Cache.php 14.2 KB
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<?php
/**
 * @link http://www.yiiframework.com/
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 * @copyright Copyright (c) 2008 Yii Software LLC
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 * @license http://www.yiiframework.com/license/
 */

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namespace yii\caching;

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use Yii;
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use yii\base\Component;
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use yii\base\InvalidConfigException;
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use yii\helpers\StringHelper;
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/**
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 * Cache is the base class for cache classes supporting different cache storage implementation.
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 *
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 * A data item can be stored in cache by calling [[set()]] and be retrieved back
 * later (in the same or different request) by [[get()]]. In both operations,
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 * a key identifying the data item is required. An expiration time and/or a [[Dependency|dependency]]
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 * can also be specified when calling [[set()]]. If the data item expires or the dependency
 * changes at the time of calling [[get()]], the cache will return no data.
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 *
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 * A typical usage pattern of cache is like the following:
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 *
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 * ~~~
 * $key = 'demo';
 * $data = $cache->get($key);
 * if ($data === false) {
 *     // ...generate $data here...
 *     $cache->set($key, $data, $expire, $dependency);
 * }
 * ~~~
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 *
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 * Because Cache implements the ArrayAccess interface, it can be used like an array. For example,
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 *
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 * ~~~
 * $cache['foo'] = 'some data';
 * echo $cache['foo'];
 * ~~~
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 *
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 * Derived classes should implement the following methods:
 *
 * - [[getValue()]]: retrieve the value with a key (if any) from cache
 * - [[setValue()]]: store the value with a key into cache
 * - [[addValue()]]: store the value only if the cache does not have this key before
 * - [[deleteValue()]]: delete the value with the specified key from cache
 * - [[flushValues()]]: delete all values from cache
 *
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 * @author Qiang Xue <qiang.xue@gmail.com>
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 * @since 2.0
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 */
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abstract class Cache extends Component implements \ArrayAccess
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{
	/**
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	 * @var string a string prefixed to every cache key so that it is unique. If not set,
	 * it will use a prefix generated from [[Application::id]]. You may set this property to be an empty string
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	 * if you don't want to use key prefix. It is recommended that you explicitly set this property to some
	 * static value if the cached data needs to be shared among multiple applications.
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	 *
	 * To ensure interoperability, only use alphanumeric characters should be used.
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	 */
	public $keyPrefix;
	/**
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	 * @var array|boolean the functions used to serialize and unserialize cached data. Defaults to null, meaning
	 * using the default PHP `serialize()` and `unserialize()` functions. If you want to use some more efficient
	 * serializer (e.g. [igbinary](http://pecl.php.net/package/igbinary)), you may configure this property with
	 * a two-element array. The first element specifies the serialization function, and the second the deserialization
	 * function. If this property is set false, data will be directly sent to and retrieved from the underlying
	 * cache component without any serialization or deserialization. You should not turn off serialization if
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	 * you are using [[Dependency|cache dependency]], because it relies on data serialization.
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	 */
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	public $serializer;
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	/**
	 * Initializes the application component.
	 * This method overrides the parent implementation by setting default cache key prefix.
	 */
	public function init()
	{
		parent::init();
		if ($this->keyPrefix === null) {
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			$this->keyPrefix = substr(md5(Yii::$app->id), 0, 5);
		} elseif (!ctype_alnum($this->keyPrefix)) {
			throw new InvalidConfigException(get_class($this) . '::keyPrefix should only contain alphanumeric characters.');
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		}
	}

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	/**
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	 * Builds a normalized cache key from a given key.
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	 *
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	 * If the given key is a string containing alphanumeric characters only and no more than 32 characters,
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	 * then the key will be returned back prefixed with [[keyPrefix]]. Otherwise, a normalized key
	 * is generated by serializing the given key, applying MD5 hashing, and prefixing with [[keyPrefix]].
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	 * 
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	 * @param mixed $key the key to be normalized
	 * @return string the generated cache key
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	 */
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	protected function buildKey($key)
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	{
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		if (is_string($key)) {
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			$key = ctype_alnum($key) && StringHelper::strlen($key) <= 32 ? $key : md5($key);
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		} else {
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			$key = md5(json_encode($key));
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		}
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		return $this->keyPrefix . $key;
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	}

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	/**
	 * Retrieves a value from cache with a specified key.
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	 * @param mixed $key a key identifying the cached value. This can be a simple string or
	 * a complex data structure consisting of factors representing the key.
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	 * @return mixed the value stored in cache, false if the value is not in the cache, expired,
	 * or the dependency associated with the cached data has changed.
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	 */
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	public function get($key)
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	{
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		$key = $this->buildKey($key);
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		$value = $this->getValue($key);
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		if ($value === false || $this->serializer === false) {
			return $value;
		} elseif ($this->serializer === null) {
			$value = unserialize($value);
		} else {
			$value = call_user_func($this->serializer[1], $value);
		}
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		if (is_array($value) && !($value[1] instanceof Dependency && $value[1]->getHasChanged($this))) {
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			return $value[0];
		} else {
			return false;
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		}
	}

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	/**
	 * Checks whether a specified key exists in the cache.
	 * This can be faster than getting the value from the cache if the data is big.
	 * In case a cache does not support this feature natively, this method will try to simulate it
	 * but has no performance improvement over getting it.
	 * Note that this method does not check whether the dependency associated
	 * with the cached data, if there is any, has changed. So a call to [[get]]
	 * may return false while exists returns true.
	 * @param mixed $key a key identifying the cached value. This can be a simple string or
	 * a complex data structure consisting of factors representing the key.
	 * @return boolean true if a value exists in cache, false if the value is not in the cache or expired.
	 */
	public function exists($key)
	{
		$key = $this->buildKey($key);
		$value = $this->getValue($key);
		return $value !== false;
	}

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	/**
	 * Retrieves multiple values from cache with the specified keys.
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	 * Some caches (such as memcache, apc) allow retrieving multiple cached values at the same time,
	 * which may improve the performance. In case a cache does not support this feature natively,
	 * this method will try to simulate it.
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	 * @param array $keys list of keys identifying the cached values
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	 * @return array list of cached values corresponding to the specified keys. The array
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	 * is returned in terms of (key, value) pairs.
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	 * If a value is not cached or expired, the corresponding array value will be false.
	 */
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	public function mget($keys)
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	{
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		$keyMap = array();
		foreach ($keys as $key) {
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			$keyMap[$key] = $this->buildKey($key);
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		}
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		$values = $this->getValues(array_values($keyMap));
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		$results = array();
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		foreach ($keyMap as $key => $newKey) {
			$results[$key] = false;
			if (isset($values[$newKey])) {
				if ($this->serializer === false) {
					$results[$key] = $values[$newKey];
				} else {
					$value = $this->serializer === null ? unserialize($values[$newKey])
							: call_user_func($this->serializer[1], $values[$newKey]);

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					if (is_array($value) && !($value[1] instanceof Dependency && $value[1]->getHasChanged($this))) {
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						$results[$key] = $value[0];
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					}
				}
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			}
		}
		return $results;
	}

	/**
	 * Stores a value identified by a key into cache.
	 * If the cache already contains such a key, the existing value and
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	 * expiration time will be replaced with the new ones, respectively.
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	 *
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	 * @param mixed $key a key identifying the value to be cached value. This can be a simple string or
	 * a complex data structure consisting of factors representing the key.
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	 * @param mixed $value the value to be cached
	 * @param integer $expire the number of seconds in which the cached value will expire. 0 means never expire.
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	 * @param Dependency $dependency dependency of the cached item. If the dependency changes,
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	 * the corresponding value in the cache will be invalidated when it is fetched via [[get()]].
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	 * This parameter is ignored if [[serializer]] is false.
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	 * @return boolean whether the value is successfully stored into cache
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	 */
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	public function set($key, $value, $expire = 0, $dependency = null)
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	{
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		if ($dependency !== null && $this->serializer !== false) {
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			$dependency->evaluateDependency($this);
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		}
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		if ($this->serializer === null) {
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			$value = serialize(array($value, $dependency));
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		} elseif ($this->serializer !== false) {
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			$value = call_user_func($this->serializer[0], array($value, $dependency));
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		}
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		$key = $this->buildKey($key);
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		return $this->setValue($key, $value, $expire);
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	}

	/**
	 * Stores a value identified by a key into cache if the cache does not contain this key.
	 * Nothing will be done if the cache already contains the key.
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	 * @param mixed $key a key identifying the value to be cached value. This can be a simple string or
	 * a complex data structure consisting of factors representing the key.
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	 * @param mixed $value the value to be cached
	 * @param integer $expire the number of seconds in which the cached value will expire. 0 means never expire.
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	 * @param Dependency $dependency dependency of the cached item. If the dependency changes,
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	 * the corresponding value in the cache will be invalidated when it is fetched via [[get()]].
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	 * This parameter is ignored if [[serializer]] is false.
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	 * @return boolean whether the value is successfully stored into cache
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	 */
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	public function add($key, $value, $expire = 0, $dependency = null)
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	{
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		if ($dependency !== null && $this->serializer !== false) {
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			$dependency->evaluateDependency($this);
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		}
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		if ($this->serializer === null) {
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			$value = serialize(array($value, $dependency));
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		} elseif ($this->serializer !== false) {
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			$value = call_user_func($this->serializer[0], array($value, $dependency));
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		}
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		$key = $this->buildKey($key);
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		return $this->addValue($key, $value, $expire);
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	}

	/**
	 * Deletes a value with the specified key from cache
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	 * @param mixed $key a key identifying the value to be deleted from cache. This can be a simple string or
	 * a complex data structure consisting of factors representing the key.
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	 * @return boolean if no error happens during deletion
	 */
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	public function delete($key)
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	{
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		$key = $this->buildKey($key);
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		return $this->deleteValue($key);
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	}

	/**
	 * Deletes all values from cache.
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	 * Be careful of performing this operation if the cache is shared among multiple applications.
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	 * @return boolean whether the flush operation was successful.
	 */
	public function flush()
	{
		return $this->flushValues();
	}

	/**
	 * Retrieves a value from cache with a specified key.
	 * This method should be implemented by child classes to retrieve the data
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	 * from specific cache storage.
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	 * @param string $key a unique key identifying the cached value
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	 * @return string|boolean the value stored in cache, false if the value is not in the cache or expired.
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	 */
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	abstract protected function getValue($key);
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	/**
	 * Stores a value identified by a key in cache.
	 * This method should be implemented by child classes to store the data
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	 * in specific cache storage.
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	 * @param string $key the key identifying the value to be cached
	 * @param string $value the value to be cached
	 * @param integer $expire the number of seconds in which the cached value will expire. 0 means never expire.
	 * @return boolean true if the value is successfully stored into cache, false otherwise
	 */
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	abstract protected function setValue($key, $value, $expire);
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	/**
	 * Stores a value identified by a key into cache if the cache does not contain this key.
	 * This method should be implemented by child classes to store the data
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	 * in specific cache storage.
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	 * @param string $key the key identifying the value to be cached
	 * @param string $value the value to be cached
	 * @param integer $expire the number of seconds in which the cached value will expire. 0 means never expire.
	 * @return boolean true if the value is successfully stored into cache, false otherwise
	 */
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	abstract protected function addValue($key, $value, $expire);
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	/**
	 * Deletes a value with the specified key from cache
	 * This method should be implemented by child classes to delete the data from actual cache storage.
	 * @param string $key the key of the value to be deleted
	 * @return boolean if no error happens during deletion
	 */
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	abstract protected function deleteValue($key);
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	/**
	 * Deletes all values from cache.
	 * Child classes may implement this method to realize the flush operation.
	 * @return boolean whether the flush operation was successful.
	 */
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	abstract protected function flushValues();

	/**
	 * Retrieves multiple values from cache with the specified keys.
	 * The default implementation calls [[getValue()]] multiple times to retrieve
	 * the cached values one by one. If the underlying cache storage supports multiget,
	 * this method should be overridden to exploit that feature.
	 * @param array $keys a list of keys identifying the cached values
	 * @return array a list of cached values indexed by the keys
	 */
	protected function getValues($keys)
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	{
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		$results = array();
		foreach ($keys as $key) {
			$results[$key] = $this->getValue($key);
		}
		return $results;
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	}

	/**
	 * Returns whether there is a cache entry with a specified key.
	 * This method is required by the interface ArrayAccess.
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	 * @param string $key a key identifying the cached value
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	 * @return boolean
	 */
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	public function offsetExists($key)
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	{
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		return $this->get($key) !== false;
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	}

	/**
	 * Retrieves the value from cache with a specified key.
	 * This method is required by the interface ArrayAccess.
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	 * @param string $key a key identifying the cached value
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	 * @return mixed the value stored in cache, false if the value is not in the cache or expired.
	 */
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	public function offsetGet($key)
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	{
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		return $this->get($key);
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	}

	/**
	 * Stores the value identified by a key into cache.
	 * If the cache already contains such a key, the existing value will be
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	 * replaced with the new ones. To add expiration and dependencies, use the [[set()]] method.
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	 * This method is required by the interface ArrayAccess.
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	 * @param string $key the key identifying the value to be cached
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	 * @param mixed $value the value to be cached
	 */
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	public function offsetSet($key, $value)
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	{
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		$this->set($key, $value);
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	}

	/**
	 * Deletes the value with the specified key from cache
	 * This method is required by the interface ArrayAccess.
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	 * @param string $key the key of the value to be deleted
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	 */
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	public function offsetUnset($key)
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	{
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		$this->delete($key);
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	}
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}