Proyectos de Subversion Moodle

<?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/>.

namespace core\lock;

use coding_exception;

/**

 * MySQL / MariaDB locking factory.

 *

 * @package   core

 * @category  lock

 * @copyright Brendan Heywood <brendan@catalyst-au.net>

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

 */

class mysql_lock_factory implements lock_factory {

    /** @var string $dbprefix - used as a namespace for these types of locks */

    protected $dbprefix = '';

    /** @var \moodle_database $db Hold a reference to the global $DB */

    protected $db;

    /** @var array $openlocks - List of held locks - used by auto-release */

    protected $openlocks = [];

    /**

     * Return a unique prefix based on the database name and prefix.

     * @param string $type - Used to prefix lock keys.

     * @return string

     */

    protected function get_unique_db_prefix($type) {

        global $CFG;

        $prefix = $CFG->dbname . ':';

        if (isset($CFG->prefix)) {

            $prefix .= $CFG->prefix;

        }

        $prefix .= '_' . $type . '_';

        return $prefix;

    }

    /**

     * Lock constructor.

     * @param string $type - Used to prefix lock keys.

     */

    public function __construct($type) {

        global $DB;

        $this->dbprefix = $this->get_unique_db_prefix($type);

        // 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([$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() === 'mysql';

    }

    /**

     * 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;

    }

    /**

     * @deprecated since Moodle 3.10.

     */

    public function supports_recursion() {

        throw new coding_exception('The function supports_recursion() has been removed, please do not use it anymore.');

    }

    /**

     * 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) {

        // We sha1 to avoid long key names hitting the mysql str limit.

        $resourcekey = sha1($this->dbprefix . $resource);

        // Even though some versions of MySQL and MariaDB can support stacked locks

        // just never stack them and always fail fast.

        if (isset($this->openlocks[$resourcekey])) {

            return false;

        }

        $params = [

            'resourcekey' => $resourcekey,

            'timeout' => $timeout

        ];

        $result = $this->db->get_record_sql('SELECT GET_LOCK(:resourcekey, :timeout) AS locked', $params);

        $locked = $result->locked == 1;

        if ($locked) {

            $this->openlocks[$resourcekey] = 1;

            return new lock($resourcekey, $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 = [

            'resourcekey' => $lock->get_key()

        ];

        $result = $this->db->get_record_sql('SELECT RELEASE_LOCK(:resourcekey) AS unlocked', $params);

        $result = $result->unlocked == 1;

        if ($result) {

            unset($this->openlocks[$lock->get_key()]);

        }

        return $result;

    }

    /**

     * @deprecated since Moodle 3.10.

     */

    public function extend_lock() {

        throw new coding_exception('The function extend_lock() has been removed, please do not use it anymore.');

    }

    /**

     * 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();

        }

    }

}