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<?php
/**
* CCache class file.
*
* @author Qiang Xue <qiang.xue@gmail.com>
* @link http://www.yiiframework.com/
* @copyright Copyright &copy; 2008-2009 Yii Software LLC
* @license http://www.yiiframework.com/license/
*/
/**
* CCache is the base class for cache classes with different cache storage implementation.
*
* A data item can be stored in cache by calling {@link set} and be retrieved back
* later by {@link get}. In both operations, a key identifying the data item is required.
* An expiration time and/or a dependency can also be specified when calling {@link set}.
* If the data item expires or the dependency changes, calling {@link get} will not
* return back the data item.
*
* Note, by definition, cache does not ensure the existence of a value
* even if it does not expire. Cache is not meant to be a persistent storage.
*
* CCache implements the interface {@link ICache} with the following methods:
* <ul>
* <li>{@link get} : retrieve the value with a key (if any) from cache</li>
* <li>{@link set} : store the value with a key into cache</li>
* <li>{@link add} : store the value only if cache does not have this key</li>
* <li>{@link delete} : delete the value with the specified key from cache</li>
* <li>{@link flush} : delete all values from cache</li>
* </ul>
*
* Child classes must implement the following methods:
* <ul>
* <li>{@link getValue}</li>
* <li>{@link setValue}</li>
* <li>{@link addValue}</li>
* <li>{@link deleteValue}</li>
* <li>{@link flush} (optional)</li>
* </ul>
*
* CCache also implements ArrayAccess so that it can be used like an array.
*
* @author Qiang Xue <qiang.xue@gmail.com>
* @version $Id$
* @package system.caching
* @since 1.0
*/
abstract class CCache extends CApplicationComponent implements ICache, ArrayAccess
{
/**
* @var string a string prefixed to every cache key so that it is unique. Defaults to {@link CApplication::getId() application ID}.
*/
public $keyPrefix;
/**
* Initializes the application component.
* This method overrides the parent implementation by setting default cache key prefix.
*/
public function init()
{
parent::init();
if($this->keyPrefix===null)
$this->keyPrefix=Yii::app()->getId();
}
/**
* @param string a key identifying a value to be cached
* @return sring a key generated from the provided key which ensures the uniqueness across applications
*/
protected function generateUniqueKey($key)
{
return md5($this->keyPrefix.$key);
}
/**
* Retrieves a value from cache with a specified key.
* @param string a key identifying the cached value
* @return mixed the value stored in cache, false if the value is not in the cache, expired or the dependency has changed.
*/
public function get($id)
{
if(($value=$this->getValue($this->generateUniqueKey($id)))!==false)
{
$data=unserialize($value);
if(!is_array($data))
return false;
if(!($data[1] instanceof ICacheDependency) || !$data[1]->getHasChanged())
{
Yii::trace('Serving "'.$id.'" from cache','system.caching.'.get_class($this));
return $data[0];
}
}
return false;
}
/**
* Retrieves multiple values from cache with the specified keys.
* Some caches (such as memcache, apc) allow retrieving multiple cached values at one time,
* which may improve the performance since it reduces the communication cost.
* In case a cache doesn't support this feature natively, it will be simulated by this method.
* @param array list of keys identifying the cached values
* @return array list of cached values corresponding to the specified keys. The array
* is returned in terms of (key,value) pairs.
* If a value is not cached or expired, the corresponding array value will be false.
* @since 1.0.8
*/
public function mget($ids)
{
$values=$this->getValues($ids);
$results=array();
foreach($values as $id=>$value)
{
$data=unserialize($value);
if(is_array($data) && (!($data[1] instanceof ICacheDependency) || !$data[1]->getHasChanged()))
{
Yii::trace('Serving "'.$id.'" from cache','system.caching.'.get_class($this));
$results[$id]=$data[0];
}
else
$results[$id]=false;
}
}
/**
* Stores a value identified by a key into cache.
* If the cache already contains such a key, the existing value and
* expiration time will be replaced with the new ones.
*
* @param string the key identifying the value to be cached
* @param mixed the value to be cached
* @param integer the number of seconds in which the cached value will expire. 0 means never expire.
* @param ICacheDependency dependency of the cached item. If the dependency changes, the item is labeled invalid.
* @return boolean true if the value is successfully stored into cache, false otherwise
*/
public function set($id,$value,$expire=0,$dependency=null)
{
Yii::trace('Saving "'.$id.'" to cache','system.caching.'.get_class($this));
if($dependency!==null)
$dependency->evaluateDependency();
$data=array($value,$dependency);
return $this->setValue($this->generateUniqueKey($id),serialize($data),$expire);
}
/**
* Stores a value identified by a key into cache if the cache does not contain this key.
* Nothing will be done if the cache already contains the key.
* @param string the key identifying the value to be cached
* @param mixed the value to be cached
* @param integer the number of seconds in which the cached value will expire. 0 means never expire.
* @param ICacheDependency dependency of the cached item. If the dependency changes, the item is labeled invalid.
* @return boolean true if the value is successfully stored into cache, false otherwise
*/
public function add($id,$value,$expire=0,$dependency=null)
{
Yii::trace('Adding "'.$id.'" to cache','system.caching.'.get_class($this));
if($dependency!==null)
$dependency->evaluateDependency();
$data=array($value,$dependency);
return $this->addValue($this->generateUniqueKey($id),serialize($data),$expire);
}
/**
* Deletes a value with the specified key from cache
* @param string the key of the value to be deleted
* @return boolean if no error happens during deletion
*/
public function delete($id)
{
Yii::trace('Deleting "'.$id.'" to cache','system.caching.'.get_class($this));
return $this->deleteValue($this->generateUniqueKey($id));
}
/**
* Deletes all values from cache.
* Be careful of performing this operation if the cache is shared by multiple applications.
* Child classes may implement this method to realize the flush operation.
* @throws CException if this method is not overridden by child classes
*/
public function flush()
{
Yii::trace('Flushign cache','system.caching.'.get_class($this));
throw new CException(Yii::t('yii','{className} does not support flush() functionality.',
array('{className}'=>get_class($this))));
}
/**
* Retrieves a value from cache with a specified key.
* This method should be implemented by child classes to retrieve the data
* from specific cache storage. The uniqueness and dependency are handled
* in {@link get()} already. So only the implementation of data retrieval
* is needed.
* @param string a unique key identifying the cached value
* @return string the value stored in cache, false if the value is not in the cache or expired.
*/
protected function getValue($key)
{
throw new CException(Yii::t('yii','{className} does not support get() functionality.',
array('{className}'=>get_class($this))));
}
/**
* Retrieves multiple values from cache with the specified keys.
* The default implementation simply calls {@link getValue} multiple
* times to retrieve the cached values one by one.
* If the underlying cache storage supports multiget, this method should
* be overridden to exploit that feature.
* @param array a list of keys identifying the cached values
* @return array a list of cached values indexed by the keys
* @since 1.0.8
*/
protected function getValues($keys)
{
$results=array();
foreach($keys as $key)
$results[$key]=$this->getValue($key);
return $results;
}
/**
* Stores a value identified by a key in cache.
* This method should be implemented by child classes to store the data
* in specific cache storage. The uniqueness and dependency are handled
* in {@link set()} already. So only the implementation of data storage
* is needed.
*
* @param string the key identifying the value to be cached
* @param string the value to be cached
* @param integer the number of seconds in which the cached value will expire. 0 means never expire.
* @return boolean true if the value is successfully stored into cache, false otherwise
*/
protected function setValue($key,$value,$expire)
{
throw new CException(Yii::t('yii','{className} does not support set() functionality.',
array('{className}'=>get_class($this))));
}
/**
* Stores a value identified by a key into cache if the cache does not contain this key.
* This method should be implemented by child classes to store the data
* in specific cache storage. The uniqueness and dependency are handled
* in {@link add()} already. So only the implementation of data storage
* is needed.
*
* @param string the key identifying the value to be cached
* @param string the value to be cached
* @param integer the number of seconds in which the cached value will expire. 0 means never expire.
* @return boolean true if the value is successfully stored into cache, false otherwise
*/
protected function addValue($key,$value,$expire)
{
throw new CException(Yii::t('yii','{className} does not support add() functionality.',
array('{className}'=>get_class($this))));
}
/**
* Deletes a value with the specified key from cache
* This method should be implemented by child classes to delete the data from actual cache storage.
* @param string the key of the value to be deleted
* @return boolean if no error happens during deletion
*/
protected function deleteValue($key)
{
throw new CException(Yii::t('yii','{className} does not support delete() functionality.',
array('{className}'=>get_class($this))));
}
/**
* Returns whether there is a cache entry with a specified key.
* This method is required by the interface ArrayAccess.
* @param string a key identifying the cached value
* @return boolean
*/
public function offsetExists($id)
{
return $this->get($id)!==false;
}
/**
* Retrieves the value from cache with a specified key.
* This method is required by the interface ArrayAccess.
* @param string a key identifying the cached value
* @return mixed the value stored in cache, false if the value is not in the cache or expired.
*/
public function offsetGet($id)
{
return $this->get($id);
}
/**
* Stores the value identified by a key into cache.
* If the cache already contains such a key, the existing value will be
* replaced with the new ones. To add expiration and dependencies, use the set() method.
* This method is required by the interface ArrayAccess.
* @param string the key identifying the value to be cached
* @param mixed the value to be cached
*/
public function offsetSet($id, $value)
{
$this->set($id, $value);
}
/**
* Deletes the value with the specified key from cache
* This method is required by the interface ArrayAccess.
* @param string the key of the value to be deleted
* @return boolean if no error happens during deletion
*/
public function offsetUnset($id)
{
$this->delete($id);
}
}
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