MDL_context Class Reference

#include <mdl.h>

Collaboration diagram for MDL_context:

Public Types
typedef I_P_List< MDL_ticket, I_P_List_adapter< MDL_ticket,&MDL_ticket::next_in_context,&MDL_ticket::prev_in_context > >	Ticket_list
typedef Ticket_list::Iterator	Ticket_iterator

Public Member Functions
	MDL_context ()
void	destroy ()
bool	try_acquire_lock (MDL_request *mdl_request)
bool	acquire_lock (MDL_request *mdl_request, ulong lock_wait_timeout)
bool	acquire_locks (MDL_request_list *requests, ulong lock_wait_timeout)
bool	upgrade_shared_lock (MDL_ticket *mdl_ticket, enum_mdl_type new_type, ulong lock_wait_timeout)
bool	clone_ticket (MDL_request *mdl_request)
void	release_all_locks_for_name (MDL_ticket *ticket)
void	release_lock (MDL_ticket *ticket)
bool	is_lock_owner (MDL_key::enum_mdl_namespace mdl_namespace, const char *db, const char *name, enum_mdl_type mdl_type)
bool	has_lock (const MDL_savepoint &mdl_savepoint, MDL_ticket *mdl_ticket)
bool	has_locks () const
MDL_savepoint	mdl_savepoint ()
void	set_explicit_duration_for_all_locks ()
void	set_transaction_duration_for_all_locks ()
void	set_lock_duration (MDL_ticket *mdl_ticket, enum_mdl_duration duration)
void	release_statement_locks ()
void	release_transactional_locks ()
void	rollback_to_savepoint (const MDL_savepoint &mdl_savepoint)
MDL_context_owner *	get_owner ()
uint	get_deadlock_weight () const
void	init (MDL_context_owner *arg)
void	set_needs_thr_lock_abort (bool needs_thr_lock_abort)
bool	get_needs_thr_lock_abort () const
void	find_deadlock ()
bool	visit_subgraph (MDL_wait_for_graph_visitor *dvisitor)
void	will_wait_for (MDL_wait_for_subgraph *waiting_for_arg)
void	done_waiting_for ()
void	lock_deadlock_victim ()
void	unlock_deadlock_victim ()

Public Attributes
MDL_wait	m_wait

Detailed Description

Context of the owner of metadata locks. I.e. each server connection has such a context.

Definition at line 727 of file mdl.h.

Constructor & Destructor Documentation

MDL_context::MDL_context

(

)

Initialize a metadata locking context.

This is to be called when a new server connection is created.

Definition at line 1057 of file mdl.cc.

Member Function Documentation

bool MDL_context::acquire_lock	(	MDL_request *	mdl_request,
		ulong	lock_wait_timeout
	)

Acquire one lock with waiting for conflicting locks to go away if needed.

Parameters

mdl_request	[in/out] Lock request object for lock to be acquired
lock_wait_timeout	[in] Seconds to wait before timeout.

Return values

FALSE	Success. MDL_request::ticket points to the ticket for the lock.
TRUE	Failure (Out of resources or waiting is aborted),

Definition at line 2163 of file mdl.cc.

Here is the call graph for this function:

bool MDL_context::acquire_locks	(	MDL_request_list *	mdl_requests,
		ulong	lock_wait_timeout
	)

Acquire exclusive locks. There must be no granted locks in the context.

This is a replacement of lock_table_names(). It is used in RENAME, DROP and other DDL SQL statements.

Parameters

mdl_requests	List of requests for locks to be acquired.
lock_wait_timeout	Seconds to wait before timeout.

Note

The list of requests should not contain non-exclusive lock requests. There should not be any acquired locks in the context.

Assumes that one already owns scoped intention exclusive lock.

Return values

FALSE	Success
TRUE	Failure

Definition at line 2310 of file mdl.cc.

bool MDL_context::clone_ticket

(

MDL_request *

mdl_request

)

Create a copy of a granted ticket. This is used to make sure that HANDLER ticket is never shared with a ticket that belongs to a transaction, so that when we HANDLER CLOSE, we don't release a transactional ticket, and vice versa – when we COMMIT, we don't mistakenly release a ticket for an open HANDLER.

Return values

TRUE	Out of memory.
FALSE	Success.

Definition at line 2051 of file mdl.cc.

Here is the call graph for this function:

void MDL_context::destroy

(

)

Destroy metadata locking context.

Assumes and asserts that there are no active or pending locks associated with this context at the time of the destruction.

Currently does nothing. Asserts that there are no pending or satisfied lock requests. The pending locks must be released prior to destruction. This is a new way to express the assertion that all tables are closed before a connection is destroyed.

Definition at line 1079 of file mdl.cc.

void MDL_context::done_waiting_for ( )

inline

Remove the wait-for edge from the graph after we're done waiting.

Definition at line 924 of file mdl.h.

Here is the caller graph for this function:

void MDL_context::find_deadlock

(

)

Try to find a deadlock. This function produces no errors.

Note

If during deadlock resolution context which performs deadlock detection is chosen as a victim it will be informed about the fact by setting VICTIM status to its wait slot.

Return values

TRUE	A deadlock is found.
FALSE	No deadlock found.

Definition at line 2638 of file mdl.cc.

Here is the call graph for this function:

Here is the caller graph for this function:

uint MDL_context::get_deadlock_weight ( ) const

inline

Precondition

Only valid if we started waiting for lock.

Definition at line 783 of file mdl.h.

bool MDL_context::has_lock	(	const MDL_savepoint &	mdl_savepoint,
		MDL_ticket *	mdl_ticket
	)

Does this savepoint have this lock?

Return values

TRUE	The ticket is older than the savepoint or is an LT, HA or GLR ticket. Thus it belongs to the savepoint or has explicit duration.
FALSE	The ticket is newer than the savepoint. and is not an LT, HA or GLR ticket.

Definition at line 2926 of file mdl.cc.

void MDL_context::init ( MDL_context_owner *  arg )

inline

Post signal to the context (and wake it up if necessary).

Return values

FALSE	- Success, signal was posted.
TRUE	- Failure, signal was not posted since context already has received some signal or closed signal slot.

Definition at line 793 of file mdl.h.

bool MDL_context::is_lock_owner	(	MDL_key::enum_mdl_namespace	mdl_namespace,
		const char *	db,
		const char *	name,
		enum_mdl_type	mdl_type
	)

Auxiliary function which allows to check if we have some kind of lock on a object. Returns TRUE if we have a lock of a given or stronger type.

Parameters

mdl_namespace	Id of object namespace
db	Name of the database
name	Name of the object
mdl_type	Lock type. Pass in the weakest type to find out if there is at least some lock.

Returns

TRUE if current context contains satisfied lock for the object, FALSE otherwise.

Definition at line 2839 of file mdl.cc.

Here is the call graph for this function:

void MDL_context::release_all_locks_for_name

(

MDL_ticket *

name

)

Release all explicit locks in the context which correspond to the same name/object as this lock request.

Parameters

ticket

One of the locks for the name/object for which all locks should be released.

Definition at line 2769 of file mdl.cc.

void MDL_context::release_lock

(

MDL_ticket *

ticket

)

Release lock with explicit duration.

Parameters

ticket

Ticket for lock to be released.

Definition at line 2720 of file mdl.cc.

void MDL_context::release_transactional_locks

(

)

Release locks acquired by normal statements (SELECT, UPDATE, DELETE, etc) in the course of a transaction. Do not release HANDLER locks, if there are any.

This method is used at the end of a transaction, in implementation of COMMIT (implicit or explicit) and ROLLBACK.

Definition at line 2899 of file mdl.cc.

void MDL_context::rollback_to_savepoint

(

const MDL_savepoint &

mdl_savepoint

)

Releases metadata locks that were acquired after a specific savepoint.

Note

Used to release tickets acquired during a savepoint unit.

It's safe to iterate and unlock any locks after taken after this savepoint because other statements that take other special locks cause a implicit commit (ie LOCK TABLES).

Definition at line 2878 of file mdl.cc.

void MDL_context::set_explicit_duration_for_all_locks

(

)

Set explicit duration for all locks in the context.

Definition at line 2977 of file mdl.cc.

void MDL_context::set_lock_duration	(	MDL_ticket *	mdl_ticket,
		enum_mdl_duration	duration
	)

Change lock duration for transactional lock.

Parameters

ticket	Ticket representing lock.
duration	Lock duration to be set.

Note

This method only supports changing duration of transactional lock to some other duration.

Definition at line 2959 of file mdl.cc.

void MDL_context::set_transaction_duration_for_all_locks

(

)

Set transactional duration for all locks in the context.

Definition at line 3017 of file mdl.cc.

bool MDL_context::try_acquire_lock

(

MDL_request *

mdl_request

)

Try to acquire one lock.

Unlike exclusive locks, shared locks are acquired one by one. This is interface is chosen to simplify introduction of the new locking API to the system. MDL_context::try_acquire_lock() is currently used from open_table(), and there we have only one table to work with.

This function may also be used to try to acquire an exclusive lock on a destination table, by ALTER TABLE ... RENAME.

Returns immediately without any side effect if encounters a lock conflict. Otherwise takes the lock.

FIXME: Compared to lock_table_name_if_not_cached() (from 5.1) it gives slightly more false negatives.

Parameters

mdl_request

[in/out] Lock request object for lock to be acquired

Return values

FALSE	Success. The lock may have not been acquired. Check the ticket, if it's NULL, a conflicting lock exists.
TRUE	Out of resources, an error has been reported.

Definition at line 1910 of file mdl.cc.

bool MDL_context::upgrade_shared_lock	(	MDL_ticket *	mdl_ticket,
		enum_mdl_type	new_type,
		ulong	lock_wait_timeout
	)

Upgrade a shared metadata lock.

Used in ALTER TABLE and CREATE TABLE.

Parameters

mdl_ticket	Lock to upgrade.
new_type	Lock type to upgrade to.
lock_wait_timeout	Seconds to wait before timeout.

Note

In case of failure to upgrade lock (e.g. because upgrader was killed) leaves lock in its original state (locked in shared mode).

There can be only one upgrader for a lock or we will have deadlock. This invariant is ensured by the fact that upgradeable locks SU, SNW and SNRW are not compatible with each other and themselves in case of ALTER TABLE operation. In case of CREATE TABLE operation there is chance of deadlock as 'S' is compatible with 'S'. But the deadlock is recovered by backoff and retry mechanism.

Return values

FALSE	Success
TRUE	Failure (thread was killed)

Definition at line 2385 of file mdl.cc.

Here is the call graph for this function:

bool MDL_context::visit_subgraph

(

MDL_wait_for_graph_visitor *

gvisitor

)

A fragment of recursive traversal of the wait-for graph of MDL contexts in the server in search for deadlocks. Assume this MDL context is a node in the wait-for graph, and direct the visitor to all adjacent nodes. As long as the starting node is remembered in the visitor, a deadlock is found when the same node is visited twice. One MDL context is connected to another in the wait-for graph if it waits on a resource that is held by the other context.

Return values

TRUE	A deadlock is found. A pointer to deadlock victim is saved in the visitor.
FALSE

Definition at line 2612 of file mdl.cc.

Here is the caller graph for this function:

void MDL_context::will_wait_for ( MDL_wait_for_subgraph *  waiting_for_arg )

inline

Inform the deadlock detector there is an edge in the wait-for graph.

Definition at line 916 of file mdl.h.

Here is the caller graph for this function:

Member Data Documentation

MDL_wait MDL_context::m_wait

If our request for a lock is scheduled, or aborted by the deadlock detector, the result is recorded in this class.

Definition at line 816 of file mdl.h.

---

The documentation for this class was generated from the following files:

• sql/mdl.h
• sql/mdl.cc