Adding multihost - locking

Adding Unit-Tests for it

src/Core/Cache/TraitCompareSet.php

@@ -0,0 +1,48 @@
+<?php
+
+namespace Friendica\Core\Cache;
+
+use Friendica\Core\Cache;
+
+/**
+ * Trait TraitCompareSetDelete
+ *
+ * @brief This Trait is to compensate non native "exclusive" sets/deletes in caches
+ *
+ * @package Friendica\Core\Cache
+ */
+trait TraitCompareSet
+{
+	abstract public function get($key);
+
+	abstract public function set($key, $value, $ttl = Cache::FIVE_MINUTES);
+
+	abstract public function delete($key);
+
+	abstract public function add($key, $value, $ttl = Cache::FIVE_MINUTES);
+
+	/**
+	 * @brief NonNative - Compares if the old value is set and sets the new value
+	 *
+	 * @param string $key         The cache key
+	 * @param mixed  $oldValue    The old value we know from the cache
+	 * @param mixed  $newValue    The new value we want to set
+	 * @param int    $ttl      The cache lifespan, must be one of the Cache constants
+	 *
+	 * @return bool
+	 */
+	public function compareSet($key, $oldValue, $newValue, $ttl = Cache::FIVE_MINUTES) {
+		if ($this->add($key . "_lock", true)) {
+			if ($this->get($key) === $oldValue) {
+				$this->set($key, $newValue, $ttl);
+				$this->delete($key . "_lock");
+				return true;
+ 			} else {
+				$this->delete($key . "_lock");
+				return false;
+			}
+		} else {
+			return false;
+		}
+	}
+}