Lock abstraction (like the Cache)

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

src/Core/Lock/DatabaseLockDriver.php

@@ -0,0 +1,83 @@
+<?php
+
+namespace Friendica\Core\Lock;
+
+use dba;
+use Friendica\Database\DBM;
+
+/**
+ * Locking driver that stores the locks in the database
+ */
+class DatabaseLockDriver implements ILockDriver
+{
+	/**
+	 * @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)
+	{
+		$got_lock = false;
+		$start = time();
+
+		do {
+			dba::lock('locks');
+			$lock = dba::selectFirst('locks', ['locked', 'pid'], ['name' => $key]);
+
+			if (DBM::is_result($lock)) {
+				if ($lock['locked']) {
+					// When the process id isn't used anymore, we can safely claim the lock for us.
+					if (!posix_kill($lock['pid'], 0)) {
+						$lock['locked'] = false;
+					}
+					// We want to lock something that was already locked by us? So we got the lock.
+					if ($lock['pid'] == getmypid()) {
+						$got_lock = true;
+					}
+				}
+				if (!$lock['locked']) {
+					dba::update('locks', ['locked' => true, 'pid' => getmypid()], ['name' => $key]);
+					$got_lock = true;
+				}
+			} elseif (!DBM::is_result($lock)) {
+				dba::insert('locks', ['name' => $key, 'locked' => true, 'pid' => getmypid()]);
+				$got_lock = true;
+			}
+
+			dba::unlock();
+
+			if (!$got_lock && ($timeout > 0)) {
+				usleep(rand(100000, 2000000));
+			}
+		} while (!$got_lock && ((time() - $start) < $timeout));
+
+		return $got_lock;
+	}
+
+	/**
+	 * @brief Removes a lock if it was set by us
+	 *
+	 * @param string $key Name of the lock
+	 *
+	 * @return mixed
+	 */
+	public function releaseLock($key)
+	{
+		dba::update('locks', ['locked' => false, 'pid' => 0], ['name' => $key, 'pid' => getmypid()]);
+
+		return;
+	}
+
+	/**
+	 * @brief Removes all lock that were set by us
+	 *
+	 * @return void
+	 */
+	public function releaseAll()
+	{
+		dba::update('locks', ['locked' => false, 'pid' => 0], ['pid' => getmypid()]);
+	}
+}