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<?php
/**
* file_lock.php
* Simple lock mechanism on a file basis.
*
* With the help of this class you can manage persistent locks. Locks are
* stored in files and potential additional data is stored as json.
*
* This program 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 2 of the License, or (at your option)
* any later version.
*
* @author Jan-Hendrik Willms <tleilax+studip@gmail.com>
* @copyright 2013 Stud.IP Core-Group
* @license http://www.gnu.org/licenses/gpl-2.0.html GPL version 2
* @category Stud.IP
* @since 2.4
*/
class FileLock
{
protected $file;
/**
* Constructs a new lock object with the provided id.
*
* @param String $id Identifier of the lock
*/
public function __construct($id)
{
$this->file = fopen("{$GLOBALS['TMP_PATH']}/$id.json", 'c+');
if (!$this->file) {
throw new RuntimeException('failed to create lock file.');
}
}
/**
* Try to aquire a file lock. The provided lock information will
* be stored with the lock. If the lock cannot be aquired, the
* lock information in $data is updated from the lock file.
*
* @param array $data additional data to be stored with the lock
* @return boolean true on success or false on failure
*/
public function tryLock(&$data = [])
{
rewind($this->file);
if (flock($this->file, LOCK_EX | LOCK_NB)) {
ftruncate($this->file, 0);
fwrite($this->file, json_encode($data));
fflush($this->file);
return true;
} else {
$json = stream_get_contents($this->file);
$data = json_decode($json, true);
return false;
}
}
/**
* Releases a previously obtained lock
*
* @return boolean true on success or false on failure
*/
public function release()
{
return flock($this->file, LOCK_UN);
}
}
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