X-Recipient: archive-cygwin@delorie.com X-SWARE-Spam-Status: No, hits=-2.8 required=5.0 tests=AWL,BAYES_00,RCVD_IN_DNSWL_LOW X-Spam-Check-By: sourceware.org Message-ID: <4C7B9E4B.2060800@dronecode.org.uk> Date: Mon, 30 Aug 2010 13:04:27 +0100 From: Jon TURNEY User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2.8) Gecko/20100802 Thunderbird/3.1.2 MIME-Version: 1.0 To: cygwin-xfree@cygwin.com, cygwin@cygwin.com Subject: Re: /dev/windows and select() [was Re: Slow response to keypresses in xorg-server-1.8.0-1] References: <4BDC3161.9070101@cornell.edu> <4BDDE5F1.9080204@cornell.edu> <4C2B8171.5020409@dronecode.org.uk> <4C5B08AE.4080902@pobox.com> <4C5DD910.9050809@dronecode.org.uk> <4C7A62FD.10506@dronecode.org.uk> <20100830112313.GN6726@calimero.vinschen.de> In-Reply-To: <20100830112313.GN6726@calimero.vinschen.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Mailing-List: contact cygwin-help@cygwin.com; run by ezmlm List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: cygwin-owner@cygwin.com Mail-Followup-To: cygwin@cygwin.com Delivered-To: mailing list cygwin@cygwin.com On 30/08/2010 12:23, 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? >>> >>> I think you're right, a call to PeekMessage is needed for proper >>> select() semantics: it shouldn't block if data is available for >>> reading. >> >> Attached is a small test-case which seems to demonstrate this problem. >> >> Run ./dev-windows-select-test and observe select() blocks for the >> full timeout, despite the fact that the /dev/windows fd is ready for >> reading (and it reported as such as the end of the timeout) >> >> If you run './dev-windows-select-test -skip' to skip the >> PeekMessage(), select() returns immediately, indicating the >> /dev/windows fd is ready for reading. > > Again, thanks for the testcase. I applied a patch to Cygwin which > should make select on /dev/windows fully functional. > > The blessed solution is to replace the call to MsgWaitForMultipleObjects > with a call to MsgWaitForMultipleObjectsEx with the MWMO_INPUTAVAILABLE > flag set. This flag is defined to do exactly what we need. > > The only downside is that this flag does not exist on NT4 and its usage > results in an "invalid argument" error. So, for NT4, I added the > workaround I described in my yesterday's soliloquy. > > I'm planning to release Cygwin 1.7.7 tomorrow at the latest, so please > give it a test as soon as possible. Here's a binary DLL for testing > (build w/o optimization, so it's probably a bit slow): > > http://cygwin.de/cygwin-177/new-cygwin1.dll.bz2 > (md5sum: 7e07fd9eafd021697a0861c1ae4fa94e) Thanks Corinna :-) I tried that cygwin DLL with my test case, and with an X server with what I now realize is the workaround I'd applied reverted [1] and it seems to work fine. [1] http://cgit.freedesktop.org/~yselkowitz/xserver/commit/?h=cygwin-release-1.8&id=6da3190eacae2c2b021060f8fd9427816ac06f21 -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple