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From: "Trollope, David" <dtrollope AT informatica DOT com>
To: <cygwin-xfree AT cygwin DOT com>
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Subject: Re: /dev/windows and select() [was Re: Slow response to keypresses in xorg-server-1.8.0-1]
Date: Sun, 29 Aug 2010 09:58:07 -0500
Cc: <cygwin AT cygwin DOT com>, <cygwin-xfree AT cygwin DOT com>
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We are listening and learning :-)

Dave

Sent from my iPad

On Aug 29, 2010, at 9:51 AM, "Corinna Vinschen" <corinna-cygwin AT cygwin DOT com>=
 wrote:

> 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 immed=
iately
>>>>>> see that when waiting on /dev/windows, it checks that the message qu=
eue has
>>>>>> old messages on it before waiting.  The MSDN documentation for
>>>>>> MsgWaitForMultipleObjects() seems to says that messages which had ar=
rived
>>>>>> before the last PeekMessage() etc. aren't considered new and so don'=
t end
>>>>>> the wait?
>>>>> [...]
>>>=20
>>> 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
>>>=20
>>>  PeekMessage (&m, (HWND) h, 0, 0, PM_NOREMOVE)
>>>=20
>>> to
>>>=20
>>>  PeekMessage (&m, (HWND) h, 1, UINT_MAX, PM_NOREMOVE)
>>>=20
>>> 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.
>>=20
>> Hmm, this ignores the potential WM_NULL message, afaics.  For some
>> reason, using
>>=20
>>  PeekMessage (&m, (HWND) h, 0, UINT_MAX, PM_NOREMOVE)
>>=20
>> results in MsgWaitForMultipleObjects hanging, too.  OTOH, using
>>=20
>>  PeekMessage (&m, (HWND) h, 0, 16, PM_NOREMOVE)
>>  && PeekMessage (&m, (HWND) h, 17, UINT_MAX, PM_NOREMOVE)
>>=20
>> does not.  Go figure.
>=20
> Yeah, I realize I'm talking to myself, but this works, too:
>=20
>  PeekMessage (&m, (HWND) h, 0, UINT_MAX - 1, PM_NOREMOVE)
>=20
>=20
> Corinna
>=20
> --=20
> Corinna Vinschen                  Please, send mails regarding Cygwin to
> Cygwin Project Co-Leader          cygwin AT cygwin DOT com
> Red Hat
>=20
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>=20

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