1 files changed, 138 insertions, 0 deletions
diff --git a/phpBB/includes/lock/db.php b/phpBB/includes/lock/db.php
new file mode 100644
index 0000000000..20dbb63e0c
--- /dev/null
+++ b/phpBB/includes/lock/db.php
@@ -0,0 +1,138 @@
+<?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 phpbb_config
+	*/
+	private $config;
+
+	/**
+	* A database connection
+	* @var dbal
+	*/
+	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	dbal	$db				A database connection
+	*/
+	public function __construct($config_name, phpbb_config $config, dbal $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 $this->locked;
+	}
+
+	/**
+	* Releases the lock.
+	*
+	* The lock must have been previously obtained, that is, acquire() call
+	* was issued and returned true.
+	*
+	* Note: Attempting to release a lock that is already released,
+	* that is, calling release() multiple times, is harmless.
+	*
+	* @return void
+	*/
+	public function release()
+	{
+		if ($this->locked)
+		{
+			$this->config->set_atomic($this->config_name, $this->unique_id, '0', false);
+			$this->locked = false;
+		}
+	}
+}