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Date: Sun, 29 Aug 2010 16:50:41 +0200
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com, cygwin-xfree AT cygwin DOT com
Subject: Re: /dev/windows and select() [was Re: Slow response to keypresses in xorg-server-1.8.0-1]
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On Aug 29 16:41, Corinna Vinschen wrote:
> On Aug 29 16:17, Corinna Vinschen wrote:
> > On Aug 29 14:39, Jon TURNEY wrote:
> > > On 08/08/2010 12:04, Andy Koppe wrote:
> > > >On 7 August 2010 23:07, Jon TURNEY wrote:
> > > >>Hmmm, looking again at the implementation of select(), I don't immediately
> > > >>see that when waiting on /dev/windows, it checks that the message queue has
> > > >>old messages on it before waiting.  The MSDN documentation for
> > > >>MsgWaitForMultipleObjects() seems to says that messages which had arrived
> > > >>before the last PeekMessage() etc. aren't considered new and so don't end
> > > >>the wait?
> > > >[...]
> > 
> > Thanks for the testcase.  I examined this and I think I have a
> > workaround.  MSDN states that there's a flag QS_ALLPOSTMESSAGE for
> > MsgWaitForMultipleObjects, which is not cleared by PeekMessage, if the
> > wMsgFilterMin and wMsgFilterMax arguments are not both 0.  So, what I
> > did was to add the QS_ALLPOSTMESSAGE flag to the
> > MsgWaitForMultipleObjects call in select.cc, and to change the
> > PeekMessage call in select.cc:peek_windows() from
> > 
> >   PeekMessage (&m, (HWND) h, 0, 0, PM_NOREMOVE)
> > 
> > to
> > 
> >   PeekMessage (&m, (HWND) h, 1, UINT_MAX, PM_NOREMOVE)
> > 
> > Same in your above test application.  This appears to do the trick.
> > However, I'm not exactly sure if that's a valid fix.  Patch below.
> 
> Hmm, this ignores the potential WM_NULL message, afaics.  For some
> reason, using
> 
>   PeekMessage (&m, (HWND) h, 0, UINT_MAX, PM_NOREMOVE)
> 
> results in MsgWaitForMultipleObjects hanging, too.  OTOH, using
> 
>   PeekMessage (&m, (HWND) h, 0, 16, PM_NOREMOVE)
>   && PeekMessage (&m, (HWND) h, 17, UINT_MAX, PM_NOREMOVE)
> 
> does not.  Go figure.

Yeah, I realize I'm talking to myself, but this works, too:

  PeekMessage (&m, (HWND) h, 0, UINT_MAX - 1, PM_NOREMOVE)


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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