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Diffstat (limited to 'sql/lock.cc')
| -rw-r--r-- | sql/lock.cc | 1234 |
1 files changed, 1234 insertions, 0 deletions
diff --git a/sql/lock.cc b/sql/lock.cc new file mode 100644 index 00000000..559f1195 --- /dev/null +++ b/sql/lock.cc @@ -0,0 +1,1234 @@ +/* + Copyright (c) 2000, 2011, Oracle and/or its affiliates. + Copyright (c) 2020, 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 */ + + +/** + @file + + Locking functions for mysql. + + Because of the new concurrent inserts, we must first get external locks + before getting internal locks. If we do it in the other order, the status + information is not up to date when called from the lock handler. + + GENERAL DESCRIPTION OF LOCKING + + When not using LOCK TABLES: + + - For each SQL statement mysql_lock_tables() is called for all involved + tables. + - mysql_lock_tables() will call + table_handler->external_lock(thd,locktype) for each table. + This is followed by a call to thr_multi_lock() for all tables. + + - When statement is done, we call mysql_unlock_tables(). + table_handler->external_lock(thd, F_UNLCK) followed by + thr_multi_unlock() for each table. + + - Note that mysql_unlock_tables() may be called several times as + MySQL in some cases can free some tables earlier than others. + + - The above is true both for normal and temporary tables. + + - Temporary non transactional tables are never passed to thr_multi_lock() + and we never call external_lock(thd, F_UNLOCK) on these. + + When using LOCK TABLES: + + - LOCK TABLE will call mysql_lock_tables() for all tables. + mysql_lock_tables() will call + table_handler->external_lock(thd,locktype) for each table. + This is followed by a call to thr_multi_lock() for all tables. + + - For each statement, we will call table_handler->start_stmt(THD) + to inform the table handler that we are using the table. + + The tables used can only be tables used in LOCK TABLES or a + temporary table. + + - When statement is done, we will call ha_commit_stmt(thd); + + - When calling UNLOCK TABLES we call mysql_unlock_tables() for all + tables used in LOCK TABLES + + If table_handler->external_lock(thd, locktype) fails, we call + table_handler->external_lock(thd, F_UNLCK) for each table that was locked, + excluding one that caused failure. That means handler must cleanup itself + in case external_lock() fails. +*/ + +#include "mariadb.h" +#include "sql_priv.h" +#include "debug_sync.h" +#include "lock.h" +#include "sql_base.h" // close_tables_for_reopen +#include "sql_parse.h" // is_log_table_write_query +#include "sql_handler.h" +#include <hash.h> +#include "wsrep_mysqld.h" + +/** + @defgroup Locking Locking + @{ +*/ + +extern HASH open_cache; + +static int lock_external(THD *thd, TABLE **table,uint count); +static int unlock_external(THD *thd, TABLE **table,uint count); + + +/* Map the return value of thr_lock to an error from errmsg.txt */ +static int thr_lock_errno_to_mysql[]= +{ 0, ER_LOCK_ABORTED, ER_LOCK_WAIT_TIMEOUT, ER_LOCK_DEADLOCK }; + +/** + Perform semantic checks for mysql_lock_tables. + @param thd The current thread + @param tables The tables to lock + @param count The number of tables to lock + @param flags Lock flags + @return 0 if all the check passed, non zero if a check failed. +*/ + +static int +lock_tables_check(THD *thd, TABLE **tables, uint count, uint flags) +{ + uint system_count, i; + bool ignore_read_only, log_table_write_query; + + DBUG_ENTER("lock_tables_check"); + + system_count= 0; + ignore_read_only= + (thd->security_ctx->master_access & PRIV_IGNORE_READ_ONLY) != NO_ACL; + log_table_write_query= (is_log_table_write_query(thd->lex->sql_command) + || ((flags & MYSQL_LOCK_LOG_TABLE) != 0)); + + for (i=0 ; i<count; i++) + { + TABLE *t= tables[i]; + + /* Protect against 'fake' partially initialized TABLE_SHARE */ + DBUG_ASSERT(t->s->table_category != TABLE_UNKNOWN_CATEGORY); + + /* + Table I/O to performance schema tables is performed + only internally by the server implementation. + When a user is requesting a lock, the following + constraints are enforced: + */ + if (t->s->require_write_privileges() && + ! log_table_write_query) + { + /* + A user should not be able to prevent writes, + or hold any type of lock in a session, + since this would be a DOS attack. + */ + if ((t->reginfo.lock_type >= TL_READ_NO_INSERT) + || (thd->lex->sql_command == SQLCOM_LOCK_TABLES)) + { + my_error(ER_CANT_LOCK_LOG_TABLE, MYF(0)); + DBUG_RETURN(1); + } + } + + if (t->reginfo.lock_type >= TL_WRITE_ALLOW_WRITE) + { + if (t->s->table_category == TABLE_CATEGORY_SYSTEM) + system_count++; + + if (t->db_stat & HA_READ_ONLY) + { + my_error(ER_OPEN_AS_READONLY, MYF(0), t->alias.c_ptr_safe()); + DBUG_RETURN(1); + } + } + + /* + If we are going to lock a non-temporary table we must own metadata + lock of appropriate type on it (I.e. for table to be locked for + write we must own metadata lock of MDL_SHARED_WRITE or stronger + type. For table to be locked for read we must own metadata lock + of MDL_SHARED_READ or stronger type). + */ + DBUG_ASSERT(t->s->tmp_table || + thd->mdl_context.is_lock_owner(MDL_key::TABLE, + t->s->db.str, t->s->table_name.str, + t->reginfo.lock_type >= TL_WRITE_ALLOW_WRITE ? + MDL_SHARED_WRITE : MDL_SHARED_READ)); + + /* + Prevent modifications to base tables if READ_ONLY is activated. + In any case, read only does not apply to temporary tables. + */ + if (!(flags & MYSQL_LOCK_IGNORE_GLOBAL_READ_ONLY) && !t->s->tmp_table) + { + if (t->reginfo.lock_type >= TL_WRITE_ALLOW_WRITE && + !ignore_read_only && opt_readonly && !thd->slave_thread) + { + my_error(ER_OPTION_PREVENTS_STATEMENT, MYF(0), "--read-only"); + DBUG_RETURN(1); + } + } + } + + /* + Locking of system tables is restricted: + locking a mix of system and non-system tables in the same lock + is prohibited, to prevent contention. + */ + if ((system_count > 0) && (system_count < count)) + { + my_error(ER_WRONG_LOCK_OF_SYSTEM_TABLE, MYF(0)); + DBUG_RETURN(1); + } + + DBUG_RETURN(0); +} + +/** + Reset lock type in lock data + + @param mysql_lock Lock structures to reset. + @param unlock If set, then set lock type to TL_UNLOCK, + otherwise set to original lock type from + get_store_lock(). + + @note After a locking error we want to quit the locking of the table(s). + The test case in the bug report for Bug #18544 has the following + cases: 1. Locking error in lock_external() due to InnoDB timeout. + 2. Locking error in get_lock_data() due to missing write permission. + 3. Locking error in wait_if_global_read_lock() due to lock conflict. + + @note In all these cases we have already set the lock type into the lock + data of the open table(s). If the table(s) are in the open table + cache, they could be reused with the non-zero lock type set. This + could lead to ignoring a different lock type with the next lock. + + @note Clear the lock type of all lock data. This ensures that the next + lock request will set its lock type properly. +*/ + + +void reset_lock_data(MYSQL_LOCK *sql_lock, bool unlock) +{ + THR_LOCK_DATA **ldata, **ldata_end; + DBUG_ENTER("reset_lock_data"); + + /* Clear the lock type of all lock data to avoid reusage. */ + for (ldata= sql_lock->locks, ldata_end= ldata + sql_lock->lock_count; + ldata < ldata_end; + ldata++) + (*ldata)->type= unlock ? TL_UNLOCK : (*ldata)->org_type; + DBUG_VOID_RETURN; +} + + +/** + Scan array of tables for access types; update transaction tracker + accordingly. + + @param thd The current thread. + @param tables An array of pointers to the tables to lock. + @param count The number of tables to lock. +*/ + +#ifndef EMBEDDED_LIBRARY +static void track_table_access(THD *thd, TABLE **tables, size_t count) +{ + if (thd->variables.session_track_transaction_info > TX_TRACK_NONE) + { + while (count--) + { + if (TABLE *t= tables[count]) + thd->session_tracker.transaction_info.add_trx_state(thd, + t->reginfo.lock_type, t->file->has_transaction_manager()); + } + } +} +#else +#define track_table_access(A,B,C) +#endif //EMBEDDED_LIBRARY + + + +/** + Lock tables. + + @param thd The current thread. + @param tables An array of pointers to the tables to lock. + @param count The number of tables to lock. + @param flags Options: + MYSQL_LOCK_IGNORE_GLOBAL_READ_ONLY Ignore SET GLOBAL READ_ONLY + MYSQL_LOCK_IGNORE_TIMEOUT Use maximum timeout value. + + @retval A lock structure pointer on success. + @retval NULL if an error or if wait on a lock was killed. +*/ + +MYSQL_LOCK *mysql_lock_tables(THD *thd, TABLE **tables, uint count, uint flags) +{ + MYSQL_LOCK *sql_lock; + uint gld_flags= GET_LOCK_STORE_LOCKS; + DBUG_ENTER("mysql_lock_tables(tables)"); + + if (lock_tables_check(thd, tables, count, flags)) + DBUG_RETURN(NULL); + + if (!(thd->variables.option_bits & OPTION_TABLE_LOCK) && + !(flags & MYSQL_LOCK_USE_MALLOC)) + gld_flags|= GET_LOCK_ON_THD; + + if (! (sql_lock= get_lock_data(thd, tables, count, gld_flags))) + DBUG_RETURN(NULL); + + if (mysql_lock_tables(thd, sql_lock, flags)) + { + /* Clear the lock type of all lock data to avoid reusage. */ + reset_lock_data(sql_lock, 1); + if (!(gld_flags & GET_LOCK_ON_THD)) + my_free(sql_lock); + sql_lock= 0; + } + + track_table_access(thd, tables, count); + + DBUG_RETURN(sql_lock); +} + +/** + Lock tables based on a MYSQL_LOCK structure. + + mysql_lock_tables() + + @param thd The current thread. + @param sql_lock Tables that should be locked + @param flags See mysql_lock_tables() above + + @return 0 ok + @return 1 error +*/ + +bool mysql_lock_tables(THD *thd, MYSQL_LOCK *sql_lock, uint flags) +{ + int rc= 1; + ulong timeout= (flags & MYSQL_LOCK_IGNORE_TIMEOUT) ? + LONG_TIMEOUT : thd->variables.lock_wait_timeout; + PSI_stage_info org_stage; + DBUG_ENTER("mysql_lock_tables(sql_lock)"); + + thd->backup_stage(&org_stage); + THD_STAGE_INFO(thd, stage_system_lock); + if (sql_lock->table_count && lock_external(thd, sql_lock->table, + sql_lock->table_count)) + goto end; + + THD_STAGE_INFO(thd, stage_table_lock); + + /* Copy the lock data array. thr_multi_lock() reorders its contents. */ + memmove(sql_lock->locks + sql_lock->lock_count, sql_lock->locks, + sql_lock->lock_count * sizeof(*sql_lock->locks)); + + /* Lock on the copied half of the lock data array. */ + rc= thr_lock_errno_to_mysql[(int) thr_multi_lock(sql_lock->locks + + sql_lock->lock_count, + sql_lock->lock_count, + &thd->lock_info, timeout)]; + if (rc && sql_lock->table_count) + (void) unlock_external(thd, sql_lock->table, sql_lock->table_count); + +end: + THD_STAGE_INFO(thd, org_stage); + + if (thd->killed) + { + thd->send_kill_message(); + if (!rc) + { + mysql_unlock_tables(thd, sql_lock, 0); + THD_STAGE_INFO(thd, stage_after_table_lock); + } + rc= 1; + } + else if (rc > 1) + my_error(rc, MYF(0)); + + thd->set_time_after_lock(); + DBUG_RETURN(rc); +} + + +static int lock_external(THD *thd, TABLE **tables, uint count) +{ + uint i; + int lock_type,error; + DBUG_ENTER("lock_external"); + + DBUG_PRINT("info", ("count %d", count)); + for (i=1 ; i <= count ; i++, tables++) + { + DBUG_ASSERT((*tables)->reginfo.lock_type >= TL_READ); + lock_type=F_WRLCK; /* Lock exclusive */ + if ((*tables)->db_stat & HA_READ_ONLY || + ((*tables)->reginfo.lock_type >= TL_READ && + (*tables)->reginfo.lock_type <= TL_READ_NO_INSERT)) + lock_type=F_RDLCK; + + if (unlikely((error=(*tables)->file->ha_external_lock(thd,lock_type)))) + { + (*tables)->file->print_error(error, MYF(0)); + while (--i) + { + tables--; + (*tables)->file->ha_external_unlock(thd); + (*tables)->current_lock=F_UNLCK; + } + DBUG_RETURN(error); + } + else + { + (*tables)->current_lock= lock_type; + } + } + DBUG_RETURN(0); +} + + +int mysql_unlock_tables(THD *thd, MYSQL_LOCK *sql_lock) +{ + return mysql_unlock_tables(thd, sql_lock, + (thd->variables.option_bits & OPTION_TABLE_LOCK) || + !(sql_lock->flags & GET_LOCK_ON_THD)); +} + + +int mysql_unlock_tables(THD *thd, MYSQL_LOCK *sql_lock, bool free_lock) +{ + bool errors= thd->is_error(); + int error= 0; + PSI_stage_info org_stage; + DBUG_ENTER("mysql_unlock_tables"); + + thd->backup_stage(&org_stage); + THD_STAGE_INFO(thd, stage_unlocking_tables); + + if (sql_lock->table_count) + error= unlock_external(thd, sql_lock->table, sql_lock->table_count); + if (sql_lock->lock_count) + thr_multi_unlock(sql_lock->locks, sql_lock->lock_count, 0); + if (free_lock) + { + DBUG_ASSERT(!(sql_lock->flags & GET_LOCK_ON_THD)); + my_free(sql_lock); + } + if (likely(!errors && !error)) + thd->clear_error(); + THD_STAGE_INFO(thd, org_stage); + if (error) + DBUG_PRINT("exit", ("error: %d", error)); + DBUG_RETURN(error); +} + +/** + Unlock some of the tables locked by mysql_lock_tables. + + This will work even if get_lock_data fails (next unlock will free all) +*/ + +int mysql_unlock_some_tables(THD *thd, TABLE **table,uint count, uint flag) +{ + int error; + MYSQL_LOCK *sql_lock; + if (!(sql_lock= get_lock_data(thd, table, count, + GET_LOCK_UNLOCK | GET_LOCK_ON_THD | flag))) + error= ER_OUTOFMEMORY; + else + error= mysql_unlock_tables(thd, sql_lock, 0); + return error; +} + + +/** + unlock all tables locked for read. +*/ + +int mysql_unlock_read_tables(THD *thd, MYSQL_LOCK *sql_lock) +{ + uint i,found; + int error= 0; + DBUG_ENTER("mysql_unlock_read_tables"); + + /* Call external lock for all tables to be unlocked */ + + /* Move all write locked tables first */ + TABLE **table=sql_lock->table; + for (i=found=0 ; i < sql_lock->table_count ; i++) + { + DBUG_ASSERT(sql_lock->table[i]->lock_position == i); + if ((uint) sql_lock->table[i]->reginfo.lock_type > TL_WRITE_ALLOW_WRITE) + { + swap_variables(TABLE *, *table, sql_lock->table[i]); + table++; + found++; + } + } + /* Unlock all read locked tables */ + if (i != found) + { + error= unlock_external(thd,table,i-found); + sql_lock->table_count=found; + } + + /* Call thr_unlock() for all tables to be unlocked */ + + /* Move all write locks first */ + THR_LOCK_DATA **lock=sql_lock->locks; + for (i=found=0 ; i < sql_lock->lock_count ; i++) + { + if (sql_lock->locks[i]->type >= TL_WRITE_ALLOW_WRITE) + { + swap_variables(THR_LOCK_DATA *, *lock, sql_lock->locks[i]); + lock++; + found++; + } + } + /* unlock the read locked tables */ + if (i != found) + { + thr_multi_unlock(lock, i-found, 0); + sql_lock->lock_count= found; + } + + /* Fix the lock positions in TABLE */ + table= sql_lock->table; + found= 0; + for (i= 0; i < sql_lock->table_count; i++) + { + TABLE *tbl= *table; + tbl->lock_position= (uint) (table - sql_lock->table); + tbl->lock_data_start= found; + found+= tbl->lock_count; + table++; + } + DBUG_RETURN(error); +} + + +/** + Try to find the table in the list of locked tables. + In case of success, unlock the table and remove it from this list. + If a table has more than one lock instance, removes them all. + + @param thd thread context + @param locked list of locked tables + @param table the table to unlock +*/ + +int mysql_lock_remove(THD *thd, MYSQL_LOCK *locked,TABLE *table) +{ + int error= 0; + if (locked) + { + uint i; + for (i=0; i < locked->table_count; i++) + { + if (locked->table[i] == table) + { + uint j, removed_locks, old_tables; + int tmp_error; + TABLE *tbl; + uint lock_data_end; + + DBUG_ASSERT(table->lock_position == i); + + /* Unlock the table. */ + if ((tmp_error= mysql_unlock_some_tables(thd, &table, + /* table count */ 1, 0))) + { + table->file->print_error(tmp_error, MYF(0)); + if (!error) + error= tmp_error; + } + + /* Decrement table_count in advance, making below expressions easier */ + old_tables= --locked->table_count; + + /* The table has 'removed_locks' lock data elements in locked->locks */ + removed_locks= table->lock_count; + + /* Move down all table pointers above 'i'. */ + bmove((char*) (locked->table+i), + (char*) (locked->table+i+1), + (old_tables - i) * sizeof(TABLE*)); + + lock_data_end= table->lock_data_start + table->lock_count; + /* Move down all lock data pointers above 'table->lock_data_end-1' */ + bmove((char*) (locked->locks + table->lock_data_start), + (char*) (locked->locks + lock_data_end), + (locked->lock_count - lock_data_end) * + sizeof(THR_LOCK_DATA*)); + + /* + Fix moved table elements. + lock_position is the index in the 'locked->table' array, + it must be fixed by one. + table->lock_data_start is pointer to the lock data for this table + in the 'locked->locks' array, they must be fixed by 'removed_locks', + the lock data count of the removed table. + */ + for (j= i ; j < old_tables; j++) + { + tbl= locked->table[j]; + tbl->lock_position--; + DBUG_ASSERT(tbl->lock_position == j); + tbl->lock_data_start-= removed_locks; + } + + /* Finally adjust lock_count. */ + locked->lock_count-= removed_locks; + break; + } + } + } + return error; +} + + +/** + Abort one thread / table combination. + + @param thd Thread handler + @param table Table that should be removed from lock queue + + @retval + 0 Table was not locked by another thread + @retval + 1 Table was locked by at least one other thread +*/ + +bool mysql_lock_abort_for_thread(THD *thd, TABLE *table) +{ + MYSQL_LOCK *locked; + bool result= FALSE; + DBUG_ENTER("mysql_lock_abort_for_thread"); + + if ((locked= get_lock_data(thd, &table, 1, GET_LOCK_UNLOCK | GET_LOCK_ON_THD))) + { + for (uint i=0; i < locked->lock_count; i++) + { + if (thr_abort_locks_for_thread(locked->locks[i]->lock, + table->in_use->thread_id)) + result= TRUE; + } + } + DBUG_RETURN(result); +} + + +/** + Merge two thr_lock:s + mysql_lock_merge() + + @param a Original locks + @param b New locks + + @retval New lock structure that contains a and b + + @note + a and b are freed with my_free() +*/ + +MYSQL_LOCK *mysql_lock_merge(MYSQL_LOCK *a,MYSQL_LOCK *b) +{ + MYSQL_LOCK *sql_lock; + TABLE **table, **end_table; + DBUG_ENTER("mysql_lock_merge"); + DBUG_PRINT("enter", ("a->lock_count: %u b->lock_count: %u", + a->lock_count, b->lock_count)); + + if (!(sql_lock= (MYSQL_LOCK*) + my_malloc(key_memory_MYSQL_LOCK, sizeof(*sql_lock) + + sizeof(THR_LOCK_DATA*)*((a->lock_count+b->lock_count)*2) + + sizeof(TABLE*)*(a->table_count+b->table_count),MYF(MY_WME)))) + DBUG_RETURN(0); // Fatal error + sql_lock->lock_count=a->lock_count+b->lock_count; + sql_lock->table_count=a->table_count+b->table_count; + sql_lock->locks=(THR_LOCK_DATA**) (sql_lock+1); + sql_lock->table=(TABLE**) (sql_lock->locks+sql_lock->lock_count*2); + sql_lock->flags= 0; + memcpy(sql_lock->locks,a->locks,a->lock_count*sizeof(*a->locks)); + memcpy(sql_lock->locks+a->lock_count,b->locks, + b->lock_count*sizeof(*b->locks)); + memcpy(sql_lock->table,a->table,a->table_count*sizeof(*a->table)); + memcpy(sql_lock->table+a->table_count,b->table, + b->table_count*sizeof(*b->table)); + + /* + Now adjust lock_position and lock_data_start for all objects that was + moved in 'b' (as there is now all objects in 'a' before these). + */ + for (table= sql_lock->table + a->table_count, + end_table= table + b->table_count; + table < end_table; + table++) + { + (*table)->lock_position+= a->table_count; + (*table)->lock_data_start+= a->lock_count; + } + + /* + Ensure that locks of the same tables share same data structures if we + reopen a table that is already open. This can happen for example with + MERGE tables. + */ + + /* Copy the lock data array. thr_merge_lock() reorders its content */ + memcpy(sql_lock->locks + sql_lock->lock_count, sql_lock->locks, + sql_lock->lock_count * sizeof(*sql_lock->locks)); + thr_merge_locks(sql_lock->locks + sql_lock->lock_count, + a->lock_count, b->lock_count); + + /* Delete old, not needed locks */ + my_free(a); + my_free(b); + DBUG_RETURN(sql_lock); +} + + +/** Unlock a set of external. */ + +static int unlock_external(THD *thd, TABLE **table,uint count) +{ + int error,error_code; + DBUG_ENTER("unlock_external"); + + error_code=0; + do + { + if ((*table)->current_lock != F_UNLCK) + { + (*table)->current_lock = F_UNLCK; + if (unlikely((error=(*table)->file->ha_external_unlock(thd)))) + { + error_code= error; + (*table)->file->print_error(error, MYF(0)); + } + } + table++; + } while (--count); + DBUG_RETURN(error_code); +} + + +/** + Get lock structures from table structs and initialize locks. + + @param thd Thread handler + @param table_ptr Pointer to tables that should be locks + @param flags One of: + - GET_LOCK_UNLOCK : If we should send TL_IGNORE to store lock + - GET_LOCK_STORE_LOCKS : Store lock info in TABLE + - GET_LOCK_SKIP_SEQUENCES : Ignore sequences (for temporary unlock) + - GET_LOCK_ON_THD : Store lock in thd->mem_root + + Temporary tables are not locked (as these are single user), except for + TRANSACTIONAL_TMP_TABLES as locking is needed to handle transactions. +*/ + +MYSQL_LOCK *get_lock_data(THD *thd, TABLE **table_ptr, uint count, uint flags) +{ + uint i,lock_count,table_count; + MYSQL_LOCK *sql_lock; + THR_LOCK_DATA **locks, **locks_buf; + TABLE **to, **table_buf; + DBUG_ENTER("get_lock_data"); + + DBUG_PRINT("info", ("count %d", count)); + + for (i=lock_count=table_count=0 ; i < count ; i++) + { + TABLE *t= table_ptr[i]; + + if ((likely(!t->s->tmp_table) || + (t->s->tmp_table == TRANSACTIONAL_TMP_TABLE)) && + (!(flags & GET_LOCK_SKIP_SEQUENCES) || t->s->sequence == 0)) + { + lock_count+= t->file->lock_count(); + table_count++; + } + } + + /* + Allocating twice the number of pointers for lock data for use in + thr_multi_lock(). This function reorders the lock data, but cannot + update the table values. So the second part of the array is copied + from the first part immediately before calling thr_multi_lock(). + */ + size_t amount= sizeof(*sql_lock) + + sizeof(THR_LOCK_DATA*) * lock_count * 2 + + sizeof(table_ptr) * table_count; + if (!(sql_lock= (MYSQL_LOCK*) (flags & GET_LOCK_ON_THD ? + thd->alloc(amount) : + my_malloc(key_memory_MYSQL_LOCK, amount, + MYF(0))))) + DBUG_RETURN(0); + locks= locks_buf= sql_lock->locks= (THR_LOCK_DATA**) (sql_lock + 1); + to= table_buf= sql_lock->table= (TABLE**) (locks + lock_count * 2); + sql_lock->table_count= table_count; + sql_lock->flags= flags; + + for (i=0 ; i < count ; i++) + { + TABLE *table= table_ptr[i]; + enum thr_lock_type lock_type; + THR_LOCK_DATA **locks_start; + + if (!((likely(!table->s->tmp_table) || + (table->s->tmp_table == TRANSACTIONAL_TMP_TABLE)) && + (!(flags & GET_LOCK_SKIP_SEQUENCES) || table->s->sequence == 0))) + continue; + lock_type= table->reginfo.lock_type; + DBUG_ASSERT(lock_type != TL_WRITE_DEFAULT && lock_type != TL_READ_DEFAULT); + locks_start= locks; + locks= table->file->store_lock(thd, locks, + (flags & GET_LOCK_ACTION_MASK) == GET_LOCK_UNLOCK ? TL_IGNORE : + lock_type); + if ((flags & GET_LOCK_ACTION_MASK) == GET_LOCK_STORE_LOCKS) + { + table->lock_position= (uint) (to - table_buf); + table->lock_data_start= (uint) (locks_start - locks_buf); + table->lock_count= (uint) (locks - locks_start); + } + *to++= table; + if (locks) + { + for ( ; locks_start != locks ; locks_start++) + { + (*locks_start)->debug_print_param= (void *) table; + (*locks_start)->m_psi= table->file->m_psi; + (*locks_start)->lock->name= table->alias.c_ptr(); + (*locks_start)->org_type= (*locks_start)->type; + } + } + } + /* + We do not use 'lock_count', because there are cases where store_lock() + returns less locks than lock_count() claimed. This can happen when + a FLUSH TABLES tries to abort locks from a MERGE table of another + thread. When that thread has just opened the table, but not yet + attached its children, it cannot return the locks. lock_count() + always returns the number of locks that an attached table has. + This is done to avoid the reverse situation: If lock_count() would + return 0 for a non-attached MERGE table, and that table becomes + attached between the calls to lock_count() and store_lock(), then + we would have allocated too little memory for the lock data. Now + we may allocate too much, but better safe than memory overrun. + And in the FLUSH case, the memory is released quickly anyway. + */ + sql_lock->lock_count= (uint)(locks - locks_buf); + DBUG_ASSERT(sql_lock->lock_count <= lock_count); + DBUG_PRINT("info", ("sql_lock->table_count %d sql_lock->lock_count %d", + sql_lock->table_count, sql_lock->lock_count)); + DBUG_RETURN(sql_lock); +} + + +/** + Obtain an exclusive metadata lock on a schema name. + + @param thd Thread handle. + @param db The database name. + + To avoid deadlocks, we do not try to obtain exclusive metadata + locks in LOCK TABLES mode, since in this mode there may be + other metadata locks already taken by the current connection, + and we must not wait for MDL locks while holding locks. + + @retval FALSE Success. + @retval TRUE Failure: we're in LOCK TABLES mode, or out of memory, + or this connection was killed. +*/ + +bool lock_schema_name(THD *thd, const char *db) +{ + MDL_request_list mdl_requests; + MDL_request global_request; + MDL_request mdl_request; + + if (thd->locked_tables_mode) + { + my_message(ER_LOCK_OR_ACTIVE_TRANSACTION, + ER_THD(thd, ER_LOCK_OR_ACTIVE_TRANSACTION), MYF(0)); + return TRUE; + } + + if (thd->has_read_only_protection()) + return TRUE; + MDL_REQUEST_INIT(&global_request, MDL_key::BACKUP, "", "", MDL_BACKUP_DDL, + MDL_STATEMENT); + MDL_REQUEST_INIT(&mdl_request, MDL_key::SCHEMA, db, "", MDL_EXCLUSIVE, + MDL_TRANSACTION); + + mdl_requests.push_front(&mdl_request); + mdl_requests.push_front(&global_request); + + if (thd->mdl_context.acquire_locks(&mdl_requests, + thd->variables.lock_wait_timeout)) + return TRUE; + + DEBUG_SYNC(thd, "after_wait_locked_schema_name"); + return FALSE; +} + + +/** + Obtain an exclusive metadata lock on an object name. + + @param thd Thread handle. + @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. It is enforced by asserts in MDL_context::acquire_locks(). + To avoid deadlocks, we do not try to obtain exclusive metadata + locks in LOCK TABLES mode, since in this mode there may be + other metadata locks already taken by the current connection, + and we must not wait for MDL locks while holding locks. + + @retval FALSE Success. + @retval TRUE Failure: we're in LOCK TABLES mode, or out of memory, + or this connection was killed. +*/ + +bool lock_object_name(THD *thd, MDL_key::enum_mdl_namespace mdl_type, + const char *db, const char *name) +{ + MDL_request_list mdl_requests; + MDL_request global_request; + MDL_request schema_request; + MDL_request mdl_request; + + DBUG_SLOW_ASSERT(ok_for_lower_case_names(db)); + + if (thd->locked_tables_mode) + { + my_message(ER_LOCK_OR_ACTIVE_TRANSACTION, + ER_THD(thd, ER_LOCK_OR_ACTIVE_TRANSACTION), MYF(0)); + return TRUE; + } + + DBUG_ASSERT(name); + DEBUG_SYNC(thd, "before_wait_locked_pname"); + + if (thd->has_read_only_protection()) + return TRUE; + MDL_REQUEST_INIT(&global_request, MDL_key::BACKUP, "", "", MDL_BACKUP_DDL, + MDL_STATEMENT); + MDL_REQUEST_INIT(&schema_request, MDL_key::SCHEMA, db, "", + MDL_INTENTION_EXCLUSIVE, MDL_TRANSACTION); + MDL_REQUEST_INIT(&mdl_request, mdl_type, db, name, MDL_EXCLUSIVE, + MDL_TRANSACTION); + + mdl_requests.push_front(&mdl_request); + mdl_requests.push_front(&schema_request); + mdl_requests.push_front(&global_request); + + if (thd->mdl_context.acquire_locks(&mdl_requests, + thd->variables.lock_wait_timeout)) + return TRUE; + + DEBUG_SYNC(thd, "after_wait_locked_pname"); + return FALSE; +} + + +/**************************************************************************** + 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(). + + How blocking of threads by global read lock is achieved: that's + 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 MDL_BACKUP_STMT 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 MDL_BACKUP_FTWRL1 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 + log. + + Why getting the global read lock is two steps and not one. Because FLUSH + TABLES WITH READ LOCK needs to insert one other step between the two: + flushing tables. So the order is + 1) lock_global_read_lock() (prevents any new table write locks, i.e. stalls + all new updates) + 2) close_cached_tables() (the FLUSH TABLES), which will wait for tables + currently opened and being updated to close (so it's possible that there is + a moment where all new updates of server are stalled *and* FLUSH TABLES WITH + READ LOCK is, too). + 3) make_global_read_lock_block_commit(). + If we have merged 1) and 3) into 1), we would have had this deadlock: + imagine thread 1 and 2, in non-autocommit mode, thread 3, and an InnoDB + table t. + thd1: SELECT * FROM t FOR UPDATE; + thd2: UPDATE t SET a=1; # blocked by row-level locks of thd1 + thd3: FLUSH TABLES WITH READ LOCK; # blocked in close_cached_tables() by the + table instance of thd2 + thd1: COMMIT; # blocked by thd3. + thd1 blocks thd2 which blocks thd3 which blocks thd1: deadlock. + + Note that we need to support that one thread does + FLUSH TABLES WITH READ LOCK; and then COMMIT; + (that's what innobackup does, for some good reason). + So in this exceptional case the COMMIT should not be blocked by the FLUSH + TABLES WITH READ LOCK. + +****************************************************************************/ + +/** + Take global read lock, wait if there is protection against lock. + + If the global read lock is already taken by this thread, then nothing is + done. + + Concurrent thread can acquire protection against global read lock either + before or after it got table metadata lock. This may lead to a deadlock if + there is pending global read lock request. E.g. + t1 does DML, holds SHARED table lock, waiting for t3 (GRL protection) + t2 does DDL, holds GRL protection, waiting for t1 (EXCLUSIVE) + t3 does FTWRL, has pending GRL, waiting for t2 (GRL) + + Since this is very seldom deadlock and FTWRL connection must not hold any + other locks, FTWRL connection is made deadlock victim and attempt to acquire + GRL retried. + + See also "Handling of global read locks" above. + + @param thd Reference to thread. + + @retval False Success, global read lock set, commits are NOT blocked. + @retval True Failure, thread was killed. +*/ + +bool Global_read_lock::lock_global_read_lock(THD *thd) +{ + DBUG_ENTER("lock_global_read_lock"); + + if (!m_state) + { + MDL_deadlock_and_lock_abort_error_handler mdl_deadlock_handler; + MDL_request mdl_request; + bool result; + + if (thd->current_backup_stage != BACKUP_FINISHED) + { + my_error(ER_BACKUP_LOCK_IS_ACTIVE, MYF(0)); + DBUG_RETURN(1); + } + + /* + Release HANDLER OPEN by the current THD as they may cause deadlocks + if another thread is trying to simultaneous drop the table + */ + mysql_ha_cleanup_no_free(thd); + DEBUG_SYNC(thd, "ftwrl_before_lock"); + + DBUG_ASSERT(! thd->mdl_context.is_lock_owner(MDL_key::BACKUP, "", "", + MDL_BACKUP_FTWRL1)); + DBUG_ASSERT(! thd->mdl_context.is_lock_owner(MDL_key::BACKUP, "", "", + MDL_BACKUP_FTWRL2)); + MDL_REQUEST_INIT(&mdl_request, MDL_key::BACKUP, "", "", MDL_BACKUP_FTWRL1, + MDL_EXPLICIT); + + do + { + mdl_deadlock_handler.init(); + thd->push_internal_handler(&mdl_deadlock_handler); + result= thd->mdl_context.acquire_lock(&mdl_request, + thd->variables.lock_wait_timeout); + thd->pop_internal_handler(); + } while (mdl_deadlock_handler.need_reopen()); + + if (result) + DBUG_RETURN(true); + + m_mdl_global_read_lock= mdl_request.ticket; + m_state= GRL_ACQUIRED; + } + /* + We DON'T set global_read_lock_blocks_commit now, it will be set after + tables are flushed (as the present function serves for FLUSH TABLES WITH + READ LOCK only). Doing things in this order is necessary to avoid + deadlocks (we must allow COMMIT until all tables are closed; we should not + forbid it before, or we can have a 3-thread deadlock if 2 do SELECT FOR + UPDATE and one does FLUSH TABLES WITH READ LOCK). + */ + DBUG_RETURN(0); +} + + +/** + Unlock global read lock. + + Commits may or may not be blocked when this function is called. + + See also "Handling of global read locks" above. + + @param thd Reference to thread. +*/ + +void Global_read_lock::unlock_global_read_lock(THD *thd) +{ + DBUG_ENTER("unlock_global_read_lock"); + + DBUG_ASSERT(m_mdl_global_read_lock && m_state); + + if (thd->global_disable_checkpoint) + { + thd->global_disable_checkpoint= 0; + if (!--global_disable_checkpoint) + { + ha_checkpoint_state(0); // Enable checkpoints + } + } + + thd->mdl_context.release_lock(m_mdl_global_read_lock); + +#ifdef WITH_WSREP + if (m_state == GRL_ACQUIRED_AND_BLOCKS_COMMIT && + wsrep_locked_seqno != WSREP_SEQNO_UNDEFINED) + { + Wsrep_server_state& server_state= Wsrep_server_state::instance(); + if (server_state.state() == Wsrep_server_state::s_donor || + (WSREP_NNULL(thd) && + server_state.state() != Wsrep_server_state::s_synced)) + { + server_state.resume(); + wsrep_locked_seqno= WSREP_SEQNO_UNDEFINED; + } + else if (WSREP_NNULL(thd) && + server_state.state() == Wsrep_server_state::s_synced) + { + server_state.resume_and_resync(); + wsrep_locked_seqno= WSREP_SEQNO_UNDEFINED; + } + } +#endif /* WITH_WSREP */ + + m_mdl_global_read_lock= NULL; + m_state= GRL_NONE; + + DBUG_VOID_RETURN; +} + + +/** + Make global read lock also block commits. + + The scenario is: + - This thread has the global read lock. + - Global read lock blocking of commits is not set. + + See also "Handling of global read locks" above. + + @param thd Reference to thread. + + @retval False Success, global read lock set, commits are blocked. + @retval True Failure, thread was killed. +*/ + +bool Global_read_lock::make_global_read_lock_block_commit(THD *thd) +{ + DBUG_ENTER("make_global_read_lock_block_commit"); + /* + If we didn't succeed lock_global_read_lock(), or if we already succeeded + make_global_read_lock_block_commit(), do nothing. + */ + + if (m_state != GRL_ACQUIRED) + DBUG_RETURN(0); + + if (thd->mdl_context.upgrade_shared_lock(m_mdl_global_read_lock, + MDL_BACKUP_FTWRL2, + thd->variables.lock_wait_timeout)) + DBUG_RETURN(TRUE); + + m_state= GRL_ACQUIRED_AND_BLOCKS_COMMIT; + +#ifdef WITH_WSREP + /* Native threads should bail out before wsrep operations to follow. + Donor servicing thread is an exception, it should pause provider + but not desync, as it is already desynced in donor state. + Desync should be called only when we are in synced state. + */ + Wsrep_server_state& server_state= Wsrep_server_state::instance(); + wsrep::seqno paused_seqno; + if (server_state.state() == Wsrep_server_state::s_donor || + (WSREP_NNULL(thd) && + server_state.state() != Wsrep_server_state::s_synced)) + { + paused_seqno= server_state.pause(); + } + else if (WSREP_NNULL(thd) && + server_state.state() == Wsrep_server_state::s_synced) + { + paused_seqno= server_state.desync_and_pause(); + } + else + { + DBUG_RETURN(FALSE); + } + WSREP_INFO("Server paused at: %lld", paused_seqno.get()); + if (paused_seqno.get() >= 0) + { + wsrep_locked_seqno= paused_seqno.get(); + } +#endif /* WITH_WSREP */ + DBUG_RETURN(FALSE); +} + + +/** + Set explicit duration for metadata locks which are used to implement GRL. + + @param thd Reference to thread. +*/ + +void Global_read_lock::set_explicit_lock_duration(THD *thd) +{ + if (m_mdl_global_read_lock) + thd->mdl_context.set_lock_duration(m_mdl_global_read_lock, MDL_EXPLICIT); +} + +/** + @} (end of group Locking) +*/ |