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/* Copyright (C) 2000 MySQL AB & MySQL Finland AB & TCX DataKonsult AB
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */
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/* locking functions for mysql */
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Because of the new concurrent inserts, we must first get external locks
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before getting internal locks. If we do it in the other order, the status
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information is not up to date when called from the lock handler.
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GENERAL DESCRIPTION OF LOCKING
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When not using LOCK TABLES:
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- For each SQL statement mysql_lock_tables() is called for all involved
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- mysql_lock_tables() will call
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table_handler->external_lock(thd,locktype) for each table.
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This is followed by a call to thr_multi_lock() for all tables.
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- When statement is done, we call mysql_unlock_tables().
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This will call thr_multi_unlock() followed by
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table_handler->external_lock(thd, F_UNLCK) for each table.
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- Note that mysql_unlock_tables() may be called several times as
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MySQL in some cases can free some tables earlier than others.
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- The above is true both for normal and temporary tables.
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- Temporary non transactional tables are never passed to thr_multi_lock()
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and we never call external_lock(thd, F_UNLOCK) on these.
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When using LOCK TABLES:
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- LOCK TABLE will call mysql_lock_tables() for all tables.
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mysql_lock_tables() will call
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table_handler->external_lock(thd,locktype) for each table.
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This is followed by a call to thr_multi_lock() for all tables.
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- For each statement, we will call table_handler->start_stmt(THD)
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to inform the table handler that we are using the table.
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The tables used can only be tables used in LOCK TABLES or a
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- When statement is done, we will call ha_commit_stmt(thd);
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- When calling UNLOCK TABLES we call mysql_unlock_tables() for all
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tables used in LOCK TABLES
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Change to use my_malloc() ONLY when using LOCK TABLES command or when
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we are forced to use mysql_lock_merge.
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#include "mysql_priv.h"
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extern HASH open_cache;
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/* flags for get_lock_data */
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#define GET_LOCK_UNLOCK 1
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#define GET_LOCK_STORE_LOCKS 2
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static MYSQL_LOCK *get_lock_data(THD *thd, TABLE **table,uint count,
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uint flags, TABLE **write_locked);
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static void reset_lock_data(MYSQL_LOCK *sql_lock);
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static int lock_external(THD *thd, TABLE **table,uint count);
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static int unlock_external(THD *thd, TABLE **table,uint count);
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static void print_lock_error(int error, const char *);
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thd The current thread.
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tables An array of pointers to the tables to lock.
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count The number of tables to lock.
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MYSQL_LOCK_IGNORE_GLOBAL_READ_LOCK Ignore a global read lock
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MYSQL_LOCK_IGNORE_FLUSH Ignore a flush tables.
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MYSQL_LOCK_NOTIFY_IF_NEED_REOPEN Instead of reopening altered
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or dropped tables by itself,
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mysql_lock_tables() should
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notify upper level and rely
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on caller doing this.
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need_reopen Out parameter, TRUE if some tables were altered
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or deleted and should be reopened by caller.
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A lock structure pointer on success.
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NULL on error or if some tables should be reopen.
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/* Map the return value of thr_lock to an error from errmsg.txt */
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static int thr_lock_errno_to_mysql[]=
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{ 0, 1, ER_LOCK_WAIT_TIMEOUT, ER_LOCK_DEADLOCK };
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MYSQL_LOCK *mysql_lock_tables(THD *thd, TABLE **tables, uint count,
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uint flags, bool *need_reopen)
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MYSQL_LOCK *sql_lock;
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TABLE *write_lock_used;
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DBUG_ENTER("mysql_lock_tables");
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if (! (sql_lock= get_lock_data(thd, tables, count, GET_LOCK_STORE_LOCKS,
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if (global_read_lock && write_lock_used &&
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! (flags & MYSQL_LOCK_IGNORE_GLOBAL_READ_LOCK))
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Someone has issued LOCK ALL TABLES FOR READ and we want a write lock
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Wait until the lock is gone
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if (wait_if_global_read_lock(thd, 1, 1))
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/* Clear the lock type of all lock data to avoid reusage. */
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reset_lock_data(sql_lock);
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my_free((gptr) sql_lock,MYF(0));
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if (thd->version != refresh_version)
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/* Clear the lock type of all lock data to avoid reusage. */
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reset_lock_data(sql_lock);
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my_free((gptr) sql_lock,MYF(0));
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thd->proc_info="System lock";
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if (lock_external(thd, tables, count))
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/* Clear the lock type of all lock data to avoid reusage. */
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reset_lock_data(sql_lock);
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my_free((gptr) sql_lock,MYF(0));
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thd->proc_info="Table lock";
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/* Copy the lock data array. thr_multi_lock() reorders its contens. */
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memcpy(sql_lock->locks + sql_lock->lock_count, sql_lock->locks,
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sql_lock->lock_count * sizeof(*sql_lock->locks));
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/* Lock on the copied half of the lock data array. */
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rc= thr_lock_errno_to_mysql[(int) thr_multi_lock(sql_lock->locks +
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sql_lock->lock_count,
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sql_lock->lock_count,
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if (rc > 1) /* a timeout or a deadlock */
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my_error(rc, MYF(0));
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my_free((gptr) sql_lock,MYF(0));
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else if (rc == 1) /* aborted */
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thd->some_tables_deleted=1; // Try again
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sql_lock->lock_count= 0; // Locks are already freed
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else if (!thd->some_tables_deleted || (flags & MYSQL_LOCK_IGNORE_FLUSH))
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else if (!thd->open_tables)
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// Only using temporary tables, no need to unlock
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thd->some_tables_deleted=0;
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/* some table was altered or deleted. reopen tables marked deleted */
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mysql_unlock_tables(thd,sql_lock);
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if (flags & MYSQL_LOCK_NOTIFY_IF_NEED_REOPEN)
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if (wait_for_tables(thd))
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break; // Couldn't open tables
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thd->send_kill_message();
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mysql_unlock_tables(thd,sql_lock);
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DBUG_RETURN (sql_lock);
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static int lock_external(THD *thd, TABLE **tables, uint count)
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DBUG_ENTER("lock_external");
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for (i=1 ; i <= count ; i++, tables++)
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DBUG_ASSERT((*tables)->reginfo.lock_type >= TL_READ);
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lock_type=F_WRLCK; /* Lock exclusive */
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if ((*tables)->db_stat & HA_READ_ONLY ||
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((*tables)->reginfo.lock_type >= TL_READ &&
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(*tables)->reginfo.lock_type <= TL_READ_NO_INSERT))
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if ((error=(*tables)->file->external_lock(thd,lock_type)))
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print_lock_error(error, (*tables)->file->table_type());
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for (; i-- ; tables--)
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(*tables)->file->external_lock(thd, F_UNLCK);
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(*tables)->current_lock=F_UNLCK;
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(*tables)->db_stat &= ~ HA_BLOCK_LOCK;
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(*tables)->current_lock= lock_type;
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void mysql_unlock_tables(THD *thd, MYSQL_LOCK *sql_lock)
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DBUG_ENTER("mysql_unlock_tables");
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if (sql_lock->lock_count)
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thr_multi_unlock(sql_lock->locks,sql_lock->lock_count);
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if (sql_lock->table_count)
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VOID(unlock_external(thd,sql_lock->table,sql_lock->table_count));
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my_free((gptr) sql_lock,MYF(0));
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Unlock some of the tables locked by mysql_lock_tables
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This will work even if get_lock_data fails (next unlock will free all)
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void mysql_unlock_some_tables(THD *thd, TABLE **table,uint count)
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MYSQL_LOCK *sql_lock;
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TABLE *write_lock_used;
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if ((sql_lock= get_lock_data(thd, table, count, GET_LOCK_UNLOCK,
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mysql_unlock_tables(thd, sql_lock);
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** unlock all tables locked for read.
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void mysql_unlock_read_tables(THD *thd, MYSQL_LOCK *sql_lock)
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DBUG_ENTER("mysql_unlock_read_tables");
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/* Move all write locks first */
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THR_LOCK_DATA **lock=sql_lock->locks;
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for (i=found=0 ; i < sql_lock->lock_count ; i++)
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if (sql_lock->locks[i]->type >= TL_WRITE_ALLOW_READ)
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swap_variables(THR_LOCK_DATA *, *lock, sql_lock->locks[i]);
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/* unlock the read locked tables */
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thr_multi_unlock(lock,i-found);
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sql_lock->lock_count= found;
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/* Then do the same for the external locks */
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/* Move all write locked tables first */
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TABLE **table=sql_lock->table;
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for (i=found=0 ; i < sql_lock->table_count ; i++)
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DBUG_ASSERT(sql_lock->table[i]->lock_position == i);
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if ((uint) sql_lock->table[i]->reginfo.lock_type >= TL_WRITE_ALLOW_READ)
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swap_variables(TABLE *, *table, sql_lock->table[i]);
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/* Unlock all read locked tables */
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VOID(unlock_external(thd,table,i-found));
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sql_lock->table_count=found;
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/* Fix the lock positions in TABLE */
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table= sql_lock->table;
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for (i= 0; i < sql_lock->table_count; i++)
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tbl->lock_position= table - sql_lock->table;
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tbl->lock_data_start= found;
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found+= tbl->lock_count;
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void mysql_lock_remove(THD *thd, MYSQL_LOCK *locked,TABLE *table)
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mysql_unlock_some_tables(thd, &table,1);
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for (i=0; i < locked->table_count; i++)
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if (locked->table[i] == table)
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uint j, removed_locks, old_tables;
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DBUG_ASSERT(table->lock_position == i);
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/* Decrement table_count in advance, making below expressions easier */
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old_tables= --locked->table_count;
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/* The table has 'removed_locks' lock data elements in locked->locks */
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removed_locks= table->lock_count;
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/* Move down all table pointers above 'i'. */
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bmove((char*) (locked->table+i),
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(char*) (locked->table+i+1),
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(old_tables - i) * sizeof(TABLE*));
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lock_data_end= table->lock_data_start + table->lock_count;
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/* Move down all lock data pointers above 'table->lock_data_end-1' */
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bmove((char*) (locked->locks + table->lock_data_start),
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(char*) (locked->locks + lock_data_end),
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(locked->lock_count - lock_data_end) *
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sizeof(THR_LOCK_DATA*));
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Fix moved table elements.
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lock_position is the index in the 'locked->table' array,
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it must be fixed by one.
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table->lock_data_start is pointer to the lock data for this table
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in the 'locked->locks' array, they must be fixed by 'removed_locks',
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the lock data count of the removed table.
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for (j= i ; j < old_tables; j++)
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tbl= locked->table[j];
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tbl->lock_position--;
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DBUG_ASSERT(tbl->lock_position == j);
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tbl->lock_data_start-= removed_locks;
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/* Finally adjust lock_count. */
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locked->lock_count-= removed_locks;
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/* abort all other threads waiting to get lock in table */
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void mysql_lock_abort(THD *thd, TABLE *table)
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TABLE *write_lock_used;
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if ((locked= get_lock_data(thd, &table, 1, GET_LOCK_UNLOCK,
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for (uint i=0; i < locked->lock_count; i++)
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thr_abort_locks(locked->locks[i]->lock);
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my_free((gptr) locked,MYF(0));
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Abort one thread / table combination
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mysql_lock_abort_for_thread()
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table Table that should be removed from lock queue
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0 Table was not locked by another thread
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1 Table was locked by at least one other thread
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bool mysql_lock_abort_for_thread(THD *thd, TABLE *table)
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TABLE *write_lock_used;
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DBUG_ENTER("mysql_lock_abort_for_thread");
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if ((locked= get_lock_data(thd, &table, 1, GET_LOCK_UNLOCK,
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for (uint i=0; i < locked->lock_count; i++)
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if (thr_abort_locks_for_thread(locked->locks[i]->lock,
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table->in_use->real_id))
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my_free((gptr) locked,MYF(0));
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MYSQL_LOCK *mysql_lock_merge(MYSQL_LOCK *a,MYSQL_LOCK *b)
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MYSQL_LOCK *sql_lock;
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TABLE **table, **end_table;
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DBUG_ENTER("mysql_lock_merge");
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if (!(sql_lock= (MYSQL_LOCK*)
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my_malloc(sizeof(*sql_lock)+
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sizeof(THR_LOCK_DATA*)*(a->lock_count+b->lock_count)+
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sizeof(TABLE*)*(a->table_count+b->table_count),MYF(MY_WME))))
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DBUG_RETURN(0); // Fatal error
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sql_lock->lock_count=a->lock_count+b->lock_count;
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sql_lock->table_count=a->table_count+b->table_count;
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sql_lock->locks=(THR_LOCK_DATA**) (sql_lock+1);
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sql_lock->table=(TABLE**) (sql_lock->locks+sql_lock->lock_count);
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memcpy(sql_lock->locks,a->locks,a->lock_count*sizeof(*a->locks));
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memcpy(sql_lock->locks+a->lock_count,b->locks,
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b->lock_count*sizeof(*b->locks));
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memcpy(sql_lock->table,a->table,a->table_count*sizeof(*a->table));
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memcpy(sql_lock->table+a->table_count,b->table,
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b->table_count*sizeof(*b->table));
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Now adjust lock_position and lock_data_start for all objects that was
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moved in 'b' (as there is now all objects in 'a' before these).
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for (table= sql_lock->table + a->table_count,
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end_table= table + b->table_count;
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(*table)->lock_position+= a->table_count;
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(*table)->lock_data_start+= a->lock_count;
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/* Delete old, not needed locks */
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my_free((gptr) a,MYF(0));
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my_free((gptr) b,MYF(0));
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DBUG_RETURN(sql_lock);
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Find duplicate lock in tables.
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mysql_lock_have_duplicate()
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thd The current thread.
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needle The table to check for duplicate lock.
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haystack The list of tables to search for the dup lock.
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This is mainly meant for MERGE tables in INSERT ... SELECT
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situations. The 'real', underlying tables can be found only after
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the MERGE tables are opened. This function assumes that the tables are
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Temporary tables are ignored here like they are ignored in
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get_lock_data(). If we allow two opens on temporary tables later,
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both functions should be checked.
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NULL No duplicate lock found.
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! NULL First table from 'haystack' that matches a lock on 'needle'.
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TABLE_LIST *mysql_lock_have_duplicate(THD *thd, TABLE_LIST *needle,
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TABLE_LIST *haystack)
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THR_LOCK_DATA **lock_locks;
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THR_LOCK_DATA **table_lock_data;
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THR_LOCK_DATA **end_data;
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THR_LOCK_DATA **lock_data2;
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THR_LOCK_DATA **end_data2;
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DBUG_ENTER("mysql_lock_have_duplicate");
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Table may not be defined for derived or view tables.
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Table may not be part of a lock for delayed operations.
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if (! (table= needle->table) || ! table->lock_count)
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/* A temporary table does not have locks. */
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if (table->s->tmp_table == TMP_TABLE)
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/* Get command lock or LOCK TABLES lock. Maybe empty for INSERT DELAYED. */
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if (! (mylock= thd->lock ? thd->lock : thd->locked_tables))
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/* If we have less than two tables, we cannot have duplicates. */
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if (mylock->table_count < 2)
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lock_locks= mylock->locks;
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lock_tables= mylock->table;
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/* Prepare table related variables that don't change in loop. */
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DBUG_ASSERT((table->lock_position < mylock->table_count) &&
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(table == lock_tables[table->lock_position]));
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table_lock_data= lock_locks + table->lock_data_start;
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end_data= table_lock_data + table->lock_count;
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for (; haystack; haystack= haystack->next_global)
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if (haystack->placeholder() || haystack->schema_table)
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table2= haystack->table;
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if (table2->s->tmp_table == TMP_TABLE)
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/* All tables in list must be in lock. */
577
DBUG_ASSERT((table2->lock_position < mylock->table_count) &&
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(table2 == lock_tables[table2->lock_position]));
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for (lock_data2= lock_locks + table2->lock_data_start,
581
end_data2= lock_data2 + table2->lock_count;
582
lock_data2 < end_data2;
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THR_LOCK_DATA **lock_data;
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THR_LOCK *lock2= (*lock_data2)->lock;
588
for (lock_data= table_lock_data;
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lock_data < end_data;
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if ((*lock_data)->lock == lock2)
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DBUG_PRINT("info", ("haystack match: '%s'", haystack->table_name));
595
DBUG_RETURN(haystack);
602
DBUG_PRINT("info", ("no duplicate found"));
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/* unlock a set of external */
609
static int unlock_external(THD *thd, TABLE **table,uint count)
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int error,error_code;
612
DBUG_ENTER("unlock_external");
617
if ((*table)->current_lock != F_UNLCK)
619
(*table)->current_lock = F_UNLCK;
620
if ((error=(*table)->file->external_lock(thd, F_UNLCK)))
623
print_lock_error(error_code, (*table)->file->table_type());
628
DBUG_RETURN(error_code);
633
Get lock structures from table structs and initialize locks
638
table_ptr Pointer to tables that should be locks
640
GET_LOCK_UNLOCK: If we should send TL_IGNORE to
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GET_LOCK_STORE_LOCKS: Store lock info in TABLE
643
write_lock_used Store pointer to last table with WRITE_ALLOW_WRITE
647
static MYSQL_LOCK *get_lock_data(THD *thd, TABLE **table_ptr, uint count,
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uint flags, TABLE **write_lock_used)
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uint i,tables,lock_count;
651
MYSQL_LOCK *sql_lock;
652
THR_LOCK_DATA **locks, **locks_buf, **locks_start;
653
TABLE **to, **table_buf;
654
DBUG_ENTER("get_lock_data");
657
for (i=tables=lock_count=0 ; i < count ; i++)
659
if (table_ptr[i]->s->tmp_table != TMP_TABLE)
661
tables+=table_ptr[i]->file->lock_count();
665
To be able to open and lock for reading system tables like 'mysql.proc',
666
when we already have some tables opened and locked, and avoid deadlocks
667
we have to disallow write-locking of these tables with any other tables.
669
if (table_ptr[i]->s->system_table &&
670
table_ptr[i]->reginfo.lock_type >= TL_WRITE_ALLOW_WRITE &&
673
my_error(ER_WRONG_LOCK_OF_SYSTEM_TABLE, MYF(0), table_ptr[i]->s->db,
674
table_ptr[i]->s->table_name);
680
Allocating twice the number of pointers for lock data for use in
681
thr_mulit_lock(). This function reorders the lock data, but cannot
682
update the table values. So the second part of the array is copied
683
from the first part immediately before calling thr_multi_lock().
685
if (!(sql_lock= (MYSQL_LOCK*)
686
my_malloc(sizeof(*sql_lock) +
687
sizeof(THR_LOCK_DATA*) * tables * 2 +
688
sizeof(table_ptr) * lock_count,
691
locks= locks_buf= sql_lock->locks= (THR_LOCK_DATA**) (sql_lock + 1);
692
to= table_buf= sql_lock->table= (TABLE**) (locks + tables * 2);
693
sql_lock->table_count=lock_count;
694
sql_lock->lock_count=tables;
696
for (i=0 ; i < count ; i++)
699
enum thr_lock_type lock_type;
701
if ((table=table_ptr[i])->s->tmp_table == TMP_TABLE)
703
lock_type= table->reginfo.lock_type;
704
if (lock_type >= TL_WRITE_ALLOW_WRITE)
706
*write_lock_used=table;
707
if (table->db_stat & HA_READ_ONLY)
709
my_error(ER_OPEN_AS_READONLY,MYF(0),table->alias);
710
/* Clear the lock type of the lock data that are stored already. */
711
sql_lock->lock_count= locks - sql_lock->locks;
712
reset_lock_data(sql_lock);
713
my_free((gptr) sql_lock,MYF(0));
717
THR_LOCK_DATA **org_locks = locks;
719
locks= table->file->store_lock(thd, locks,
720
(flags & GET_LOCK_UNLOCK) ? TL_IGNORE :
722
if (flags & GET_LOCK_STORE_LOCKS)
724
table->lock_position= (uint) (to - table_buf);
725
table->lock_data_start= (uint) (locks_start - locks_buf);
726
table->lock_count= (uint) (locks - locks_start);
730
for ( ; org_locks != locks ; org_locks++)
731
(*org_locks)->debug_print_param= (void *) table;
733
DBUG_RETURN(sql_lock);
738
Reset lock type in lock data.
742
sql_lock The MySQL lock.
746
After a locking error we want to quit the locking of the table(s).
747
The test case in the bug report for Bug #18544 has the following
748
cases: 1. Locking error in lock_external() due to InnoDB timeout.
749
2. Locking error in get_lock_data() due to missing write permission.
750
3. Locking error in wait_if_global_read_lock() due to lock conflict.
752
In all these cases we have already set the lock type into the lock
753
data of the open table(s). If the table(s) are in the open table
754
cache, they could be reused with the non-zero lock type set. This
755
could lead to ignoring a different lock type with the next lock.
757
Clear the lock type of all lock data. This ensures that the next
758
lock request will set its lock type properly.
764
static void reset_lock_data(MYSQL_LOCK *sql_lock)
766
THR_LOCK_DATA **ldata;
767
THR_LOCK_DATA **ldata_end;
769
for (ldata= sql_lock->locks, ldata_end= ldata + sql_lock->lock_count;
773
/* Reset lock type. */
774
(*ldata)->type= TL_UNLOCK;
779
/*****************************************************************************
780
Lock table based on the name.
781
This is used when we need total access to a closed, not open table
782
*****************************************************************************/
785
Lock and wait for the named lock.
788
lock_and_wait_for_table_name()
790
table_list Lock first table in this list
794
Works together with global read lock.
801
int lock_and_wait_for_table_name(THD *thd, TABLE_LIST *table_list)
805
DBUG_ENTER("lock_and_wait_for_table_name");
807
if (wait_if_global_read_lock(thd, 0, 1))
809
VOID(pthread_mutex_lock(&LOCK_open));
810
if ((lock_retcode = lock_table_name(thd, table_list)) < 0)
812
if (lock_retcode && wait_for_locked_table_names(thd, table_list))
814
unlock_table_name(thd, table_list);
820
pthread_mutex_unlock(&LOCK_open);
821
start_waiting_global_read_lock(thd);
827
Put a not open table with an old refresh version in the table cache.
832
table_list Lock first table in this list
835
If you are going to update the table, you should use
836
lock_and_wait_for_table_name instead of this function as this works
837
together with 'FLUSH TABLES WITH READ LOCK'
840
This will force any other threads that uses the table to release it
844
One must have a lock on LOCK_open !
849
> 0 table locked, but someone is using it
852
int lock_table_name(THD *thd, TABLE_LIST *table_list)
855
char key[MAX_DBKEY_LENGTH];
856
char *db= table_list->db;
857
int table_in_key_offset;
859
HASH_SEARCH_STATE state;
860
DBUG_ENTER("lock_table_name");
861
DBUG_PRINT("enter",("db: %s name: %s", db, table_list->table_name));
863
safe_mutex_assert_owner(&LOCK_open);
865
table_in_key_offset= strmov(key, db) - key + 1;
866
key_length= (uint)(strmov(key + table_in_key_offset, table_list->table_name)
870
/* Only insert the table if we haven't insert it already */
871
for (table=(TABLE*) hash_first(&open_cache, (byte*)key, key_length, &state);
873
table = (TABLE*) hash_next(&open_cache, (byte*)key, key_length, &state))
874
if (table->in_use == thd)
878
Create a table entry with the right key and with an old refresh version
879
Note that we must use my_malloc() here as this is freed by the table
882
if (!(table= (TABLE*) my_malloc(sizeof(*table)+key_length,
883
MYF(MY_WME | MY_ZEROFILL))))
885
table->s= &table->share_not_to_be_used;
886
memcpy((table->s->table_cache_key= (char*) (table+1)), key, key_length);
887
table->s->db= table->s->table_cache_key;
888
table->s->table_name= table->s->table_cache_key + table_in_key_offset;
889
table->s->key_length=key_length;
891
table->locked_by_name=1;
892
table_list->table=table;
894
if (my_hash_insert(&open_cache, (byte*) table))
896
my_free((gptr) table,MYF(0));
900
/* Return 1 if table is in use */
901
DBUG_RETURN(test(remove_table_from_cache(thd, db, table_list->table_name,
906
void unlock_table_name(THD *thd, TABLE_LIST *table_list)
908
if (table_list->table)
910
hash_delete(&open_cache, (byte*) table_list->table);
916
static bool locked_named_table(THD *thd, TABLE_LIST *table_list)
918
for (; table_list ; table_list=table_list->next_local)
920
if (table_list->table && table_is_used(table_list->table,0))
923
return 0; // All tables are locked
927
bool wait_for_locked_table_names(THD *thd, TABLE_LIST *table_list)
930
DBUG_ENTER("wait_for_locked_table_names");
931
safe_mutex_assert_owner(&LOCK_open);
933
while (locked_named_table(thd,table_list))
940
wait_for_refresh(thd);
941
pthread_mutex_lock(&LOCK_open);
948
Lock all tables in list with a name lock
953
table_list Names of tables to lock
956
If you are just locking one table, you should use
957
lock_and_wait_for_table_name().
960
One must have a lock on LOCK_open when calling this
964
1 Fatal error (end of memory ?)
967
bool lock_table_names(THD *thd, TABLE_LIST *table_list)
969
bool got_all_locks=1;
970
TABLE_LIST *lock_table;
972
for (lock_table= table_list; lock_table; lock_table= lock_table->next_local)
975
if ((got_lock=lock_table_name(thd,lock_table)) < 0)
976
goto end; // Fatal error
978
got_all_locks=0; // Someone is using table
981
/* If some table was in use, wait until we got the lock */
982
if (!got_all_locks && wait_for_locked_table_names(thd, table_list))
987
unlock_table_names(thd, table_list, lock_table);
993
Unlock all tables in list with a name lock
998
table_list Names of tables to unlock
999
last_table Don't unlock any tables after this one.
1000
(default 0, which will unlock all tables)
1003
One must have a lock on LOCK_open when calling this.
1004
This function will broadcast refresh signals to inform other threads
1005
that the name locks are removed.
1009
1 Fatal error (end of memory ?)
1012
void unlock_table_names(THD *thd, TABLE_LIST *table_list,
1013
TABLE_LIST *last_table)
1015
for (TABLE_LIST *table= table_list;
1016
table != last_table;
1017
table= table->next_local)
1018
unlock_table_name(thd,table);
1019
broadcast_refresh();
1023
static void print_lock_error(int error, const char *table)
1026
DBUG_ENTER("print_lock_error");
1029
case HA_ERR_LOCK_WAIT_TIMEOUT:
1030
textno=ER_LOCK_WAIT_TIMEOUT;
1032
case HA_ERR_READ_ONLY_TRANSACTION:
1033
textno=ER_READ_ONLY_TRANSACTION;
1035
case HA_ERR_LOCK_DEADLOCK:
1036
textno=ER_LOCK_DEADLOCK;
1038
case HA_ERR_WRONG_COMMAND:
1039
textno=ER_ILLEGAL_HA;
1042
textno=ER_CANT_LOCK;
1046
if ( textno == ER_ILLEGAL_HA )
1047
my_error(textno, MYF(ME_BELL+ME_OLDWIN+ME_WAITTANG), table);
1049
my_error(textno, MYF(ME_BELL+ME_OLDWIN+ME_WAITTANG), error);
1055
/****************************************************************************
1056
Handling of global read locks
1058
Taking the global read lock is TWO steps (2nd step is optional; without
1059
it, COMMIT of existing transactions will be allowed):
1060
lock_global_read_lock() THEN make_global_read_lock_block_commit().
1062
The global locks are handled through the global variables:
1064
count of threads which have the global read lock (i.e. have completed at
1065
least the first step above)
1066
global_read_lock_blocks_commit
1067
count of threads which have the global read lock and block
1068
commits (i.e. are in or have completed the second step above)
1069
waiting_for_read_lock
1070
count of threads which want to take a global read lock but cannot
1071
protect_against_global_read_lock
1072
count of threads which have set protection against global read lock.
1074
access to them is protected with a mutex LOCK_global_read_lock
1076
(XXX: one should never take LOCK_open if LOCK_global_read_lock is
1077
taken, otherwise a deadlock may occur. Other mutexes could be a
1078
problem too - grep the code for global_read_lock if you want to use
1079
any other mutex here) Also one must not hold LOCK_open when calling
1080
wait_if_global_read_lock(). When the thread with the global read lock
1081
tries to close its tables, it needs to take LOCK_open in
1082
close_thread_table().
1084
How blocking of threads by global read lock is achieved: that's
1085
advisory. Any piece of code which should be blocked by global read lock must
1086
be designed like this:
1087
- call to wait_if_global_read_lock(). When this returns 0, no global read
1088
lock is owned; if argument abort_on_refresh was 0, none can be obtained.
1090
- if abort_on_refresh was 0, call to start_waiting_global_read_lock() to
1091
allow other threads to get the global read lock. I.e. removal of the
1093
(Note: it's a bit like an implementation of rwlock).
1095
[ I am sorry to mention some SQL syntaxes below I know I shouldn't but found
1096
no better descriptive way ]
1098
Why does FLUSH TABLES WITH READ LOCK need to block COMMIT: because it's used
1099
to read a non-moving SHOW MASTER STATUS, and a COMMIT writes to the binary
1102
Why getting the global read lock is two steps and not one. Because FLUSH
1103
TABLES WITH READ LOCK needs to insert one other step between the two:
1104
flushing tables. So the order is
1105
1) lock_global_read_lock() (prevents any new table write locks, i.e. stalls
1107
2) close_cached_tables() (the FLUSH TABLES), which will wait for tables
1108
currently opened and being updated to close (so it's possible that there is
1109
a moment where all new updates of server are stalled *and* FLUSH TABLES WITH
1111
3) make_global_read_lock_block_commit().
1112
If we have merged 1) and 3) into 1), we would have had this deadlock:
1113
imagine thread 1 and 2, in non-autocommit mode, thread 3, and an InnoDB
1115
thd1: SELECT * FROM t FOR UPDATE;
1116
thd2: UPDATE t SET a=1; # blocked by row-level locks of thd1
1117
thd3: FLUSH TABLES WITH READ LOCK; # blocked in close_cached_tables() by the
1118
table instance of thd2
1119
thd1: COMMIT; # blocked by thd3.
1120
thd1 blocks thd2 which blocks thd3 which blocks thd1: deadlock.
1122
Note that we need to support that one thread does
1123
FLUSH TABLES WITH READ LOCK; and then COMMIT;
1124
(that's what innobackup does, for some good reason).
1125
So in this exceptional case the COMMIT should not be blocked by the FLUSH
1126
TABLES WITH READ LOCK.
1128
****************************************************************************/
1130
volatile uint global_read_lock=0;
1131
volatile uint global_read_lock_blocks_commit=0;
1132
static volatile uint protect_against_global_read_lock=0;
1133
static volatile uint waiting_for_read_lock=0;
1135
#define GOT_GLOBAL_READ_LOCK 1
1136
#define MADE_GLOBAL_READ_LOCK_BLOCK_COMMIT 2
1138
bool lock_global_read_lock(THD *thd)
1140
DBUG_ENTER("lock_global_read_lock");
1142
if (!thd->global_read_lock)
1144
const char *old_message;
1145
(void) pthread_mutex_lock(&LOCK_global_read_lock);
1146
old_message=thd->enter_cond(&COND_global_read_lock, &LOCK_global_read_lock,
1147
"Waiting to get readlock");
1149
("waiting_for: %d protect_against: %d",
1150
waiting_for_read_lock, protect_against_global_read_lock));
1152
waiting_for_read_lock++;
1153
while (protect_against_global_read_lock && !thd->killed)
1154
pthread_cond_wait(&COND_global_read_lock, &LOCK_global_read_lock);
1155
waiting_for_read_lock--;
1158
thd->exit_cond(old_message);
1161
thd->global_read_lock= GOT_GLOBAL_READ_LOCK;
1163
thd->exit_cond(old_message); // this unlocks LOCK_global_read_lock
1166
We DON'T set global_read_lock_blocks_commit now, it will be set after
1167
tables are flushed (as the present function serves for FLUSH TABLES WITH
1168
READ LOCK only). Doing things in this order is necessary to avoid
1169
deadlocks (we must allow COMMIT until all tables are closed; we should not
1170
forbid it before, or we can have a 3-thread deadlock if 2 do SELECT FOR
1171
UPDATE and one does FLUSH TABLES WITH READ LOCK).
1177
void unlock_global_read_lock(THD *thd)
1180
DBUG_ENTER("unlock_global_read_lock");
1182
("global_read_lock: %u global_read_lock_blocks_commit: %u",
1183
global_read_lock, global_read_lock_blocks_commit));
1185
pthread_mutex_lock(&LOCK_global_read_lock);
1186
tmp= --global_read_lock;
1187
if (thd->global_read_lock == MADE_GLOBAL_READ_LOCK_BLOCK_COMMIT)
1188
--global_read_lock_blocks_commit;
1189
pthread_mutex_unlock(&LOCK_global_read_lock);
1190
/* Send the signal outside the mutex to avoid a context switch */
1193
DBUG_PRINT("signal", ("Broadcasting COND_global_read_lock"));
1194
pthread_cond_broadcast(&COND_global_read_lock);
1196
thd->global_read_lock= 0;
1201
#define must_wait (global_read_lock && \
1203
global_read_lock_blocks_commit))
1205
bool wait_if_global_read_lock(THD *thd, bool abort_on_refresh,
1208
const char *old_message;
1209
bool result= 0, need_exit_cond;
1210
DBUG_ENTER("wait_if_global_read_lock");
1212
LINT_INIT(old_message);
1214
Assert that we do not own LOCK_open. If we would own it, other
1215
threads could not close their tables. This would make a pretty
1218
safe_mutex_assert_not_owner(&LOCK_open);
1220
(void) pthread_mutex_lock(&LOCK_global_read_lock);
1221
if ((need_exit_cond= must_wait))
1223
if (thd->global_read_lock) // This thread had the read locks
1226
my_message(ER_CANT_UPDATE_WITH_READLOCK,
1227
ER(ER_CANT_UPDATE_WITH_READLOCK), MYF(0));
1228
(void) pthread_mutex_unlock(&LOCK_global_read_lock);
1230
We allow FLUSHer to COMMIT; we assume FLUSHer knows what it does.
1231
This allowance is needed to not break existing versions of innobackup
1232
which do a BEGIN; INSERT; FLUSH TABLES WITH READ LOCK; COMMIT.
1234
DBUG_RETURN(is_not_commit);
1236
old_message=thd->enter_cond(&COND_global_read_lock, &LOCK_global_read_lock,
1237
"Waiting for release of readlock");
1238
while (must_wait && ! thd->killed &&
1239
(!abort_on_refresh || thd->version == refresh_version))
1241
DBUG_PRINT("signal", ("Waiting for COND_global_read_lock"));
1242
(void) pthread_cond_wait(&COND_global_read_lock, &LOCK_global_read_lock);
1243
DBUG_PRINT("signal", ("Got COND_global_read_lock"));
1248
if (!abort_on_refresh && !result)
1249
protect_against_global_read_lock++;
1251
The following is only true in case of a global read locks (which is rare)
1252
and if old_message is set
1254
if (unlikely(need_exit_cond))
1255
thd->exit_cond(old_message); // this unlocks LOCK_global_read_lock
1257
pthread_mutex_unlock(&LOCK_global_read_lock);
1258
DBUG_RETURN(result);
1262
void start_waiting_global_read_lock(THD *thd)
1265
DBUG_ENTER("start_waiting_global_read_lock");
1266
if (unlikely(thd->global_read_lock))
1268
(void) pthread_mutex_lock(&LOCK_global_read_lock);
1269
tmp= (!--protect_against_global_read_lock &&
1270
(waiting_for_read_lock || global_read_lock_blocks_commit));
1271
(void) pthread_mutex_unlock(&LOCK_global_read_lock);
1273
pthread_cond_broadcast(&COND_global_read_lock);
1278
bool make_global_read_lock_block_commit(THD *thd)
1281
const char *old_message;
1282
DBUG_ENTER("make_global_read_lock_block_commit");
1284
If we didn't succeed lock_global_read_lock(), or if we already suceeded
1285
make_global_read_lock_block_commit(), do nothing.
1287
if (thd->global_read_lock != GOT_GLOBAL_READ_LOCK)
1289
pthread_mutex_lock(&LOCK_global_read_lock);
1290
/* increment this BEFORE waiting on cond (otherwise race cond) */
1291
global_read_lock_blocks_commit++;
1292
/* For testing we set up some blocking, to see if we can be killed */
1293
DBUG_EXECUTE_IF("make_global_read_lock_block_commit_loop",
1294
protect_against_global_read_lock++;);
1295
old_message= thd->enter_cond(&COND_global_read_lock, &LOCK_global_read_lock,
1296
"Waiting for all running commits to finish");
1297
while (protect_against_global_read_lock && !thd->killed)
1298
pthread_cond_wait(&COND_global_read_lock, &LOCK_global_read_lock);
1299
DBUG_EXECUTE_IF("make_global_read_lock_block_commit_loop",
1300
protect_against_global_read_lock--;);
1301
if ((error= test(thd->killed)))
1302
global_read_lock_blocks_commit--; // undo what we did
1304
thd->global_read_lock= MADE_GLOBAL_READ_LOCK_BLOCK_COMMIT;
1305
thd->exit_cond(old_message); // this unlocks LOCK_global_read_lock
1311
Broadcast COND_refresh and COND_global_read_lock.
1318
Due to a bug in a threading library it could happen that a signal
1319
did not reach its target. A condition for this was that the same
1320
condition variable was used with different mutexes in
1321
pthread_cond_wait(). Some time ago we changed LOCK_open to
1322
LOCK_global_read_lock in global read lock handling. So COND_refresh
1323
was used with LOCK_open and LOCK_global_read_lock.
1325
We did now also change from COND_refresh to COND_global_read_lock
1326
in global read lock handling. But now it is necessary to signal
1327
both conditions at the same time.
1330
When signalling COND_global_read_lock within the global read lock
1331
handling, it is not necessary to also signal COND_refresh.
1337
void broadcast_refresh(void)
1339
VOID(pthread_cond_broadcast(&COND_refresh));
1340
VOID(pthread_cond_broadcast(&COND_global_read_lock));
added
removed
libmysqld/lock.cc
