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956ada2e2d0c21dff07b2bc6c808f0fd8689762d
mariadb/sql/lock.cc
Konstantin Osipov 8673d2b20f Commit on behalf of Dmitry Lenev. 
Merge his patch for Bug#52044 into 5.5, and apply 
review comments.
2010-08-12 17:50:23 +04:00

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/* Copyright 2000-2008 MySQL AB, 2008-2009 Sun Microsystems, Inc.
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, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 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().
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
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.
@todo
Change to use my_malloc() ONLY when using LOCK TABLES command or when
we are forced to use mysql_lock_merge.
*/
#include "sql_priv.h"
#include "debug_sync.h"
#include "unireg.h" // REQUIRED: for other includes
#include "lock.h"
#include "sql_base.h" // close_tables_for_reopen
#include "sql_parse.h" // is_log_table_write_query
#include "sql_acl.h" // SUPER_ACL
#include <hash.h>
#include <assert.h>
/**
@defgroup Locking Locking
@{
*/
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_ptr, uint count,
uint flags);
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, const char *);
/* 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 is_superuser, log_table_write_query;
DBUG_ENTER("lock_tables_check");
system_count= 0;
is_superuser= thd->security_ctx->master_access & SUPER_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);
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).
The only exception are HANDLER statements which are allowed to
lock table for read while having only MDL_SHARED lock on it.
*/
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) ||
(t->open_by_handler &&
thd->mdl_context.is_lock_owner(MDL_key::TABLE,
t->s->db.str, t->s->table_name.str,
MDL_SHARED)));
/*
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 &&
!is_superuser && 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.
@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.
*/
static void reset_lock_data(MYSQL_LOCK *sql_lock)
{
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++)
{
/* Reset lock type. */
(*ldata)->type= TL_UNLOCK;
}
DBUG_VOID_RETURN;
}
/**
Reset lock type in lock data and free.
@param mysql_lock Lock structures to reset.
*/
static void reset_lock_data_and_free(MYSQL_LOCK **mysql_lock)
{
reset_lock_data(*mysql_lock);
my_free(*mysql_lock);
*mysql_lock= 0;
}
/**
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)
{
int rc;
MYSQL_LOCK *sql_lock;
ulong timeout= (flags & MYSQL_LOCK_IGNORE_TIMEOUT) ?
LONG_TIMEOUT : thd->variables.lock_wait_timeout;
DBUG_ENTER("mysql_lock_tables");
if (lock_tables_check(thd, tables, count, flags))
DBUG_RETURN(NULL);
if (! (sql_lock= get_lock_data(thd, tables, count, GET_LOCK_STORE_LOCKS)))
DBUG_RETURN(NULL);
thd_proc_info(thd, "System lock");
DBUG_PRINT("info", ("thd->proc_info %s", thd->proc_info));
if (sql_lock->table_count && lock_external(thd, sql_lock->table,
sql_lock->table_count))
{
/* Clear the lock type of all lock data to avoid reusage. */
reset_lock_data_and_free(&sql_lock);
goto end;
}
/* Copy the lock data array. thr_multi_lock() reorders its contents. */
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. */
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)
{
if (sql_lock->table_count)
(void) unlock_external(thd, sql_lock->table, sql_lock->table_count);
reset_lock_data_and_free(&sql_lock);
if (! thd->killed)
my_error(rc, MYF(0));
}
end:
thd_proc_info(thd, 0);
if (thd->killed)
{
thd->send_kill_message();
if (sql_lock)
{
mysql_unlock_tables(thd, sql_lock);
sql_lock= 0;
}
}
thd->set_time_after_lock();
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");
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 ((error=(*tables)->file->ha_external_lock(thd,lock_type)))
{
print_lock_error(error, (*tables)->file->table_type());
while (--i)
{
tables--;
(*tables)->file->ha_external_lock(thd, F_UNLCK);
(*tables)->current_lock=F_UNLCK;
}
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(sql_lock);
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;
if ((sql_lock= get_lock_data(thd, table, count, GET_LOCK_UNLOCK)))
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_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);
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_WRITE)
{
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= (uint) (table - sql_lock->table);
tbl->lock_data_start= found;
found+= tbl->lock_count;
table++;
}
DBUG_VOID_RETURN;
}
/**
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
*/
void mysql_lock_remove(THD *thd, MYSQL_LOCK *locked,TABLE *table)
{
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);
/* Unlock the table. */
mysql_unlock_some_tables(thd, &table, /* table count */ 1);
/* 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, bool upgrade_lock)
{
MYSQL_LOCK *locked;
DBUG_ENTER("mysql_lock_abort");
if ((locked= get_lock_data(thd, &table, 1, GET_LOCK_UNLOCK)))
{
for (uint i=0; i < locked->lock_count; i++)
thr_abort_locks(locked->locks[i]->lock, upgrade_lock);
my_free(locked);
}
DBUG_VOID_RETURN;
}
/**
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)))
{
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;
}
my_free(locked);
}
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(a);
my_free(b);
thr_lock_merge_status(sql_lock->locks, sql_lock->lock_count);
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 ((error=(*table)->file->ha_external_lock(thd, F_UNLCK)))
{
error_code=error;
print_lock_error(error_code, (*table)->file->table_type());
}
}
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
*/
static MYSQL_LOCK *get_lock_data(THD *thd, TABLE **table_ptr, uint count,
uint flags)
{
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");
DBUG_ASSERT((flags == GET_LOCK_UNLOCK) || (flags == GET_LOCK_STORE_LOCKS));
DBUG_PRINT("info", ("count %d", count));
for (i=tables=lock_count=0 ; i < count ; i++)
{
TABLE *t= table_ptr[i];
if (t->s->tmp_table != NON_TRANSACTIONAL_TMP_TABLE)
{
tables+= t->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;
for (i=0 ; i < count ; i++)
{
TABLE *table;
enum thr_lock_type lock_type;
THR_LOCK_DATA **org_locks = locks;
if ((table=table_ptr[i])->s->tmp_table == NON_TRANSACTIONAL_TMP_TABLE)
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_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;
}
/*
We do not use 'tables', 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= locks - locks_buf;
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.
This function cannot be called while holding LOCK_open mutex.
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(ER_LOCK_OR_ACTIVE_TRANSACTION), MYF(0));
return TRUE;
}
global_request.init(MDL_key::GLOBAL, "", "", MDL_INTENTION_EXCLUSIVE);
mdl_request.init(MDL_key::SCHEMA, db, "", MDL_EXCLUSIVE);
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 the stored routine name.
@param thd Thread handle.
@param is_function Stored routine type (only functions or procedures
are name-locked.
@param db The schema the routine belongs to.
@param name Routine name.
This function assumes that no metadata locks were acquired
before calling it. Additionally, it cannot be called while
holding LOCK_open mutex. Both these invariants are 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_routine_name(THD *thd, bool is_function,
const char *db, const char *name)
{
MDL_key::enum_mdl_namespace mdl_type= (is_function ?
MDL_key::FUNCTION :
MDL_key::PROCEDURE);
MDL_request_list mdl_requests;
MDL_request global_request;
MDL_request schema_request;
MDL_request mdl_request;
if (thd->locked_tables_mode)
{
my_message(ER_LOCK_OR_ACTIVE_TRANSACTION,
ER(ER_LOCK_OR_ACTIVE_TRANSACTION), MYF(0));
return TRUE;
}
DBUG_ASSERT(name);
DEBUG_SYNC(thd, "before_wait_locked_pname");
global_request.init(MDL_key::GLOBAL, "", "", MDL_INTENTION_EXCLUSIVE);
schema_request.init(MDL_key::SCHEMA, db, "", MDL_INTENTION_EXCLUSIVE);
mdl_request.init(mdl_type, db, name, MDL_EXCLUSIVE);
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;
}
static void print_lock_error(int error, const char *table)
{
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;
case HA_ERR_LOCK_DEADLOCK:
textno=ER_LOCK_DEADLOCK;
break;
case HA_ERR_WRONG_COMMAND:
textno=ER_ILLEGAL_HA;
break;
default:
textno=ER_CANT_LOCK;
break;
}
if ( textno == ER_ILLEGAL_HA )
my_error(textno, MYF(ME_BELL+ME_OLDWIN+ME_WAITTANG), table);
else
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.
access to them is protected with a mutex LOCK_global_read_lock
(XXX: one should never take LOCK_open if LOCK_global_read_lock is
taken, otherwise a deadlock may occur. Other mutexes could be a
problem too - grep the code for global_read_lock if you want to use
any other mutex here) Also one must not hold LOCK_open when calling
wait_if_global_read_lock(). When the thread with the global read lock
tries to close its tables, it needs to take LOCK_open in
close_thread_table().
How blocking of threads by global read lock is achieved: that's
advisory. Any piece of code which should be blocked by global read lock must
be designed like this:
- call to wait_if_global_read_lock(). When this returns 0, no global read
lock is owned; if argument abort_on_refresh was 0, none can be obtained.
- job
- if abort_on_refresh was 0, call to start_waiting_global_read_lock() to
allow other threads to get the global read lock. I.e. removal of the
protection.
(Note: it's a bit like an implementation of rwlock).
[ I am sorry to mention some SQL syntaxes below I know I shouldn't but found
no better descriptive way ]
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.
****************************************************************************/
volatile uint global_read_lock=0;
volatile uint global_read_lock_blocks_commit=0;
static volatile uint protect_against_global_read_lock=0;
static volatile uint waiting_for_read_lock=0;
/**
Take global read lock, wait if there is protection against lock.
If the global read lock is already taken by this thread, then nothing is done.
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_request mdl_request;
const char *old_message;
const char *new_message= "Waiting to get readlock";
(void) mysql_mutex_lock(&LOCK_global_read_lock);
#if defined(ENABLED_DEBUG_SYNC)
/*
The below sync point fires if we have to wait for
protect_against_global_read_lock.
WARNING: Beware to use WAIT_FOR with this sync point. We hold
LOCK_global_read_lock here.
Call the sync point before calling enter_cond() as it does use
enter_cond() and exit_cond() itself if a WAIT_FOR action is
executed in spite of the above warning.
Pre-set proc_info so that it is available immediately after the
sync point sends a SIGNAL. This makes tests more reliable.
*/
if (protect_against_global_read_lock)
{
thd_proc_info(thd, new_message);
DEBUG_SYNC(thd, "wait_lock_global_read_lock");
}
#endif /* defined(ENABLED_DEBUG_SYNC) */
old_message=thd->enter_cond(&COND_global_read_lock, &LOCK_global_read_lock,
new_message);
DBUG_PRINT("info",
("waiting_for: %d protect_against: %d",
waiting_for_read_lock, protect_against_global_read_lock));
waiting_for_read_lock++;
while (protect_against_global_read_lock && !thd->killed)
mysql_cond_wait(&COND_global_read_lock, &LOCK_global_read_lock);
waiting_for_read_lock--;
if (thd->killed)
{
thd->exit_cond(old_message);
DBUG_RETURN(1);
}
m_state= GRL_ACQUIRED;
global_read_lock++;
thd->exit_cond(old_message); // this unlocks LOCK_global_read_lock
/*
When we perform FLUSH TABLES or ALTER TABLE under LOCK TABLES,
tables being reopened are protected only by meta-data locks at
some point. To avoid sneaking in with our global read lock at
this moment we have to take global shared meta data lock.
TODO: We should change this code to acquire global shared metadata
lock before acquiring global read lock. But in order to do
this we have to get rid of all those places in which
wait_if_global_read_lock() is called before acquiring
metadata locks first. Also long-term we should get rid of
redundancy between metadata locks, global read lock and DDL
blocker (see WL#4399 and WL#4400).
*/
DBUG_ASSERT(! thd->mdl_context.is_lock_owner(MDL_key::GLOBAL, "", "",
MDL_SHARED));
mdl_request.init(MDL_key::GLOBAL, "", "", MDL_SHARED);
if (thd->mdl_context.acquire_lock(&mdl_request,
thd->variables.lock_wait_timeout))
{
/* Our thread was killed -- return back to initial state. */
mysql_mutex_lock(&LOCK_global_read_lock);
if (!(--global_read_lock))
{
DBUG_PRINT("signal", ("Broadcasting COND_global_read_lock"));
mysql_cond_broadcast(&COND_global_read_lock);
}
mysql_mutex_unlock(&LOCK_global_read_lock);
m_state= GRL_NONE;
DBUG_RETURN(1);
}
thd->mdl_context.move_ticket_after_trans_sentinel(mdl_request.ticket);
m_mdl_global_shared_lock= mdl_request.ticket;
}
/*
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)
{
uint tmp;
DBUG_ENTER("unlock_global_read_lock");
DBUG_PRINT("info",
("global_read_lock: %u global_read_lock_blocks_commit: %u",
global_read_lock, global_read_lock_blocks_commit));
DBUG_ASSERT(m_mdl_global_shared_lock && m_state);
thd->mdl_context.release_lock(m_mdl_global_shared_lock);
m_mdl_global_shared_lock= NULL;
mysql_mutex_lock(&LOCK_global_read_lock);
tmp= --global_read_lock;
if (m_state == GRL_ACQUIRED_AND_BLOCKS_COMMIT)
--global_read_lock_blocks_commit;
mysql_mutex_unlock(&LOCK_global_read_lock);
/* Send the signal outside the mutex to avoid a context switch */
if (!tmp)
{
DBUG_PRINT("signal", ("Broadcasting COND_global_read_lock"));
mysql_cond_broadcast(&COND_global_read_lock);
}
m_state= GRL_NONE;
DBUG_VOID_RETURN;
}
/**
Wait if the global read lock is set, and optionally seek protection against
global read lock.
See also "Handling of global read locks" above.
@param thd Reference to thread.
@param abort_on_refresh If True, abort waiting if a refresh occurs,
do NOT seek protection against GRL.
If False, wait until the GRL is released and seek
protection against GRL.
@param is_not_commit If False, called from a commit operation,
wait only if commit blocking is also enabled.
@retval False Success, protection against global read lock is set
(if !abort_on_refresh)
@retval True Failure, wait was aborted or thread was killed.
*/
#define must_wait (global_read_lock && \
(is_not_commit || \
global_read_lock_blocks_commit))
bool Global_read_lock::
wait_if_global_read_lock(THD *thd, bool abort_on_refresh,
bool is_not_commit)
{
const char *UNINIT_VAR(old_message);
bool result= 0, need_exit_cond;
DBUG_ENTER("wait_if_global_read_lock");
/*
If we already have protection against global read lock,
just increment the counter.
*/
if (unlikely(m_protection_count > 0))
{
if (!abort_on_refresh)
m_protection_count++;
DBUG_RETURN(FALSE);
}
/*
Assert that we do not own LOCK_open. If we would own it, other
threads could not close their tables. This would make a pretty
deadlock.
*/
mysql_mutex_assert_not_owner(&LOCK_open);
mysql_mutex_lock(&LOCK_global_read_lock);
if ((need_exit_cond= must_wait))
{
if (m_state) // This thread had the read locks
{
if (is_not_commit)
my_message(ER_CANT_UPDATE_WITH_READLOCK,
ER(ER_CANT_UPDATE_WITH_READLOCK), MYF(0));
mysql_mutex_unlock(&LOCK_global_read_lock);
/*
We allow FLUSHer to COMMIT; we assume FLUSHer knows what it does.
This allowance is needed to not break existing versions of innobackup
which do a BEGIN; INSERT; FLUSH TABLES WITH READ LOCK; COMMIT.
*/
DBUG_RETURN(is_not_commit);
}
old_message=thd->enter_cond(&COND_global_read_lock, &LOCK_global_read_lock,
"Waiting for release of readlock");
while (must_wait && ! thd->killed &&
(!abort_on_refresh || !thd->open_tables ||
thd->open_tables->s->version == refresh_version))
{
DBUG_PRINT("signal", ("Waiting for COND_global_read_lock"));
mysql_cond_wait(&COND_global_read_lock, &LOCK_global_read_lock);
DBUG_PRINT("signal", ("Got COND_global_read_lock"));
}
if (thd->killed)
result=1;
}
if (!abort_on_refresh && !result)
{
m_protection_count++;
protect_against_global_read_lock++;
DBUG_PRINT("sql_lock", ("protect_against_global_read_lock incr: %u",
protect_against_global_read_lock));
}
/*
The following is only true in case of a global read locks (which is rare)
and if old_message is set
*/
if (unlikely(need_exit_cond))
thd->exit_cond(old_message); // this unlocks LOCK_global_read_lock
else
mysql_mutex_unlock(&LOCK_global_read_lock);
DBUG_RETURN(result);
}
/**
Release protection against global read lock and restart
global read lock waiters.
Should only be called if we have protection against global read lock.
See also "Handling of global read locks" above.
@param thd Reference to thread.
*/
void Global_read_lock::start_waiting_global_read_lock(THD *thd)
{
bool tmp;
DBUG_ENTER("start_waiting_global_read_lock");
/*
Ignore request if we do not have protection against global read lock.
(Note that this is a violation of the interface contract, hence the assert).
*/
DBUG_ASSERT(m_protection_count > 0);
if (unlikely(m_protection_count == 0))
DBUG_VOID_RETURN;
/* Decrement local read lock protection counter, return if we still have it */
if (unlikely(--m_protection_count > 0))
DBUG_VOID_RETURN;
if (unlikely(m_state))
DBUG_VOID_RETURN;
mysql_mutex_lock(&LOCK_global_read_lock);
DBUG_ASSERT(protect_against_global_read_lock);
tmp= (!--protect_against_global_read_lock &&
(waiting_for_read_lock || global_read_lock_blocks_commit));
mysql_mutex_unlock(&LOCK_global_read_lock);
if (tmp)
mysql_cond_broadcast(&COND_global_read_lock);
DBUG_VOID_RETURN;
}
/**
Make global read lock also block commits.
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)
{
bool error;
const char *old_message;
DBUG_ENTER("make_global_read_lock_block_commit");
/*
If we didn't succeed lock_global_read_lock(), or if we already suceeded
make_global_read_lock_block_commit(), do nothing.
*/
if (m_state != GRL_ACQUIRED)
DBUG_RETURN(0);
mysql_mutex_lock(&LOCK_global_read_lock);
/* increment this BEFORE waiting on cond (otherwise race cond) */
global_read_lock_blocks_commit++;
/* For testing we set up some blocking, to see if we can be killed */
DBUG_EXECUTE_IF("make_global_read_lock_block_commit_loop",
protect_against_global_read_lock++;);
old_message= thd->enter_cond(&COND_global_read_lock, &LOCK_global_read_lock,
"Waiting for all running commits to finish");
while (protect_against_global_read_lock && !thd->killed)
mysql_cond_wait(&COND_global_read_lock, &LOCK_global_read_lock);
DBUG_EXECUTE_IF("make_global_read_lock_block_commit_loop",
protect_against_global_read_lock--;);
if ((error= test(thd->killed)))
global_read_lock_blocks_commit--; // undo what we did
else
m_state= GRL_ACQUIRED_AND_BLOCKS_COMMIT;
thd->exit_cond(old_message); // this unlocks LOCK_global_read_lock
DBUG_RETURN(error);
}
/**
Broadcast COND_global_read_lock.
TODO/FIXME: Dmitry thinks that we broadcast on COND_global_read_lock
when old instance of table is closed to avoid races
between incrementing refresh_version and
wait_if_global_read_lock(thd, TRUE, FALSE) call.
Once global read lock implementation starts using MDL
infrastructure this will became unnecessary and should
be removed.
*/
void broadcast_refresh(void)
{
mysql_cond_broadcast(&COND_global_read_lock);
}
/**
@} (end of group Locking)
*/
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