The biggest problem of TThread is that it only allows communication to flow from the background thread to the owner.  As you've seen in the previous chapter, we can use different mechanisms for that—Windows messages, Synchronize, Queue, and polling. There is, however, no built-in way to send messages in a different direction, so you have to build such a mechanism yourself. This is not entirely trivial.

Another problem with built-in mechanisms is that they make for unreadable code. Synchronize and Queue are both inherently messy because they wrap a code that executes in one thread inside a code executing in a different thread. Messages and polling have a different problem. They decouple code through many different methods, which sometimes makes it hard to understand the system.

To fix all these problems (and undoubtedly introduce some new ones as, sadly, no code is perfect), I have built a better base class TCommThread. You can find it in unit DHPThreads,...