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mariadb/sql/lock.cc
unknown 9d85b0a616 BUG#21310 - Trees in SQL causing a "crashed" table with MyISAM storage engine 
An update that used a join of a table to itself and modified the
table on one side of the join reported the table as crashed or
updated wrong rows.

Fixed by creating temporary table for self-joined multi update statement.


mysql-test/r/myisam.result:
  A test case for BUG#21310.
mysql-test/t/myisam.test:
  A test case for BUG#21310.
sql/lock.cc:
  Exclude 'table' param from check.
sql/sql_update.cc:
  Disabling record cache for self-joined multi update statement is wrong.
  The join must only see the table as it was at the beginning of the statement.
  safe_update_on_fly check if it is safe to update first table on the fly, that is
  not creating temporary table. It is possible in case a row from this table is
  never read more than once. safe_update_on_fly now detect self-joined table and
  refuse to update this table on the fly.
2006-12-20 19:05:35 +04:00

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/* Copyright (C) 2000 MySQL AB & MySQL Finland AB & TCX DataKonsult AB
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; either version 2 of the License, or
(at your option) any later version.
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, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */
/* 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().
This will call thr_multi_unlock() followed by
table_handler->external_lock(thd, F_UNLCK) 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
TODO:
Change to use my_malloc() ONLY when using LOCK TABLES command or when
we are forced to use mysql_lock_merge.
*/
#include "mysql_priv.h"
#include <hash.h>
#include <assert.h>
extern HASH open_cache;
/* flags for get_lock_data */
#define GET_LOCK_UNLOCK 1
#define GET_LOCK_STORE_LOCKS 2
static MYSQL_LOCK *get_lock_data(THD *thd, TABLE **table,uint count,
uint flags, TABLE **write_locked);
static void reset_lock_data(MYSQL_LOCK *sql_lock);
static int lock_external(THD *thd, TABLE **table,uint count);
static int unlock_external(THD *thd, TABLE **table,uint count);
static void print_lock_error(int error);
/*
Lock tables.
SYNOPSIS
mysql_lock_tables()
thd The current thread.
tables An array of pointers to the tables to lock.
count The number of tables to lock.
flags Options:
MYSQL_LOCK_IGNORE_GLOBAL_READ_LOCK Ignore a global read lock
MYSQL_LOCK_IGNORE_FLUSH Ignore a flush tables.
RETURN
A lock structure pointer on success.
NULL on error.
*/
MYSQL_LOCK *mysql_lock_tables(THD *thd, TABLE **tables, uint count, uint flags)
{
MYSQL_LOCK *sql_lock;
TABLE *write_lock_used;
DBUG_ENTER("mysql_lock_tables");
for (;;)
{
if (! (sql_lock= get_lock_data(thd, tables, count, GET_LOCK_STORE_LOCKS,
&write_lock_used)))
break;
if (global_read_lock && write_lock_used &&
! (flags & MYSQL_LOCK_IGNORE_GLOBAL_READ_LOCK))
{
/*
Someone has issued LOCK ALL TABLES FOR READ and we want a write lock
Wait until the lock is gone
*/
if (wait_if_global_read_lock(thd, 1, 1))
{
/* Clear the lock type of all lock data to avoid reusage. */
reset_lock_data(sql_lock);
my_free((gptr) sql_lock,MYF(0));
sql_lock=0;
break;
}
if (thd->version != refresh_version)
{
/* Clear the lock type of all lock data to avoid reusage. */
reset_lock_data(sql_lock);
my_free((gptr) sql_lock,MYF(0));
goto retry;
}
}
thd->proc_info="System lock";
if (lock_external(thd, tables, count))
{
/* Clear the lock type of all lock data to avoid reusage. */
reset_lock_data(sql_lock);
my_free((gptr) sql_lock,MYF(0));
sql_lock=0;
thd->proc_info=0;
break;
}
thd->proc_info="Table lock";
thd->locked=1;
/* Copy the lock data array. thr_multi_lock() reorders its contens. */
memcpy(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. */
if (thr_multi_lock(sql_lock->locks + sql_lock->lock_count,
sql_lock->lock_count))
{
thd->some_tables_deleted=1; // Try again
sql_lock->lock_count=0; // Locks are alread freed
}
else if (!thd->some_tables_deleted || (flags & MYSQL_LOCK_IGNORE_FLUSH))
{
thd->locked=0;
break;
}
else if (!thd->open_tables)
{
// Only using temporary tables, no need to unlock
thd->some_tables_deleted=0;
thd->locked=0;
break;
}
thd->proc_info=0;
/* some table was altered or deleted. reopen tables marked deleted */
mysql_unlock_tables(thd,sql_lock);
thd->locked=0;
retry:
sql_lock=0;
if (wait_for_tables(thd))
break; // Couldn't open tables
}
thd->proc_info=0;
if (thd->killed)
{
my_error(ER_SERVER_SHUTDOWN,MYF(0));
if (sql_lock)
{
mysql_unlock_tables(thd,sql_lock);
sql_lock=0;
}
}
thd->lock_time();
DBUG_RETURN (sql_lock);
}
static int lock_external(THD *thd, TABLE **tables, uint count)
{
reg1 uint i;
int lock_type,error;
DBUG_ENTER("lock_external");
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 ((error=(*tables)->file->external_lock(thd,lock_type)))
{
for (; i-- ; tables--)
{
(*tables)->file->external_lock(thd, F_UNLCK);
(*tables)->current_lock=F_UNLCK;
}
print_lock_error(error);
DBUG_RETURN(error);
}
else
{
(*tables)->db_stat &= ~ HA_BLOCK_LOCK;
(*tables)->current_lock= lock_type;
}
}
DBUG_RETURN(0);
}
void mysql_unlock_tables(THD *thd, MYSQL_LOCK *sql_lock)
{
DBUG_ENTER("mysql_unlock_tables");
if (sql_lock->lock_count)
thr_multi_unlock(sql_lock->locks,sql_lock->lock_count);
if (sql_lock->table_count)
VOID(unlock_external(thd,sql_lock->table,sql_lock->table_count));
my_free((gptr) sql_lock,MYF(0));
DBUG_VOID_RETURN;
}
/*
Unlock some of the tables locked by mysql_lock_tables
This will work even if get_lock_data fails (next unlock will free all)
*/
void mysql_unlock_some_tables(THD *thd, TABLE **table,uint count)
{
MYSQL_LOCK *sql_lock;
TABLE *write_lock_used;
if ((sql_lock= get_lock_data(thd, table, count, GET_LOCK_UNLOCK,
&write_lock_used)))
mysql_unlock_tables(thd, sql_lock);
}
/*
** unlock all tables locked for read.
*/
void mysql_unlock_read_tables(THD *thd, MYSQL_LOCK *sql_lock)
{
uint i,found;
DBUG_ENTER("mysql_unlock_read_tables");
/* 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_READ)
{
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);
sql_lock->lock_count= found;
}
/* Then do the same for the external locks */
/* 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_READ)
{
swap_variables(TABLE *, *table, sql_lock->table[i]);
table++;
found++;
}
}
/* Unlock all read locked tables */
if (i != found)
{
VOID(unlock_external(thd,table,i-found));
sql_lock->table_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= table - sql_lock->table;
tbl->lock_data_start= found;
found+= tbl->lock_count;
table++;
}
DBUG_VOID_RETURN;
}
void mysql_lock_remove(THD *thd, MYSQL_LOCK *locked,TABLE *table)
{
mysql_unlock_some_tables(thd, &table,1);
if (locked)
{
reg1 uint i;
for (i=0; i < locked->table_count; i++)
{
if (locked->table[i] == table)
{
uint j, removed_locks, old_tables;
TABLE *tbl;
uint lock_data_end;
DBUG_ASSERT(table->lock_position == i);
/* 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;
}
}
}
}
/* abort all other threads waiting to get lock in table */
void mysql_lock_abort(THD *thd, TABLE *table)
{
MYSQL_LOCK *locked;
TABLE *write_lock_used;
if ((locked= get_lock_data(thd, &table, 1, GET_LOCK_UNLOCK,
&write_lock_used)))
{
for (uint i=0; i < locked->lock_count; i++)
thr_abort_locks(locked->locks[i]->lock);
my_free((gptr) locked,MYF(0));
}
}
/*
Abort one thread / table combination
SYNOPSIS
mysql_lock_abort_for_thread()
thd Thread handler
table Table that should be removed from lock queue
RETURN
0 Table was not locked by another thread
1 Table was locked by at least one other thread
*/
bool mysql_lock_abort_for_thread(THD *thd, TABLE *table)
{
MYSQL_LOCK *locked;
TABLE *write_lock_used;
bool result= FALSE;
DBUG_ENTER("mysql_lock_abort_for_thread");
if ((locked= get_lock_data(thd, &table, 1, GET_LOCK_UNLOCK,
&write_lock_used)))
{
for (uint i=0; i < locked->lock_count; i++)
{
if (thr_abort_locks_for_thread(locked->locks[i]->lock,
table->in_use->real_id))
result= TRUE;
}
my_free((gptr) locked,MYF(0));
}
DBUG_RETURN(result);
}
MYSQL_LOCK *mysql_lock_merge(MYSQL_LOCK *a,MYSQL_LOCK *b)
{
MYSQL_LOCK *sql_lock;
TABLE **table, **end_table;
DBUG_ENTER("mysql_lock_merge");
if (!(sql_lock= (MYSQL_LOCK*)
my_malloc(sizeof(*sql_lock)+
sizeof(THR_LOCK_DATA*)*(a->lock_count+b->lock_count)+
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);
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;
}
/* Delete old, not needed locks */
my_free((gptr) a,MYF(0));
my_free((gptr) b,MYF(0));
DBUG_RETURN(sql_lock);
}
/*
Find duplicate lock in tables.
SYNOPSIS
mysql_lock_have_duplicate()
thd The current thread.
table The table to check for duplicate lock.
tables The list of tables to search for the dup lock.
NOTE
This is mainly meant for MERGE tables in INSERT ... SELECT
situations. The 'real', underlying tables can be found only after
the MERGE tables are opened. This function assumes that the tables are
already locked.
Temporary tables are ignored here like they are ignored in
get_lock_data(). If we allow two opens on temporary tables later,
both functions should be checked.
RETURN
1 A table from 'tables' matches a lock on 'table'.
0 No duplicate lock found.
*/
int mysql_lock_have_duplicate(THD *thd, TABLE *table, TABLE_LIST *tables)
{
MYSQL_LOCK *mylock;
TABLE **lock_tables;
TABLE *table2;
THR_LOCK_DATA **lock_locks, **table_lock_data;
THR_LOCK_DATA **end_data;
THR_LOCK_DATA **lock_data2;
THR_LOCK_DATA **end_data2;
DBUG_ENTER("mysql_lock_have_duplicate");
/* A temporary table does not have locks. */
if (table->tmp_table == TMP_TABLE)
goto end;
/* Get command lock or LOCK TABLES lock. */
mylock= thd->lock ? thd->lock : thd->locked_tables;
DBUG_ASSERT(mylock);
/* If we have less than two tables, we cannot have duplicates. */
if (mylock->table_count < 2)
goto end;
lock_locks= mylock->locks;
lock_tables= mylock->table;
/* Prepare table related variables that don't change in loop. */
DBUG_ASSERT(table == lock_tables[table->lock_position]);
table_lock_data= lock_locks + table->lock_data_start;
end_data= table_lock_data + table->lock_count;
for (; tables; tables= tables->next)
{
table2= tables->table;
if (table2->tmp_table == TMP_TABLE || table == table2)
continue;
/* All tables in list must be in lock. */
DBUG_ASSERT(table2 == lock_tables[table2->lock_position]);
for (lock_data2= lock_locks + table2->lock_data_start,
end_data2= lock_data2 + table2->lock_count;
lock_data2 < end_data2;
lock_data2++)
{
THR_LOCK_DATA **lock_data;
THR_LOCK *lock2= (*lock_data2)->lock;
for (lock_data= table_lock_data;
lock_data < end_data;
lock_data++)
{
if ((*lock_data)->lock == lock2)
DBUG_RETURN(1);
}
}
}
end:
DBUG_RETURN(0);
}
/* 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 ((error=(*table)->file->external_lock(thd, F_UNLCK)))
error_code=error;
}
table++;
} while (--count);
if (error_code)
print_lock_error(error_code);
DBUG_RETURN(error_code);
}
/*
Get lock structures from table structs and initialize locks
SYNOPSIS
get_lock_data()
thd Thread handler
table_ptr Pointer to tables that should be locks
flags One of:
GET_LOCK_UNLOCK: If we should send TL_IGNORE to
store lock
GET_LOCK_STORE_LOCKS: Store lock info in TABLE
write_lock_used Store pointer to last table with WRITE_ALLOW_WRITE
*/
static MYSQL_LOCK *get_lock_data(THD *thd, TABLE **table_ptr, uint count,
uint flags, TABLE **write_lock_used)
{
uint i,tables,lock_count;
MYSQL_LOCK *sql_lock;
THR_LOCK_DATA **locks, **locks_buf, **locks_start;
TABLE **to, **table_buf;
DBUG_ENTER("get_lock_data");
*write_lock_used=0;
for (i=tables=lock_count=0 ; i < count ; i++)
{
if (table_ptr[i]->tmp_table != TMP_TABLE)
{
tables+=table_ptr[i]->file->lock_count();
lock_count++;
}
}
/*
Allocating twice the number of pointers for lock data for use in
thr_mulit_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().
*/
if (!(sql_lock= (MYSQL_LOCK*)
my_malloc(sizeof(*sql_lock) +
sizeof(THR_LOCK_DATA*) * tables * 2 +
sizeof(table_ptr) * lock_count,
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 + tables * 2);
sql_lock->table_count=lock_count;
sql_lock->lock_count=tables;
for (i=0 ; i < count ; i++)
{
TABLE *table;
enum thr_lock_type lock_type;
if ((table=table_ptr[i])->tmp_table == TMP_TABLE)
continue;
lock_type= table->reginfo.lock_type;
if (lock_type >= TL_WRITE_ALLOW_WRITE)
{
*write_lock_used=table;
if (table->db_stat & HA_READ_ONLY)
{
my_error(ER_OPEN_AS_READONLY,MYF(0),table->table_name);
/* Clear the lock type of the lock data that are stored already. */
sql_lock->lock_count= locks - sql_lock->locks;
reset_lock_data(sql_lock);
my_free((gptr) sql_lock,MYF(0));
DBUG_RETURN(0);
}
}
THR_LOCK_DATA **org_locks = locks;
locks_start= locks;
locks= table->file->store_lock(thd, locks,
(flags & GET_LOCK_UNLOCK) ? TL_IGNORE :
lock_type);
if (flags & 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 ( ; org_locks != locks ; org_locks++)
(*org_locks)->debug_print_param= (void *) table;
}
DBUG_RETURN(sql_lock);
}
/*
Reset lock type in lock data.
SYNOPSIS
reset_lock_data()
sql_lock The MySQL lock.
DESCRIPTION
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.
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.
Clear the lock type of all lock data. This ensures that the next
lock request will set its lock type properly.
RETURN
void
*/
static void reset_lock_data(MYSQL_LOCK *sql_lock)
{
THR_LOCK_DATA **ldata;
THR_LOCK_DATA **ldata_end;
for (ldata= sql_lock->locks, ldata_end= ldata + sql_lock->lock_count;
ldata < ldata_end;
ldata++)
{
/* Reset lock type. */
(*ldata)->type= TL_UNLOCK;
}
}
/*****************************************************************************
Lock table based on the name.
This is used when we need total access to a closed, not open table
*****************************************************************************/
/*
Lock and wait for the named lock.
SYNOPSIS
lock_and_wait_for_table_name()
thd Thread handler
table_list Lock first table in this list
NOTES
Works together with global read lock.
RETURN
0 ok
1 error
*/
int lock_and_wait_for_table_name(THD *thd, TABLE_LIST *table_list)
{
int lock_retcode;
int error= -1;
DBUG_ENTER("lock_and_wait_for_table_name");
if (wait_if_global_read_lock(thd, 0, 1))
DBUG_RETURN(1);
VOID(pthread_mutex_lock(&LOCK_open));
if ((lock_retcode = lock_table_name(thd, table_list)) < 0)
goto end;
if (lock_retcode && wait_for_locked_table_names(thd, table_list))
{
unlock_table_name(thd, table_list);
goto end;
}
error=0;
end:
pthread_mutex_unlock(&LOCK_open);
start_waiting_global_read_lock(thd);
DBUG_RETURN(error);
}
/*
Put a not open table with an old refresh version in the table cache.
SYNPOSIS
lock_table_name()
thd Thread handler
table_list Lock first table in this list
WARNING
If you are going to update the table, you should use
lock_and_wait_for_table_name instead of this function as this works
together with 'FLUSH TABLES WITH READ LOCK'
NOTES
This will force any other threads that uses the table to release it
as soon as possible.
REQUIREMENTS
One must have a lock on LOCK_open !
RETURN:
< 0 error
== 0 table locked
> 0 table locked, but someone is using it
*/
int lock_table_name(THD *thd, TABLE_LIST *table_list)
{
TABLE *table;
char key[MAX_DBKEY_LENGTH];
char *db= table_list->db;
uint key_length;
HASH_SEARCH_STATE state;
DBUG_ENTER("lock_table_name");
DBUG_PRINT("enter",("db: %s name: %s", db, table_list->real_name));
safe_mutex_assert_owner(&LOCK_open);
key_length=(uint) (strmov(strmov(key,db)+1,table_list->real_name)
-key)+ 1;
/* Only insert the table if we haven't insert it already */
for (table=(TABLE*) hash_first(&open_cache, (byte*)key, key_length, &state);
table ;
table = (TABLE*) hash_next(&open_cache, (byte*)key, key_length, &state))
if (table->in_use == thd)
DBUG_RETURN(0);
/*
Create a table entry with the right key and with an old refresh version
Note that we must use my_malloc() here as this is freed by the table
cache
*/
if (!(table= (TABLE*) my_malloc(sizeof(*table)+key_length,
MYF(MY_WME | MY_ZEROFILL))))
DBUG_RETURN(-1);
memcpy((table->table_cache_key= (char*) (table+1)), key, key_length);
table->key_length=key_length;
table->in_use=thd;
table->locked_by_name=1;
table_list->table=table;
if (my_hash_insert(&open_cache, (byte*) table))
{
my_free((gptr) table,MYF(0));
DBUG_RETURN(-1);
}
if (remove_table_from_cache(thd, db, table_list->real_name, RTFC_NO_FLAG))
{
DBUG_RETURN(1); // Table is in use
}
DBUG_RETURN(0);
}
void unlock_table_name(THD *thd, TABLE_LIST *table_list)
{
if (table_list->table)
{
hash_delete(&open_cache, (byte*) table_list->table);
(void) pthread_cond_broadcast(&COND_refresh);
}
}
static bool locked_named_table(THD *thd, TABLE_LIST *table_list)
{
for (; table_list ; table_list=table_list->next)
{
if (table_list->table && table_is_used(table_list->table,0))
return 1;
}
return 0; // All tables are locked
}
bool wait_for_locked_table_names(THD *thd, TABLE_LIST *table_list)
{
bool result=0;
DBUG_ENTER("wait_for_locked_table_names");
safe_mutex_assert_owner(&LOCK_open);
while (locked_named_table(thd,table_list))
{
if (thd->killed)
{
result=1;
break;
}
wait_for_refresh(thd);
pthread_mutex_lock(&LOCK_open);
}
DBUG_RETURN(result);
}
/*
Lock all tables in list with a name lock
SYNOPSIS
lock_table_names()
thd Thread handle
table_list Names of tables to lock
NOTES
If you are just locking one table, you should use
lock_and_wait_for_table_name().
REQUIREMENTS
One must have a lock on LOCK_open when calling this
RETURN
0 ok
1 Fatal error (end of memory ?)
*/
bool lock_table_names(THD *thd, TABLE_LIST *table_list)
{
bool got_all_locks=1;
TABLE_LIST *lock_table;
for (lock_table=table_list ; lock_table ; lock_table=lock_table->next)
{
int got_lock;
if ((got_lock=lock_table_name(thd,lock_table)) < 0)
goto end; // Fatal error
if (got_lock)
got_all_locks=0; // Someone is using table
}
/* If some table was in use, wait until we got the lock */
if (!got_all_locks && wait_for_locked_table_names(thd, table_list))
goto end;
return 0;
end:
unlock_table_names(thd, table_list, lock_table);
return 1;
}
/*
Unlock all tables in list with a name lock
SYNOPSIS
unlock_table_names()
thd Thread handle
table_list Names of tables to unlock
last_table Don't unlock any tables after this one.
(default 0, which will unlock all tables)
NOTES
One must have a lock on LOCK_open when calling this
This function will send a COND_refresh signal to inform other threads
that the name locks are removed
RETURN
0 ok
1 Fatal error (end of memory ?)
*/
void unlock_table_names(THD *thd, TABLE_LIST *table_list,
TABLE_LIST *last_table)
{
for (TABLE_LIST *table=table_list ; table != last_table ; table=table->next)
unlock_table_name(thd,table);
pthread_cond_broadcast(&COND_refresh);
}
static void print_lock_error(int error)
{
int textno;
DBUG_ENTER("print_lock_error");
switch (error) {
case HA_ERR_LOCK_WAIT_TIMEOUT:
textno=ER_LOCK_WAIT_TIMEOUT;
break;
case HA_ERR_READ_ONLY_TRANSACTION:
textno=ER_READ_ONLY_TRANSACTION;
break;
default:
textno=ER_CANT_LOCK;
break;
}
my_error(textno,MYF(ME_BELL+ME_OLDWIN+ME_WAITTANG),error);
DBUG_VOID_RETURN;
}
/****************************************************************************
Handling of global read locks
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.
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 ]
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.
TODO in MySQL 5.x: make_global_read_lock_block_commit() should be
killable. Normally CPU does not spend a long time in this function (COMMITs
are quite fast), but it would still be nice.
****************************************************************************/
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;
#define GOT_GLOBAL_READ_LOCK 1
#define MADE_GLOBAL_READ_LOCK_BLOCK_COMMIT 2
bool lock_global_read_lock(THD *thd)
{
DBUG_ENTER("lock_global_read_lock");
if (!thd->global_read_lock)
{
(void) pthread_mutex_lock(&LOCK_open);
const char *old_message=thd->enter_cond(&COND_refresh, &LOCK_open,
"Waiting to get readlock");
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)
pthread_cond_wait(&COND_refresh, &LOCK_open);
waiting_for_read_lock--;
if (thd->killed)
{
thd->exit_cond(old_message);
DBUG_RETURN(1);
}
thd->global_read_lock= GOT_GLOBAL_READ_LOCK;
global_read_lock++;
thd->exit_cond(old_message);
}
/*
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);
}
void unlock_global_read_lock(THD *thd)
{
uint tmp;
pthread_mutex_lock(&LOCK_open);
tmp= --global_read_lock;
if (thd->global_read_lock == MADE_GLOBAL_READ_LOCK_BLOCK_COMMIT)
--global_read_lock_blocks_commit;
pthread_mutex_unlock(&LOCK_open);
/* Send the signal outside the mutex to avoid a context switch */
if (!tmp)
pthread_cond_broadcast(&COND_refresh);
thd->global_read_lock= 0;
}
#define must_wait (global_read_lock && \
(is_not_commit || \
global_read_lock_blocks_commit))
bool wait_if_global_read_lock(THD *thd, bool abort_on_refresh,
bool is_not_commit)
{
const char *old_message;
bool result= 0, need_exit_cond;
DBUG_ENTER("wait_if_global_read_lock");
LINT_INIT(old_message);
(void) pthread_mutex_lock(&LOCK_open);
if ((need_exit_cond= must_wait))
{
if (thd->global_read_lock) // This thread had the read locks
{
if (is_not_commit)
my_error(ER_CANT_UPDATE_WITH_READLOCK,MYF(0));
(void) pthread_mutex_unlock(&LOCK_open);
/*
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_refresh, &LOCK_open,
"Waiting for release of readlock");
while (must_wait && ! thd->killed &&
(!abort_on_refresh || thd->version == refresh_version))
(void) pthread_cond_wait(&COND_refresh,&LOCK_open);
if (thd->killed)
result=1;
}
if (!abort_on_refresh && !result)
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);
else
pthread_mutex_unlock(&LOCK_open);
DBUG_RETURN(result);
}
void start_waiting_global_read_lock(THD *thd)
{
bool tmp;
DBUG_ENTER("start_waiting_global_read_lock");
if (unlikely(thd->global_read_lock))
DBUG_VOID_RETURN;
(void) pthread_mutex_lock(&LOCK_open);
tmp= (!--protect_against_global_read_lock &&
(waiting_for_read_lock || global_read_lock_blocks_commit));
(void) pthread_mutex_unlock(&LOCK_open);
if (tmp)
pthread_cond_broadcast(&COND_refresh);
DBUG_VOID_RETURN;
}
void make_global_read_lock_block_commit(THD *thd)
{
/*
If we didn't succeed lock_global_read_lock(), or if we already suceeded
make_global_read_lock_block_commit(), do nothing.
*/
if (thd->global_read_lock != GOT_GLOBAL_READ_LOCK)
return;
pthread_mutex_lock(&LOCK_open);
/* increment this BEFORE waiting on cond (otherwise race cond) */
global_read_lock_blocks_commit++;
while (protect_against_global_read_lock)
pthread_cond_wait(&COND_refresh, &LOCK_open);
pthread_mutex_unlock(&LOCK_open);
thd->global_read_lock= MADE_GLOBAL_READ_LOCK_BLOCK_COMMIT;
}
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