class CachedSQL : public CallbackThread
{
public:
	void GetDataGiveToAnswerer(String request)
	{
		int rqIndex = data.Find(request);
		bool needAdd = false;
		String answer;
		if (rqIndex < 0)
		{
			answer = FetchFromDatabase(request);
			needAdd = true;
		}
		else
			answer = data[rqIndex];
		
		theAnswersProcessor.AddTask(HttpAnswersProcessor::ProcessData, request, answer);
		
		if (needAdd)
			data.Add(request, answer);
	}
};

class HttpRequestsProcessor : public CallThread
{
public:
	void ProcessHttpRequest(String rq)
	{
		//some processing here
		
		//ok, you need users`s info
		theCachedSQL.AddTask(CachedSQL::GetDataGiveToAnswerer, user);
		
		//optional additional processing
	}
};

class HttpAnswersProcessor : public CallThread
{
public:
	void ProcessHttpAnswer(String userInfo)
	{
		//some processing and sending answer
	}
};

///////////////////////////////////////////////////////////////////////////
// Let`s imagine 2 users sent their requests simultaneously.
//
// Time offset:
// 0         1        2         3         4         5         6         7
// 0123456789012345689012345678901234567890123456789012345678901234567890
//--------------------------------------------------------------------------
// Synchronous work
// |--request1--|--sql1--|--answer1--|--request2--|--sql2--|--answer2--|...
// user1 will wait 3.5
// user2 will wait 6.9
//--------------------------------------------------------------------------
// Asyncronous work; '%' symbol stands for queue event i/o/thread-awake
// |--request1--|
//            %|--sql1--| *cache-miss; adding to data AFTER answer answer sent to httpAnswerer*
//                   %|--answer1--|
//              |--request2--|
//                         %|--sql2--| *value cached, no need to add this time*
//                                   %|--answer2--|
// user1 will wait 3.2
// user2 will wait 4.8
//--------------------------------------------------------------------------