postthreadmessage and peekmessage problem in delphi 2006

Question

I created a multichilded application. The application windows (W[n]: TMyWindows) are all the same and all have an private object class instance associated with them (E: TMyObject). The child windows generate through this objects some messages. I have created in the main application two threads which process these messages depending on the content of the messages. For example lets have the following asynchronous calls:

W[1].E.Service(thread1service)
W[2].E.Service(thread2service)

the TMyObject.Service(servicetype) is

case servicetype of
  thread1service: PostThreadMessage(thread1id,...);
  thread2service: PostThreadMessage(thread2id,...);
end;

Now, in the Execute Method of each thread i have something like that:

while not terminated do
begin
 ...
 if peekmessage(msg,0,thread1message_1,thread1message_n,pm_remove) then
      process message
 do other things;
end

All goes fine exept that the second thread doesn't receive any messages. Do you have any idea why?

Answer 1

I would check to make sure that the range you are supplying to PeekMessage() is valid. Try putting zeros in instead to receive all messages, like this:

PeekMessage(msg, 0, 0, 0, PM_REMOVE)

If that doesn't work, I would check the result of the PostThreadMessage() function... It may be that the thread hasn't called PeekMessage() yet, that's what prompts windows to create the message queue for you.

As stated in this article (under "Remarks"), you can either check the result of the call to PostThreadMessage(), and Sleep() if it fails, or use an event to signal to the main thread that the child thread is ready to receive messages.

HTH,

N@

Answer 2

Nat, thanks for the replay.

Unfortunately, I already tried all the things you recommended. Still, no change. I even let only the second thread to process messages, it didn't work either. I'm starting to believe that my computer is damaged or something :)

Answer 3

So, I had to give up as I didn't find any rational explanation.

I've decided to send messages using a critical section with event signaling to tell the working threads that they have a message to process. Unfortunately, this means that the main thread have to check that the working thread processes any message before sending a new one.