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[feature/system-cron] Abstract the database locking mechanism out of cron.

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Added a number of tests for the locking mechanism which can now lock
arbitrary config variables.

PHPBB3-9596
This commit is contained in:
Nils Adermann
2011-01-07 20:58:28 +01:00
committed by Oleg Pudeyev
parent 6e5e4721d8
commit 3a3a8bb96d
5 changed files with 243 additions and 109 deletions
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158
phpBB/includes/lock/db.php Normal file
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<?php
/**
*
* @package phpBB3
* @copyright (c) 2010 phpBB Group
* @license http://opensource.org/licenses/gpl-license.php GNU Public License
*
*/
/**
* @ignore
*/
if (!defined('IN_PHPBB'))
{
exit;
}
/**
* Database locking class
* @package phpBB3
*/
class phpbb_lock_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 array
*/
private $config;
/**
* A database connection
* @var dbal
*/
private $db;
/**
* Creates a named released instance of the lock.
*
* You have to call lock to actually create the lock.
*
* @param string $config_name A config variable to be used for locking
* @param array $config The phpBB configuration
* @param dbal $db A database connection
*/
public function __construct($config_name, $config, dbal $db)
{
$this->config_name = $config_name;
$this->config = $config;
$this->db = $db;
}
/**
* Tries to acquire the cron lock by updating
* the 'cron_lock' configuration variable in the database.
*
* As a lock may only be held by one process at a time, lock
* acquisition may fail if another process is holding the lock
* or if another process obtained the lock but never released it.
* Locks are forcibly released after a timeout of 1 hour.
*
* @return bool true if lock was acquired
* false otherwise
*/
public function lock()
{
if ($this->locked)
{
return true;
}
if (!isset($this->config[$this->config_name]))
{
set_config($this->config_name, '0', true);
global $config;
$this->config = $config;
}
$lock_value = $this->config[$this->config_name];
// make sure cron doesn't run multiple times in parallel
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();
$sql = 'UPDATE ' . CONFIG_TABLE . "
SET config_value = '" . $this->db->sql_escape($this->unique_id) . "'
WHERE config_name = '" . $this->db->sql_escape($this->config_name) . "'
AND config_value = '" . $this->db->sql_escape($lock_value) . "'";
$this->db->sql_query($sql);
if ($this->db->sql_affectedrows())
{
$this->locked = true;
}
else
{
// another cron process altered the table between script start and
// UPDATE query so return false
$this->locked = false;
}
return $this->locked;
}
/**
* Releases the cron lock.
*
* The lock must have been previously obtained, that is, lock() call
* was issued and returned true.
*
* Note: Attempting to release a cron lock that is already released,
* that is, calling unlock() multiple times, is harmless.
*
* @return void
*/
public function unlock()
{
if ($this->locked)
{
$sql = 'UPDATE ' . CONFIG_TABLE . "
SET config_value = '0'
WHERE config_name = '" . $this->db->sql_escape($this->config_name) . "'
AND config_value = '" . $this->db->sql_escape($this->unique_id) . "'";
$this->db->sql_query($sql);
$this->locked = false;
}
}
}