diff options
Diffstat (limited to 'sql/lock.cc')
| -rw-r--r-- | sql/lock.cc | 363 |
1 files changed, 59 insertions, 304 deletions
diff --git a/sql/lock.cc b/sql/lock.cc index 26a8a1ba35b..e88fa252517 100644 --- a/sql/lock.cc +++ b/sql/lock.cc @@ -806,8 +806,11 @@ bool lock_schema_name(THD *thd, const char *db) return TRUE; } - global_request.init(MDL_key::GLOBAL, "", "", MDL_INTENTION_EXCLUSIVE); - mdl_request.init(MDL_key::SCHEMA, db, "", MDL_EXCLUSIVE); + if (thd->global_read_lock.can_acquire_protection()) + return TRUE; + global_request.init(MDL_key::GLOBAL, "", "", MDL_INTENTION_EXCLUSIVE, + MDL_STATEMENT); + mdl_request.init(MDL_key::SCHEMA, db, "", MDL_EXCLUSIVE, MDL_TRANSACTION); mdl_requests.push_front(&mdl_request); mdl_requests.push_front(&global_request); @@ -822,13 +825,13 @@ bool lock_schema_name(THD *thd, const char *db) /** - Obtain an exclusive metadata lock on the stored routine name. + Obtain an exclusive metadata lock on an object name. @param thd Thread handle. - @param is_function Stored routine type (only functions or procedures - are name-locked. - @param db The schema the routine belongs to. - @param name Routine name. + @param mdl_type Object type (currently functions, procedures + and events can be name-locked). + @param db The schema the object belongs to. + @param name Object name in the schema. This function assumes that no metadata locks were acquired before calling it. Additionally, it cannot be called while @@ -844,12 +847,9 @@ bool lock_schema_name(THD *thd, const char *db) or this connection was killed. */ -bool lock_routine_name(THD *thd, bool is_function, +bool lock_object_name(THD *thd, MDL_key::enum_mdl_namespace mdl_type, const char *db, const char *name) { - MDL_key::enum_mdl_namespace mdl_type= (is_function ? - MDL_key::FUNCTION : - MDL_key::PROCEDURE); MDL_request_list mdl_requests; MDL_request global_request; MDL_request schema_request; @@ -865,9 +865,13 @@ bool lock_routine_name(THD *thd, bool is_function, DBUG_ASSERT(name); DEBUG_SYNC(thd, "before_wait_locked_pname"); - global_request.init(MDL_key::GLOBAL, "", "", MDL_INTENTION_EXCLUSIVE); - schema_request.init(MDL_key::SCHEMA, db, "", MDL_INTENTION_EXCLUSIVE); - mdl_request.init(mdl_type, db, name, MDL_EXCLUSIVE); + if (thd->global_read_lock.can_acquire_protection()) + return TRUE; + global_request.init(MDL_key::GLOBAL, "", "", MDL_INTENTION_EXCLUSIVE, + MDL_STATEMENT); + schema_request.init(MDL_key::SCHEMA, db, "", MDL_INTENTION_EXCLUSIVE, + MDL_TRANSACTION); + mdl_request.init(mdl_type, db, name, MDL_EXCLUSIVE, MDL_TRANSACTION); mdl_requests.push_front(&mdl_request); mdl_requests.push_front(&schema_request); @@ -917,45 +921,24 @@ static void print_lock_error(int error, const char *table) /**************************************************************************** Handling of global read locks + Global read lock is implemented using metadata lock infrastructure. + Taking the global read lock is TWO steps (2nd step is optional; without it, COMMIT of existing transactions will be allowed): lock_global_read_lock() THEN make_global_read_lock_block_commit(). - The global locks are handled through the global variables: - global_read_lock - count of threads which have the global read lock (i.e. have completed at - least the first step above) - global_read_lock_blocks_commit - count of threads which have the global read lock and block - commits (i.e. are in or have completed the second step above) - waiting_for_read_lock - count of threads which want to take a global read lock but cannot - protect_against_global_read_lock - count of threads which have set protection against global read lock. - - access to them is protected with a mutex LOCK_global_read_lock - - (XXX: one should never take LOCK_open if LOCK_global_read_lock is - taken, otherwise a deadlock may occur. Other mutexes could be a - problem too - grep the code for global_read_lock if you want to use - any other mutex here) Also one must not hold LOCK_open when calling - wait_if_global_read_lock(). When the thread with the global read lock - tries to close its tables, it needs to take LOCK_open in - close_thread_table(). - How blocking of threads by global read lock is achieved: that's - advisory. Any piece of code which should be blocked by global read lock must - be designed like this: - - call to wait_if_global_read_lock(). When this returns 0, no global read - lock is owned; if argument abort_on_refresh was 0, none can be obtained. - - job - - if abort_on_refresh was 0, call to start_waiting_global_read_lock() to - allow other threads to get the global read lock. I.e. removal of the - protection. - (Note: it's a bit like an implementation of rwlock). - - [ I am sorry to mention some SQL syntaxes below I know I shouldn't but found - no better descriptive way ] + semi-automatic. We assume that any statement which should be blocked + by global read lock will either open and acquires write-lock on tables + or acquires metadata locks on objects it is going to modify. For any + such statement global IX metadata lock is automatically acquired for + its duration (in case of LOCK TABLES until end of LOCK TABLES mode). + And lock_global_read_lock() simply acquires global S metadata lock + and thus prohibits execution of statements which modify data (unless + they modify only temporary tables). If deadlock happens it is detected + by MDL subsystem and resolved in the standard fashion (by backing-off + metadata locks acquired so far and restarting open tables process + if possible). Why does FLUSH TABLES WITH READ LOCK need to block COMMIT: because it's used to read a non-moving SHOW MASTER STATUS, and a COMMIT writes to the binary @@ -989,11 +972,6 @@ static void print_lock_error(int error, const char *table) ****************************************************************************/ -volatile uint global_read_lock=0; -volatile uint global_read_lock_blocks_commit=0; -static volatile uint protect_against_global_read_lock=0; -static volatile uint waiting_for_read_lock=0; - /** Take global read lock, wait if there is protection against lock. @@ -1014,85 +992,17 @@ bool Global_read_lock::lock_global_read_lock(THD *thd) if (!m_state) { MDL_request mdl_request; - const char *old_message; - const char *new_message= "Waiting to get readlock"; - (void) mysql_mutex_lock(&LOCK_global_read_lock); - -#if defined(ENABLED_DEBUG_SYNC) - /* - The below sync point fires if we have to wait for - protect_against_global_read_lock. - - WARNING: Beware to use WAIT_FOR with this sync point. We hold - LOCK_global_read_lock here. - - Call the sync point before calling enter_cond() as it does use - enter_cond() and exit_cond() itself if a WAIT_FOR action is - executed in spite of the above warning. - - Pre-set proc_info so that it is available immediately after the - sync point sends a SIGNAL. This makes tests more reliable. - */ - if (protect_against_global_read_lock) - { - thd_proc_info(thd, new_message); - DEBUG_SYNC(thd, "wait_lock_global_read_lock"); - } -#endif /* defined(ENABLED_DEBUG_SYNC) */ - - old_message=thd->enter_cond(&COND_global_read_lock, &LOCK_global_read_lock, - new_message); - DBUG_PRINT("info", - ("waiting_for: %d protect_against: %d", - waiting_for_read_lock, protect_against_global_read_lock)); - - waiting_for_read_lock++; - while (protect_against_global_read_lock && !thd->killed) - mysql_cond_wait(&COND_global_read_lock, &LOCK_global_read_lock); - waiting_for_read_lock--; - if (thd->killed) - { - thd->exit_cond(old_message); - DBUG_RETURN(1); - } - m_state= GRL_ACQUIRED; - global_read_lock++; - thd->exit_cond(old_message); // this unlocks LOCK_global_read_lock - /* - When we perform FLUSH TABLES or ALTER TABLE under LOCK TABLES, - tables being reopened are protected only by meta-data locks at - some point. To avoid sneaking in with our global read lock at - this moment we have to take global shared meta data lock. - - TODO: We should change this code to acquire global shared metadata - lock before acquiring global read lock. But in order to do - this we have to get rid of all those places in which - wait_if_global_read_lock() is called before acquiring - metadata locks first. Also long-term we should get rid of - redundancy between metadata locks, global read lock and DDL - blocker (see WL#4399 and WL#4400). - */ DBUG_ASSERT(! thd->mdl_context.is_lock_owner(MDL_key::GLOBAL, "", "", MDL_SHARED)); - mdl_request.init(MDL_key::GLOBAL, "", "", MDL_SHARED); + mdl_request.init(MDL_key::GLOBAL, "", "", MDL_SHARED, MDL_EXPLICIT); if (thd->mdl_context.acquire_lock(&mdl_request, thd->variables.lock_wait_timeout)) - { - /* Our thread was killed -- return back to initial state. */ - mysql_mutex_lock(&LOCK_global_read_lock); - if (!(--global_read_lock)) - { - DBUG_PRINT("signal", ("Broadcasting COND_global_read_lock")); - mysql_cond_broadcast(&COND_global_read_lock); - } - mysql_mutex_unlock(&LOCK_global_read_lock); - m_state= GRL_NONE; DBUG_RETURN(1); - } - thd->mdl_context.move_ticket_after_trans_sentinel(mdl_request.ticket); + m_mdl_global_shared_lock= mdl_request.ticket; + m_state= GRL_ACQUIRED; } /* We DON'T set global_read_lock_blocks_commit now, it will be set after @@ -1118,166 +1028,22 @@ bool Global_read_lock::lock_global_read_lock(THD *thd) void Global_read_lock::unlock_global_read_lock(THD *thd) { - uint tmp; DBUG_ENTER("unlock_global_read_lock"); - DBUG_PRINT("info", - ("global_read_lock: %u global_read_lock_blocks_commit: %u", - global_read_lock, global_read_lock_blocks_commit)); DBUG_ASSERT(m_mdl_global_shared_lock && m_state); - thd->mdl_context.release_lock(m_mdl_global_shared_lock); - m_mdl_global_shared_lock= NULL; - - mysql_mutex_lock(&LOCK_global_read_lock); - tmp= --global_read_lock; - if (m_state == GRL_ACQUIRED_AND_BLOCKS_COMMIT) - --global_read_lock_blocks_commit; - mysql_mutex_unlock(&LOCK_global_read_lock); - /* Send the signal outside the mutex to avoid a context switch */ - if (!tmp) + if (m_mdl_blocks_commits_lock) { - DBUG_PRINT("signal", ("Broadcasting COND_global_read_lock")); - mysql_cond_broadcast(&COND_global_read_lock); + thd->mdl_context.release_lock(m_mdl_blocks_commits_lock); + m_mdl_blocks_commits_lock= NULL; } + thd->mdl_context.release_lock(m_mdl_global_shared_lock); + m_mdl_global_shared_lock= NULL; m_state= GRL_NONE; DBUG_VOID_RETURN; } -/** - Wait if the global read lock is set, and optionally seek protection against - global read lock. - - See also "Handling of global read locks" above. - - @param thd Reference to thread. - @param abort_on_refresh If True, abort waiting if a refresh occurs, - do NOT seek protection against GRL. - If False, wait until the GRL is released and seek - protection against GRL. - @param is_not_commit If False, called from a commit operation, - wait only if commit blocking is also enabled. - - @retval False Success, protection against global read lock is set - (if !abort_on_refresh) - @retval True Failure, wait was aborted or thread was killed. -*/ - -#define must_wait (global_read_lock && \ - (is_not_commit || \ - global_read_lock_blocks_commit)) - -bool Global_read_lock:: -wait_if_global_read_lock(THD *thd, bool abort_on_refresh, - bool is_not_commit) -{ - const char *UNINIT_VAR(old_message); - bool result= 0, need_exit_cond; - DBUG_ENTER("wait_if_global_read_lock"); - - /* - If we already have protection against global read lock, - just increment the counter. - */ - if (unlikely(m_protection_count > 0)) - { - if (!abort_on_refresh) - m_protection_count++; - DBUG_RETURN(FALSE); - } - /* - Assert that we do not own LOCK_open. If we would own it, other - threads could not close their tables. This would make a pretty - deadlock. - */ - mysql_mutex_assert_not_owner(&LOCK_open); - - mysql_mutex_lock(&LOCK_global_read_lock); - if ((need_exit_cond= must_wait)) - { - if (m_state) // This thread had the read locks - { - if (is_not_commit) - my_message(ER_CANT_UPDATE_WITH_READLOCK, - ER(ER_CANT_UPDATE_WITH_READLOCK), MYF(0)); - mysql_mutex_unlock(&LOCK_global_read_lock); - /* - We allow FLUSHer to COMMIT; we assume FLUSHer knows what it does. - This allowance is needed to not break existing versions of innobackup - which do a BEGIN; INSERT; FLUSH TABLES WITH READ LOCK; COMMIT. - */ - DBUG_RETURN(is_not_commit); - } - old_message=thd->enter_cond(&COND_global_read_lock, &LOCK_global_read_lock, - "Waiting for release of readlock"); - while (must_wait && ! thd->killed && - (!abort_on_refresh || !thd->open_tables || - thd->open_tables->s->version == refresh_version)) - { - DBUG_PRINT("signal", ("Waiting for COND_global_read_lock")); - mysql_cond_wait(&COND_global_read_lock, &LOCK_global_read_lock); - DBUG_PRINT("signal", ("Got COND_global_read_lock")); - } - if (thd->killed) - result=1; - } - if (!abort_on_refresh && !result) - { - m_protection_count++; - protect_against_global_read_lock++; - DBUG_PRINT("sql_lock", ("protect_against_global_read_lock incr: %u", - protect_against_global_read_lock)); - } - /* - The following is only true in case of a global read locks (which is rare) - and if old_message is set - */ - if (unlikely(need_exit_cond)) - thd->exit_cond(old_message); // this unlocks LOCK_global_read_lock - else - mysql_mutex_unlock(&LOCK_global_read_lock); - DBUG_RETURN(result); -} - - -/** - Release protection against global read lock and restart - global read lock waiters. - - Should only be called if we have protection against global read lock. - - See also "Handling of global read locks" above. - - @param thd Reference to thread. -*/ - -void Global_read_lock::start_waiting_global_read_lock(THD *thd) -{ - bool tmp; - DBUG_ENTER("start_waiting_global_read_lock"); - /* - Ignore request if we do not have protection against global read lock. - (Note that this is a violation of the interface contract, hence the assert). - */ - DBUG_ASSERT(m_protection_count > 0); - if (unlikely(m_protection_count == 0)) - DBUG_VOID_RETURN; - /* Decrement local read lock protection counter, return if we still have it */ - if (unlikely(--m_protection_count > 0)) - DBUG_VOID_RETURN; - if (unlikely(m_state)) - DBUG_VOID_RETURN; - mysql_mutex_lock(&LOCK_global_read_lock); - DBUG_ASSERT(protect_against_global_read_lock); - tmp= (!--protect_against_global_read_lock && - (waiting_for_read_lock || global_read_lock_blocks_commit)); - mysql_mutex_unlock(&LOCK_global_read_lock); - if (tmp) - mysql_cond_broadcast(&COND_global_read_lock); - DBUG_VOID_RETURN; -} - /** Make global read lock also block commits. @@ -1296,8 +1062,7 @@ void Global_read_lock::start_waiting_global_read_lock(THD *thd) bool Global_read_lock::make_global_read_lock_block_commit(THD *thd) { - bool error; - const char *old_message; + MDL_request mdl_request; DBUG_ENTER("make_global_read_lock_block_commit"); /* If we didn't succeed lock_global_read_lock(), or if we already suceeded @@ -1305,42 +1070,32 @@ bool Global_read_lock::make_global_read_lock_block_commit(THD *thd) */ if (m_state != GRL_ACQUIRED) DBUG_RETURN(0); - mysql_mutex_lock(&LOCK_global_read_lock); - /* increment this BEFORE waiting on cond (otherwise race cond) */ - global_read_lock_blocks_commit++; - /* For testing we set up some blocking, to see if we can be killed */ - DBUG_EXECUTE_IF("make_global_read_lock_block_commit_loop", - protect_against_global_read_lock++;); - old_message= thd->enter_cond(&COND_global_read_lock, &LOCK_global_read_lock, - "Waiting for all running commits to finish"); - while (protect_against_global_read_lock && !thd->killed) - mysql_cond_wait(&COND_global_read_lock, &LOCK_global_read_lock); - DBUG_EXECUTE_IF("make_global_read_lock_block_commit_loop", - protect_against_global_read_lock--;); - if ((error= test(thd->killed))) - global_read_lock_blocks_commit--; // undo what we did - else - m_state= GRL_ACQUIRED_AND_BLOCKS_COMMIT; - thd->exit_cond(old_message); // this unlocks LOCK_global_read_lock - DBUG_RETURN(error); + + mdl_request.init(MDL_key::COMMIT, "", "", MDL_SHARED, MDL_EXPLICIT); + + if (thd->mdl_context.acquire_lock(&mdl_request, + thd->variables.lock_wait_timeout)) + DBUG_RETURN(TRUE); + + m_mdl_blocks_commits_lock= mdl_request.ticket; + m_state= GRL_ACQUIRED_AND_BLOCKS_COMMIT; + + DBUG_RETURN(FALSE); } /** - Broadcast COND_global_read_lock. - - TODO/FIXME: Dmitry thinks that we broadcast on COND_global_read_lock - when old instance of table is closed to avoid races - between incrementing refresh_version and - wait_if_global_read_lock(thd, TRUE, FALSE) call. - Once global read lock implementation starts using MDL - infrastructure this will became unnecessary and should - be removed. + Set explicit duration for metadata locks which are used to implement GRL. + + @param thd Reference to thread. */ -void broadcast_refresh(void) +void Global_read_lock::set_explicit_lock_duration(THD *thd) { - mysql_cond_broadcast(&COND_global_read_lock); + if (m_mdl_global_shared_lock) + thd->mdl_context.set_lock_duration(m_mdl_global_shared_lock, MDL_EXPLICIT); + if (m_mdl_blocks_commits_lock) + thd->mdl_context.set_lock_duration(m_mdl_blocks_commits_lock, MDL_EXPLICIT); } /** |