[I might be wrong about these] TIdTCPServer Server is multithreaded in Borland C++ builder. It handles all client's on seperate threads. This is written in help of Borland c++.
Now is my problem & question.
For example, ShowMessage(String ..) method should be called on main (gui) thread. But as I say above, TCPServer is multithreaded and handles OnExecute event on different threads. When I use ShowMessage method in OnExecute event (which is handled on a different thread than main thread), I get weird results. Sometimes ShowMessage() works as expected, sometimes it is shown without any text on it with different box sizes(infinite lengt, very long, normal, etc). The other user interface changes causes no problem(update TEdit, TMemo. Only ShowMessage() has problem for now)
I think this problem is the result of calling ShowMessage() method not on the main (gui) thread but on TCPServer's thread which is created for client connections internally by TIdTCPServer.
So how can I fix it?
All changes to the user interface should be done in the main thread. You can use the TThread::Queue function for executing a function in the main thread. It posts a message to the main message queue, and the TThreadMethod passed as a parameter gets executed when the main thread handles messages.
If you need to pass data to the main thread, e.g. the message to be shown, you'll have to do that separately, as function parameters cannot be passed via the Queue function.