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<?php
/**
*
* @package phpBB3
* @copyright (c) 2010 phpBB Group
* @license http://opensource.org/licenses/gpl-2.0.php GNU General Public License v2
*
*/
namespace phpbb\lock;
/**
* Database locking class
* @package phpBB3
*/
class db
{
/**
* Name of the config variable this lock uses
* @var string
*/
private $config_name;
/**
* Unique identifier for this lock.
*
* @var string
*/
private $unique_id;
/**
* Stores the state of this lock
* @var bool
*/
private $locked;
/**
* The phpBB configuration
* @var \phpbb\config\config
*/
private $config;
/**
* A database connection
* @var \phpbb\db\driver\driver
*/
private $db;
/**
* Creates a named released instance of the lock.
*
* You have to call acquire() to actually create the lock.
*
* @param string $config_name A config variable to be used for locking
* @param array $config The phpBB configuration
* @param \phpbb\db\driver\driver $db A database connection
*/
public function __construct($config_name, \phpbb\config\config $config, \phpbb\db\driver\driver $db)
{
$this->config_name = $config_name;
$this->config = $config;
$this->db = $db;
}
/**
* Tries to acquire the lock by updating
* the configuration variable in the database.
*
* As a lock may only be held by one process at a time, lock
* acquisition may fail if another process is holding the lock
* or if another process obtained the lock but never released it.
* Locks are forcibly released after a timeout of 1 hour.
*
* @return bool true if lock was acquired
* false otherwise
*/
public function acquire()
{
if ($this->locked)
{
return false;
}
if (!isset($this->config[$this->config_name]))
{
$this->config->set($this->config_name, '0', false);
}
$lock_value = $this->config[$this->config_name];
// make sure lock cannot be acquired by multiple processes
if ($lock_value)
{
// if the other process is running more than an hour already we have to assume it
// aborted without cleaning the lock
$time = explode(' ', $lock_value);
$time = $time[0];
if ($time + 3600 >= time())
{
return false;
}
}
$this->unique_id = time() . ' ' . unique_id();
// try to update the config value, if it was already modified by another
// process we failed to acquire the lock.
$this->locked = $this->config->set_atomic($this->config_name, $lock_value, $this->unique_id, false);
return $this->locked;
}
/**
* Does this process own the lock?
*
* @return bool true if lock is owned
* false otherwise
*/
public function owns_lock()
{
return (bool) $this->locked;
}
/**
* Releases the lock.
*
* The lock must have been previously obtained, that is, acquire() call
* was issued and returned true.
*
* Note: Attempting to release a lock that is already released,
* that is, calling release() multiple times, is harmless.
*
* @return null
*/
public function release()
{
if ($this->locked)
{
$this->config->set_atomic($this->config_name, $this->unique_id, '0', false);
$this->locked = false;
}
}
}
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