Locking

Defines
#define	GET_LOCK_UNLOCK   1
#define	GET_LOCK_STORE_LOCKS   2
Functions
MYSQL_LOCK *	mysql_lock_tables (THD *thd, TABLE **tables, uint count, uint flags)
void	mysql_unlock_tables (THD *thd, MYSQL_LOCK *sql_lock)
void	mysql_unlock_some_tables (THD *thd, TABLE **table, uint count)
void	mysql_unlock_read_tables (THD *thd, MYSQL_LOCK *sql_lock)
void	mysql_lock_remove (THD *thd, MYSQL_LOCK *locked, TABLE *table)
void	mysql_lock_abort (THD *thd, TABLE *table, bool upgrade_lock)
bool	mysql_lock_abort_for_thread (THD *thd, TABLE *table)
MYSQL_LOCK *	mysql_lock_merge (MYSQL_LOCK *a, MYSQL_LOCK *b)
bool	lock_schema_name (THD *thd, const char *db)
bool	lock_object_name (THD *thd, MDL_key::enum_mdl_namespace mdl_type, const char *db, const char *name)
Variables
HASH	open_cache

---

Function Documentation

bool lock_object_name	(	THD *	thd,
		MDL_key::enum_mdl_namespace	mdl_type,
		const char *	db,
		const char *	name
	)

Obtain an exclusive metadata lock on an object name.

Parameters:

thd	Thread handle.
mdl_type	Object type (currently functions, procedures and events can be name-locked).
db	The schema the object belongs to.
name	Object name in the schema.

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.

Return values:

FALSE	Success.
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
	)

Obtain an exclusive metadata lock on a schema name.

Parameters:

thd	Thread handle.
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.

Return values:

FALSE	Success.
TRUE	Failure: we're in LOCK TABLES mode, or out of memory, or this connection was killed.

void mysql_lock_abort	(	THD *	thd,
		TABLE *	table,
		bool	upgrade_lock
	)

Abort all other threads waiting to get lock in table.

bool mysql_lock_abort_for_thread	(	THD *	thd,
		TABLE *	table
	)

Abort one thread / table combination.

Parameters:

thd	Thread handler
table	Table that should be removed from lock queue

Return values:

0	Table was not locked by another thread
1	Table was locked by at least one other thread

void mysql_lock_remove	(	THD *	thd,
		MYSQL_LOCK *	locked,
		TABLE *	table
	)

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.

Parameters:

thd	thread context
locked	list of locked tables
table	the table to unlock

MYSQL_LOCK* mysql_lock_tables	(	THD *	thd,
		TABLE **	tables,
		uint	count,
		uint	flags
	)

Lock tables.

Parameters:

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_ONLY Ignore SET GLOBAL READ_ONLY MYSQL_LOCK_IGNORE_TIMEOUT Use maximum timeout value.

Return values:

A	lock structure pointer on success.
NULL	if an error or if wait on a lock was killed.

void mysql_unlock_read_tables	(	THD *	thd,
		MYSQL_LOCK *	sql_lock
	)

unlock all tables locked for read.

void mysql_unlock_some_tables	(	THD *	thd,
		TABLE **	table,
		uint	count
	)

Unlock some of the tables locked by mysql_lock_tables.

This will work even if get_lock_data fails (next unlock will free all)