diff --git a/api/src/Cache.php b/api/src/Cache.php
new file mode 100644
index 0000000000..e0215da9ad
--- /dev/null
+++ b/api/src/Cache.php
@@ -0,0 +1,744 @@
+<?php
+/**
+ * EGroupware API: Caching data
+ *
+ * @link http://www.egroupware.org
+ * @license http://opensource.org/licenses/gpl-license.php GPL - GNU General Public License
+ * @package api
+ * @subpackage cache
+ * @author Ralf Becker <RalfBecker-AT-outdoor-training.de>
+ * @copyright (c) 2009-16 by Ralf Becker <RalfBecker-AT-outdoor-training.de>
+ * @version $Id$
+ */
+
+namespace EGroupware\Api;
+
+use egw_exception_db;
+use egw_exception_wrong_parameter;
+use egw_session;
+
+/**
+ * Class to manage caching in eGroupware.
+ *
+ * It allows to cache on 4 levels:
+ * a) tree:     for all instances/domains runining on a certain source path
+ * b) instance: for all sessions on a given instance
+ * c) session:  for all requests of a session, same as egw_session::appsession()
+ * d) request:  just for this request (same as using a static variable)
+ *
+ * There's a get, a set and a unset method for each level: eg. getTree() or setInstance(),
+ * as well as a variant allowing to specify the level as first parameter: eg. unsetCache()
+ *
+ * getXXX($app,$location,$callback=null,array $callback_params,$expiration=0)
+ * has three optional parameters allowing to specify:
+ * 3. a callback if requested data is not yes stored. In that case the callback is called
+ *    and it's value is stored in the cache AND retured
+ * 4. parameters to pass to the callback as array, see call_user_func_array
+ * 5. an expiration time in seconds to specify how long data should be cached,
+ *    default 0 means infinit (this time is not garantied and not supported for all levels!)
+ *
+ * Data is stored under an application name and a location, like egw_session::appsession().
+ * In fact data stored at cache level Api\Cache::SESSION, is stored in the same way as
+ * egw_session::appsession() so both methods can be used with each other.
+ *
+ * The $app parameter should be either the app or the class name, which both are unique.
+ *
+ * The tree and instance wide cache uses a certain provider class, to store the data
+ * eg. in memcached or if there's nothing else configured in the filesystem (eGW's temp_dir).
+ *
+ * "Admin >> clear cache and register hooks" allways only clears instance level cache of
+ * calling instance. It never clears tree level cache, which makes it important to set
+ * resonable expiry times or think about an other means of clearing that particular item.
+ * (Not clearing of tree-level cache is important, as regenerating it is an expensive
+ * operation for a huge scale EGroupware hosting operation.)
+ *
+ * Apps needing to talk to multiple EGroupware instances (eg. Stylite Managementserver)
+ * can use install_id of instance as $level parameter to (set|get|unset)Cache method.
+ */
+class Cache
+{
+	/**
+	 * tree-wide storage
+	 */
+	const TREE = 'Tree';
+	/**
+	 * instance-wide storage
+	 */
+	const INSTANCE = 'Instance';
+	/**
+	 * session-wide storage
+	 */
+	const SESSION = 'Session';
+	/**
+	 * request-wide storage
+	 */
+	const REQUEST = 'Request';
+
+	/**
+	 * Default provider for tree and instance data
+	 *
+	 * Can be specified eg. in the header.inc.php by setting:
+	 * $GLOBALS['egw_info']['server']['cache_provider_instance'] and optional
+	 * $GLOBALS['egw_info']['server']['cache_provider_tree'] (defaults to instance)
+	 *
+	 * Default is set (if not set here) after class definition to Cache\Apc or Cache\Files,
+	 * depending on function 'apc_fetch' exists or not
+	 *
+	 * @var array
+	 */
+	static $default_provider;	// = array('EGroupware\Api\Cache\Files');// array('EGroupware\Api\Cache\Memcache','localhost');
+
+	/**
+	 * Maximum expiration time, if set unlimited expiration (=0) or bigger expiration times are replaced with that time
+	 *
+	 * @var int
+	 */
+	static $max_expiration;
+
+	/**
+	 * Used to determine keys for tree- and instance-level caches
+	 *
+	 * @var string
+	 */
+	static $egw_server_root = EGW_SERVER_ROOT;
+
+	/**
+	 * Add some data in the cache, only if the key does not yet exist
+	 *
+	 * @param string $level use Api\Cache::(TREE|INSTANCE)
+	 * @param string $app application storing data
+	 * @param string $location location name for data
+	 * @param mixed $data
+	 * @param int $expiration =0 expiration time in seconds, default 0 = never
+	 * @return boolean true if data could be stored, false otherwise incl. key already existed
+	 */
+	static public function addCache($level,$app,$location,$data,$expiration=0)
+	{
+		//error_log(__METHOD__."('$level','$app','$location',".array2string($data).",$expiration)");
+		switch($level)
+		{
+			case self::SESSION:
+			case self::REQUEST:
+				throw new egw_exception_wrong_parameter(__METHOD__."('$level', ...) unsupported level parameter!");
+
+			case self::INSTANCE:
+			case self::TREE:
+			default:
+				if (!($provider = self::get_provider($level)))
+				{
+					return false;
+				}
+				// limit expiration to configured maximum time
+				if (isset(self::$max_expiration) && (!$expiration || $expiration > self::$max_expiration))
+				{
+					$expiration = self::$max_expiration;
+				}
+				return $provider->add(self::keys($level,$app,$location),$data,$expiration);
+		}
+		throw new egw_exception_wrong_parameter(__METHOD__."() unknown level '$level'!");
+	}
+
+	/**
+	 * Set some data in the cache
+	 *
+	 * @param string $level use Api\Cache::(TREE|INSTANCE|SESSION|REQUEST)
+	 * @param string $app application storing data
+	 * @param string $location location name for data
+	 * @param mixed $data
+	 * @param int $expiration =0 expiration time in seconds, default 0 = never
+	 * @return boolean true if data could be stored, false otherwise
+	 */
+	static public function setCache($level,$app,$location,$data,$expiration=0)
+	{
+		//error_log(__METHOD__."('$level','$app','$location',".array2string($data).",$expiration)");
+		switch($level)
+		{
+			case self::SESSION:
+			case self::REQUEST:
+				return call_user_func(array(__CLASS__,'set'.$level),$app,$location,$data,$expiration);
+
+			case self::INSTANCE:
+			case self::TREE:
+			default:
+				if (!($provider = self::get_provider($level)))
+				{
+					return false;
+				}
+				// limit expiration to configured maximum time
+				if (isset(self::$max_expiration) && (!$expiration || $expiration > self::$max_expiration))
+				{
+					$expiration = self::$max_expiration;
+				}
+				return $provider->set(self::keys($level,$app,$location),$data,$expiration);
+		}
+		throw new egw_exception_wrong_parameter(__METHOD__."() unknown level '$level'!");
+	}
+
+	/**
+	 * Get some data from the cache
+	 *
+	 * @param string $level use Api\Cache::(TREE|INSTANCE|SESSION|REQUEST)
+	 * @param string $app application storing data
+	 * @param string|array $location location(s) name for data
+	 * @param callback $callback =null callback to get/create the value, if it's not cache
+	 * @param array $callback_params =array() array with parameters for the callback
+	 * @param int $expiration =0 expiration time in seconds, default 0 = never
+	 * @return mixed NULL if data not found in cache (and no callback specified) or
+	 * 	if $location is an array: location => data pairs for existing location-data, non-existing is not returned
+	 */
+	static public function getCache($level,$app,$location,$callback=null,array $callback_params=array(),$expiration=0)
+	{
+		switch($level)
+		{
+			case self::SESSION:
+			case self::REQUEST:
+				foreach((array)$location as $l)
+				{
+					$data[$l] = call_user_func(array(__CLASS__,'get'.$level),$app,$l,$callback,$callback_params,$expiration);
+				}
+				return is_array($location) ? $data : $data[$l];
+
+			case self::INSTANCE:
+			case self::TREE:
+			default:
+				if (!($provider = self::get_provider($level)))
+				{
+					return null;
+				}
+				try {
+					if (is_array($location))
+					{
+						if (!is_null($callback))
+						{
+							throw new egw_exception_wrong_parameter(__METHOD__."() you can NOT use multiple locations (\$location parameter is an array) together with a callback!");
+						}
+						if (is_a($provider, 'EGroupware\Api\Cache\ProviderMultiple'))
+						{
+							$data = $provider->mget($keys=self::keys($level,$app,$location));
+						}
+						else	// default implementation calls get multiple times
+						{
+							$data = array();
+							foreach($location as $l)
+							{
+								$data[$l] = $provider->get($keys=self::keys($level,$app,$l));
+								if (!isset($data[$l])) unset($data[$l]);
+							}
+						}
+					}
+					else
+					{
+						$data = $provider->get($keys=self::keys($level,$app,$location));
+						if (is_null($data) && !is_null($callback))
+						{
+							$data = call_user_func_array($callback,$callback_params);
+							// limit expiration to configured maximum time
+							if (isset(self::$max_expiration) && (!$expiration || $expiration > self::$max_expiration))
+							{
+								$expiration = self::$max_expiration;
+							}
+							$provider->set($keys,$data,$expiration);
+						}
+					}
+				}
+				catch(Exception $e) {
+					unset($e);
+					$data = null;
+				}
+				return $data;
+		}
+		throw new egw_exception_wrong_parameter(__METHOD__."() unknown level '$level'!");
+	}
+
+	/**
+	 * Unset some data in the cache
+	 *
+	 * @param string $level use Api\Cache::(TREE|INSTANCE|SESSION|REQUEST)
+	 * @param string $app application storing data
+	 * @param string $location location name for data
+	 * @return boolean true if data was set, false if not (like isset())
+	 */
+	static public function unsetCache($level,$app,$location)
+	{
+		switch($level)
+		{
+			case self::SESSION:
+			case self::REQUEST:
+				return call_user_func(array(__CLASS__,'unset'.$level),$app,$location);
+
+			case self::INSTANCE:
+			case self::TREE:
+			default:
+				if (!($provider = self::get_provider($level, false)))
+				{
+					return false;
+				}
+				return $provider->delete(self::keys($level,$app,$location));
+		}
+		throw new egw_exception_wrong_parameter(__METHOD__."() unknown level '$level'!");
+	}
+
+	/**
+	 * Set some data in the cache for the whole source tree (all instances)
+	 *
+	 * @param string $app application storing data
+	 * @param string $location location name for data
+	 * @param mixed $data
+	 * @param int $expiration =0 expiration time in seconds, default 0 = never
+	 * @return boolean true if data could be stored, false otherwise
+	 */
+	static public function setTree($app,$location,$data,$expiration=0)
+	{
+		//error_log(__METHOD__."('$app','$location',".array2string($data).",$expiration)");
+		return self::setCache(self::TREE,$app,$location,$data,$expiration);
+	}
+
+	/**
+	 * Get some data from the cache for the whole source tree (all instances)
+	 *
+	 * @param string $app application storing data
+	 * @param string $location location name for data
+	 * @param callback $callback =null callback to get/create the value, if it's not cache
+	 * @param array $callback_params =array() array with parameters for the callback
+	 * @param int $expiration =0 expiration time in seconds, default 0 = never
+	 * @return mixed NULL if data not found in cache (and no callback specified)
+	 */
+	static public function getTree($app,$location,$callback=null,array $callback_params=array(),$expiration=0)
+	{
+		return self::getCache(self::TREE,$app,$location,$callback,$callback_params,$expiration);
+	}
+
+	/**
+	 * Unset some data in the cache for the whole source tree (all instances)
+	 *
+	 * @param string $app application storing data
+	 * @param string $location location name for data
+	 * @return boolean true if data was set, false if not (like isset())
+	 */
+	static public function unsetTree($app,$location)
+	{
+		return self::unsetCache(self::TREE,$app,$location);
+	}
+
+	/**
+	 * Set some data in the cache for the whole source tree (all instances)
+	 *
+	 * @param string $app application storing data
+	 * @param string $location location name for data
+	 * @param mixed $data
+	 * @param int $expiration =0 expiration time in seconds, default 0 = never
+	 * @return boolean true if data could be stored, false otherwise
+	 */
+	static public function setInstance($app,$location,$data,$expiration=0)
+	{
+		return self::setCache(self::INSTANCE,$app,$location,$data,$expiration);
+	}
+
+	/**
+	 * Get some data from the cache for the whole source tree (all instances)
+	 *
+	 * @param string $app application storing data
+	 * @param string $location location name for data
+	 * @param callback $callback =null callback to get/create the value, if it's not cache
+	 * @param array $callback_params =array() array with parameters for the callback
+	 * @param int $expiration =0 expiration time in seconds, default 0 = never
+	 * @return mixed NULL if data not found in cache (and no callback specified)
+	 */
+	static public function getInstance($app,$location,$callback=null,array $callback_params=array(),$expiration=0)
+	{
+		return self::getCache(self::INSTANCE,$app,$location,$callback,$callback_params,$expiration);
+	}
+
+	/**
+	 * Unset some data in the cache for the whole source tree (all instances)
+	 *
+	 * @param string $app application storing data
+	 * @param string $location location name for data
+	 * @return boolean true if data was set, false if not (like isset())
+	 */
+	static public function unsetInstance($app,$location)
+	{
+		return self::unsetCache(self::INSTANCE,$app,$location);
+	}
+
+	/**
+	 * Set some data in the cache for the whole source tree (all instances)
+	 *
+	 * @param string $app application storing data
+	 * @param string $location location name for data
+	 * @param mixed $data
+	 * @param int $expiration =0 expiration time in seconds, default 0 = never
+	 * @return boolean true if data could be stored, false otherwise
+	 */
+	static public function setSession($app,$location,$data,$expiration=0)
+	{
+		unset($expiration);	// not used, but required by function signature
+		if (isset($_SESSION[egw_session::EGW_SESSION_ENCRYPTED]))
+		{
+			if (egw_session::ERROR_LOG_DEBUG) error_log(__METHOD__.' called after session was encrypted --> ignored!');
+			return false;	// can no longer store something in the session, eg. because commit_session() was called
+		}
+		$_SESSION[egw_session::EGW_APPSESSION_VAR][$app][$location] = $data;
+
+		return true;
+	}
+
+	/**
+	 * Get some data from the cache for the whole source tree (all instances)
+	 *
+	 * Returns a reference to the var in the session!
+	 *
+	 * @param string $app application storing data
+	 * @param string $location location name for data
+	 * @param callback $callback =null callback to get/create the value, if it's not cache
+	 * @param array $callback_params =array() array with parameters for the callback
+	 * @param int $expiration =0 expiration time in seconds, default 0 = never
+	 * @return mixed NULL if data not found in cache (and no callback specified)
+	 */
+	static public function &getSession($app,$location,$callback=null,array $callback_params=array(),$expiration=0)
+	{
+		unset($expiration);	// not used, but required by function signature
+		if (isset($_SESSION[egw_session::EGW_SESSION_ENCRYPTED]))
+		{
+			if (egw_session::ERROR_LOG_DEBUG) error_log(__METHOD__.' called after session was encrypted --> ignored!');
+			return null;	// can no longer store something in the session, eg. because commit_session() was called
+		}
+		if (!isset($_SESSION[egw_session::EGW_APPSESSION_VAR][$app][$location]) && !is_null($callback))
+		{
+			$_SESSION[egw_session::EGW_APPSESSION_VAR][$app][$location] = call_user_func_array($callback,$callback_params);
+		}
+		return $_SESSION[egw_session::EGW_APPSESSION_VAR][$app][$location];
+	}
+
+	/**
+	 * Unset some data in the cache for the whole source tree (all instances)
+	 *
+	 * @param string $app application storing data
+	 * @param string $location location name for data
+	 * @return boolean true if data was set, false if not (like isset())
+	 */
+	static public function unsetSession($app,$location)
+	{
+		if (isset($_SESSION[egw_session::EGW_SESSION_ENCRYPTED]))
+		{
+			if (egw_session::ERROR_LOG_DEBUG) error_log(__METHOD__.' called after session was encrypted --> ignored!');
+			return false;	// can no longer store something in the session, eg. because commit_session() was called
+		}
+		if (!isset($_SESSION[egw_session::EGW_APPSESSION_VAR][$app][$location]))
+		{
+			return false;
+		}
+		unset($_SESSION[egw_session::EGW_APPSESSION_VAR][$app][$location]);
+
+		return true;
+	}
+
+	/**
+	 * Static varible to cache request wide
+	 *
+	 * @var array
+	 */
+	private static $request_cache = array();
+
+	/**
+	 * Set some data in the cache for the whole source tree (all instances)
+	 *
+	 * @param string $app application storing data
+	 * @param string $location location name for data
+	 * @param mixed $data
+	 * @param int $expiration =0 expiration time is NOT used for REQUEST!
+	 * @return boolean true if data could be stored, false otherwise
+	 */
+	static public function setRequest($app,$location,$data,$expiration=0)
+	{
+		unset($expiration);	// not used, but required by function signature
+		self::$request_cache[$app][$location] = $data;
+
+		return true;
+	}
+
+	/**
+	 * Get some data from the cache for the whole source tree (all instances)
+	 *
+	 * @param string $app application storing data
+	 * @param string $location location name for data
+	 * @param callback $callback =null callback to get/create the value, if it's not cache
+	 * @param array $callback_params =array() array with parameters for the callback
+	 * @param int $expiration =0 expiration time is NOT used for REQUEST!
+	 * @return mixed NULL if data not found in cache (and no callback specified)
+	 */
+	static public function getRequest($app,$location,$callback=null,array $callback_params=array(),$expiration=0)
+	{
+		unset($expiration);	// not used, but required by function signature
+		if (!isset(self::$request_cache[$app][$location]) && !is_null($callback))
+		{
+			self::$request_cache[$app][$location] = call_user_func_array($callback,$callback_params);
+		}
+		return self::$request_cache[$app][$location];
+	}
+
+	/**
+	 * Unset some data in the cache for the whole source tree (all instances)
+	 *
+	 * @param string $app application storing data
+	 * @param string $location location name for data
+	 * @return boolean true if data was set, false if not (like isset())
+	 */
+	static public function unsetRequest($app,$location)
+	{
+		if (!isset(self::$request_cache[$app][$location]))
+		{
+			return false;
+		}
+		unset(self::$request_cache[$app][$location]);
+
+		return true;
+	}
+
+	/**
+	 * Get a caching provider for tree or instance level
+	 *
+	 * The returned provider already has an opened connection
+	 *
+	 * @param string $level Api\Cache::(TREE|INSTANCE) or install_id
+	 * @param boolean $log_not_found =true false do not log if no provider found, used eg. to supress error via unsetCache during installation
+	 * @return Api\Cache\Provider
+	 */
+	static protected function get_provider($level, $log_not_found=true)
+	{
+		static $providers = array();
+
+		if ($level != self::TREE) $level = self::INSTANCE;
+
+		if (!isset($providers[$level]))
+		{
+			$params = $GLOBALS['egw_info']['server']['cache_provider_'.strtolower($level)];
+			if (!isset($params) && $level == self::INSTANCE && isset(self::$default_provider))
+			{
+				$params = self::$default_provider;
+			}
+			if (!isset($params))
+			{
+				if ($level == self::TREE)	// if no tree level provider use the instance level one
+				{
+					$providers[$level] = self::get_provider(self::INSTANCE);
+				}
+				else
+				{
+					$providers[$level] = false;	// no provider specified
+					$reason = 'no provider specified';
+				}
+			}
+			elseif (!$params)
+			{
+					$providers[$level] = false;	// cache for $level disabled
+					$reason = "cache for $level disabled";
+			}
+			else
+			{
+				if (!is_array($params)) $params = (array)$params;
+
+				$class = array_shift($params);
+				if (!class_exists($class))
+				{
+					$providers[$level] = false;	// provider class not found
+					$reason = "provider $class not found";
+				}
+				else
+				{
+					try
+					{
+						$providers[$level] = new $class($params);
+					}
+					catch(Exception $e)
+					{
+						$providers[$level] = false;	// eg. could not open connection to backend
+						$reason = "error instanciating provider $class: ".$e->getMessage();
+					}
+				}
+			}
+			if (!$providers[$level] && $log_not_found) error_log(__METHOD__."($level) no provider found ($reason)!".function_backtrace());
+		}
+		//error_log(__METHOD__."($level) = ".array2string($providers[$level]).', cache_provider='.array2string($GLOBALS['egw_info']['server']['cache_provider_'.strtolower($level)]));
+		return $providers[$level];
+	}
+
+	/**
+	 * Get a system configuration, even if in setup and it's not read
+	 *
+	 * @param string $name
+	 * @param boolean $throw =true throw an exception, if we can't retriev the value
+	 * @return string|boolean string with config or false if not found and !$throw
+	 */
+	static public function get_system_config($name,$throw=true)
+	{
+		if(!isset($GLOBALS['egw_info']['server'][$name]))
+		{
+			if (isset($GLOBALS['egw_setup']) && isset($GLOBALS['egw_setup']->db) || $GLOBALS['egw']->db)
+			{
+				$db = $GLOBALS['egw']->db ? $GLOBALS['egw']->db : $GLOBALS['egw_setup']->db;
+
+				try {
+					if (($rs = $db->select(config::TABLE,'config_value',array(
+						'config_app'	=> 'phpgwapi',
+						'config_name'	=> $name,
+					),__LINE__,__FILE__)))
+					{
+						$GLOBALS['egw_info']['server'][$name] = $rs->fetchColumn();
+					}
+					else
+					{
+						error_log(__METHOD__."('$name', $throw) config value NOT found!");//.function_backtrace());
+					}
+				}
+				catch(egw_exception_db $e)
+				{
+					if ($throw) error_log(__METHOD__."('$name', $throw) cound NOT query value: ".$e->getMessage());//.function_backtrace());
+				}
+			}
+			if (!$GLOBALS['egw_info']['server'][$name] && $throw)
+			{
+				throw new Exception (__METHOD__."($name) \$GLOBALS['egw_info']['server']['$name'] is NOT set!");
+			}
+		}
+		return $GLOBALS['egw_info']['server'][$name];
+	}
+
+	/**
+	 * Flush (delete) whole (instance) cache or application/class specific part of it
+	 *
+	 * @param string $level =self::INSTANCE
+	 * @param string $app =null
+	 */
+	static public function flush($level=self::INSTANCE, $app=null)
+	{
+		$ret = true;
+		if (!($provider = self::get_provider($level)))
+		{
+			$ret = false;
+		}
+		else
+		{
+			if (!$provider->flush(self::keys($level, $app)))
+			{
+				if ($level == self::INSTANCE)
+				{
+					self::generate_instance_key();
+				}
+				else
+				{
+					$ret = false;
+				}
+			}
+		}
+		//error_log(__METHOD__."('$level', '$app') returning ".array2string($ret));
+		return $ret;
+	}
+
+	/**
+	 * Unset instance key, so it get read again and re-read install_id from database
+	 */
+	static public function unset_instance_key()
+	{
+		self::$instance_key = null;
+		$GLOBALS['egw_info']['server']['install_id'] = self::get_system_config('install_id', false);
+	}
+
+	/**
+	 * Key used for instance specific data
+	 *
+	 * @var string
+	 */
+	private static $instance_key;
+
+	/**
+	 * Generate a new instance key and by doing so effectivly flushes whole instance cache
+	 *
+	 * @param string $install_id =null default use install_id of current instance
+	 * @return string new key also stored in self::$instance_key
+	 */
+	static public function generate_instance_key($install_id=null)
+	{
+		if (!isset($install_id))
+		{
+			self::$instance_key = null;
+			$install_id = self::get_system_config('install_id');
+		}
+		$instance_key = self::INSTANCE.'-'.$install_id.'-'.microtime(true);
+		self::setTree(__CLASS__, $install_id, $instance_key);
+
+		//error_log(__METHOD__."(install_id='$install_id') returning '".$instance_key."'");
+		return $instance_key;
+	}
+
+	/**
+	 * Get keys array from $level, $app and $location
+	 *
+	 * @param string $level Api\Cache::(TREE|INSTANCE) or instance_id
+	 * @param string $app =null
+	 * @param string $location =null
+	 * @return array
+	 */
+	static public function keys($level, $app=null, $location=null)
+	{
+		static $tree_key = null;
+
+		switch($level)
+		{
+			case self::TREE:
+				if (!isset($tree_key))
+				{
+					$tree_key = $level.'-'.str_replace(array(':','/','\\'),'-', self::$egw_server_root);
+					// add charset to key, if not utf-8 (as everything we store depends on charset!)
+					if (($charset = self::get_system_config('system_charset',false)) && $charset != 'utf-8')
+					{
+						$tree_key .= '-'.$charset;
+					}
+				}
+				$level_key = $tree_key;
+				break;
+			default:	// arbitrary install_id given --> check for current instance
+				if ($level !== $GLOBALS['egw_info']['server']['install_id'])
+				{
+					$level_key = self::getTree(__CLASS__, $level);
+					if (!isset($level_key)) $level_key = self::generate_instance_key($level);
+					break;
+				}
+				// fall-through for current instance
+			case self::INSTANCE:
+				if (!isset(self::$instance_key))
+				{
+					self::$instance_key = self::getTree(__CLASS__, self::get_system_config('install_id'));
+					//error_log(__METHOD__."('$level',...) instance_key read from tree-cache=".array2string(self::$instance_key));
+					if (!isset(self::$instance_key)) self::$instance_key = self::generate_instance_key();
+				}
+				$level_key = self::$instance_key;
+				break;
+		}
+		$keys = array($level_key);
+		if (isset($app))
+		{
+			$keys[] = $app;
+			if (isset($location)) $keys[] = $location;
+		}
+		return $keys;
+	}
+
+	/**
+	 * Let everyone know the methods of this class should be used only statically
+	 *
+	 */
+	function __construct()
+	{
+		throw new egw_exception_wrong_parameter("All methods of class ".__CLASS__." should be called static!");
+	}
+}
+
+// setting apc as default provider, if apc_fetch function exists AND further checks in Api\Cache\Apc recommed it
+if (is_null(Cache::$default_provider))
+{
+	Cache::$default_provider = function_exists('apc_fetch') && Cache\Apc::available() ?
+		'EGroupware\Api\Cache\Apc' : 'EGroupware\Api\Cache\Files';
+}
+
+//error_log('Cache::$default_provider='.array2string(Cache::$default_provider));
diff --git a/phpgwapi/inc/class.egw_cache_apc.inc.php b/api/src/Cache/Apc.php
similarity index 95%
rename from phpgwapi/inc/class.egw_cache_apc.inc.php
rename to api/src/Cache/Apc.php
index e83d3431f2..d170bcc596 100644
--- a/phpgwapi/inc/class.egw_cache_apc.inc.php
+++ b/api/src/Cache/Apc.php
@@ -7,17 +7,19 @@
  * @package api
  * @subpackage cache
  * @author Ralf Becker <RalfBecker-AT-outdoor-training.de>
- * @copyright (c) 2010-15 by Ralf Becker <RalfBecker-AT-outdoor-training.de>
+ * @copyright (c) 2010-16 by Ralf Becker <RalfBecker-AT-outdoor-training.de>
  * @version $Id$
  */
 
+namespace EGroupware\Api\Cache;
+
 /**
  * Caching provider storing data in PHP's APC or APCu extension / shared memory.
  *
  * The provider concats all $keys with '::' to get a single string.
  *
  * This provider is used by default, if it is available or explicit enabled in your header.inc.php:
- * $GLOBALS['egw_info']['server']['cache_provider_instance'] = array('egw_cache_apc');
+ * $GLOBALS['egw_info']['server']['cache_provider_instance'] = array('EGroupware\Api\Cache\Apc');
  * and optional also $GLOBALS['egw_info']['server']['cache_provider_tree'] (defaults to instance)
  *
  * APC(u) and CLI:
@@ -25,14 +27,14 @@
  * APC(u) is not enabled by default for CLI (apc.enable_cli), nor would it access same shared memory!
  * It makes no sense to fall back to files cache, as this is probably quite outdated,
  * if PHP via Webserver uses APC. Better to use no cache at all.
- * egw_cache::get*() will return NULL for not found and egw_cache::[un]set*()
+ * Api\Cache::get*() will return NULL for not found and Api\Cache::[un]set*()
  * false for not being able to (un)set anything.
  * It also does not make sense to report failure by throwing an Exception and filling
  * up cron logs.
  * --> if APC(u) is available for Webserver, we report availability for CLI too,
  *     but use no cache at all!
  */
-class egw_cache_apc extends egw_cache_provider_check implements egw_cache_provider
+class Apc extends Base implements Provider
 {
 	/**
 	 * Constructor, eg. opens the connection to the backend
diff --git a/api/src/Cache/Base.php b/api/src/Cache/Base.php
new file mode 100644
index 0000000000..83f2b5e0c4
--- /dev/null
+++ b/api/src/Cache/Base.php
@@ -0,0 +1,206 @@
+<?php
+/**
+ * EGroupware API: Base class for all caching providers
+ *
+ * @link http://www.egroupware.org
+ * @license http://opensource.org/licenses/gpl-license.php GPL - GNU General Public License
+ * @package api
+ * @subpackage cache
+ * @author Ralf Becker <RalfBecker-AT-outdoor-training.de>
+ * @copyright (c) 2009-16 by Ralf Becker <RalfBecker-AT-outdoor-training.de>
+ * @version $Id$
+ */
+
+namespace EGroupware\Api\Cache;
+
+use EGroupware\Api;
+
+/**
+ * Base class for all caching providers
+ *
+ * Implements some checks used for testing providers.
+ */
+abstract class Base implements Provider
+{
+	/**
+	 * Run several checks on a caching provider
+	 *
+	 * @param boolean $verbose =false true: echo failed checks
+	 * @return int number of failed checks
+	 */
+	function check($verbose=false)
+	{
+		// set us up as provider for Api\Cache class
+		$GLOBALS['egw_info']['server']['install_id'] = md5(microtime(true));
+		unset($GLOBALS['egw_info']['server']['cache_provider_instance']);
+		unset($GLOBALS['egw_info']['server']['cache_provider_tree']);
+		Api\Cache::$default_provider = get_class($this);
+
+		$failed = 0;
+		foreach(array(
+			Api\Cache::TREE => 'tree',
+			Api\Cache::INSTANCE => 'instance',
+		) as $level => $label)
+		{
+			$locations = array();
+			foreach(array('string',123,true,false,null,array(),array(1,2,3)) as $data)
+			{
+				$location = md5(microtime(true).$label.serialize($data));
+				$get_before_set = $this->get(array($level,__CLASS__,$location));
+				if (!is_null($get_before_set))
+				{
+					if ($verbose) echo "$label: get_before_set=".array2string($get_before_set)." != NULL\n";
+					++$failed;
+				}
+				if (($set = $this->set(array($level,__CLASS__,$location), $data, 10)) !== true)
+				{
+					if ($verbose) echo "$label: set returned ".array2string($set)." !== TRUE\n";
+					++$failed;
+				}
+				$get_after_set = $this->get(array($level,__CLASS__,$location));
+				if ($get_after_set !== $data)
+				{
+					if ($verbose) echo "$label: get_after_set=".array2string($get_after_set)." !== ".array2string($data)."\n";
+					++$failed;
+				}
+				if (is_a($this, 'EGroupware\Api\Cache\ProviderMultiple'))
+				{
+					$mget_after_set = $this->mget(array($level,__CLASS__,array($location)));
+					if ($mget_after_set[$location] !== $data)
+					{
+						if ($verbose) echo "$label: mget_after_set['$location']=".array2string($mget_after_set[$location])." !== ".array2string($data)."\n";
+						++$failed;
+					}
+				}
+				$add_after_set = $this->add(array($level,__CLASS__,$location), 'other-data');
+				if ($add_after_set !== false)
+				{
+					if ($verbose) echo "$label: add_after_set=".array2string($add_after_set)."\n";
+					++$failed;
+				}
+				if (($delete = $this->delete(array($level,__CLASS__,$location))) !== true)
+				{
+					if ($verbose) echo "$label: delete returned ".array2string($delete)." !== TRUE\n";
+					++$failed;
+				}
+				$get_after_delete = $this->get(array($level,__CLASS__,$location));
+				if (!is_null($get_after_delete))
+				{
+					if ($verbose) echo "$label: get_after_delete=".array2string($get_after_delete)." != NULL\n";
+					++$failed;
+				}
+				// prepare for mget of everything
+				if (is_a($this, 'EGroupware\Api\Cache\ProviderMultiple'))
+				{
+					$locations[$location] = $data;
+					$mget_after_delete = $this->mget(array($level,__CLASS__,array($location)));
+					if (isset($mget_after_delete[$location]))
+					{
+						if ($verbose) echo "$label: mget_after_delete['$location']=".array2string($mget_after_delete[$location])." != NULL\n";
+						++$failed;
+					}
+				}
+				elseif (!is_null($data))	// emulation can NOT distinquish between null and not set
+				{
+					$locations[$location] = $data;
+				}
+				$add_after_delete = $this->add(array($level,__CLASS__,$location), $data, 10);
+				if ($add_after_delete !== true)
+				{
+					if ($verbose) echo "$label: add_after_delete=".array2string($add_after_delete)."\n";
+					++$failed;
+				}
+				else
+				{
+					$get_after_add = $this->get(array($level,__CLASS__,$location));
+					if ($get_after_add !== $data)
+					{
+						if ($verbose) echo "$label: get_after_add=".array2string($get_after_add)." !== ".array2string($data)."\n";
+						++$failed;
+					}
+				}
+			}
+			// get all above in one request
+			$keys = array_keys($locations);
+			$keys_bogus = array_merge(array('not-set'),array_keys($locations),array('not-set-too'));
+			if (is_a($this, 'EGroupware\Api\Cache\ProviderMultiple'))
+			{
+				$mget = $this->mget(array($level,__CLASS__,$keys));
+				$mget_bogus = $this->mget(array($level,__CLASS__,$keys_bogus));
+			/* Api\Cache::getCache() gives a different result, as it does NOT use $level direkt
+			}
+			else
+			{
+				$mget = Api\Cache::getCache($level, __CLASS__, $keys);
+				$mget_bogus = Api\Cache::getCache($level, __CLASS__, $keys_bogus);
+			}*/
+				if ($mget !== $locations)
+				{
+					if ($verbose) echo "$label: mget=\n".array2string($mget)." !==\n".array2string($locations)."\n";
+					++$failed;
+				}
+				if ($mget_bogus !== $locations)
+				{
+					if ($verbose) echo "$label: mget(".array2string($keys_bogus).")=\n".array2string($mget_bogus)." !==\n".array2string($locations)."\n";
+					++$failed;
+				}
+			}
+		}
+
+		return $failed;
+	}
+
+	/**
+	 * Delete all data under given keys
+	 *
+	 * Providers can return false, if they do not support flushing part of the cache (eg. memcache)
+	 *
+	 * @param array $keys eg. array($level,$app,$location)
+	 * @return boolean true on success, false on error (eg. $key not set)
+	 */
+	function flush(array $keys)
+	{
+		unset($keys);	// required by function signature
+		return false;
+	}
+}
+
+// some testcode, if this file is called via it's URL
+// can be run on command-line: sudo php -d apc.enable_cli=1 -f api/src/Cache/Base.php
+/*if (isset($_SERVER['SCRIPT_FILENAME']) && realpath($_SERVER['SCRIPT_FILENAME']) == __FILE__)
+{
+	if (!isset($_SERVER['HTTP_HOST']))
+	{
+		chdir(dirname(__FILE__));	// to enable our relative pathes to work
+	}
+	$GLOBALS['egw_info'] = array(
+		'flags' => array(
+			'noapi' => true,
+		),
+	);
+	include_once '../../../header.inc.php';
+
+	if (isset($_SERVER['HTTP_HOST'])) echo "<pre style='whitespace: nowrap'>\n";
+
+	foreach(array(
+		'EGroupware\Api\Cache\Apc' => array(),
+		'EGroupware\Api\Cache\Memcache' => array('localhost'),
+		'EGroupware\Api\Cache\Files' => array('/tmp'),
+	) as $class => $param)
+	{
+		echo "Checking $class:\n";
+		try {
+			$start = microtime(true);
+			$provider = new $class($param);
+			$n = 100;
+			for($i=1; $i <= $n; ++$i)
+			{
+				$failed = $provider->check($i == 1);
+			}
+			printf("$failed checks failed, $n iterations took %5.3f sec\n\n", microtime(true)-$start);
+		}
+		catch (Exception $e) {
+			printf($e->getMessage()."\n\n");
+		}
+	}
+}*/
diff --git a/phpgwapi/inc/class.egw_cache_files.inc.php b/api/src/Cache/Files.php
similarity index 95%
rename from phpgwapi/inc/class.egw_cache_files.inc.php
rename to api/src/Cache/Files.php
index fc05905c04..6d4f075c5c 100644
--- a/phpgwapi/inc/class.egw_cache_files.inc.php
+++ b/api/src/Cache/Files.php
@@ -7,17 +7,21 @@
  * @package api
  * @subpackage cache
  * @author Ralf Becker <RalfBecker-AT-outdoor-training.de>
- * @copyright (c) 2009-15 by Ralf Becker <RalfBecker-AT-outdoor-training.de>
+ * @copyright (c) 2009-16 by Ralf Becker <RalfBecker-AT-outdoor-training.de>
  * @version $Id$
  */
 
+namespace EGroupware\Api\Cache;
+
+use EGroupware\Api;
+
 /**
  * Caching provider storing data in files
  *
  * The provider creates subdirs under a given path
  * for each values in $key
  */
-class egw_cache_files extends egw_cache_provider_check implements egw_cache_provider
+class Files extends Base implements Provider
 {
 	/**
 	 * Extension of file used to store expiration > 0
@@ -45,7 +49,7 @@ class egw_cache_files extends egw_cache_provider_check implements egw_cache_prov
 		}
 		else
 		{
-			$this->base_path = egw_cache::get_system_config('temp_dir', false);
+			$this->base_path = Api\Cache::get_system_config('temp_dir', false);
 			if (isset($this->base_path)) $this->base_path .= '/egw_cache';
 		}
 		if (!isset($this->base_path) || !file_exists($this->base_path) && !mkdir($this->base_path,0700,true))
diff --git a/phpgwapi/inc/class.egw_cache_memcache.inc.php b/api/src/Cache/Memcache.php
similarity index 95%
rename from phpgwapi/inc/class.egw_cache_memcache.inc.php
rename to api/src/Cache/Memcache.php
index dcdfd92043..7c66217155 100644
--- a/phpgwapi/inc/class.egw_cache_memcache.inc.php
+++ b/api/src/Cache/Memcache.php
@@ -7,24 +7,26 @@
  * @package api
  * @subpackage cache
  * @author Ralf Becker <RalfBecker-AT-outdoor-training.de>
- * @copyright (c) 2009-15 by Ralf Becker <RalfBecker-AT-outdoor-training.de>
+ * @copyright (c) 2009-16 by Ralf Becker <RalfBecker-AT-outdoor-training.de>
  * @version $Id$
  */
 
+namespace EGroupware\Api\Cache;
+
 /**
  * Caching provider storing data in memcached via PHP's memcache extension
  *
  * The provider concats all $keys with '::' to get a single string.
  *
  * To use this provider set in your header.inc.php:
- * $GLOBALS['egw_info']['server']['cache_provider_instance'] = array('egw_cache_memcache','localhost'[,'otherhost:port']);
+ * $GLOBALS['egw_info']['server']['cache_provider_instance'] = array('EGroupware\Api\Cache\Memcache','localhost'[,'otherhost:port']);
  * and optional also $GLOBALS['egw_info']['server']['cache_provider_tree'] (defaults to instance)
  *
  * You can set more then one server and specify a port, if it's not the default one 11211.
  *
  * If igbinary extension is available, it is prefered over PHP (un)serialize.
  */
-class egw_cache_memcache extends egw_cache_provider_check implements egw_cache_provider_multiple
+class Memcache extends Base implements ProviderMultiple
 {
 	/**
 	 * Instance of Memcache
diff --git a/phpgwapi/inc/class.egw_cache_memcached.inc.php b/api/src/Cache/Memcached.php
similarity index 97%
rename from phpgwapi/inc/class.egw_cache_memcached.inc.php
rename to api/src/Cache/Memcached.php
index 49dec8076e..df77ac1411 100644
--- a/phpgwapi/inc/class.egw_cache_memcached.inc.php
+++ b/api/src/Cache/Memcached.php
@@ -7,17 +7,19 @@
  * @package api
  * @subpackage cache
  * @author Ralf Becker <RalfBecker-AT-outdoor-training.de>
- * @copyright (c) 2009-15 by Ralf Becker <RalfBecker-AT-outdoor-training.de>
+ * @copyright (c) 2009-16 by Ralf Becker <RalfBecker-AT-outdoor-training.de>
  * @version $Id$
  */
 
+namespace EGroupware\Api\Cache;
+
 /**
  * Caching provider storing data in memcached via PHP's memcached extension
  *
  * The provider concats all $keys with '::' to get a single string.
  *
  * To use this provider set in your header.inc.php:
- * $GLOBALS['egw_info']['server']['cache_provider_instance'] = array('egw_cache_memcached','localhost'[,'otherhost:port']);
+ * $GLOBALS['egw_info']['server']['cache_provider_instance'] = array('EGroupware\Api\Cache\Memcached','localhost'[,'otherhost:port']);
  * and optional also $GLOBALS['egw_info']['server']['cache_provider_tree'] (defaults to instance)
  *
  * You can set more then one server and specify a port, if it's not the default one 11211.
@@ -26,7 +28,7 @@
  *
  * If igbinary extension is available, it is prefered over PHP (un)serialize.
  */
-class egw_cache_memcached extends egw_cache_provider_check implements egw_cache_provider_multiple
+class Memcached extends Base implements ProviderMultiple
 {
 	/**
 	 * Instance of Memcached
diff --git a/api/src/Cache/Provider.php b/api/src/Cache/Provider.php
new file mode 100644
index 0000000000..77a7ceb6cb
--- /dev/null
+++ b/api/src/Cache/Provider.php
@@ -0,0 +1,78 @@
+<?php
+/**
+ * EGroupware API: Caching provider interface
+ *
+ * @link http://www.egroupware.org
+ * @license http://opensource.org/licenses/gpl-license.php GPL - GNU General Public License
+ * @package api
+ * @subpackage cache
+ * @author Ralf Becker <RalfBecker-AT-outdoor-training.de>
+ * @copyright (c) 2009-16 by Ralf Becker <RalfBecker-AT-outdoor-training.de>
+ * @version $Id$
+ */
+
+namespace EGroupware\Api\Cache;
+
+/**
+ * Interface for a caching provider for tree and instance level
+ *
+ * The provider can eg. create subdirs under /tmp for each key
+ * to store data as a file or concat them with a separator to
+ * get a single string key to eg. store data in memcached
+ */
+interface Provider
+{
+	/**
+	 * Constructor, eg. opens the connection to the backend
+	 *
+	 * @throws Exception if connection to backend could not be established
+	 * @param array $params eg. array(host,port) or array(directory) depending on the provider
+	 */
+	function __construct(array $params);
+
+	/**
+	 * Stores some data in the cache, if it does NOT already exists there
+	 *
+	 * @param array $keys eg. array($level,$app,$location)
+	 * @param mixed $data
+	 * @param int $expiration =0
+	 * @return boolean true on success, false on error, incl. key already exists in cache
+	 */
+	function add(array $keys,$data,$expiration=0);
+
+	/**
+	 * Stores some data in the cache
+	 *
+	 * @param array $keys eg. array($level,$app,$location)
+	 * @param mixed $data
+	 * @param int $expiration =0
+	 * @return boolean true on success, false on error
+	 */
+	function set(array $keys,$data,$expiration=0);
+
+	/**
+	 * Get some data from the cache
+	 *
+	 * @param array $keys eg. array($level,$app,$location)
+	 * @return mixed data stored or NULL if not found in cache
+	 */
+	function get(array $keys);
+
+	/**
+	 * Delete some data from the cache
+	 *
+	 * @param array $keys eg. array($level,$app,$location)
+	 * @return boolean true on success, false on error (eg. $key not set)
+	 */
+	function delete(array $keys);
+
+	/**
+	 * Delete all data under given keys
+	 *
+	 * Providers can return false, if they do not support flushing part of the cache (eg. memcache)
+	 *
+	 * @param array $keys eg. array($level,$app,$location)
+	 * @return boolean true on success, false on error (eg. $key not set)
+	 */
+	function flush(array $keys);
+}
diff --git a/api/src/Cache/ProviderMultiple.php b/api/src/Cache/ProviderMultiple.php
new file mode 100644
index 0000000000..29675d8c9a
--- /dev/null
+++ b/api/src/Cache/ProviderMultiple.php
@@ -0,0 +1,28 @@
+<?php
+/**
+ * EGroupware API: Caching data
+ *
+ * @link http://www.egroupware.org
+ * @license http://opensource.org/licenses/gpl-license.php GPL - GNU General Public License
+ * @package api
+ * @subpackage cache
+ * @author Ralf Becker <RalfBecker-AT-outdoor-training.de>
+ * @copyright (c) 2009-16 by Ralf Becker <RalfBecker-AT-outdoor-training.de>
+ * @version $Id$
+ */
+
+namespace EGroupware\Api\Cache;
+
+/**
+ * Interface for a caching provider being able to retrieve multiple entires
+ */
+interface ProviderMultiple
+{
+	/**
+	 * Get multiple data from the cache
+	 *
+	 * @param array $keys eg. array of array($level,$app,array $locations)
+	 * @return array key => data stored, not found keys are NOT returned
+	 */
+	function mget(array $keys);
+}
diff --git a/api/src/Db.php b/api/src/Db.php
index 11963a7e57..03dfc95ad6 100644
--- a/api/src/Db.php
+++ b/api/src/Db.php
@@ -13,7 +13,6 @@
 
 namespace EGroupware\Api;
 
-use egw_cache;
 use egw_exception_db_connection;
 use egw_exception_db_invalid_sql;
 use egw_exception_wrong_parameter;
@@ -406,7 +405,7 @@ class Db
 	{
 		$hosts = explode(';', $this->Host[0] == '@' ? getenv(substr($this->Host, 1)) : $this->Host);
 		$num_hosts = count($hosts);
-		$n =& egw_cache::getSession(__CLASS__, $this->Host);
+		$n =& Cache::getSession(__CLASS__, $this->Host);
 		if (!isset($n)) $n = 0;
 
 		if ($next && ++$n >= $num_hosts+2)
diff --git a/api/src/Db/Backup.php b/api/src/Db/Backup.php
index ca784bfe31..e070ab0263 100644
--- a/api/src/Db/Backup.php
+++ b/api/src/Db/Backup.php
@@ -14,8 +14,8 @@
 namespace EGroupware\Api\Db;
 
 use EGroupware\Api;
+
 use egw_exception_db_invalid_sql;
-use egw_cache;
 use config;
 use translation;
 use html;
@@ -493,9 +493,9 @@ class Backup
 				return lang('Restore failed');
 			}
 		}
-		// generate an install_id if we dont have one (it breaks egw_cache::flush() stalling the upgrade)
+		// generate an install_id if we dont have one (it breaks Api\Cache::flush() stalling the upgrade)
 		unset($GLOBALS['egw_info']['server']['install_id']);
-		if (!($GLOBALS['egw_info']['server']['install_id'] = egw_cache::get_system_config('install_id', false)))
+		if (!($GLOBALS['egw_info']['server']['install_id'] = Api\Cache::get_system_config('install_id', false)))
 		{
 			$GLOBALS['egw_info']['server']['install_id'] = md5(microtime(true).$_SERVER['HTTP_HOST']);
 			$this->db->insert('egw_config', array(
@@ -506,7 +506,7 @@ class Backup
 			), __LINE__, __FILE__);
 		}
 		// flush instance cache
-		egw_cache::flush(egw_cache::INSTANCE);
+		Api\Cache::flush(Api\Cache::INSTANCE);
 
 		// search-and-register-hooks
 		$GLOBALS['egw']->hooks->register_all_hooks();
diff --git a/api/src/Vfs.php b/api/src/Vfs.php
index 8c139811e4..09980cc09b 100644
--- a/api/src/Vfs.php
+++ b/api/src/Vfs.php
@@ -27,7 +27,6 @@ use egw_exception_wrong_parameter;
 use egw_exception_wrong_userinput;
 use egw_exception;
 use egw_time;
-use egw_cache;
 
 /**
  * Class containing static methods to use the new eGW virtual file system
@@ -987,7 +986,7 @@ class Vfs extends Vfs\StreamWrapper
 	{
 		if ($session_only)
 		{
-			$session_eacls =& egw_cache::getSession(__CLASS__, self::SESSION_EACL);
+			$session_eacls =& Cache::getSession(__CLASS__, self::SESSION_EACL);
 			$session_eacls[] = array(
 				'path'   => $url[0] == '/' ? $url : self::parse_url($url, PHP_URL_PATH),
 				'owner'  => $owner ? $owner : self::$user,
@@ -1010,7 +1009,7 @@ class Vfs extends Vfs\StreamWrapper
 	{
 		$eacls = self::_call_on_backend('get_eacl',array($path),true);	// true = fail silent (no PHP Warning)
 
-		$session_eacls =& egw_cache::getSession(__CLASS__, self::SESSION_EACL);
+		$session_eacls =& Cache::getSession(__CLASS__, self::SESSION_EACL);
 		if ($session_eacls)
 		{
 			// eacl is recursive, therefore we have to match all parent-dirs too
diff --git a/api/src/Vfs/Sqlfs/StreamWrapper.php b/api/src/Vfs/Sqlfs/StreamWrapper.php
index 5c16198bfb..dce5bec684 100644
--- a/api/src/Vfs/Sqlfs/StreamWrapper.php
+++ b/api/src/Vfs/Sqlfs/StreamWrapper.php
@@ -7,19 +7,18 @@
  * @package api
  * @subpackage vfs
  * @author Ralf Becker <RalfBecker-AT-outdoor-training.de>
- * @copyright (c) 2008-15 by Ralf Becker <RalfBecker-AT-outdoor-training.de>
+ * @copyright (c) 2008-16 by Ralf Becker <RalfBecker-AT-outdoor-training.de>
  * @version $Id$
  */
 
 namespace EGroupware\Api\Vfs\Sqlfs;
 
 use EGroupware\Api\Vfs;
+use EGroupware\Api;
 
 // explicitly import old phpgwapi classes used:
-use egw_cache;
 use mime_magic;
 use config;
-use translation;
 use egw_exception_db;
 use egw_exception_wrong_parameter;
 use egw_exception_assertion_failed;
@@ -186,7 +185,7 @@ class StreamWrapper implements Vfs\StreamWrapperIface
 
 		self::$stat_cache = array();
 
-		egw_cache::setSession(self::EACL_APPNAME, 'extended_acl', self::$extended_acl = null);
+		Api\Cache::setSession(self::EACL_APPNAME, 'extended_acl', self::$extended_acl = null);
 	}
 
 	/**
@@ -1377,7 +1376,7 @@ class StreamWrapper implements Vfs\StreamWrapperIface
 	 */
 	static protected function _read_extended_acl()
 	{
-		if ((self::$extended_acl = egw_cache::getSession(self::EACL_APPNAME, 'extended_acl')))
+		if ((self::$extended_acl = Api\Cache::getSession(self::EACL_APPNAME, 'extended_acl')))
 		{
 			return;		// ext. ACL read from session.
 		}
@@ -1398,7 +1397,7 @@ class StreamWrapper implements Vfs\StreamWrapperIface
 		uksort(self::$extended_acl, function($a,$b) {
 			return strlen($b)-strlen($a);
 		});
-		egw_cache::setSession(self::EACL_APPNAME, 'extended_acl', self::$extended_acl);
+		Api\Cache::setSession(self::EACL_APPNAME, 'extended_acl', self::$extended_acl);
 		if (self::LOG_LEVEL > 1) error_log(__METHOD__.'() '.array2string(self::$extended_acl));
 	}
 
@@ -1464,7 +1463,7 @@ class StreamWrapper implements Vfs\StreamWrapperIface
 		}
 		if ($ret)
 		{
-			egw_cache::setSession(self::EACL_APPNAME, 'extended_acl', self::$extended_acl);
+			Api\Cache::setSession(self::EACL_APPNAME, 'extended_acl', self::$extended_acl);
 		}
 		if (self::LOG_LEVEL > 1) error_log(__METHOD__."($path,$rights,$owner,$fs_id)=".(int)$ret);
 		return $ret;
diff --git a/phpgwapi/inc/class.egw_cache.inc.php b/phpgwapi/inc/class.egw_cache.inc.php
index 9f610f2145..54c806b3bb 100644
--- a/phpgwapi/inc/class.egw_cache.inc.php
+++ b/phpgwapi/inc/class.egw_cache.inc.php
@@ -7,996 +7,20 @@
  * @package api
  * @subpackage cache
  * @author Ralf Becker <RalfBecker-AT-outdoor-training.de>
- * @copyright (c) 2009-15 by Ralf Becker <RalfBecker-AT-outdoor-training.de>
+ * @copyright (c) 2009-16 by Ralf Becker <RalfBecker-AT-outdoor-training.de>
  * @version $Id$
  */
 
+use EGroupware\Api;
+
 /**
  * Class to manage caching in eGroupware.
  *
- * It allows to cache on 4 levels:
- * a) tree:     for all instances/domains runining on a certain source path
- * b) instance: for all sessions on a given instance
- * c) session:  for all requests of a session, same as egw_session::appsession()
- * d) request:  just for this request (same as using a static variable)
- *
- * There's a get, a set and a unset method for each level: eg. getTree() or setInstance(),
- * as well as a variant allowing to specify the level as first parameter: eg. unsetCache()
- *
- * getXXX($app,$location,$callback=null,array $callback_params,$expiration=0)
- * has three optional parameters allowing to specify:
- * 3. a callback if requested data is not yes stored. In that case the callback is called
- *    and it's value is stored in the cache AND retured
- * 4. parameters to pass to the callback as array, see call_user_func_array
- * 5. an expiration time in seconds to specify how long data should be cached,
- *    default 0 means infinit (this time is not garantied and not supported for all levels!)
- *
- * Data is stored under an application name and a location, like egw_session::appsession().
- * In fact data stored at cache level egw_cache::SESSION, is stored in the same way as
- * egw_session::appsession() so both methods can be used with each other.
- *
- * The $app parameter should be either the app or the class name, which both are unique.
- *
- * The tree and instance wide cache uses a certain provider class, to store the data
- * eg. in memcached or if there's nothing else configured in the filesystem (eGW's temp_dir).
- *
- * "Admin >> clear cache and register hooks" allways only clears instance level cache of
- * calling instance. It never clears tree level cache, which makes it important to set
- * resonable expiry times or think about an other means of clearing that particular item.
- * (Not clearing of tree-level cache is important, as regenerating it is an expensive
- * operation for a huge scale EGroupware hosting operation.)
- *
- * Apps needing to talk to multiple EGroupware instances (eg. Stylite Managementserver)
- * can use install_id of instance as $level parameter to (set|get|unset)Cache method.
+ * @deprecated use Api\Cache instead
  */
-class egw_cache
-{
-	/**
-	 * tree-wide storage
-	 */
-	const TREE = 'Tree';
-	/**
-	 * instance-wide storage
-	 */
-	const INSTANCE = 'Instance';
-	/**
-	 * session-wide storage
-	 */
-	const SESSION = 'Session';
-	/**
-	 * request-wide storage
-	 */
-	const REQUEST = 'Request';
+class egw_cache extends Api\Cache {}
 
-	/**
-	 * Default provider for tree and instance data
-	 *
-	 * Can be specified eg. in the header.inc.php by setting:
-	 * $GLOBALS['egw_info']['server']['cache_provider_instance'] and optional
-	 * $GLOBALS['egw_info']['server']['cache_provider_tree'] (defaults to instance)
-	 *
-	 * Default is set (if not set here) after class definition to egw_cache_apc or egw_cache_files,
-	 * depending on function 'apc_fetch' exists or not
-	 *
-	 * @var array
-	 */
-	static $default_provider;	// = array('egw_cache_files');// array('egw_cache_memcache','localhost');
-
-	/**
-	 * Maximum expiration time, if set unlimited expiration (=0) or bigger expiration times are replaced with that time
-	 *
-	 * @var int
-	 */
-	static $max_expiration;
-
-	/**
-	 * Used to determine keys for tree- and instance-level caches
-	 *
-	 * @var string
-	 */
-	static $egw_server_root = EGW_SERVER_ROOT;
-
-	/**
-	 * Add some data in the cache, only if the key does not yet exist
-	 *
-	 * @param string $level use egw_cache::(TREE|INSTANCE)
-	 * @param string $app application storing data
-	 * @param string $location location name for data
-	 * @param mixed $data
-	 * @param int $expiration =0 expiration time in seconds, default 0 = never
-	 * @return boolean true if data could be stored, false otherwise incl. key already existed
-	 */
-	static public function addCache($level,$app,$location,$data,$expiration=0)
-	{
-		//error_log(__METHOD__."('$level','$app','$location',".array2string($data).",$expiration)");
-		switch($level)
-		{
-			case self::SESSION:
-			case self::REQUEST:
-				throw new egw_exception_wrong_parameter(__METHOD__."('$level', ...) unsupported level parameter!");
-
-			case self::INSTANCE:
-			case self::TREE:
-			default:
-				if (!($provider = self::get_provider($level)))
-				{
-					return false;
-				}
-				// limit expiration to configured maximum time
-				if (isset(self::$max_expiration) && (!$expiration || $expiration > self::$max_expiration))
-				{
-					$expiration = self::$max_expiration;
-				}
-				return $provider->add(self::keys($level,$app,$location),$data,$expiration);
-		}
-		throw new egw_exception_wrong_parameter(__METHOD__."() unknown level '$level'!");
-	}
-
-	/**
-	 * Set some data in the cache
-	 *
-	 * @param string $level use egw_cache::(TREE|INSTANCE|SESSION|REQUEST)
-	 * @param string $app application storing data
-	 * @param string $location location name for data
-	 * @param mixed $data
-	 * @param int $expiration =0 expiration time in seconds, default 0 = never
-	 * @return boolean true if data could be stored, false otherwise
-	 */
-	static public function setCache($level,$app,$location,$data,$expiration=0)
-	{
-		//error_log(__METHOD__."('$level','$app','$location',".array2string($data).",$expiration)");
-		switch($level)
-		{
-			case self::SESSION:
-			case self::REQUEST:
-				return call_user_func(array(__CLASS__,'set'.$level),$app,$location,$data,$expiration);
-
-			case self::INSTANCE:
-			case self::TREE:
-			default:
-				if (!($provider = self::get_provider($level)))
-				{
-					return false;
-				}
-				// limit expiration to configured maximum time
-				if (isset(self::$max_expiration) && (!$expiration || $expiration > self::$max_expiration))
-				{
-					$expiration = self::$max_expiration;
-				}
-				return $provider->set(self::keys($level,$app,$location),$data,$expiration);
-		}
-		throw new egw_exception_wrong_parameter(__METHOD__."() unknown level '$level'!");
-	}
-
-	/**
-	 * Get some data from the cache
-	 *
-	 * @param string $level use egw_cache::(TREE|INSTANCE|SESSION|REQUEST)
-	 * @param string $app application storing data
-	 * @param string|array $location location(s) name for data
-	 * @param callback $callback =null callback to get/create the value, if it's not cache
-	 * @param array $callback_params =array() array with parameters for the callback
-	 * @param int $expiration =0 expiration time in seconds, default 0 = never
-	 * @return mixed NULL if data not found in cache (and no callback specified) or
-	 * 	if $location is an array: location => data pairs for existing location-data, non-existing is not returned
-	 */
-	static public function getCache($level,$app,$location,$callback=null,array $callback_params=array(),$expiration=0)
-	{
-		switch($level)
-		{
-			case self::SESSION:
-			case self::REQUEST:
-				foreach((array)$location as $l)
-				{
-					$data[$l] = call_user_func(array(__CLASS__,'get'.$level),$app,$l,$callback,$callback_params,$expiration);
-				}
-				return is_array($location) ? $data : $data[$l];
-
-			case self::INSTANCE:
-			case self::TREE:
-			default:
-				if (!($provider = self::get_provider($level)))
-				{
-					return null;
-				}
-				try {
-					if (is_array($location))
-					{
-						if (!is_null($callback))
-						{
-							throw new egw_exception_wrong_parameter(__METHOD__."() you can NOT use multiple locations (\$location parameter is an array) together with a callback!");
-						}
-						if (is_a($provider, 'egw_cache_provider_multiple'))
-						{
-							$data = $provider->mget($keys=self::keys($level,$app,$location));
-						}
-						else	// default implementation calls get multiple times
-						{
-							$data = array();
-							foreach($location as $l)
-							{
-								$data[$l] = $provider->get($keys=self::keys($level,$app,$l));
-								if (!isset($data[$l])) unset($data[$l]);
-							}
-						}
-					}
-					else
-					{
-						$data = $provider->get($keys=self::keys($level,$app,$location));
-						if (is_null($data) && !is_null($callback))
-						{
-							$data = call_user_func_array($callback,$callback_params);
-							// limit expiration to configured maximum time
-							if (isset(self::$max_expiration) && (!$expiration || $expiration > self::$max_expiration))
-							{
-								$expiration = self::$max_expiration;
-							}
-							$provider->set($keys,$data,$expiration);
-						}
-					}
-				}
-				catch(Exception $e) {
-					unset($e);
-					$data = null;
-				}
-				return $data;
-		}
-		throw new egw_exception_wrong_parameter(__METHOD__."() unknown level '$level'!");
-	}
-
-	/**
-	 * Unset some data in the cache
-	 *
-	 * @param string $level use egw_cache::(TREE|INSTANCE|SESSION|REQUEST)
-	 * @param string $app application storing data
-	 * @param string $location location name for data
-	 * @return boolean true if data was set, false if not (like isset())
-	 */
-	static public function unsetCache($level,$app,$location)
-	{
-		switch($level)
-		{
-			case self::SESSION:
-			case self::REQUEST:
-				return call_user_func(array(__CLASS__,'unset'.$level),$app,$location);
-
-			case self::INSTANCE:
-			case self::TREE:
-			default:
-				if (!($provider = self::get_provider($level, false)))
-				{
-					return false;
-				}
-				return $provider->delete(self::keys($level,$app,$location));
-		}
-		throw new egw_exception_wrong_parameter(__METHOD__."() unknown level '$level'!");
-	}
-
-	/**
-	 * Set some data in the cache for the whole source tree (all instances)
-	 *
-	 * @param string $app application storing data
-	 * @param string $location location name for data
-	 * @param mixed $data
-	 * @param int $expiration =0 expiration time in seconds, default 0 = never
-	 * @return boolean true if data could be stored, false otherwise
-	 */
-	static public function setTree($app,$location,$data,$expiration=0)
-	{
-		//error_log(__METHOD__."('$app','$location',".array2string($data).",$expiration)");
-		return self::setCache(self::TREE,$app,$location,$data,$expiration);
-	}
-
-	/**
-	 * Get some data from the cache for the whole source tree (all instances)
-	 *
-	 * @param string $app application storing data
-	 * @param string $location location name for data
-	 * @param callback $callback =null callback to get/create the value, if it's not cache
-	 * @param array $callback_params =array() array with parameters for the callback
-	 * @param int $expiration =0 expiration time in seconds, default 0 = never
-	 * @return mixed NULL if data not found in cache (and no callback specified)
-	 */
-	static public function getTree($app,$location,$callback=null,array $callback_params=array(),$expiration=0)
-	{
-		return self::getCache(self::TREE,$app,$location,$callback,$callback_params,$expiration);
-	}
-
-	/**
-	 * Unset some data in the cache for the whole source tree (all instances)
-	 *
-	 * @param string $app application storing data
-	 * @param string $location location name for data
-	 * @return boolean true if data was set, false if not (like isset())
-	 */
-	static public function unsetTree($app,$location)
-	{
-		return self::unsetCache(self::TREE,$app,$location);
-	}
-
-	/**
-	 * Set some data in the cache for the whole source tree (all instances)
-	 *
-	 * @param string $app application storing data
-	 * @param string $location location name for data
-	 * @param mixed $data
-	 * @param int $expiration =0 expiration time in seconds, default 0 = never
-	 * @return boolean true if data could be stored, false otherwise
-	 */
-	static public function setInstance($app,$location,$data,$expiration=0)
-	{
-		return self::setCache(self::INSTANCE,$app,$location,$data,$expiration);
-	}
-
-	/**
-	 * Get some data from the cache for the whole source tree (all instances)
-	 *
-	 * @param string $app application storing data
-	 * @param string $location location name for data
-	 * @param callback $callback =null callback to get/create the value, if it's not cache
-	 * @param array $callback_params =array() array with parameters for the callback
-	 * @param int $expiration =0 expiration time in seconds, default 0 = never
-	 * @return mixed NULL if data not found in cache (and no callback specified)
-	 */
-	static public function getInstance($app,$location,$callback=null,array $callback_params=array(),$expiration=0)
-	{
-		return self::getCache(self::INSTANCE,$app,$location,$callback,$callback_params,$expiration);
-	}
-
-	/**
-	 * Unset some data in the cache for the whole source tree (all instances)
-	 *
-	 * @param string $app application storing data
-	 * @param string $location location name for data
-	 * @return boolean true if data was set, false if not (like isset())
-	 */
-	static public function unsetInstance($app,$location)
-	{
-		return self::unsetCache(self::INSTANCE,$app,$location);
-	}
-
-	/**
-	 * Set some data in the cache for the whole source tree (all instances)
-	 *
-	 * @param string $app application storing data
-	 * @param string $location location name for data
-	 * @param mixed $data
-	 * @param int $expiration =0 expiration time in seconds, default 0 = never
-	 * @return boolean true if data could be stored, false otherwise
-	 */
-	static public function setSession($app,$location,$data,$expiration=0)
-	{
-		unset($expiration);	// not used, but required by function signature
-		if (isset($_SESSION[egw_session::EGW_SESSION_ENCRYPTED]))
-		{
-			if (egw_session::ERROR_LOG_DEBUG) error_log(__METHOD__.' called after session was encrypted --> ignored!');
-			return false;	// can no longer store something in the session, eg. because commit_session() was called
-		}
-		$_SESSION[egw_session::EGW_APPSESSION_VAR][$app][$location] = $data;
-
-		return true;
-	}
-
-	/**
-	 * Get some data from the cache for the whole source tree (all instances)
-	 *
-	 * Returns a reference to the var in the session!
-	 *
-	 * @param string $app application storing data
-	 * @param string $location location name for data
-	 * @param callback $callback =null callback to get/create the value, if it's not cache
-	 * @param array $callback_params =array() array with parameters for the callback
-	 * @param int $expiration =0 expiration time in seconds, default 0 = never
-	 * @return mixed NULL if data not found in cache (and no callback specified)
-	 */
-	static public function &getSession($app,$location,$callback=null,array $callback_params=array(),$expiration=0)
-	{
-		unset($expiration);	// not used, but required by function signature
-		if (isset($_SESSION[egw_session::EGW_SESSION_ENCRYPTED]))
-		{
-			if (egw_session::ERROR_LOG_DEBUG) error_log(__METHOD__.' called after session was encrypted --> ignored!');
-			return null;	// can no longer store something in the session, eg. because commit_session() was called
-		}
-		if (!isset($_SESSION[egw_session::EGW_APPSESSION_VAR][$app][$location]) && !is_null($callback))
-		{
-			$_SESSION[egw_session::EGW_APPSESSION_VAR][$app][$location] = call_user_func_array($callback,$callback_params);
-		}
-		return $_SESSION[egw_session::EGW_APPSESSION_VAR][$app][$location];
-	}
-
-	/**
-	 * Unset some data in the cache for the whole source tree (all instances)
-	 *
-	 * @param string $app application storing data
-	 * @param string $location location name for data
-	 * @return boolean true if data was set, false if not (like isset())
-	 */
-	static public function unsetSession($app,$location)
-	{
-		if (isset($_SESSION[egw_session::EGW_SESSION_ENCRYPTED]))
-		{
-			if (egw_session::ERROR_LOG_DEBUG) error_log(__METHOD__.' called after session was encrypted --> ignored!');
-			return false;	// can no longer store something in the session, eg. because commit_session() was called
-		}
-		if (!isset($_SESSION[egw_session::EGW_APPSESSION_VAR][$app][$location]))
-		{
-			return false;
-		}
-		unset($_SESSION[egw_session::EGW_APPSESSION_VAR][$app][$location]);
-
-		return true;
-	}
-
-	/**
-	 * Static varible to cache request wide
-	 *
-	 * @var array
-	 */
-	private static $request_cache = array();
-
-	/**
-	 * Set some data in the cache for the whole source tree (all instances)
-	 *
-	 * @param string $app application storing data
-	 * @param string $location location name for data
-	 * @param mixed $data
-	 * @param int $expiration =0 expiration time is NOT used for REQUEST!
-	 * @return boolean true if data could be stored, false otherwise
-	 */
-	static public function setRequest($app,$location,$data,$expiration=0)
-	{
-		unset($expiration);	// not used, but required by function signature
-		self::$request_cache[$app][$location] = $data;
-
-		return true;
-	}
-
-	/**
-	 * Get some data from the cache for the whole source tree (all instances)
-	 *
-	 * @param string $app application storing data
-	 * @param string $location location name for data
-	 * @param callback $callback =null callback to get/create the value, if it's not cache
-	 * @param array $callback_params =array() array with parameters for the callback
-	 * @param int $expiration =0 expiration time is NOT used for REQUEST!
-	 * @return mixed NULL if data not found in cache (and no callback specified)
-	 */
-	static public function getRequest($app,$location,$callback=null,array $callback_params=array(),$expiration=0)
-	{
-		unset($expiration);	// not used, but required by function signature
-		if (!isset(self::$request_cache[$app][$location]) && !is_null($callback))
-		{
-			self::$request_cache[$app][$location] = call_user_func_array($callback,$callback_params);
-		}
-		return self::$request_cache[$app][$location];
-	}
-
-	/**
-	 * Unset some data in the cache for the whole source tree (all instances)
-	 *
-	 * @param string $app application storing data
-	 * @param string $location location name for data
-	 * @return boolean true if data was set, false if not (like isset())
-	 */
-	static public function unsetRequest($app,$location)
-	{
-		if (!isset(self::$request_cache[$app][$location]))
-		{
-			return false;
-		}
-		unset(self::$request_cache[$app][$location]);
-
-		return true;
-	}
-
-	/**
-	 * Get a caching provider for tree or instance level
-	 *
-	 * The returned provider already has an opened connection
-	 *
-	 * @param string $level egw_cache::(TREE|INSTANCE) or install_id
-	 * @param boolean $log_not_found =true false do not log if no provider found, used eg. to supress error via unsetCache during installation
-	 * @return egw_cache_provider
-	 */
-	static protected function get_provider($level, $log_not_found=true)
-	{
-		static $providers = array();
-
-		if ($level != self::TREE) $level = self::INSTANCE;
-
-		if (!isset($providers[$level]))
-		{
-			$params = $GLOBALS['egw_info']['server']['cache_provider_'.strtolower($level)];
-			if (!isset($params) && $level == self::INSTANCE && isset(self::$default_provider))
-			{
-				$params = self::$default_provider;
-			}
-			if (!isset($params))
-			{
-				if ($level == self::TREE)	// if no tree level provider use the instance level one
-				{
-					$providers[$level] = self::get_provider(self::INSTANCE);
-				}
-				else
-				{
-					$providers[$level] = false;	// no provider specified
-					$reason = 'no provider specified';
-				}
-			}
-			elseif (!$params)
-			{
-					$providers[$level] = false;	// cache for $level disabled
-					$reason = "cache for $level disabled";
-			}
-			else
-			{
-				if (!is_array($params)) $params = (array)$params;
-
-				$class = array_shift($params);
-				if (!class_exists($class))
-				{
-					$providers[$level] = false;	// provider class not found
-					$reason = "provider $class not found";
-				}
-				else
-				{
-					try
-					{
-						$providers[$level] = new $class($params);
-					}
-					catch(Exception $e)
-					{
-						$providers[$level] = false;	// eg. could not open connection to backend
-						$reason = "error instanciating provider $class: ".$e->getMessage();
-					}
-				}
-			}
-			if (!$providers[$level] && $log_not_found) error_log(__METHOD__."($level) no provider found ($reason)!".function_backtrace());
-		}
-		//error_log(__METHOD__."($level) = ".array2string($providers[$level]).', cache_provider='.array2string($GLOBALS['egw_info']['server']['cache_provider_'.strtolower($level)]));
-		return $providers[$level];
-	}
-
-	/**
-	 * Get a system configuration, even if in setup and it's not read
-	 *
-	 * @param string $name
-	 * @param boolean $throw =true throw an exception, if we can't retriev the value
-	 * @return string|boolean string with config or false if not found and !$throw
-	 */
-	static public function get_system_config($name,$throw=true)
-	{
-		if(!isset($GLOBALS['egw_info']['server'][$name]))
-		{
-			if (isset($GLOBALS['egw_setup']) && isset($GLOBALS['egw_setup']->db) || $GLOBALS['egw']->db)
-			{
-				$db = $GLOBALS['egw']->db ? $GLOBALS['egw']->db : $GLOBALS['egw_setup']->db;
-
-				try {
-					if (($rs = $db->select(config::TABLE,'config_value',array(
-						'config_app'	=> 'phpgwapi',
-						'config_name'	=> $name,
-					),__LINE__,__FILE__)))
-					{
-						$GLOBALS['egw_info']['server'][$name] = $rs->fetchColumn();
-					}
-					else
-					{
-						error_log(__METHOD__."('$name', $throw) config value NOT found!");//.function_backtrace());
-					}
-				}
-				catch(egw_exception_db $e)
-				{
-					if ($throw) error_log(__METHOD__."('$name', $throw) cound NOT query value: ".$e->getMessage());//.function_backtrace());
-				}
-			}
-			if (!$GLOBALS['egw_info']['server'][$name] && $throw)
-			{
-				throw new Exception (__METHOD__."($name) \$GLOBALS['egw_info']['server']['$name'] is NOT set!");
-			}
-		}
-		return $GLOBALS['egw_info']['server'][$name];
-	}
-
-	/**
-	 * Flush (delete) whole (instance) cache or application/class specific part of it
-	 *
-	 * @param string $level =self::INSTANCE
-	 * @param string $app =null
-	 */
-	static public function flush($level=self::INSTANCE, $app=null)
-	{
-		$ret = true;
-		if (!($provider = self::get_provider($level)))
-		{
-			$ret = false;
-		}
-		else
-		{
-			if (!$provider->flush(self::keys($level, $app)))
-			{
-				if ($level == self::INSTANCE)
-				{
-					self::generate_instance_key();
-				}
-				else
-				{
-					$ret = false;
-				}
-			}
-		}
-		//error_log(__METHOD__."('$level', '$app') returning ".array2string($ret));
-		return $ret;
-	}
-
-	/**
-	 * Unset instance key, so it get read again and re-read install_id from database
-	 */
-	static public function unset_instance_key()
-	{
-		self::$instance_key = null;
-		$GLOBALS['egw_info']['server']['install_id'] = egw_cache::get_system_config('install_id', false);
-	}
-
-	/**
-	 * Key used for instance specific data
-	 *
-	 * @var string
-	 */
-	private static $instance_key;
-
-	/**
-	 * Generate a new instance key and by doing so effectivly flushes whole instance cache
-	 *
-	 * @param string $install_id =null default use install_id of current instance
-	 * @return string new key also stored in self::$instance_key
-	 */
-	static public function generate_instance_key($install_id=null)
-	{
-		if (!isset($install_id))
-		{
-			self::$instance_key = null;
-			$install_id = self::get_system_config('install_id');
-		}
-		$instance_key = self::INSTANCE.'-'.$install_id.'-'.microtime(true);
-		self::setTree(__CLASS__, $install_id, $instance_key);
-
-		//error_log(__METHOD__."(install_id='$install_id') returning '".$instance_key."'");
-		return $instance_key;
-	}
-
-	/**
-	 * Get keys array from $level, $app and $location
-	 *
-	 * @param string $level egw_cache::(TREE|INSTANCE) or instance_id
-	 * @param string $app =null
-	 * @param string $location =null
-	 * @return array
-	 */
-	static public function keys($level, $app=null, $location=null)
-	{
-		static $tree_key = null;
-
-		switch($level)
-		{
-			case self::TREE:
-				if (!isset($tree_key))
-				{
-					$tree_key = $level.'-'.str_replace(array(':','/','\\'),'-', self::$egw_server_root);
-					// add charset to key, if not utf-8 (as everything we store depends on charset!)
-					if (($charset = self::get_system_config('system_charset',false)) && $charset != 'utf-8')
-					{
-						$tree_key .= '-'.$charset;
-					}
-				}
-				$level_key = $tree_key;
-				break;
-			default:	// arbitrary install_id given --> check for current instance
-				if ($level !== $GLOBALS['egw_info']['server']['install_id'])
-				{
-					$level_key = self::getTree(__CLASS__, $level);
-					if (!isset($level_key)) $level_key = self::generate_instance_key($level);
-					break;
-				}
-				// fall-through for current instance
-			case self::INSTANCE:
-				if (!isset(self::$instance_key))
-				{
-					self::$instance_key = self::getTree(__CLASS__, self::get_system_config('install_id'));
-					//error_log(__METHOD__."('$level',...) instance_key read from tree-cache=".array2string(self::$instance_key));
-					if (!isset(self::$instance_key)) self::$instance_key = self::generate_instance_key();
-				}
-				$level_key = self::$instance_key;
-				break;
-		}
-		$keys = array($level_key);
-		if (isset($app))
-		{
-			$keys[] = $app;
-			if (isset($location)) $keys[] = $location;
-		}
-		return $keys;
-	}
-
-	/**
-	 * Let everyone know the methods of this class should be used only statically
-	 *
-	 */
-	function __construct()
-	{
-		throw new egw_exception_wrong_parameter("All methods of class ".__CLASS__." should be called static!");
-	}
-}
-
-/**
- * Interface for a caching provider for tree and instance level
- *
- * The provider can eg. create subdirs under /tmp for each key
- * to store data as a file or concat them with a separator to
- * get a single string key to eg. store data in memcached
- */
-interface egw_cache_provider
-{
-	/**
-	 * Constructor, eg. opens the connection to the backend
-	 *
-	 * @throws Exception if connection to backend could not be established
-	 * @param array $params eg. array(host,port) or array(directory) depending on the provider
-	 */
-	function __construct(array $params);
-
-	/**
-	 * Stores some data in the cache, if it does NOT already exists there
-	 *
-	 * @param array $keys eg. array($level,$app,$location)
-	 * @param mixed $data
-	 * @param int $expiration =0
-	 * @return boolean true on success, false on error, incl. key already exists in cache
-	 */
-	function add(array $keys,$data,$expiration=0);
-
-	/**
-	 * Stores some data in the cache
-	 *
-	 * @param array $keys eg. array($level,$app,$location)
-	 * @param mixed $data
-	 * @param int $expiration =0
-	 * @return boolean true on success, false on error
-	 */
-	function set(array $keys,$data,$expiration=0);
-
-	/**
-	 * Get some data from the cache
-	 *
-	 * @param array $keys eg. array($level,$app,$location)
-	 * @return mixed data stored or NULL if not found in cache
-	 */
-	function get(array $keys);
-
-	/**
-	 * Delete some data from the cache
-	 *
-	 * @param array $keys eg. array($level,$app,$location)
-	 * @return boolean true on success, false on error (eg. $key not set)
-	 */
-	function delete(array $keys);
-
-	/**
-	 * Delete all data under given keys
-	 *
-	 * Providers can return false, if they do not support flushing part of the cache (eg. memcache)
-	 *
-	 * @param array $keys eg. array($level,$app,$location)
-	 * @return boolean true on success, false on error (eg. $key not set)
-	 */
-	function flush(array $keys);
-}
-
-/**
- * Interface for a caching provider for tree and instance level
- *
- * The provider can eg. create subdirs under /tmp for each key
- * to store data as a file or concat them with a separator to
- * get a single string key to eg. store data in memcached
- */
-interface egw_cache_provider_multiple
-{
-	/**
-	 * Get multiple data from the cache
-	 *
-	 * @param array $keys eg. array of array($level,$app,array $locations)
-	 * @return array key => data stored, not found keys are NOT returned
-	 */
-	function mget(array $keys);
-}
-
-abstract class egw_cache_provider_check implements egw_cache_provider
-{
-	/**
-	 * Run several checks on a caching provider
-	 *
-	 * @param boolean $verbose =false true: echo failed checks
-	 * @return int number of failed checks
-	 */
-	function check($verbose=false)
-	{
-		// set us up as provider for egw_cache class
-		$GLOBALS['egw_info']['server']['install_id'] = md5(microtime(true));
-		unset($GLOBALS['egw_info']['server']['cache_provider_instance']);
-		unset($GLOBALS['egw_info']['server']['cache_provider_tree']);
-		egw_cache::$default_provider = get_class($this);
-
-		$failed = 0;
-		foreach(array(
-			egw_cache::TREE => 'tree',
-			egw_cache::INSTANCE => 'instance',
-		) as $level => $label)
-		{
-			$locations = array();
-			foreach(array('string',123,true,false,null,array(),array(1,2,3)) as $data)
-			{
-				$location = md5(microtime(true).$label.serialize($data));
-				$get_before_set = $this->get(array($level,__CLASS__,$location));
-				if (!is_null($get_before_set))
-				{
-					if ($verbose) echo "$label: get_before_set=".array2string($get_before_set)." != NULL\n";
-					++$failed;
-				}
-				if (($set = $this->set(array($level,__CLASS__,$location), $data, 10)) !== true)
-				{
-					if ($verbose) echo "$label: set returned ".array2string($set)." !== TRUE\n";
-					++$failed;
-				}
-				$get_after_set = $this->get(array($level,__CLASS__,$location));
-				if ($get_after_set !== $data)
-				{
-					if ($verbose) echo "$label: get_after_set=".array2string($get_after_set)." !== ".array2string($data)."\n";
-					++$failed;
-				}
-				if (is_a($this, 'egw_cache_provider_multiple'))
-				{
-					$mget_after_set = $this->mget(array($level,__CLASS__,array($location)));
-					if ($mget_after_set[$location] !== $data)
-					{
-						if ($verbose) echo "$label: mget_after_set['$location']=".array2string($mget_after_set[$location])." !== ".array2string($data)."\n";
-						++$failed;
-					}
-				}
-				$add_after_set = $this->add(array($level,__CLASS__,$location), 'other-data');
-				if ($add_after_set !== false)
-				{
-					if ($verbose) echo "$label: add_after_set=".array2string($add_after_set)."\n";
-					++$failed;
-				}
-				if (($delete = $this->delete(array($level,__CLASS__,$location))) !== true)
-				{
-					if ($verbose) echo "$label: delete returned ".array2string($delete)." !== TRUE\n";
-					++$failed;
-				}
-				$get_after_delete = $this->get(array($level,__CLASS__,$location));
-				if (!is_null($get_after_delete))
-				{
-					if ($verbose) echo "$label: get_after_delete=".array2string($get_after_delete)." != NULL\n";
-					++$failed;
-				}
-				// prepare for mget of everything
-				if (is_a($this, 'egw_cache_provider_multiple'))
-				{
-					$locations[$location] = $data;
-					$mget_after_delete = $this->mget(array($level,__CLASS__,array($location)));
-					if (isset($mget_after_delete[$location]))
-					{
-						if ($verbose) echo "$label: mget_after_delete['$location']=".array2string($mget_after_delete[$location])." != NULL\n";
-						++$failed;
-					}
-				}
-				elseif (!is_null($data))	// emulation can NOT distinquish between null and not set
-				{
-					$locations[$location] = $data;
-				}
-				$add_after_delete = $this->add(array($level,__CLASS__,$location), $data, 10);
-				if ($add_after_delete !== true)
-				{
-					if ($verbose) echo "$label: add_after_delete=".array2string($add_after_delete)."\n";
-					++$failed;
-				}
-				else
-				{
-					$get_after_add = $this->get(array($level,__CLASS__,$location));
-					if ($get_after_add !== $data)
-					{
-						if ($verbose) echo "$label: get_after_add=".array2string($get_after_add)." !== ".array2string($data)."\n";
-						++$failed;
-					}
-				}
-			}
-			// get all above in one request
-			$keys = array_keys($locations);
-			$keys_bogus = array_merge(array('not-set'),array_keys($locations),array('not-set-too'));
-			if (is_a($this, 'egw_cache_provider_multiple'))
-			{
-				$mget = $this->mget(array($level,__CLASS__,$keys));
-				$mget_bogus = $this->mget(array($level,__CLASS__,$keys_bogus));
-			/* egw_cache::getCache() gives a different result, as it does NOT use $level direkt
-			}
-			else
-			{
-				$mget = egw_cache::getCache($level, __CLASS__, $keys);
-				$mget_bogus = egw_cache::getCache($level, __CLASS__, $keys_bogus);
-			}*/
-				if ($mget !== $locations)
-				{
-					if ($verbose) echo "$label: mget=\n".array2string($mget)." !==\n".array2string($locations)."\n";
-					++$failed;
-				}
-				if ($mget_bogus !== $locations)
-				{
-					if ($verbose) echo "$label: mget(".array2string($keys_bogus).")=\n".array2string($mget_bogus)." !==\n".array2string($locations)."\n";
-					++$failed;
-				}
-			}
-		}
-
-		return $failed;
-	}
-
-	/**
-	 * Delete all data under given keys
-	 *
-	 * Providers can return false, if they do not support flushing part of the cache (eg. memcache)
-	 *
-	 * @param array $keys eg. array($level,$app,$location)
-	 * @return boolean true on success, false on error (eg. $key not set)
-	 */
-	function flush(array $keys)
-	{
-		unset($keys);	// required by function signature
-		return false;
-	}
-}
-
-// some testcode, if this file is called via it's URL
-// can be run on command-line: sudo php -d apc.enable_cli=1 -f phpgwapi/inc/class.egw_cache.inc.php
-/*if (isset($_SERVER['SCRIPT_FILENAME']) && realpath($_SERVER['SCRIPT_FILENAME']) == __FILE__)
-{
-	if (!isset($_SERVER['HTTP_HOST']))
-	{
-		chdir(dirname(__FILE__));	// to enable our relative pathes to work
-	}
-	$GLOBALS['egw_info'] = array(
-		'flags' => array(
-			'noapi' => true,
-		),
-	);
-	include_once '../../header.inc.php';
-
-	if (isset($_SERVER['HTTP_HOST'])) echo "<pre style='whitespace: nowrap'>\n";
-
-	foreach(array(
-		'egw_cache_apc' => array(),
-		'egw_cache_memcache' => array('localhost'),
-		'egw_cache_files' => array('/tmp'),
-	) as $class => $param)
-	{
-		echo "Checking $class:\n";
-		try {
-			$start = microtime(true);
-			$provider = new $class($param);
-			$n = 100;
-			for($i=1; $i <= $n; ++$i)
-			{
-				$failed = $provider->check($i == 1);
-			}
-			printf("$failed checks failed, $n iterations took %5.3f sec\n\n", microtime(true)-$start);
-		}
-		catch (Exception $e) {
-			printf($e->getMessage()."\n\n");
-		}
-	}
-}*/
-
-// setting apc as default provider, if apc_fetch function exists AND further checks in egw_cache_apc recommed it
-if (is_null(egw_cache::$default_provider))
-{
-	egw_cache::$default_provider = function_exists('apc_fetch') && egw_cache_apc::available() ? 'egw_cache_apc' : 'egw_cache_files';
-}
+class egw_cache_apc extends Api\Cache\Apc {}
+class egw_cache_files extends Api\Cache\Files {}
+class egw_cache_memcache extends Api\Cache\Memcache {}
+class egw_cache_memcached extends Api\Cache\Memcached {}