abstractcache.h

C++ class libraries for network-centric, portable applications, integrated perfectly with the C++ St

//
// AbstractCache.h
//
// $Id: //poco/1.2/Foundation/include/Poco/AbstractCache.h#4 $
//
// Library: Foundation
// Package: Cache
// Module:  AbstractCache
//
// Definition of the AbstractCache class.
//
// Copyright (c) 2006, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// Permission is hereby granted, free of charge, to any person or organization
// obtaining a copy of the software and accompanying documentation covered by
// this license (the "Software") to use, reproduce, display, distribute,
// execute, and transmit the Software, and to prepare derivative works of the
// Software, and to permit third-parties to whom the Software is furnished to
// do so, all subject to the following:
// 
// The copyright notices in the Software and this entire statement, including
// the above license grant, this restriction and the following disclaimer,
// must be included in all copies of the Software, in whole or in part, and
// all derivative works of the Software, unless such copies or derivative
// works are solely in the form of machine-executable object code generated by
// a source language processor.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
// SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
// FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
//


#ifndef  Foundation_AbstractCache_INCLUDED
#define  Foundation_AbstractCache_INCLUDED


#include "Poco/KeyValueArgs.h"
#include "Poco/ValidArgs.h" 
#include "Poco/Mutex.h"
#include "Poco/Exception.h"
#include "Poco/BasicEvent.h"
#include "Poco/EventArgs.h"
#include "Poco/Delegate.h"
#include "Poco/SharedPtr.h"
#include <map>
#include <set>


namespace Poco {


template <class TKey, class TValue, class TStrategy> 
class AbstractCache
	/// An AbstractCache is the interface of all caches. 
{
public:
	BasicEvent<const KeyValueArgs<TKey, TValue > > Add;
	BasicEvent<const TKey>                         Remove;
	BasicEvent<const TKey>                         Get;
	BasicEvent<const EventArgs>                    Clear;

	typedef std::map<TKey, SharedPtr<TValue > > DataHolder;
	typedef typename DataHolder::iterator       Iterator;
	typedef typename DataHolder::const_iterator ConstIterator;
	typedef std::set<TKey>                      KeySet;

	AbstractCache()
	{
		initialize();
	}

	AbstractCache(const TStrategy& strat): _strategy(strat)
	{
		initialize();
	}

	virtual ~AbstractCache()
	{
		uninitialize();
	}

	void add(const TKey& key, const TValue& val)
		/// Adds the key value pair to the cache.
		/// If for the key already an entry exists, it will be overwritten.
	{
		FastMutex::ScopedLock lock(_mutex);
		doAdd(key, val);
	}

	void remove(const TKey& key)
		/// Removes an entry from the cache. If the entry is not found,
		/// the remove is ignored.
	{
		FastMutex::ScopedLock lock(_mutex);
		doRemove(key);
	}

	bool has(const TKey& key) const
		/// Returns true if the cache contains a value for the key.
	{
		FastMutex::ScopedLock lock(_mutex);
		return doHas(key);
	}

	SharedPtr<TValue> get(const TKey& key)
		/// Returns a SharedPtr of the value. The SharedPointer will remain valid
		/// even when cache replacement removes the element.
		/// If for the key no value exists, an empty SharedPtr is returned.
	{
		FastMutex::ScopedLock lock(_mutex);
		return doGet (key);
	}

	void clear()
		/// Removes all elements from the cache.
	{
		FastMutex::ScopedLock lock(_mutex);
		doClear();
	}

	std::size_t size() const
		/// Returns the number of cached elements
	{
		FastMutex::ScopedLock lock(_mutex);
		return _data.size();
	}

	void forceReplace()
		/// Forces cache replacement. Note that Poco's cache strategy use for efficiency reason no background thread
		/// which periodically triggers cache replacement. Cache Replacement is only started when the cache is modified
		/// from outside, i.e. add is called, or when a user tries to access an cache element via get.
		/// In some cases, i.e. expire based caching where for a long time no access to the cache happens,
		/// it might be desirable to be able to trigger cache replacement manually.
	{
		FastMutex::ScopedLock lock(_mutex);
		doReplace();
	}


protected:
	mutable BasicEvent<ValidArgs<TKey> > IsValid;
	mutable BasicEvent<KeySet>           Replace;

	void initialize()
		/// Sets up event registration.
	{
		Add		+= Delegate<TStrategy, const KeyValueArgs<TKey, TValue> >(&_strategy, &TStrategy::onAdd);
		Remove	+= Delegate<TStrategy, const TKey>(&_strategy, &TStrategy::onRemove);
		Get		+= Delegate<TStrategy, const TKey>(&_strategy, &TStrategy::onGet);
		Clear	+= Delegate<TStrategy, const EventArgs>(&_strategy, &TStrategy::onClear);
		IsValid	+= Delegate<TStrategy, ValidArgs<TKey> >(&_strategy, &TStrategy::onIsValid);
		Replace	+= Delegate<TStrategy, KeySet>(&_strategy, &TStrategy::onReplace);
	}

	void uninitialize()
		/// Reverts event registration.
	{
		Add		-= Delegate<TStrategy, const KeyValueArgs<TKey, TValue> >(&_strategy, &TStrategy::onAdd );
		Remove	-= Delegate<TStrategy, const TKey>(&_strategy, &TStrategy::onRemove);
		Get		-= Delegate<TStrategy, const TKey>(&_strategy, &TStrategy::onGet);
		Clear	-= Delegate<TStrategy, const EventArgs>(&_strategy, &TStrategy::onClear);
		IsValid	-= Delegate<TStrategy, ValidArgs<TKey> >(&_strategy, &TStrategy::onIsValid);
		Replace	-= Delegate<TStrategy, KeySet>(&_strategy, &TStrategy::onReplace);
	}

	void doAdd(const TKey& key, const TValue& val)
		/// Adds the key value pair to the cache.
		/// If for the key already an entry exists, it will be overwritten.
	{
		if (doHas(key))
		{
			doRemove(key);
		}

		KeyValueArgs<TKey, TValue> args(key, val);
		Add.notify(this, args);
		_data.insert(std::make_pair(key, SharedPtr<TValue>(new TValue(val))));
		
		doReplace();
	}

	void doRemove(const TKey& key) 
		/// Removes an entry from the cache. If the entry is not found
		/// the remove is ignored.
	{
		Remove.notify(this, key);
		_data.erase(key);
	}

	bool doHas(const TKey& key) const
		/// Returns true if the cache contains a value for the key
	{
		// ask the strategy if the key is valid
		ConstIterator it = _data.find(key);
		bool result = false;

		if (it != _data.end())
		{
			ValidArgs<TKey> args(key);
			IsValid.notify(this, args);
			result = args.isValid();
		}

		return result;
	}

	SharedPtr<TValue> doGet(const TKey& key) 
		/// Returns a SharedPtr of the cache entry, returns 0 if for
		/// the key no value was found
	{
		Iterator it = _data.find(key);
		SharedPtr<TValue> result;

		if (it != _data.end())
		{	
			// inform all strategies that a read-access to an element happens
			Get.notify(this, key);
			// ask all strategies if the key is valid
			ValidArgs<TKey> args(key);
			IsValid.notify(this, args);

			if (!args.isValid())
			{
				doRemove(key);
			}
			else
			{
				result = it->second;
			}
		}

		return result;
	}

	void doClear()
	{
		static EventArgs _emptyArgs;
		Clear.notify(this, _emptyArgs);
		_data.clear();
	}

	void doReplace()
	{
		std::set<TKey> delMe;
		Replace.notify(this, delMe);
		// delMe contains the to be removed elements
		typename std::set<TKey>::const_iterator it    = delMe.begin();
		typename std::set<TKey>::const_iterator endIt = delMe.end();

		for (; it != endIt; ++it)
		{
			doRemove(*it);
		}
	}

	TStrategy          _strategy;
	mutable DataHolder _data;
	mutable FastMutex  _mutex;

private:
	AbstractCache(const AbstractCache& aCache);
	AbstractCache& operator = (const AbstractCache& aCache);
};


} // namespace Poco


#endif