core\lock\postgres_lock_factory Class Reference

Postgres advisory locking factory. More...

Inheritance diagram for core\lock\postgres_lock_factory:

Public Member Functions
	__construct ($type)
	Almighty constructor.
	auto_release ()
	Auto release any open locks on shutdown.
	extend_lock (lock $lock, $maxlifetime=86400)
	Extend a lock that was previously obtained with @lock.
	get_lock ($resource, $timeout, $maxlifetime=86400)
	Create and get a lock.
	is_available ()
	Is available.
	release_lock (lock $lock)
	Release a lock that was previously obtained with @lock.
	supports_auto_release ()
	Will this lock type will be automatically released when a process ends.
	supports_recursion ()
	Multiple locks for the same resource can NOT be held by a single process.
	supports_timeout ()
	Return information about the blocking behaviour of the lock type on this platform.

Protected Member Functions
	get_index_from_key ($key)
	This function generates the unique index for a specific lock key using a sha1 prefix converted to decimal.
	get_unique_db_instance_id ()
	Calculate a unique instance id based on the database name and prefix.

Protected Attributes
moodle_database	$db
	$db Hold a reference to the global $DB
int	$dblockid = -1
	$dblockid - used as a namespace for these types of locks (separate from session locks)
array	$openlocks = array()
	$openlocks - List of held locks - used by auto-release
string	$type
	$type Used to prefix lock keys

Static Protected Attributes
static array	$lockidcache = array()
	$lockidcache - static cache for string -> int conversions required for pg advisory locks.

Detailed Description

Postgres advisory locking factory.

Postgres locking implementation using advisory locks. Some important points. Postgres has 2 different forms of lock functions, some accepting a single int, and some accepting 2 ints. This implementation uses the 2 int version so that it uses a separate namespace from the session locking. The second note, is because postgres uses integer keys for locks, we first need to map strings to a unique integer. This is done using a prefix of a sha1 hash converted to an integer.

Copyright

Damyon Wiese 2013

License

http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later

Constructor & Destructor Documentation

__construct()

core\lock\postgres_lock_factory::__construct

(

$type

)

Almighty constructor.

Parameters

string

$type

- Used to prefix lock keys.

Implements core\lock\lock_factory.

Member Function Documentation

auto_release()

core\lock\postgres_lock_factory::auto_release

(

)

Auto release any open locks on shutdown.

This is required, because we may be using persistent DB connections.

extend_lock()

core\lock\postgres_lock_factory::extend_lock	(	lock	$lock,
			$maxlifetime = 86400 )

Extend a lock that was previously obtained with @lock.

Deprecated

since Moodle 3.10.

Parameters

lock	$lock	- a lock obtained from this factory.
int	$maxlifetime	- the new lifetime for the lock (in seconds).

Return values

boolean

- true if the lock was extended.

Implements core\lock\lock_factory.

get_index_from_key()

core\lock\postgres_lock_factory::get_index_from_key ( $key )

protected

This function generates the unique index for a specific lock key using a sha1 prefix converted to decimal.

Parameters

string

$key

Return values

int

Exceptions

moodle_exception

get_lock()

core\lock\postgres_lock_factory::get_lock	(		$resource,
			$timeout,
			$maxlifetime = 86400 )

Create and get a lock.

Parameters

string	$resource	- The identifier for the lock. Should use frankenstyle prefix.
int	$timeout	- The number of seconds to wait for a lock before giving up.
int	$maxlifetime	- Unused by this lock type.

Return values

boolean

- true if a lock was obtained.

Implements core\lock\lock_factory.

get_unique_db_instance_id()

core\lock\postgres_lock_factory::get_unique_db_instance_id ( )

protected

Calculate a unique instance id based on the database name and prefix.

Return values

int.

is_available()

core\lock\postgres_lock_factory::is_available

(

)

Is available.

Return values

boolean

- True if this lock type is available in this environment.

Implements core\lock\lock_factory.

release_lock()

core\lock\postgres_lock_factory::release_lock

(

lock

$lock

)

Release a lock that was previously obtained with @lock.

Parameters

lock

$lock

- a lock obtained from this factory.

Return values

boolean

- true if the lock is no longer held (including if it was never held).

Implements core\lock\lock_factory.

supports_auto_release()

core\lock\postgres_lock_factory::supports_auto_release

(

)

Will this lock type will be automatically released when a process ends.

Return values

boolean

- Via shutdown handler.

Implements core\lock\lock_factory.

supports_recursion()

core\lock\postgres_lock_factory::supports_recursion

(

)

Multiple locks for the same resource can NOT be held by a single process.

Deprecated

since Moodle 3.10.

Return values

boolean

- false.

Implements core\lock\lock_factory.

supports_timeout()

core\lock\postgres_lock_factory::supports_timeout

(

)

Return information about the blocking behaviour of the lock type on this platform.

Return values

boolean

- Defer to the DB driver.

Implements core\lock\lock_factory.

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

• lib/classes/lock/postgres_lock_factory.php