Re: cygwin.dll: bug with select on Windows console

[Corinna Vinschen <corinna-cygwin@cygwin.com>]

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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.  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 Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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