Ticket for the request in case when lock + has not been acquired. + + @retval FALSE Success. The lock may have not been acquired. + Check MDL_request::ticket, if it's NULL, a conflicting + lock exists. In this case "out_ticket" out parameter + points to ticket which was constructed for the request. + MDL_ticket::m_lock points to the corresponding MDL_lock + object and MDL_lock::m_rwlock write-locked. + @retval TRUE Out of resources, an error has been reported. +*/ + +bool +MDL_context::try_acquire_lock_impl(MDL_request *mdl_request, + MDL_ticket **out_ticket) +{ + MDL_lock *lock; + MDL_key *key= &mdl_request->key; + MDL_ticket *ticket; + enum_mdl_duration found_duration; + + /* Don't take chances in production. */ + DBUG_ASSERT(mdl_request->ticket == NULL); + mdl_request->ticket= NULL; + + /* + Check whether the context already holds a shared lock on the object, + and if so, grant the request. + */ + if ((ticket= find_ticket(mdl_request, &found_duration))) + { + DBUG_ASSERT(ticket->m_lock); + DBUG_ASSERT(ticket->has_stronger_or_equal_type(mdl_request->type)); + /* + If the request is for a transactional lock, and we found + a transactional lock, just reuse the found ticket. + + It's possible that we found a transactional lock, + but the request is for a HANDLER lock. In that case HANDLER + code will clone the ticket (see below why it's needed). + + If the request is for a transactional lock, and we found + a HANDLER lock, create a copy, to make sure that when user + does HANDLER CLOSE, the transactional lock is not released. + + If the request is for a handler lock, and we found a + HANDLER lock, also do the clone. HANDLER CLOSE for one alias + should not release the lock on the table HANDLER opened through + a different alias. + */ + mdl_request->ticket= ticket; + if ((found_duration != mdl_request->duration || + mdl_request->duration == MDL_EXPLICIT) && + clone_ticket(mdl_request)) + { + /* Clone failed. */ + mdl_request->ticket= NULL; + return TRUE; + } + return FALSE; + } + + if (fix_pins()) + return TRUE; + + if (!(ticket= MDL_ticket::create(this, mdl_request->type +#ifndef DBUG_OFF + , mdl_request->duration +#endif + ))) + return TRUE; + + /* The below call implicitly locks MDL_lock::m_rwlock on success. */ + if (!(lock= mdl_locks.find_or_insert(m_pins, key))) + { + MDL_ticket::destroy(ticket); + return TRUE; + } + + DBUG_ASSERT(ticket->m_psi == NULL); + ticket->m_psi= mysql_mdl_create(ticket, + &mdl_request->key, + mdl_request->type, + mdl_request->duration, + MDL_ticket::PENDING, + mdl_request->m_src_file, + mdl_request->m_src_line); + + ticket->m_lock= lock; + + if (lock->can_grant_lock(mdl_request->type, this, false)) + { + lock->m_granted.add_ticket(ticket); + + mysql_prlock_unlock(&lock->m_rwlock); + + m_tickets[mdl_request->duration].push_front(ticket); + + mdl_request->ticket= ticket; + + mysql_mdl_set_status(ticket->m_psi, MDL_ticket::GRANTED); + } + else + *out_ticket= ticket; + + return FALSE; +} + + +/** + Create a copy of a granted ticket. + This is used to make sure that HANDLER ticket + is never shared with a ticket that belongs to + a transaction, so that when we HANDLER CLOSE, + we don't release a transactional ticket, and + vice versa -- when we COMMIT, we don't mistakenly + release a ticket for an open HANDLER. + + @retval TRUE Out of memory. + @retval FALSE Success. +*/ + +bool +MDL_context::clone_ticket(MDL_request *mdl_request) +{ + MDL_ticket *ticket; + + + /* + Since in theory we can clone ticket belonging to a different context + we need to prepare target context for possible attempts to release + lock and thus possible removal of MDL_lock from MDL_map container. + So we allocate pins to be able to work with this container if they + are not allocated already. + */ + if (fix_pins()) + return TRUE; + + /* + By submitting mdl_request->type to MDL_ticket::create() + we effectively downgrade the cloned lock to the level of + the request. + */ + if (!(ticket= MDL_ticket::create(this, mdl_request->type +#ifndef DBUG_OFF + , mdl_request->duration +#endif + ))) + return TRUE; + + DBUG_ASSERT(ticket->m_psi == NULL); + ticket->m_psi= mysql_mdl_create(ticket, + &mdl_request->key, + mdl_request->type, + mdl_request->duration, + MDL_ticket::PENDING, + mdl_request->m_src_file, + mdl_request->m_src_line); + + /* clone() is not supposed to be used to get a stronger lock. */ + DBUG_ASSERT(mdl_request->ticket->has_stronger_or_equal_type(ticket->m_type)); + + ticket->m_lock= mdl_request->ticket->m_lock; + mdl_request->ticket= ticket; + + mysql_prlock_wrlock(&ticket->m_lock->m_rwlock); + ticket->m_lock->m_granted.add_ticket(ticket); + mysql_prlock_unlock(&ticket->m_lock->m_rwlock); + + m_tickets[mdl_request->duration].push_front(ticket); + + mysql_mdl_set_status(ticket->m_psi, MDL_ticket::GRANTED); + + return FALSE; +} + + +/** + Check if there is any conflicting lock that could cause this thread + to wait for another thread which is not ready to commit. + This is always an error, as the upper level of parallel replication + should not allow a scheduling of a conflicting DDL until all earlier + transactions have been committed. + + This function is only called for a slave using parallel replication + and trying to get an exclusive lock for the table. +*/ + +#ifndef DBUG_OFF +bool MDL_lock::check_if_conflicting_replication_locks(MDL_context *ctx) +{ + rpl_group_info *rgi_slave= ctx->get_thd()->rgi_slave; + + if (!rgi_slave->gtid_sub_id) + return 0; + + for (const auto &conflicting_ticket : m_granted) + { + if (conflicting_ticket.get_ctx() != ctx) + { + MDL_context *conflicting_ctx= conflicting_ticket.get_ctx(); + rpl_group_info *conflicting_rgi_slave; + conflicting_rgi_slave= conflicting_ctx->get_thd()->rgi_slave; + + /* + If the conflicting thread is another parallel replication + thread for the same master and it's not in commit or post-commit stages, + then the current transaction has started too early and something is + seriously wrong. + */ + if (conflicting_rgi_slave && + conflicting_rgi_slave->gtid_sub_id && + conflicting_rgi_slave->rli == rgi_slave->rli && + conflicting_rgi_slave->current_gtid.domain_id == + rgi_slave->current_gtid.domain_id && + !((conflicting_rgi_slave->did_mark_start_commit || + conflicting_rgi_slave->worker_error) || + conflicting_rgi_slave->finish_event_group_called)) + return 1; // Fatal error + } + } + return 0; +} +#endif + + +/** + Acquire one lock with waiting for conflicting locks to go away if needed. + + @param mdl_request [in/out] Lock request object for lock to be acquired + + @param lock_wait_timeout [in] Seconds to wait before timeout. + + @retval FALSE Success. MDL_request::ticket points to the ticket + for the lock. + @retval TRUE Failure (Out of resources or waiting is aborted), +*/ + +bool +MDL_context::acquire_lock(MDL_request *mdl_request, double lock_wait_timeout) +{ + MDL_lock *lock; + MDL_ticket *ticket; + MDL_wait::enum_wait_status wait_status; + DBUG_ENTER("MDL_context::acquire_lock"); +#ifdef DBUG_TRACE + const char *mdl_lock_name= get_mdl_lock_name( + mdl_request->key.mdl_namespace(), mdl_request->type)->str; +#endif + DBUG_PRINT("enter", ("lock_type: %s timeout: %f", + mdl_lock_name, + lock_wait_timeout)); + + if (try_acquire_lock_impl(mdl_request, &ticket)) + { + DBUG_PRINT("mdl", ("OOM: %s", mdl_lock_name)); + DBUG_RETURN(TRUE); + } + + if (mdl_request->ticket) + { + /* + We have managed to acquire lock without waiting. + MDL_lock, MDL_context and MDL_request were updated + accordingly, so we can simply return success. + */ + DBUG_PRINT("info", ("Got lock without waiting")); + DBUG_PRINT("mdl", ("Seized: %s", dbug_print_mdl(mdl_request->ticket))); + DBUG_RETURN(FALSE); + } + +#ifdef DBUG_TRACE + const char *ticket_msg= dbug_print_mdl(ticket); +#endif + + /* + Our attempt to acquire lock without waiting has failed. + As a result of this attempt we got MDL_ticket with m_lock + member pointing to the corresponding MDL_lock object which + has MDL_lock::m_rwlock write-locked. + */ + lock= ticket->m_lock; + + if (lock_wait_timeout == 0) + { + DBUG_PRINT("mdl", ("Nowait: %s", ticket_msg)); + mysql_prlock_unlock(&lock->m_rwlock); + MDL_ticket::destroy(ticket); + my_error(ER_LOCK_WAIT_TIMEOUT, MYF(0)); + DBUG_RETURN(TRUE); + } + +#ifdef WITH_WSREP + if (WSREP(get_thd())) + { + THD* requester= get_thd(); + bool requester_toi= wsrep_thd_is_toi(requester) || wsrep_thd_is_applying(requester); + WSREP_DEBUG("::acquire_lock is TOI %d for %s", requester_toi, + wsrep_thd_query(requester)); + if (requester_toi) + THD_STAGE_INFO(requester, stage_waiting_ddl); + else + THD_STAGE_INFO(requester, stage_waiting_isolation); + } +#endif /* WITH_WSREP */ + + lock->m_waiting.add_ticket(ticket); + + /* + Once we added a pending ticket to the waiting queue, + we must ensure that our wait slot is empty, so + that our lock request can be scheduled. Do that in the + critical section formed by the acquired write lock on MDL_lock. + */ + m_wait.reset_status(); + + /* + Don't break conflicting locks if timeout is 0 as 0 is used + To check if there is any conflicting locks... + */ + if (lock->needs_notification(ticket) && lock_wait_timeout) + lock->notify_conflicting_locks(this); + + /* + Ensure that if we are trying to get an exclusive lock for a slave + running parallel replication, then we are not blocked by another + parallel slave thread that is not committed. This should never happen as + the parallel replication scheduler should never schedule a DDL while + DML's are still running. + */ + DBUG_SLOW_ASSERT((mdl_request->type != MDL_INTENTION_EXCLUSIVE && + mdl_request->type != MDL_EXCLUSIVE) || + !(get_thd()->rgi_slave && + get_thd()->rgi_slave->is_parallel_exec && + lock->check_if_conflicting_replication_locks(this))); + + mysql_prlock_unlock(&lock->m_rwlock); + +#ifdef HAVE_PSI_INTERFACE + PSI_metadata_locker_state state __attribute__((unused)); + PSI_metadata_locker *locker= NULL; + + if (ticket->m_psi != NULL) + locker= PSI_CALL_start_metadata_wait(&state, ticket->m_psi, __FILE__, __LINE__); +#endif + + DBUG_PRINT("mdl", ("Waiting: %s", ticket_msg)); + will_wait_for(ticket); + + /* There is a shared or exclusive lock on the object. */ + DEBUG_SYNC(get_thd(), "mdl_acquire_lock_wait"); + + find_deadlock(); + + struct timespec abs_timeout, abs_shortwait; + set_timespec_nsec(abs_timeout, + (ulonglong)(lock_wait_timeout * 1000000000ULL)); + set_timespec(abs_shortwait, 1); + wait_status= MDL_wait::EMPTY; + + while (cmp_timespec(abs_shortwait, abs_timeout) <= 0) + { + /* abs_timeout is far away. Wait a short while and notify locks. */ + wait_status= m_wait.timed_wait(m_owner, &abs_shortwait, FALSE, + mdl_request->key.get_wait_state_name()); + + if (wait_status != MDL_wait::EMPTY) + break; + /* Check if the client is gone while we were waiting. */ + if (! thd_is_connected(m_owner->get_thd())) + { + /* + * The client is disconnected. Don't wait forever: + * assume it's the same as a wait timeout, this + * ensures all error handling is correct. + */ + wait_status= MDL_wait::TIMEOUT; + break; + } + + mysql_prlock_wrlock(&lock->m_rwlock); + if (lock->needs_notification(ticket)) + lock->notify_conflicting_locks(this); + mysql_prlock_unlock(&lock->m_rwlock); + set_timespec(abs_shortwait, 1); + } + if (wait_status == MDL_wait::EMPTY) + wait_status= m_wait.timed_wait(m_owner, &abs_timeout, TRUE, + mdl_request->key.get_wait_state_name()); + + done_waiting_for(); + +#ifdef HAVE_PSI_INTERFACE + if (locker != NULL) + PSI_CALL_end_metadata_wait(locker, 0); +#endif + + if (wait_status != MDL_wait::GRANTED) + { + lock->remove_ticket(m_pins, &MDL_lock::m_waiting, ticket); + MDL_ticket::destroy(ticket); + switch (wait_status) + { + case MDL_wait::VICTIM: + DBUG_PRINT("mdl", ("Deadlock: %s", ticket_msg)); + DBUG_PRINT("mdl_locks", ("Existing locks:%s", mdl_dbug_print_locks())); + my_error(ER_LOCK_DEADLOCK, MYF(0)); + break; + case MDL_wait::TIMEOUT: + DBUG_PRINT("mdl", ("Timeout: %s", ticket_msg)); + my_error(ER_LOCK_WAIT_TIMEOUT, MYF(0)); + break; + case MDL_wait::KILLED: + DBUG_PRINT("mdl", ("Killed: %s", ticket_msg)); + get_thd()->send_kill_message(); + break; + default: + DBUG_ASSERT(0); + break; + } + DBUG_RETURN(TRUE); + } + + /* + We have been granted our request. + State of MDL_lock object is already being appropriately updated by a + concurrent thread (@sa MDL_lock:reschedule_waiters()). + So all we need to do is to update MDL_context and MDL_request objects. + */ + DBUG_ASSERT(wait_status == MDL_wait::GRANTED); + + m_tickets[mdl_request->duration].push_front(ticket); + + mdl_request->ticket= ticket; + + mysql_mdl_set_status(ticket->m_psi, MDL_ticket::GRANTED); + + DBUG_PRINT("mdl", ("Acquired: %s", ticket_msg)); + DBUG_RETURN(FALSE); +} + + +extern "C" int mdl_request_ptr_cmp(const void* ptr1, const void* ptr2) +{ + MDL_request *req1= *(MDL_request**)ptr1; + MDL_request *req2= *(MDL_request**)ptr2; + return req1->key.cmp(&req2->key); +} + + +/** + Acquire exclusive locks. There must be no granted locks in the + context. + + This is a replacement of lock_table_names(). It is used in + RENAME, DROP and other DDL SQL statements. + + @param mdl_requests List of requests for locks to be acquired. + + @param lock_wait_timeout Seconds to wait before timeout. + + @note The list of requests should not contain non-exclusive lock requests. + There should not be any acquired locks in the context. + + @note Assumes that one already owns scoped intention exclusive lock. + + @retval FALSE Success + @retval TRUE Failure +*/ + +bool MDL_context::acquire_locks(MDL_request_list *mdl_requests, + double lock_wait_timeout) +{ + MDL_request_list::Iterator it(*mdl_requests); + MDL_request **sort_buf, **p_req; + MDL_savepoint mdl_svp= mdl_savepoint(); + ssize_t req_count= static_cast<ssize_t>(mdl_requests->elements()); + DBUG_ENTER("MDL_context::acquire_locks"); + + if (req_count == 0) + DBUG_RETURN(FALSE); + + /* Sort requests according to MDL_key. */ + if (! (sort_buf= (MDL_request **)my_malloc(key_memory_MDL_context_acquire_locks, + req_count * sizeof(MDL_request*), + MYF(MY_WME)))) + DBUG_RETURN(TRUE); + + for (p_req= sort_buf; p_req < sort_buf + req_count; p_req++) + *p_req= it++; + + my_qsort(sort_buf, req_count, sizeof(MDL_request*), + mdl_request_ptr_cmp); + + for (p_req= sort_buf; p_req < sort_buf + req_count; p_req++) + { + if (acquire_lock(*p_req, lock_wait_timeout)) + goto err; + } + my_free(sort_buf); + DBUG_RETURN(FALSE); + +err: + /* + Release locks we have managed to acquire so far. + Use rollback_to_savepoint() since there may be duplicate + requests that got assigned the same ticket. + */ + rollback_to_savepoint(mdl_svp); + /* Reset lock requests back to its initial state. */ + for (req_count= p_req - sort_buf, p_req= sort_buf; + p_req < sort_buf + req_count; p_req++) + { + (*p_req)->ticket= NULL; + } + my_free(sort_buf); + DBUG_RETURN(TRUE); +} + + +/** + Upgrade a shared metadata lock. + + Used in ALTER TABLE. + + @param mdl_ticket Lock to upgrade. + @param new_type Lock type to upgrade to. + @param lock_wait_timeout Seconds to wait before timeout. + + @note In case of failure to upgrade lock (e.g. because upgrader + was killed) leaves lock in its original state (locked in + shared mode). + + @note There can be only one upgrader for a lock or we will have deadlock. + This invariant is ensured by the fact that upgradeable locks SU, SNW + and SNRW are not compatible with each other and themselves. + + @retval FALSE Success + @retval TRUE Failure (thread was killed) +*/ + +bool +MDL_context::upgrade_shared_lock(MDL_ticket *mdl_ticket, + enum_mdl_type new_type, + double lock_wait_timeout) +{ + MDL_request mdl_xlock_request; + MDL_savepoint mdl_svp= mdl_savepoint(); + bool is_new_ticket; + DBUG_ENTER("MDL_context::upgrade_shared_lock"); + DBUG_PRINT("enter",("old_type: %s new_type: %s lock_wait_timeout: %f", + mdl_ticket->get_type_name()->str, + mdl_ticket->get_type_name(new_type)->str, + lock_wait_timeout)); + DEBUG_SYNC(get_thd(), "mdl_upgrade_lock"); + + /* + Do nothing if already upgraded. Used when we FLUSH TABLE under + LOCK TABLES and a table is listed twice in LOCK TABLES list. + + In BACKUP namespace upgrade must always happen. Even though + MDL_BACKUP_START is not stronger than MDL_BACKUP_FLUSH from + has_stronger_or_equal_type(), the latter effectively blocks + new MDL_BACKUP_DML while the former doesn't. + */ + if (mdl_ticket->has_stronger_or_equal_type(new_type) && + mdl_ticket->get_key()->mdl_namespace() != MDL_key::BACKUP) + DBUG_RETURN(FALSE); + + MDL_REQUEST_INIT_BY_KEY(&mdl_xlock_request, &mdl_ticket->m_lock->key, + new_type, MDL_TRANSACTION); + + if (acquire_lock(&mdl_xlock_request, lock_wait_timeout)) + DBUG_RETURN(TRUE); + + is_new_ticket= ! has_lock(mdl_svp, mdl_xlock_request.ticket); + + /* Merge the acquired and the original lock. @todo: move to a method. */ + mysql_prlock_wrlock(&mdl_ticket->m_lock->m_rwlock); + if (is_new_ticket) + mdl_ticket->m_lock->m_granted.remove_ticket(mdl_xlock_request.ticket); + /* + Set the new type of lock in the ticket. To update state of + MDL_lock object correctly we need to temporarily exclude + ticket from the granted queue and then include it back. + */ + mdl_ticket->m_lock->m_granted.remove_ticket(mdl_ticket); + mdl_ticket->m_type= new_type; + mdl_ticket->m_lock->m_granted.add_ticket(mdl_ticket); + + mysql_prlock_unlock(&mdl_ticket->m_lock->m_rwlock); + + if (is_new_ticket) + { + m_tickets[MDL_TRANSACTION].remove(mdl_xlock_request.ticket); + MDL_ticket::destroy(mdl_xlock_request.ticket); + } + + DBUG_RETURN(FALSE); +} + + +/** + A fragment of recursive traversal of the wait-for graph + in search for deadlocks. Direct the deadlock visitor to all + contexts that own the lock the current node in the wait-for + graph is waiting for. + As long as the initial node is remembered in the visitor, + a deadlock is found when the same node is seen twice. +*/ + +bool MDL_lock::visit_subgraph(MDL_ticket *waiting_ticket, + MDL_wait_for_graph_visitor *gvisitor) +{ + MDL_context *src_ctx= waiting_ticket->get_ctx(); + bool result= TRUE; + + mysql_prlock_rdlock(&m_rwlock); + + /* + MDL_lock's waiting and granted queues and MDL_context::m_waiting_for + member are updated by different threads when the lock is granted + (see MDL_context::acquire_lock() and MDL_lock::reschedule_waiters()). + As a result, here we may encounter a situation when MDL_lock data + already reflects the fact that the lock was granted but + m_waiting_for member has not been updated yet. + + For example, imagine that: + + thread1: Owns SNW lock on table t1. + thread2: Attempts to acquire SW lock on t1, + but sees an active SNW lock. + Thus adds the ticket to the waiting queue and + sets m_waiting_for to point to the ticket. + thread1: Releases SNW lock, updates MDL_lock object to + grant SW lock to thread2 (moves the ticket for + SW from waiting to the active queue). + Attempts to acquire a new SNW lock on t1, + sees an active SW lock (since it is present in the + active queue), adds ticket for SNW lock to the waiting + queue, sets m_waiting_for to point to this ticket. + + At this point deadlock detection algorithm run by thread1 will see that: + - Thread1 waits for SNW lock on t1 (since m_waiting_for is set). + - SNW lock is not granted, because it conflicts with active SW lock + owned by thread 2 (since ticket for SW is present in granted queue). + - Thread2 waits for SW lock (since its m_waiting_for has not been + updated yet!). + - SW lock is not granted because there is pending SNW lock from thread1. + Therefore deadlock should exist [sic!]. + + To avoid detection of such false deadlocks we need to check the "actual" + status of the ticket being waited for, before analyzing its blockers. + We do this by checking the wait status of the context which is waiting + for it. To avoid races this has to be done under protection of + MDL_lock::m_rwlock lock. + */ + if (src_ctx->m_wait.get_status() != MDL_wait::EMPTY) + { + result= FALSE; + goto end; + } + + /* + To avoid visiting nodes which were already marked as victims of + deadlock detection (or whose requests were already satisfied) we + enter the node only after peeking at its wait status. + This is necessary to avoid active waiting in a situation + when previous searches for a deadlock already selected the + node we're about to enter as a victim (see the comment + in MDL_context::find_deadlock() for explanation why several searches + can be performed for the same wait). + There is no guarantee that the node isn't chosen a victim while we + are visiting it but this is OK: in the worst case we might do some + extra work and one more context might be chosen as a victim. + */ + if (gvisitor->enter_node(src_ctx)) + goto end; + + /* + We do a breadth-first search first -- that is, inspect all + edges of the current node, and only then follow up to the next + node. In workloads that involve wait-for graph loops this + has proven to be a more efficient strategy [citation missing]. + */ + for (const auto& ticket : m_granted) + { + /* Filter out edges that point to the same node. */ + if (ticket.get_ctx() != src_ctx && + ticket.is_incompatible_when_granted(waiting_ticket->get_type()) && + gvisitor->inspect_edge(ticket.get_ctx())) + { + goto end_leave_node; + } + } + + for (const auto &ticket : m_waiting) + { + /* Filter out edges that point to the same node. */ + if (ticket.get_ctx() != src_ctx && + ticket.is_incompatible_when_waiting(waiting_ticket->get_type()) && + gvisitor->inspect_edge(ticket.get_ctx())) + { + goto end_leave_node; + } + } + + /* Recurse and inspect all adjacent nodes. */ + for (const auto &ticket : m_granted) + { + if (ticket.get_ctx() != src_ctx && + ticket.is_incompatible_when_granted(waiting_ticket->get_type()) && + ticket.get_ctx()->visit_subgraph(gvisitor)) + { + goto end_leave_node; + } + } + + for (const auto &ticket : m_waiting) + { + if (ticket.get_ctx() != src_ctx && + ticket.is_incompatible_when_waiting(waiting_ticket->get_type()) && + ticket.get_ctx()->visit_subgraph(gvisitor)) + { + goto end_leave_node; + } + } + + result= FALSE; + +end_leave_node: + gvisitor->leave_node(src_ctx); + +end: + mysql_prlock_unlock(&m_rwlock); + return result; +} + + +/** + Traverse a portion of wait-for graph which is reachable + through the edge represented by this ticket and search + for deadlocks. + + @retval TRUE A deadlock is found. A pointer to deadlock + victim is saved in the visitor. + @retval FALSE +*/ + +bool MDL_ticket::accept_visitor(MDL_wait_for_graph_visitor *gvisitor) +{ + return m_lock->visit_subgraph(this, gvisitor); +} + + +/** + A fragment of recursive traversal of the wait-for graph of + MDL contexts in the server in search for deadlocks. + Assume this MDL context is a node in the wait-for graph, + and direct the visitor to all adjacent nodes. As long + as the starting node is remembered in the visitor, a + deadlock is found when the same node is visited twice. + One MDL context is connected to another in the wait-for + graph if it waits on a resource that is held by the other + context. + + @retval TRUE A deadlock is found. A pointer to deadlock + victim is saved in the visitor. + @retval FALSE +*/ + +bool MDL_context::visit_subgraph(MDL_wait_for_graph_visitor *gvisitor) +{ + bool result= FALSE; + + mysql_prlock_rdlock(&m_LOCK_waiting_for); + + if (m_waiting_for) + result= m_waiting_for->accept_visitor(gvisitor); + + mysql_prlock_unlock(&m_LOCK_waiting_for); + + return result; +} + + +/** + Try to find a deadlock. This function produces no errors. + + @note If during deadlock resolution context which performs deadlock + detection is chosen as a victim it will be informed about the + fact by setting VICTIM status to its wait slot. +*/ + +void MDL_context::find_deadlock() +{ + while (1) + { + /* + The fact that we use fresh instance of gvisitor for each + search performed by find_deadlock() below is important, + the code responsible for victim selection relies on this. + */ + Deadlock_detection_visitor dvisitor(this); + MDL_context *victim; + + if (! visit_subgraph(&dvisitor)) + { + /* No deadlocks are found! */ + break; + } + + victim= dvisitor.get_victim(); + + /* + Failure to change status of the victim is OK as it means + that the victim has received some other message and is + about to stop its waiting/to break deadlock loop. + Even when the initiator of the deadlock search is + chosen the victim, we need to set the respective wait + result in order to "close" it for any attempt to + schedule the request. + This is needed to avoid a possible race during + cleanup in case when the lock request on which the + context was waiting is concurrently satisfied. + */ + (void) victim->m_wait.set_status(MDL_wait::VICTIM); + victim->inc_deadlock_overweight(); + victim->unlock_deadlock_victim(); + + if (victim == this) + break; + /* + After adding a new edge to the waiting graph we found that it + creates a loop (i.e. there is a deadlock). We decided to destroy + this loop by removing an edge, but not the one that we added. + Since this doesn't guarantee that all loops created by addition + of the new edge are destroyed, we have to repeat the search. + */ + } +} + + +/** + Release lock. + + @param duration Lock duration. + @param ticket Ticket for lock to be released. + +*/ + +void MDL_context::release_lock(enum_mdl_duration duration, MDL_ticket *ticket) +{ + MDL_lock *lock= ticket->m_lock; + DBUG_ENTER("MDL_context::release_lock"); + DBUG_PRINT("enter", ("db: '%s' name: '%s'", + lock->key.db_name(), lock->key.name())); + + DBUG_ASSERT(this == ticket->get_ctx()); + DBUG_PRINT("mdl", ("Released: %s", dbug_print_mdl(ticket))); + + lock->remove_ticket(m_pins, &MDL_lock::m_granted, ticket); + + m_tickets[duration].remove(ticket); + MDL_ticket::destroy(ticket); + + DBUG_VOID_RETURN; +} + + +/** + Release lock with explicit duration. + + @param ticket Ticket for lock to be released. + +*/ + +void MDL_context::release_lock(MDL_ticket *ticket) +{ + DBUG_SLOW_ASSERT(ticket->m_duration == MDL_EXPLICIT); + + release_lock(MDL_EXPLICIT, ticket); +} + + +/** + Release all locks associated with the context. If the sentinel + is not NULL, do not release locks stored in the list after and + including the sentinel. + + Statement and transactional locks are added to the beginning of + the corresponding lists, i.e. stored in reverse temporal order. + This allows to employ this function to: + - back off in case of a lock conflict. + - release all locks in the end of a statement or transaction + - rollback to a savepoint. +*/ + +void MDL_context::release_locks_stored_before(enum_mdl_duration duration, + MDL_ticket *sentinel) +{ + MDL_ticket *ticket; + Ticket_iterator it(m_tickets[duration]); + DBUG_ENTER("MDL_context::release_locks_stored_before"); + + if (m_tickets[duration].is_empty()) + DBUG_VOID_RETURN; + + while ((ticket= it++) && ticket != sentinel) + { + DBUG_PRINT("info", ("found lock to release ticket=%p", ticket)); + release_lock(duration, ticket); + } + + DBUG_VOID_RETURN; +} + + +/** + Release all explicit locks in the context which correspond to the + same name/object as this lock request. + + @param ticket One of the locks for the name/object for which all + locks should be released. +*/ + +void MDL_context::release_all_locks_for_name(MDL_ticket *name) +{ + /* Use MDL_ticket::m_lock to identify other locks for the same object. */ + MDL_lock *lock= name->m_lock; + + /* Remove matching lock tickets from the context. */ + MDL_ticket *ticket; + Ticket_iterator it_ticket(m_tickets[MDL_EXPLICIT]); + + while ((ticket= it_ticket++)) + { + DBUG_ASSERT(ticket->m_lock); + if (ticket->m_lock == lock) + release_lock(MDL_EXPLICIT, ticket); + } +} + + +/** + Downgrade an EXCLUSIVE or SHARED_NO_WRITE lock to shared metadata lock. + + @param type Type of lock to which exclusive lock should be downgraded. +*/ + +void MDL_ticket::downgrade_lock(enum_mdl_type type) +{ + DBUG_ENTER("MDL_ticket::downgrade_lock"); + DBUG_PRINT("enter",("old_type: %s new_type: %s", + get_type_name()->str, + get_type_name(type)->str)); + /* + Do nothing if already downgraded. Used when we FLUSH TABLE under + LOCK TABLES and a table is listed twice in LOCK TABLES list. + Note that this code might even try to "downgrade" a weak lock + (e.g. SW) to a stronger one (e.g SNRW). So we can't even assert + here that target lock is weaker than existing lock. + */ + if (m_type == type || !has_stronger_or_equal_type(type)) + { + DBUG_PRINT("info", ("Nothing to downgrade")); + DBUG_VOID_RETURN; + } + + /* Only allow downgrade in some specific known cases */ + DBUG_ASSERT((get_key()->mdl_namespace() != MDL_key::BACKUP && + (m_type == MDL_EXCLUSIVE || + m_type == MDL_SHARED_NO_WRITE)) || + (get_key()->mdl_namespace() == MDL_key::BACKUP && + (m_type == MDL_BACKUP_DDL || + m_type == MDL_BACKUP_BLOCK_DDL || + m_type == MDL_BACKUP_WAIT_FLUSH))); + + mysql_prlock_wrlock(&m_lock->m_rwlock); + /* + To update state of MDL_lock object correctly we need to temporarily + exclude ticket from the granted queue and then include it back. + */ + m_lock->m_granted.remove_ticket(this); + m_type= type; + m_lock->m_granted.add_ticket(this); + m_lock->reschedule_waiters(); + mysql_prlock_unlock(&m_lock->m_rwlock); + DBUG_VOID_RETURN; +} + + +/** + Auxiliary function which allows to check if we have some kind of lock on + a object. Returns TRUE if we have a lock of a given or stronger type. + + @param mdl_namespace Id of object namespace + @param db Name of the database + @param name Name of the object + @param mdl_type Lock type. Pass in the weakest type to find + out if there is at least some lock. + + @return TRUE if current context contains satisfied lock for the object, + FALSE otherwise. +*/ + +bool +MDL_context::is_lock_owner(MDL_key::enum_mdl_namespace mdl_namespace, + const char *db, const char *name, + enum_mdl_type mdl_type) +{ + MDL_request mdl_request; + enum_mdl_duration not_unused; + /* We don't care about exact duration of lock here. */ + MDL_REQUEST_INIT(&mdl_request, mdl_namespace, db, name, mdl_type, + MDL_TRANSACTION); + MDL_ticket *ticket= find_ticket(&mdl_request, ¬_unused); + + DBUG_ASSERT(ticket == NULL || ticket->m_lock); + + return ticket; +} + + +/** + Return thread id of the owner of the lock or 0 if + there is no owner. + @note: Lock type is not considered at all, the function + simply checks that there is some lock for the given key. + + @return thread id of the owner of the lock or 0 +*/ + +unsigned long +MDL_context::get_lock_owner(MDL_key *key) +{ + fix_pins(); + return mdl_locks.get_lock_owner(m_pins, key); +} + + +/** + Check if we have any pending locks which conflict with existing shared lock. + + @pre The ticket must match an acquired lock. + + @return TRUE if there is a conflicting lock request, FALSE otherwise. +*/ + +bool MDL_ticket::has_pending_conflicting_lock() const +{ + return m_lock->has_pending_conflicting_lock(m_type); +} + +/** Return a key identifying this lock. */ +MDL_key *MDL_ticket::get_key() const +{ + return &m_lock->key; +} + +/** + Releases metadata locks that were acquired after a specific savepoint. + + @note Used to release tickets acquired during a savepoint unit. + @note It's safe to iterate and unlock any locks after taken after this + savepoint because other statements that take other special locks + cause a implicit commit (ie LOCK TABLES). +*/ + +void MDL_context::rollback_to_savepoint(const MDL_savepoint &mdl_savepoint) +{ + DBUG_ENTER("MDL_context::rollback_to_savepoint"); + + /* If savepoint is NULL, it is from the start of the transaction. */ + release_locks_stored_before(MDL_STATEMENT, mdl_savepoint.m_stmt_ticket); + release_locks_stored_before(MDL_TRANSACTION, mdl_savepoint.m_trans_ticket); + + DBUG_VOID_RETURN; +} + + +/** + Release locks acquired by normal statements (SELECT, UPDATE, + DELETE, etc) in the course of a transaction. Do not release + HANDLER locks, if there are any. + + This method is used at the end of a transaction, in + implementation of COMMIT (implicit or explicit) and ROLLBACK. +*/ + +void MDL_context::release_transactional_locks(THD *thd) +{ + DBUG_ENTER("MDL_context::release_transactional_locks"); + /* Fail if there are active transactions */ + DBUG_ASSERT(!(thd->server_status & + (SERVER_STATUS_IN_TRANS | SERVER_STATUS_IN_TRANS_READONLY))); + release_locks_stored_before(MDL_STATEMENT, NULL); + release_locks_stored_before(MDL_TRANSACTION, NULL); + DBUG_VOID_RETURN; +} + +void MDL_context::release_statement_locks() +{ + DBUG_ENTER("MDL_context::release_transactional_locks"); + release_locks_stored_before(MDL_STATEMENT, NULL); + DBUG_VOID_RETURN; +} + + +/** + Does this savepoint have this lock? + + @retval TRUE The ticket is older than the savepoint or + is an LT, HA or GLR ticket. Thus it belongs + to the savepoint or has explicit duration. + @retval FALSE The ticket is newer than the savepoint. + and is not an LT, HA or GLR ticket. +*/ + +bool MDL_context::has_lock(const MDL_savepoint &mdl_savepoint, + MDL_ticket *mdl_ticket) +{ + MDL_ticket *ticket; + /* Start from the beginning, most likely mdl_ticket's been just acquired. */ + MDL_context::Ticket_iterator s_it(m_tickets[MDL_STATEMENT]); + MDL_context::Ticket_iterator t_it(m_tickets[MDL_TRANSACTION]); + + while ((ticket= s_it++) && ticket != mdl_savepoint.m_stmt_ticket) + { + if (ticket == mdl_ticket) + return FALSE; + } + + while ((ticket= t_it++) && ticket != mdl_savepoint.m_trans_ticket) + { + if (ticket == mdl_ticket) + return FALSE; + } + return TRUE; +} + + +/** + Change lock duration for transactional lock. + + @param ticket Ticket representing lock. + @param duration Lock duration to be set. + + @note This method only supports changing duration of + transactional lock to some other duration. +*/ + +void MDL_context::set_lock_duration(MDL_ticket *mdl_ticket, + enum_mdl_duration duration) +{ + DBUG_SLOW_ASSERT(mdl_ticket->m_duration == MDL_TRANSACTION && + duration != MDL_TRANSACTION); + + m_tickets[MDL_TRANSACTION].remove(mdl_ticket); + m_tickets[duration].push_front(mdl_ticket); +#ifndef DBUG_OFF + mdl_ticket->m_duration= duration; +#endif +} + + +/** + Set explicit duration for all locks in the context. +*/ + +void MDL_context::set_explicit_duration_for_all_locks() +{ + int i; + MDL_ticket *ticket; + + /* + In the most common case when this function is called list + of transactional locks is bigger than list of locks with + explicit duration. So we start by swapping these two lists + and then move elements from new list of transactional + locks and list of statement locks to list of locks with + explicit duration. + */ + + m_tickets[MDL_EXPLICIT].swap(m_tickets[MDL_TRANSACTION]); + + for (i= 0; i < MDL_EXPLICIT; i++) + { + Ticket_iterator it_ticket(m_tickets[i]); + + while ((ticket= it_ticket++)) + { + m_tickets[i].remove(ticket); + m_tickets[MDL_EXPLICIT].push_front(ticket); + } + } + +#ifndef DBUG_OFF + Ticket_iterator exp_it(m_tickets[MDL_EXPLICIT]); + + while ((ticket= exp_it++)) + ticket->m_duration= MDL_EXPLICIT; +#endif +} + + +/** + Set transactional duration for all locks in the context. +*/ + +void MDL_context::set_transaction_duration_for_all_locks() +{ + MDL_ticket *ticket; + + /* + In the most common case when this function is called list + of explicit locks is bigger than two other lists (in fact, + list of statement locks is always empty). So we start by + swapping list of explicit and transactional locks and then + move contents of new list of explicit locks to list of + locks with transactional duration. + */ + + DBUG_ASSERT(m_tickets[MDL_STATEMENT].is_empty()); + + m_tickets[MDL_TRANSACTION].swap(m_tickets[MDL_EXPLICIT]); + + Ticket_iterator it_ticket(m_tickets[MDL_EXPLICIT]); + + while ((ticket= it_ticket++)) + { + m_tickets[MDL_EXPLICIT].remove(ticket); + m_tickets[MDL_TRANSACTION].push_front(ticket); + } + +#ifndef DBUG_OFF + Ticket_iterator trans_it(m_tickets[MDL_TRANSACTION]); + + while ((ticket= trans_it++)) + ticket->m_duration= MDL_TRANSACTION; +#endif +} + + + +void MDL_context::release_explicit_locks() +{ + release_locks_stored_before(MDL_EXPLICIT, NULL); +} + +bool MDL_context::has_explicit_locks() +{ + MDL_ticket *ticket = NULL; + + Ticket_iterator it(m_tickets[MDL_EXPLICIT]); + + while ((ticket = it++)) + { + return true; + } + + return false; +} + +#ifdef WITH_WSREP +static +const char *wsrep_get_mdl_namespace_name(MDL_key::enum_mdl_namespace ns) +{ + switch (ns) + { + case MDL_key::BACKUP : return "BACKUP"; + case MDL_key::SCHEMA : return "SCHEMA"; + case MDL_key::TABLE : return "TABLE"; + case MDL_key::FUNCTION : return "FUNCTION"; + case MDL_key::PROCEDURE : return "PROCEDURE"; + case MDL_key::PACKAGE_BODY: return "PACKAGE BODY"; + case MDL_key::TRIGGER : return "TRIGGER"; + case MDL_key::EVENT : return "EVENT"; + case MDL_key::USER_LOCK : return "USER_LOCK"; + default: break; + } + return "UNKNOWN"; +} + +void MDL_ticket::wsrep_report(bool debug) const +{ + if (!debug) return; + + const PSI_stage_info *psi_stage= m_lock->key.get_wait_state_name(); + WSREP_DEBUG("MDL ticket: type: %s space: %s db: %s name: %s (%s)", + get_type_name()->str, + wsrep_get_mdl_namespace_name(m_lock->key.mdl_namespace()), + m_lock->key.db_name(), + m_lock->key.name(), + psi_stage->m_name); +} +#endif /* WITH_WSREP */ |