The traditional approach is to have a process or thread that is blocked on a receive system call waiting for an incoming message. It accepts the message and then processes it whenever there is an arrival of message.
But a totally different approach is also possible using pop-up thread system.
In pop-up thread system, the arrival of message causes the system to create a new thread just to handle the message. Such a thread is called a pop-up thread.
The figure given below illustrated the pop-up thread.
The main advantage of using the pop-up threads is that they are brand new, therefore they don't have history-registers, stack etc. that must be restored.
Each one starts out fresh and is identical to all the others. Therefore, this makes it possible to create such a thread very quickly.
The new thread is given the incoming message to process.
The output of using the pop-up threads is that the latency between message arrival and the start of processing can be made very short.