cygwin.dll: bug with select on Windows console
Corinna Vinschen
corinna-cygwin@cygwin.com
Sat Jan 9 14:42:00 GMT 2016
On Jan 9 15:36, Corinna Vinschen wrote:
> On Jan 8 15:58, john hood wrote:
> > On 1/8/16 11:29 AM, Corinna Vinschen wrote:
> > > On Jan 7 13:18, John Hood wrote:
> > >> Sorry about forgetting the testcase (which was good, actually, that
> > >> version had a bug). I've attached it here. This takes a single
> > >> argument, the timeout value for select() in microseconds. A value of
> > >> 1000000 is fine for testing this issue. Type at it, or just bang on the
> > >> keyboard with random keystrokes, and it will report the results from
> > >> select() and the characters read. On a Windows console, it should
> > >> report an error within a few seconds. Moving the mouse cursor over the
> > >> Windows console window while typing seems to provoke the error as well.
> > >
> > > No chance. I tried this for a good hour now with the unpatched Cygwin
> > > DLL on 32 bit W7 and 64 bit W10 in 32 and 64 bit in a Windows console,
> > > and I can't provoke this error. It just works for me.
> >
> > My apologies for sending you down a wrong path. Try again with
> > "socket-t 1000", which only waits 1ms. I don't know what I was thinking
> > when I said the 1s timeout works fine.
>
> This helped and I found the culprit. There are, in fact, two ways to
> leave select with a timeout. One of them only occurs in the border
> cases where a device behind a descriptor generates events which are
> not supposed to generate a select event.
I forgot to mention, this affects especially consoles (window events,
mouse events) and /dev/windows.
> If that happens, the select
> loop is supposed to loop again, but the code first checks if the timeout
> has been hit in the meantime and, if so, it breaks from the loop with a
> timeout, aka, a return value of 0. However, in this single case, the
> code neglected to zero out the descriptor arrays, which then leads to
> the problem you encountered.
>
> I fixed the code and took the opportunity to clean it up a little using
> basically the (fixed) patch I proposed two days ago.
>
> I've just uploaded new developer snapshots to https://cygwin.com/snapshots/
> and a new test release 2.4.0-0.17 which contain this fix. Please give any
> of them a try.
>
>
> Thanks,
> Corinna
Corinna
--
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Maintainer cygwin AT cygwin DOT com
Red Hat
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