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<?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/>.
/**
* Flock based file locking factory.
*
* The file lock factory returns file locks locked with the flock function. Works OK, except on some
* NFS, exotic shared storage and exotic server OSes (like windows). On windows, a second attempt to get a
* lock will block indefinitely instead of timing out.
*
* @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();
/**
* Flock based file locking factory.
*
* The file lock factory returns file locks locked with the flock function. Works OK, except on some
* NFS, exotic shared storage and exotic server OSes (like windows). On windows, a second attempt to get a
* lock will block indefinitely instead of timing out.
*
* @package core
* @category lock
* @copyright Damyon Wiese 2013
* @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
*/
class file_lock_factory implements lock_factory {
/** @var string $type - The type of lock, e.g. cache, cron, session. */
protected $type;
/** @var string $lockdirectory - Full system path to the directory used to store file locks. */
protected $lockdirectory;
/** @var boolean $verbose - If true, debugging info about the owner of the lock will be written to the lock file. */
protected $verbose;
/**
* Create this lock factory.
*
* @param string $type - The type, e.g. cron, cache, session
*/
public function __construct($type) {
global $CFG;
$this->type = $type;
if (!isset($CFG->file_lock_root)) {
$this->lockdirectory = $CFG->dataroot . '/lock';
} else {
$this->lockdirectory = $CFG->file_lock_root;
}
$this->verbose = false;
if ($CFG->debugdeveloper) {
$this->verbose = true;
}
}
/**
* Return information about the blocking behaviour of the lock type on this platform.
* @return boolean - False if attempting to get a lock will block indefinitely.
*/
public function supports_timeout() {
global $CFG;
return $CFG->ostype !== 'WINDOWS';
}
/**
* This lock type will be automatically released when a process ends.
* @return boolean - True
*/
public function supports_auto_release() {
return true;
}
/**
* Is available.
* @return boolean - True if preventfilelocking is not set - or the file_lock_root is not in dataroot.
*/
public function is_available() {
global $CFG;
$preventfilelocking = !empty($CFG->preventfilelocking);
$lockdirisdataroot = true;
if (!empty($CFG->file_lock_root) && strpos($CFG->file_lock_root, $CFG->dataroot) !== 0) {
$lockdirisdataroot = false;
}
return !$preventfilelocking || !$lockdirisdataroot;
}
/**
* Multiple locks for the same resource cannot be held from a single process.
* @return boolean - False
*/
public function supports_recursion() {
return false;
}
/**
* Get some info that might be useful for debugging.
* @return boolean - string
*/
protected function get_debug_info() {
return 'host:' . php_uname('n') . ', pid:' . getmypid() . ', time:' . time();
}
/**
* Get a lock within the specified timeout or return false.
* @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;
$hash = md5($this->type . '_' . $resource);
$lockdir = $this->lockdirectory . '/' . substr($hash, 0, 2);
if (!check_dir_exists($lockdir, true, true)) {
return false;
}
$lockfilename = $lockdir . '/' . $hash;
$filehandle = fopen($lockfilename, "wb");
// Could not open the lock file.
if (!$filehandle) {
return false;
}
do {
// Will block on windows. So sad.
$wouldblock = false;
$locked = flock($filehandle, LOCK_EX | LOCK_NB, $wouldblock);
if (!$locked && $wouldblock && $timeout > 0) {
usleep(rand(10000, 250000)); // Sleep between 10 and 250 milliseconds.
}
// Try until the giveup time.
} while (!$locked && $wouldblock && time() < $giveuptime);
if (!$locked) {
fclose($filehandle);
return false;
}
if ($this->verbose) {
fwrite($filehandle, $this->get_debug_info());
}
return new lock($filehandle, $this);
}
/**
* 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) {
$handle = $lock->get_key();
if (!$handle) {
// We didn't have a lock.
return false;
}
$result = flock($handle, LOCK_UN);
fclose($handle);
return $result;
}
/**
* Extend a lock that was previously obtained with @lock.
* @param lock $lock - not used
* @param int $maxlifetime - not used
* @return boolean - true if the lock was extended.
*/
public function extend_lock(lock $lock, $maxlifetime = 86400) {
// Not supported by this factory.
return false;
}
}