Added GroupDependency.

framework/yii/caching/GroupDependency.php

+<?php
+/**
+ * @link http://www.yiiframework.com/
+ * @copyright Copyright (c) 2008 Yii Software LLC
+ * @license http://www.yiiframework.com/license/
+ */
+
+namespace yii\caching;
+
+/**
+ * GroupDependency marks a cached data item with a group name.
+ *
+ * You may invalidate the cached data items with the same group name all at once
+ * by calling [[invalidate()]].
+ *
+ * @author Qiang Xue <qiang.xue@gmail.com>
+ * @since 2.0
+ */
+class GroupDependency extends Dependency
+{
+	/**
+	 * @var string the group name
+	 */
+	public $group;
+
+	/**
+	 * Constructor.
+	 * @param string $group the group name
+	 * @param array $config name-value pairs that will be used to initialize the object properties
+	 */
+	public function __construct($group, $config = array())
+	{
+		$this->group = $group;
+		parent::__construct($config);
+	}
+
+	/**
+	 * Generates the data needed to determine if dependency has been changed.
+	 * This method does nothing in this class.
+	 * @param Cache $cache the cache component that is currently evaluating this dependency
+	 * @return mixed the data needed to determine if dependency has been changed.
+	 */
+	protected function generateDependencyData($cache)
+	{
+		if ($cache->get(array(__CLASS__, $this->group)) === false) {
+			// If the cutoff timestamp is not initialized or is swapped out of the cache, we need to set it.
+			$this->invalidate($cache, array(__CLASS__, $this->group));
+		}
+		return microtime(true);
+	}
+
+	/**
+	 * Performs the actual dependency checking.
+	 * @param Cache $cache the cache component that is currently evaluating this dependency
+	 * @return boolean whether the dependency is changed or not.
+	 */
+	public function getHasChanged($cache)
+	{
+		$time = $cache->get(array(__CLASS__, $this->group));
+		return $time === false || $time > $this->data;
+	}
+
+	/**
+	 * Invalidates all of the cached data items that have the same [[group]].
+	 * @param Cache $cache the cache component that caches the data items
+	 * @param string $group the group name
+	 */
+	public static function invalidate($cache, $group)
+	{
+		$cache->set(array(__CLASS__, $group), microtime(true));
+	}
+}