Lock abstraction (like the Cache)

- adding interface
- adding seperate drivers
- moving Lock to the Core package

src/Core/Lock.php

@@ -0,0 +1,97 @@
+<?php
+/**
+ * @file src/Core/Lock.php
+ */
+namespace Friendica\Util;
+
+/**
+ * @file src/Core/Lock.php
+ * @brief Functions for preventing parallel execution of functions
+ */
+
+use Friendica\Core\Config;
+use Friendica\Core\Lock;
+
+require_once 'include/dba.php';
+
+/**
+ * @brief This class contain Functions for preventing parallel execution of functions
+ */
+class Lock
+{
+	/**
+	 * @var Lock\ILockDriver;
+	 */
+	static $driver = null;
+
+	public static function init()
+	{
+		switch(Config::get('system', 'lock_driver', 'default')) {
+			case 'memcache':
+				self::$driver = new Lock\MemcacheLockDriver();
+				break;
+			case 'database':
+				self::$driver = new Lock\DatabaseLockDriver();
+				break;
+			case 'semaphore':
+				self::$driver = new Lock\SemaphoreLockDriver();
+				break;
+			default:
+				// Determine what's the best/fastest locking driver (default behavior in Friendica)
+				if (function_exists('sem_get') && version_compare(PHP_VERSION, '5.6.1', '>=')) {
+					self::$driver = new Lock\SemaphoreLockDriver();
+				} elseif (Config::get('system', 'cache_driver', 'database') == 'memcache') {
+					self::$driver = new Lock\MemcacheLockDriver();
+				} else {
+					self::$driver = new Lock\DatabaseLockDriver();
+				}
+		}
+	}
+
+	/**
+	 * Returns the current cache driver
+	 *
+	 * @return Lock\ILockDriver;
+	 */
+	private static function getDriver()
+	{
+		if (self::$driver === null) {
+			self::init();
+		}
+
+		return self::$driver;
+	}
+
+	/**
+	 * @brief Acquires a lock for a given name
+	 *
+	 * @param string  $key Name of the lock
+	 * @param integer $timeout Seconds until we give up
+	 *
+	 * @return boolean Was the lock successful?
+	 */
+	public static function acquireLock($key, $timeout = 120)
+	{
+		return self::getDriver()->acquireLock($key, $timeout);
+	}
+
+	/**
+	 * @brief Releases a lock if it was set by us
+	 *
+	 * @param string $key Name of the lock
+	 * @return mixed
+	 */
+	public static function releaseLock($key)
+	{
+		return self::getDriver()->releaseLock($key);
+	}
+
+	/**
+	 * @brief Releases all lock that were set by us
+	 * @return void
+	 */
+	public static function releaseAll()
+	{
+		self::getDriver()->releaseAll();
+	}
+}