Slow response to keypresses in xorg-server-1.8.0-1

Ken Brown
Thu Jul 1 02:02:00 GMT 2010

On 6/30/2010 1:40 PM, Jon TURNEY wrote:
> On 02/05/2010 21:52, Ken Brown wrote:
>> On 5/1/2010 9:49 AM, Ken Brown wrote:
>>> I'm often seeing a very slow response to keypresses under
>>> xorg-server-1.8.0-1. The problem is intermittent, but it always happens
>>> within a few minutes after starting the server (via the start menu
>>> shortcut or a slight variant). Here are some examples:
>>> 1. Switching windows with Alt-Tab sometimes takes up to 15 seconds or
>>> doesn't work at all (i.e., I get tired of waiting to see if the focus is
>>> ever going to switch).
>>> 2. When using 'less' to view a file in an xterm window, there is
>>> sometimes a delayed response to 'space' or 'q'.
>>> 3. When viewing a directory in emacs-X11, pressing 'v' to start viewing
>>> a file can sometimes result in a long delay, pressing 'space' to scroll
>>> in view mode can be slow, and pressing 'q' to exit view mode can be slow.
>>> In some of these cases, I sometimes don't get a response to the first
>>> keypress until I press a second key. For example, if I'm viewing a file
>>> with 'less', I may press 'q' and get no response. Then pressing 'q' a
>>> second time exits 'less' and also produces an echoed 'q' in xterm.
>>> Similarly, I'll sometimes press a key, see no echo, and then get two
>>> characters echoed at once after pressing a second key.
>>> Reverting to xorg-server-1.7.6-2 solves the problem.
>>> I'm attaching cygcheck output and an XWin log.
>> I found a test case that I can reproduce reliably on my system.
>> 1. With no .Xdefaults or .startxwinrc, start the X server via the start
>> menu shortcut.
>> 2. Start xfig (with 'xfig&' in the xterm window).
>> 3. Repeatedly press Alt-Tab to switch between the xterm and xfig
>> windows. At some point the focus fails to switch. When this happens,
>> press Alt and the focus switches.
> Thanks for the clear reproduction steps.  And thanks to the other reporters of
> this problem :-)
> This is fallout from a change [1] to the way we process Windows messages to
> handle large bursts of them overflowing the Xserver's internal event queue.
> It seems that sometimes /dev/windows doesn't seem ready to select() even when
> there is still Windows messages to process.  I can't quite understand how this
> happens.  I don't think this is a bug in cygwin, but probably something subtle
> to do with message ordering and nonqueued messages (like WM_ACTIVATE).
> Anyhow, I've cooked up a small additional change which should prevent this
> blocking behaviour and uploaded a build [2]. It seems to resolve the problem
> in this specific case. Perhaps you could try it out and see if it helps?

That seems to have fixed it.  I've run it for several hours without any 
problems.  Thanks.


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