trying to understand the message loop

This is a discussion on trying to understand the message loop within the Windows Programming forums, part of the Platform Specific Boards category; hello, i just started a new job and it requires c++, and i'm confused trying to implement a simple program ...

  1. #1
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    trying to understand the message loop

    hello, i just started a new job and it requires c++, and i'm confused trying to implement a simple program which watches a file for changes.

    i followed a tutorial and sample code online, and i'm trying to implement the asynchronous version using CreateFile and ReadDirectoryChangesW with a completion routine. the code seems to work fine, but only does depending on how i program the message loop.

    if i use the "standard" message loop:

    Code:
    while (GetMessage(&msg, NULL, 0, 0) > 0) {
      TranslateMessage(&msg);
      DispatchMessage(&msg);
    }
    the breakpoint i set in the completion function never hits. nothing seems to happen. however, if i use the following code:

    Code:
    while (true) {
      while (WAIT_IO_COMPLETION == MsgWaitForMultipleObjectsEx(0, NULL, INFINITE, QS_ALLINPUT, MWMO_ALERTABLE))
        /* Do nothing */;
    
      while (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE)) {
        if (msg.message == WM_QUIT) {
          return 0;
        }
        TranslateMessage(&msg);
        DispatchMessage(&msg);
      }
    }
    it works...

    what's the difference? thanks.

  2. #2
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    Hi,

    did you already looked at this http://msdn.microsoft.com/en-us/libr...28(VS.85).aspx ?


    Greetz

  3. #3
    Kernel hacker
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    Or perhaps you want to look at the MSDN MsgWaitForMultipleObjectsEx help page, where it explains what MWMO_ALERTABLE means?

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  4. #4
    Registered User Codeplug's Avatar
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    4,630
    Quote Originally Posted by MSDN
    Using a completion routine. To receive notification through a completion routine, do not associate the directory with a completion port. Specify a completion routine in lpCompletionRoutine. This routine is called whenever the operation has been completed or canceled while the thread is in an alertable wait state.
    Alertable Wait Functions

    gg

  5. #5
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    thanks for the replies...it makes a lot more sense now.

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