You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
244 lines
8.0 KiB
244 lines
8.0 KiB
2 years ago
|
<?php
|
||
|
|
// This file is part of Moodle - http://moodle.org/
|
||
|
|
//
|
||
|
|
// Moodle 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 3 of the License, or
|
||
|
|
// (at your option) any later version.
|
||
|
|
//
|
||
|
|
// Moodle 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 Moodle. If not, see <http://www.gnu.org/licenses/>.
|
||
|
|
|
||
|
|
/**
|
||
|
|
* Postgres advisory locking factory.
|
||
|
|
*
|
||
|
|
* @package core
|
||
|
|
* @category lock
|
||
|
|
* @copyright Damyon Wiese 2013
|
||
|
|
* @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
|
||
|
|
*/
|
||
|
|
|
||
|
|
namespace core\lock;
|
||
|
|
|
||
|
|
defined('MOODLE_INTERNAL') || die();
|
||
|
|
|
||
|
|
/**
|
||
|
|
* 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 by storing the strings in the lock_db table and using the auto-id returned. There is a static cache for
|
||
|
|
* id's in this function.
|
||
|
|
*
|
||
|
|
* @package core
|
||
|
|
* @category lock
|
||
|
|
* @copyright Damyon Wiese 2013
|
||
|
|
* @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
|
||
|
|
*/
|
||
|
|
class postgres_lock_factory implements lock_factory {
|
||
|
|
|
||
|
|
/** @var int $dblockid - used as a namespace for these types of locks (separate from session locks) */
|
||
|
|
protected $dblockid = -1;
|
||
|
|
|
||
|
|
/** @var array $lockidcache - static cache for string -> int conversions required for pg advisory locks. */
|
||
|
|
protected static $lockidcache = array();
|
||
|
|
|
||
|
|
/** @var \moodle_database $db Hold a reference to the global $DB */
|
||
|
|
protected $db;
|
||
|
|
|
||
|
|
/** @var string $type Used to prefix lock keys */
|
||
|
|
protected $type;
|
||
|
|
|
||
|
|
/** @var array $openlocks - List of held locks - used by auto-release */
|
||
|
|
protected $openlocks = array();
|
||
|
|
|
||
|
|
/**
|
||
|
|
* Calculate a unique instance id based on the database name and prefix.
|
||
|
|
* @return int.
|
||
|
|
*/
|
||
|
|
protected function get_unique_db_instance_id() {
|
||
|
|
global $CFG;
|
||
|
|
|
||
|
|
$strkey = $CFG->dbname . ':' . $CFG->prefix;
|
||
|
|
$intkey = crc32($strkey);
|
||
|
|
// Normalize between 64 bit unsigned int and 32 bit signed ints. Php could return either from crc32.
|
||
|
|
if (PHP_INT_SIZE == 8) {
|
||
|
|
if ($intkey > 0x7FFFFFFF) {
|
||
|
|
$intkey -= 0x100000000;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
return $intkey;
|
||
|
|
}
|
||
|
|
|
||
|
|
/**
|
||
|
|
* Almighty constructor.
|
||
|
|
* @param string $type - Used to prefix lock keys.
|
||
|
|
*/
|
||
|
|
public function __construct($type) {
|
||
|
|
global $DB;
|
||
|
|
|
||
|
|
$this->type = $type;
|
||
|
|
$this->dblockid = $this->get_unique_db_instance_id();
|
||
|
|
// Save a reference to the global $DB so it will not be released while we still have open locks.
|
||
|
|
$this->db = $DB;
|
||
|
|
|
||
|
|
\core_shutdown_manager::register_function(array($this, 'auto_release'));
|
||
|
|
}
|
||
|
|
|
||
|
|
/**
|
||
|
|
* Is available.
|
||
|
|
* @return boolean - True if this lock type is available in this environment.
|
||
|
|
*/
|
||
|
|
public function is_available() {
|
||
|
|
return $this->db->get_dbfamily() === 'postgres';
|
||
|
|
}
|
||
|
|
|
||
|
|
/**
|
||
|
|
* Return information about the blocking behaviour of the lock type on this platform.
|
||
|
|
* @return boolean - Defer to the DB driver.
|
||
|
|
*/
|
||
|
|
public function supports_timeout() {
|
||
|
|
return true;
|
||
|
|
}
|
||
|
|
|
||
|
|
/**
|
||
|
|
* Will this lock type will be automatically released when a process ends.
|
||
|
|
*
|
||
|
|
* @return boolean - Via shutdown handler.
|
||
|
|
*/
|
||
|
|
public function supports_auto_release() {
|
||
|
|
return true;
|
||
|
|
}
|
||
|
|
|
||
|
|
/**
|
||
|
|
* Multiple locks for the same resource can be held by a single process.
|
||
|
|
* @return boolean - Defer to the DB driver.
|
||
|
|
*/
|
||
|
|
public function supports_recursion() {
|
||
|
|
return true;
|
||
|
|
}
|
||
|
|
|
||
|
|
/**
|
||
|
|
* This function generates the unique index for a specific lock key.
|
||
|
|
* Once an index is assigned to a key, it never changes - so this is
|
||
|
|
* statically cached.
|
||
|
|
*
|
||
|
|
* @param string $key
|
||
|
|
* @return int
|
||
|
|
* @throws \moodle_exception
|
||
|
|
*/
|
||
|
|
protected function get_index_from_key($key) {
|
||
|
|
if (isset(self::$lockidcache[$key])) {
|
||
|
|
return self::$lockidcache[$key];
|
||
|
|
}
|
||
|
|
|
||
|
|
$index = 0;
|
||
|
|
$record = $this->db->get_record('lock_db', array('resourcekey' => $key));
|
||
|
|
if ($record) {
|
||
|
|
$index = $record->id;
|
||
|
|
}
|
||
|
|
|
||
|
|
if (!$index) {
|
||
|
|
$record = new \stdClass();
|
||
|
|
$record->resourcekey = $key;
|
||
|
|
try {
|
||
|
|
$index = $this->db->insert_record('lock_db', $record);
|
||
|
|
} catch (\dml_exception $de) {
|
||
|
|
// Race condition - never mind - now the value is guaranteed to exist.
|
||
|
|
$record = $this->db->get_record('lock_db', array('resourcekey' => $key));
|
||
|
|
if ($record) {
|
||
|
|
$index = $record->id;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
if (!$index) {
|
||
|
|
throw new \moodle_exception('Could not generate unique index for key');
|
||
|
|
}
|
||
|
|
|
||
|
|
self::$lockidcache[$key] = $index;
|
||
|
|
return $index;
|
||
|
|
}
|
||
|
|
|
||
|
|
/**
|
||
|
|
* Create and get a lock
|
||
|
|
* @param string $resource - The identifier for the lock. Should use frankenstyle prefix.
|
||
|
|
* @param int $timeout - The number of seconds to wait for a lock before giving up.
|
||
|
|
* @param int $maxlifetime - Unused by this lock type.
|
||
|
|
* @return boolean - true if a lock was obtained.
|
||
|
|
*/
|
||
|
|
public function get_lock($resource, $timeout, $maxlifetime = 86400) {
|
||
|
|
$giveuptime = time() + $timeout;
|
||
|
|
|
||
|
|
$token = $this->get_index_from_key($resource);
|
||
|
|
|
||
|
|
$params = array('locktype' => $this->dblockid,
|
||
|
|
'token' => $token);
|
||
|
|
|
||
|
|
$locked = false;
|
||
|
|
|
||
|
|
do {
|
||
|
|
$result = $this->db->get_record_sql('SELECT pg_try_advisory_lock(:locktype, :token) AS locked', $params);
|
||
|
|
$locked = $result->locked === 't';
|
||
|
|
if (!$locked && $timeout > 0) {
|
||
|
|
usleep(rand(10000, 250000)); // Sleep between 10 and 250 milliseconds.
|
||
|
|
}
|
||
|
|
// Try until the giveup time.
|
||
|
|
} while (!$locked && time() < $giveuptime);
|
||
|
|
|
||
|
|
if ($locked) {
|
||
|
|
$this->openlocks[$token] = 1;
|
||
|
|
return new lock($token, $this);
|
||
|
|
}
|
||
|
|
return false;
|
||
|
|
}
|
||
|
|
|
||
|
|
/**
|
||
|
|
* Release a lock that was previously obtained with @lock.
|
||
|
|
* @param lock $lock - a lock obtained from this factory.
|
||
|
|
* @return boolean - true if the lock is no longer held (including if it was never held).
|
||
|
|
*/
|
||
|
|
public function release_lock(lock $lock) {
|
||
|
|
$params = array('locktype' => $this->dblockid,
|
||
|
|
'token' => $lock->get_key());
|
||
|
|
$result = $this->db->get_record_sql('SELECT pg_advisory_unlock(:locktype, :token) AS unlocked', $params);
|
||
|
|
$result = $result->unlocked === 't';
|
||
|
|
if ($result) {
|
||
|
|
unset($this->openlocks[$lock->get_key()]);
|
||
|
|
}
|
||
|
|
return $result;
|
||
|
|
}
|
||
|
|
|
||
|
|
/**
|
||
|
|
* Extend a lock that was previously obtained with @lock.
|
||
|
|
* @param lock $lock - a lock obtained from this factory.
|
||
|
|
* @param int $maxlifetime - the new lifetime for the lock (in seconds).
|
||
|
|
* @return boolean - true if the lock was extended.
|
||
|
|
*/
|
||
|
|
public function extend_lock(lock $lock, $maxlifetime = 86400) {
|
||
|
|
// Not supported by this factory.
|
||
|
|
return false;
|
||
|
|
}
|
||
|
|
|
||
|
|
/**
|
||
|
|
* Auto release any open locks on shutdown.
|
||
|
|
* This is required, because we may be using persistent DB connections.
|
||
|
|
*/
|
||
|
|
public function auto_release() {
|
||
|
|
// Called from the shutdown handler. Must release all open locks.
|
||
|
|
foreach ($this->openlocks as $key => $unused) {
|
||
|
|
$lock = new lock($key, $this);
|
||
|
|
$lock->release();
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
}
|