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<?php
/**
* TCache class file.
*
* @author Qiang Xue <qiang.xue@gmail.com>
* @link http://www.pradosoft.com/
* @copyright Copyright © 2005 PradoSoft
* @license http://www.pradosoft.com/license/
* @version $Revision: $ $Date: $
* @package System.Caching
*/
/**
* TCache class
*
* TCache is the base class for cache classes with different cache storage implementation.
*
* TCache implements the interface {@link ICache} with the following methods,
* - {@link get} : retrieve the value with a key (if any) from cache
* - {@link set} : store the value with a key into cache
* - {@link add} : store the value only if cache does not have this key
* - {@link delete} : delete the value with the specified key from cache
* - {@link flush} : delete all values from cache
*
* Each value is associated with an expiration time. The {@link get} operation
* ensures that any expired value will not be returned. The expiration time by
* the number of seconds. A expiration time 0 represents never expire.
*
* By definition, cache does not ensure the existence of a value
* even if it never expires. Cache is not meant to be an persistent storage.
*
* Child classes must implement the following methods:
* - {@link getValue}
* - {@link setValue}
* - {@link addValue}
* - {@link deleteValue}
* and optionally {@link flush}
*
* @author Qiang Xue <qiang.xue@gmail.com>
* @version $Revision: $ $Date: $
* @package System.Caching
* @since 3.0
*/
abstract class TCache extends TModule implements ICache
{
private $_prefix=null;
/**
* Initializes the cache module.
* This method initializes the cache key prefix and registers the cache module
* with the application.
* @param TXmlElement the module configuration
*/
public function init($config)
{
if($this->_prefix===null)
$this->_prefix=$this->getApplication()->getUniqueID();
$this->getApplication()->setCache($this);
}
/**
* @return string a unique prefix for the keys of cached values.
* If it is not explicitly set, it will take the value of {@link TApplication::getUniqueID}.
*/
public function getKeyPrefix()
{
return $this->_prefix;
}
/**
* @param string a unique prefix for the keys of cached values
*/
public function setKeyPrefix($value)
{
$this->_prefix=$value;
}
/**
* @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->_prefix.$key);
}
/**
* Retrieves a value from cache with a specified key.
* @param string a key identifying the cached value
* @return mixed the value stored in cache, false if the value is not in the cache or expired.
*/
public function get($id)
{
if(($value=$this->getValue($this->generateUniqueKey($id)))!==false)
{
$data=unserialize($value);
if(!($data[1] instanceof ICacheDependency) || !$data[1]->getHasChanged())
return $data[0];
}
return false;
}
/**
* Stores a value identified by a key into cache.
* If the cache already contains such a key, the existing value and
* expiration time will be replaced with the new ones.
*
* @param string the key identifying the value to be cached
* @param mixed the value to be cached
* @param integer the number of seconds in which the cached value will expire. 0 means never expire.
* @param ICacheDependency dependency of the cached item. If the dependency changes, the item is labelled invalid.
* @return boolean true if the value is successfully stored into cache, false otherwise
*/
public function set($id,$value,$expire=0,$dependency=null)
{
$data=array($value,$dependency);
$expire=($expire<=0)?0:time()+$expire;
return $this->setValue($this->generateUniqueKey($id),serialize($data),$expire);
}
/**
* Stores a value identified by a key into cache if the cache does not contain this key.
* Nothing will be done if the cache already contains the key.
* @param string the key identifying the value to be cached
* @param mixed the value to be cached
* @param integer the number of seconds in which the cached value will expire. 0 means never expire.
* @param ICacheDependency dependency of the cached item. If the dependency changes, the item is labelled invalid.
* @return boolean true if the value is successfully stored into cache, false otherwise
*/
public function add($id,$value,$expire=0,$dependency=null)
{
$data=array($value,$dependency);
$expire=($expire<=0)?0:time()+$expire;
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)
{
return $this->deleteValue($this->generateUniqueKey($id));
}
/**
* Deletes all values from cache.
* Be careful of performing this operation if the cache is shared by multiple applications.
* Child classes may implement this method to realize the flush operation.
* @throws TNotSupportedException if this method is not overriden by child classes
*/
public function flush()
{
throw new TNotSupportedException('cache_flush_unsupported');
}
/**
* Retrieves a value from cache with a specified key.
* This method should be implemented by child classes to store the data
* in specific cache storage. The uniqueness and dependency are handled
* in {@link get()} already. So only the implementation of data retrieval
* is needed.
* @param string a unique key identifying the cached value
* @return string the value stored in cache, false if the value is not in the cache or expired.
*/
abstract protected function getValue($key);
/**
* 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
*/
abstract protected function setValue($key,$value,$expire);
/**
* Stores a value identified by a key into cache if the cache does not contain this key.
* This method should be implemented by child classes to store the data
* in specific cache storage. The uniqueness and dependency are handled
* in {@link add()} already. So only the implementation of data storage
* is needed.
*
* @param string the key identifying the value to be cached
* @param string the value to be cached
* @param integer the number of seconds in which the cached value will expire. 0 means never expire.
* @return boolean true if the value is successfully stored into cache, false otherwise
*/
abstract protected function addValue($key,$value,$expire);
/**
* 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
*/
abstract protected function deleteValue($key);
}
?>
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