Adding possibility to use a different cache-backend for locking and caching

- Renaming *LockDriver to *Lock since it isn't a "driver" anymore

src/Core/Lock/CacheLock.php

@@ -0,0 +1,97 @@
+<?php
+
+namespace Friendica\Core\Lock;
+
+use Friendica\Core\Cache;
+use Friendica\Core\Cache\IMemoryCache;
+
+class CacheLock extends AbstractLock
+{
+	/**
+	 * @var \Friendica\Core\Cache\ICache;
+	 */
+	private $cache;
+
+	/**
+	 * CacheLock constructor.
+	 *
+	 * @param IMemoryCache $cache The CacheDriver for this type of lock
+	 */
+	public function __construct(IMemoryCache $cache)
+	{
+		$this->cache = $cache;
+	}
+
+	/**
+	 * (@inheritdoc)
+	 */
+	public function acquireLock($key, $timeout = 120, $ttl = Cache::FIVE_MINUTES)
+	{
+		$got_lock = false;
+		$start    = time();
+
+		$cachekey = self::getLockKey($key);
+
+		do {
+			$lock = $this->cache->get($cachekey);
+			// When we do want to lock something that was already locked by us.
+			if ((int)$lock == getmypid()) {
+				$got_lock = true;
+			}
+
+			// When we do want to lock something new
+			if (is_null($lock)) {
+				// At first initialize it with "0"
+				$this->cache->add($cachekey, 0);
+				// Now the value has to be "0" because otherwise the key was used by another process meanwhile
+				if ($this->cache->compareSet($cachekey, 0, getmypid(), $ttl)) {
+					$got_lock = true;
+					$this->markAcquire($key);
+				}
+			}
+
+			if (!$got_lock && ($timeout > 0)) {
+				usleep(rand(10000, 200000));
+			}
+		} while (!$got_lock && ((time() - $start) < $timeout));
+
+		return $got_lock;
+	}
+
+	/**
+	 * (@inheritdoc)
+	 */
+	public function releaseLock($key, $override = false)
+	{
+		$cachekey = self::getLockKey($key);
+
+		if ($override) {
+			$return = $this->cache->delete($cachekey);
+		} else {
+			$return = $this->cache->compareDelete($cachekey, getmypid());
+		}
+		$this->markRelease($key);
+
+		return $return;
+	}
+
+	/**
+	 * (@inheritdoc)
+	 */
+	public function isLocked($key)
+	{
+		$cachekey = self::getLockKey($key);
+		$lock     = $this->cache->get($cachekey);
+		return isset($lock) && ($lock !== false);
+	}
+
+	/**
+	 * @param string $key The original key
+	 *
+	 * @return string        The cache key used for the cache
+	 */
+	private static function getLockKey($key)
+	{
+		return "lock:" . $key;
+	}
+}