lib/classes/lock/mysql_lock_factory.php

   1 <?php
   2 // This file is part of Moodle - http://moodle.org/
   3 //
   4 // Moodle is free software: you can redistribute it and/or modify
   5 // it under the terms of the GNU General Public License as published by
   6 // the Free Software Foundation, either version 3 of the License, or
   7 // (at your option) any later version.
   8 //
   9 // Moodle is distributed in the hope that it will be useful,
  10 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12 // GNU General Public License for more details.
  13 //
  14 // You should have received a copy of the GNU General Public License
  15 // along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
  16
  17 namespace core\lock;
  18
  19 use coding_exception;
  20
  21 /**
  22  * MySQL / MariaDB locking factory.
  23  *
  24  * @package   core
  25  * @category  lock
  26  * @copyright Brendan Heywood <brendan@catalyst-au.net>
  27  * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  28  */
  29 class mysql_lock_factory implements lock_factory {
  30
  31     /** @var string $dbprefix - used as a namespace for these types of locks */
  32     protected $dbprefix = '';
  33
  34     /** @var \moodle_database $db Hold a reference to the global $DB */
  35     protected $db;
  36
  37     /** @var array $openlocks - List of held locks - used by auto-release */
  38     protected $openlocks = [];
  39
  40     /**
  41      * Return a unique prefix based on the database name and prefix.
  42      * @param string $type - Used to prefix lock keys.
  43      * @return string
  44      */
  45     protected function get_unique_db_prefix($type) {
  46         global $CFG;
  47         $prefix = $CFG->dbname . ':';
  48         if (isset($CFG->prefix)) {
  49             $prefix .= $CFG->prefix;
  50         }
  51         $prefix .= '_' . $type . '_';
  52         return $prefix;
  53     }
  54
  55     /**
  56      * Lock constructor.
  57      * @param string $type - Used to prefix lock keys.
  58      */
  59     public function __construct($type) {
  60         global $DB;
  61
  62         $this->dbprefix = $this->get_unique_db_prefix($type);
  63         // Save a reference to the global $DB so it will not be released while we still have open locks.
  64         $this->db = $DB;
  65
  66         \core_shutdown_manager::register_function([$this, 'auto_release']);
  67     }
  68
  69     /**
  70      * Is available.
  71      * @return boolean - True if this lock type is available in this environment.
  72      */
  73     public function is_available() {
  74         return $this->db->get_dbfamily() === 'mysql';
  75     }
  76
  77     /**
  78      * Return information about the blocking behaviour of the lock type on this platform.
  79      * @return boolean - Defer to the DB driver.
  80      */
  81     public function supports_timeout() {
  82         return true;
  83     }
  84
  85     /**
  86      * Will this lock type will be automatically released when a process ends.
  87      *
  88      * @return boolean - Via shutdown handler.
  89      */
  90     public function supports_auto_release() {
  91         return true;
  92     }
  93
  94     /**
  95      * @deprecated since Moodle 3.10.
  96      */
  97     public function supports_recursion() {
  98         throw new coding_exception('The function supports_recursion() has been removed, please do not use it anymore.');
  99     }
 100
 101     /**
 102      * Create and get a lock
 103      * @param string $resource - The identifier for the lock. Should use frankenstyle prefix.
 104      * @param int $timeout - The number of seconds to wait for a lock before giving up.
 105      * @param int $maxlifetime - Unused by this lock type.
 106      * @return boolean - true if a lock was obtained.
 107      */
 108     public function get_lock($resource, $timeout, $maxlifetime = 86400) {
 109
 110         // We sha1 to avoid long key names hitting the mysql str limit.
 111         $resourcekey = sha1($this->dbprefix . $resource);
 112
 113         // Even though some versions of MySQL and MariaDB can support stacked locks
 114         // just never stack them and always fail fast.
 115         if (isset($this->openlocks[$resourcekey])) {
 116             return false;
 117         }
 118
 119         $params = [
 120             'resourcekey' => $resourcekey,
 121             'timeout' => $timeout
 122         ];
 123
 124         $result = $this->db->get_record_sql('SELECT GET_LOCK(:resourcekey, :timeout) AS locked', $params);
 125         $locked = $result->locked == 1;
 126
 127         if ($locked) {
 128             $this->openlocks[$resourcekey] = 1;
 129             return new lock($resourcekey, $this);
 130         }
 131         return false;
 132     }
 133
 134     /**
 135      * Release a lock that was previously obtained with @lock.
 136      * @param lock $lock - a lock obtained from this factory.
 137      * @return boolean - true if the lock is no longer held (including if it was never held).
 138      */
 139     public function release_lock(lock $lock) {
 140
 141         $params = [
 142             'resourcekey' => $lock->get_key()
 143         ];
 144         $result = $this->db->get_record_sql('SELECT RELEASE_LOCK(:resourcekey) AS unlocked', $params);
 145         $result = $result->unlocked == 1;
 146         if ($result) {
 147             unset($this->openlocks[$lock->get_key()]);
 148         }
 149         return $result;
 150     }
 151
 152     /**
 153      * @deprecated since Moodle 3.10.
 154      */
 155     public function extend_lock() {
 156         throw new coding_exception('The function extend_lock() has been removed, please do not use it anymore.');
 157     }
 158
 159     /**
 160      * Auto release any open locks on shutdown.
 161      * This is required, because we may be using persistent DB connections.
 162      */
 163     public function auto_release() {
 164         // Called from the shutdown handler. Must release all open locks.
 165         foreach ($this->openlocks as $key => $unused) {
 166             $lock = new lock($key, $this);
 167             $lock->release();
 168         }
 169     }
 170
 171 }