Re: How to PostThreadMessages?

Hans-J. Ude <>
Tue, 05 Jun 2007 16:28:16 +0200
You sould not use Windows messaging for thread synchronization. There
are timers, events, semaphores, ... for that purpose.

Search MSDN for "Synchronization Functions".


"jp2code" <> wrote:

All good info!

Let me give everyone a little background:

We have machines with serial ports running and collecting record data.

This app will interface with a machine to download log files or occasionally
upload a new config file.

To get a log file, we post a request and wait for the machine to transmit
the reply with the file.

A little catch is that we have to send a short keep-alive signal every X
milliseconds, or the machine will terminate the connection.

This thread will send the keep-alive signals until the User disconnects the

We can not use asynchronous data transfer, so Overlapped Results is out. I
check that the port is clear, block the port, read from the port, then
unblock. Same for writing to the port.

There is no user interface, but I do need to send occasional messages to the

Originally, I had been running a thread using CreateThread, but it looks
like that is not allowing the entire class to thread nicely.

I don't really understand what Mr. Newcomer said, "You have to create a UI
thread to handle this sort of thing, but it can't be doing anything else
interesting for any long period of time or the thread messages won't be

Every X milliseconds, the thread send a keep-alive signal, then scans the
serial port for messages.

To answer Mr. Geodakov, my ZSerialThread class is derived from CWinThread,
and I have declared my thread to start as follows:

ZSerialThread* pSerial;
(Later in code)
  pSerial = (ZSerialThread*)AfxBeginThread(RUNTIME_CLASS(ZSerialThread));

Is this correct? Is it ok for my thread "handle" to be global? This way, I
can post thread messages from within the thread or from the main dialog
application (the user interface).

Mr. McPhillips, your post was the clearest to understand, except for the
part where you said, "your thread's InitInstance will execute, and then the
thread goes to sleep until it receives a message." Is there any specific
message I need to give my thread to begin execution? I would be happy if the
thread started running my scanning loop as soon as it were created.

I have also created my Thread Message loop as follows:
void ZSerialThread::OnSerialMessage(WPARAM wParam, LPARAM lParam)
 switch (wParam)
   case NEWCOM: // change COM Port
     if (lParam != NULL)
   case STARTIT: // Start the Loop!
   case TH_DON: // End the thread
     g_LoopSerial = FALSE;

Any comments, good or bad?

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