Lock abstraction (like the Cache)

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

src/Core/Lock/SemaphoreLockDriver.php

@@ -0,0 +1,82 @@
+<?php
+
+namespace Friendica\Core\Lock;
+
+class SemaphoreLockDriver implements ILockDriver
+{
+	/**
+	 * @var array stored semaphores
+	 */
+	private static $semaphore = [];
+
+	/**
+	 * @brief Creates a semaphore key
+	 *
+	 * @param string $key Name of the lock
+	 *
+	 * @return integer the semaphore key
+	 */
+	private static function semaphoreKey($key)
+	{
+		$temp = get_temppath();
+
+		$file = $temp.'/'.$key.'.sem';
+
+		if (!file_exists($file)) {
+			file_put_contents($file, $key);
+		}
+
+		return ftok($file, 'f');
+	}
+
+	/**
+	 *
+	 * @brief Sets a lock for a given name
+	 *
+	 * @param string $key The Name of the lock
+	 * @param integer $timeout Seconds until we give up
+	 *
+	 * @return boolean Was the lock successful?
+	 */
+	public function acquireLock($key, $timeout = 120)
+	{
+		// The second parameter for "sem_acquire" doesn't exist before 5.6.1
+		if (function_exists('sem_get') && version_compare(PHP_VERSION, '5.6.1', '>=')) {
+			self::$semaphore[$key] = sem_get(self::semaphoreKey($key));
+			if (self::$semaphore[$key]) {
+				return sem_acquire(self::$semaphore[$key], ($timeout == 0));
+			}
+		}
+	}
+
+	/**
+	 * @brief Removes a lock if it was set by us
+	 *
+	 * @param string $key Name of the lock
+	 *
+	 * @return mixed
+	 */
+	public function releaseLock($key)
+	{
+		if (function_exists('sem_get') && version_compare(PHP_VERSION, '5.6.1', '>=')) {
+			if (empty(self::$semaphore[$key])) {
+				return false;
+			} else {
+				$success = @sem_release(self::$semaphore[$key]);
+				unset(self::$semaphore[$key]);
+				return $success;
+			}
+		}
+	}
+
+	/**
+	 * @brief Removes all lock that were set by us
+	 *
+	 * @return void
+	 */
+	public function releaseAll()
+	{
+		// not needed/supported
+		return;
+	}
+}