trying to understand the message loop

[bling]

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:

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:

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.

[Greenhorn__]

Hi,

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


Greetz

[matsp]

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

--
Mats

[Codeplug]

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

[bling]

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