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|
<?php
/**
*
* @package phpBB3
* @copyright (c) 2012 phpBB Group
* @license http://opensource.org/licenses/gpl-2.0.php GNU General Public License v2
*
*/
namespace phpbb\lock;
/**
* File locking class
* @package phpBB3
*/
class flock
{
/**
* Path to the file to which access is controlled
*
* @var string
*/
private $path;
/**
* File pointer for the lock file
* @var string
*/
private $lock_fp;
/**
* Constructor.
*
* You have to call acquire() to actually acquire the lock.
*
* @param string $path Path to the file to which access is controlled
*/
public function __construct($path)
{
$this->path = $path;
$this->lock_fp = null;
}
/**
* Tries to acquire the lock.
*
* If the lock is already held by another process, this call will block
* until the other process releases the lock. If a lock is acquired and
* is not released before script finishes but the process continues to
* live (apache/fastcgi) then subsequent processes trying to acquire
* the same lock will be blocked forever.
*
* If the lock is already held by the same process via another instance
* of this class, this call will block forever.
*
* If flock function is disabled in php or fails to work, lock
* acquisition will fail and false will be returned.
*
* @return bool true if lock was acquired
* false otherwise
*/
public function acquire()
{
if ($this->lock_fp)
{
return false;
}
// For systems that can't have two processes opening
// one file for writing simultaneously
if (file_exists($this->path . '.lock'))
{
$mode = 'rb';
}
else
{
$mode = 'wb';
}
$this->lock_fp = @fopen($this->path . '.lock', $mode);
if ($mode == 'wb')
{
if (!$this->lock_fp)
{
// Two processes may attempt to create lock file at the same time.
// Have the losing process try opening the lock file again for reading
// on the assumption that the winning process created it
$mode = 'rb';
$this->lock_fp = @fopen($this->path . '.lock', $mode);
}
else
{
// Only need to set mode when the lock file is written
@chmod($this->path . '.lock', 0666);
}
}
if ($this->lock_fp)
{
@flock($this->lock_fp, LOCK_EX);
}
return (bool) $this->lock_fp;
}
/**
* Does this process own the lock?
*
* @return bool true if lock is owned
* false otherwise
*/
public function owns_lock()
{
return (bool) $this->lock_fp;
}
/**
* Releases the lock.
*
* The lock must have been previously obtained, that is, acquire() call
* was issued and returned true.
*
* Note: Attempting to release a lock that is already released,
* that is, calling release() multiple times, is harmless.
*
* @return null
*/
public function release()
{
if ($this->lock_fp)
{
@flock($this->lock_fp, LOCK_UN);
fclose($this->lock_fp);
$this->lock_fp = null;
}
}
}
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