Current Path : C:/xampp/htdocs/moodle/lib/classes/lock/ |
Current File : C:/xampp/htdocs/moodle/lib/classes/lock/postgres_lock_factory.php |
<?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 * using a prefix of a sha1 hash converted to an integer. * * @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 using * a sha1 prefix converted to decimal. * * @param string $key * @return int * @throws \moodle_exception */ protected function get_index_from_key($key) { // A prefix of 7 hex chars is chosen as fffffff is the largest hex code // which when converted to decimal (268435455) fits inside a 4 byte int // which is the second param to pg_try_advisory_lock(). $hash = substr(sha1($key), 0, 7); $index = hexdec($hash); 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 = $this->get_index_from_key($this->type . '_' . $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(); } } }