add compare-and-delete to the memcache interface

lib/private/memcache/apc.php

@@ -31,6 +31,8 @@ class APC extends Cache implements IMemcache {
 		cas as casEmulated;
 	}
 
+	use CADTrait;
+
 	public function get($key) {
 		$result = apc_fetch($this->getPrefix() . $key, $success);
 		if (!$success) {

lib/private/memcache/arraycache.php

@@ -28,6 +28,8 @@ class ArrayCache extends Cache implements IMemcache {
 	/** @var array Array with the cached data */
 	protected $cachedData = array();
 
+	use CADTrait;
+
 	/**
 	 * {@inheritDoc}
 	 */

lib/private/memcache/cadtrait.php

@@ -0,0 +1,53 @@
+<?php
+/**
+ * @author Robin Appelman <icewind@owncloud.com>
+ *
+ * @copyright Copyright (c) 2015, ownCloud, Inc.
+ * @license AGPL-3.0
+ *
+ * This code is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License, version 3,
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License, version 3,
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ *
+ */
+
+namespace OC\Memcache;
+
+trait CADTrait {
+	abstract public function get($key);
+
+	abstract public function remove($key);
+
+	abstract public function add($key, $value, $ttl = 0);
+
+	/**
+	 * Compare and delete
+	 *
+	 * @param string $key
+	 * @param mixed $old
+	 * @return bool
+	 */
+	public function cad($key, $old) {
+		//no native cas, emulate with locking
+		if ($this->add($key . '_lock', true)) {
+			if ($this->get($key) === $old) {
+				$this->remove($key);
+				$this->remove($key . '_lock');
+				return true;
+			} else {
+				$this->remove($key . '_lock');
+				return false;
+			}
+		} else {
+			return false;
+		}
+	}
+}

lib/private/memcache/memcached.php

@@ -34,6 +34,8 @@ class Memcached extends Cache implements IMemcache {
 	 */
 	private static $cache = null;
 
+	use CADTrait;
+
 	public function __construct($prefix = '') {
 		parent::__construct($prefix);
 		if (is_null(self::$cache)) {

lib/private/memcache/nullcache.php

@@ -55,6 +55,10 @@ class NullCache extends Cache implements \OCP\IMemcache {
 		return true;
 	}
 
+	public function cad($key, $old) {
+		return true;
+	}
+
 	public function clear($prefix = '') {
 		return true;
 	}

lib/private/memcache/xcache.php

@@ -34,6 +34,8 @@ use OCP\IMemcache;
 class XCache extends Cache implements IMemcache {
 	use CASTrait;
 
+	use CADTrait;
+
 	/**
 	 * entries in XCache gets namespaced to prevent collisions between ownCloud instances and users
 	 */

lib/public/imemcache.php

@@ -76,4 +76,14 @@ interface IMemcache extends ICache {
 	 * @since 8.1.0
 	 */
 	public function cas($key, $old, $new);
+
+	/**
+	 * Compare and delete
+	 *
+	 * @param string $key
+	 * @param mixed $old
+	 * @return bool
+	 * @since 8.1.0
+	 */
+	public function cad($key, $old);
 }

tests/lib/memcache/cache.php

@@ -103,6 +103,18 @@ abstract class Cache extends \Test_Cache {
 		$this->assertEquals('bar1', $this->instance->get('foo'));
 	}
 
+	public function testCadNotChanged() {
+		$this->instance->set('foo', 'bar');
+		$this->assertTrue($this->instance->cad('foo', 'bar'));
+		$this->assertFalse($this->instance->hasKey('foo'));
+	}
+
+	public function testCadChanged() {
+		$this->instance->set('foo', 'bar1');
+		$this->assertFalse($this->instance->cad('foo', 'bar'));
+		$this->assertTrue($this->instance->hasKey('foo'));
+	}
+
 
 	protected function tearDown() {
 		if ($this->instance) {