[PATCH draft 0/6] Remove the fhandler_base_overlapped class

Michael Haubenwallner michael.haubenwallner@ssi-schaefer.com
Tue Jun 11 16:42:00 GMT 2019



On 6/11/19 10:48 AM, Corinna Vinschen wrote:
> Hi Ken,
> 
> On Jun  8 12:20, Ken Brown wrote:
>> On 6/7/2019 5:43 PM, Ken Brown wrote:
>>> On 6/7/2019 3:13 PM, Ken Brown wrote:
>>>> On 6/7/2019 2:31 PM, Achim Gratz wrote:
>>>>> Ken Brown writes:
>>>>>> I think I've found the problem.  I was mishandling signals that arrived during a
>>>>>> read.  But after I fix that, there's still one nagging issue involving timerfd
>>>>>> code.  I'll write to the main list with details.  I *think* it's a timerfd bug,
>>>>>> but it's puzzling that I only see it when testing my new pipe implementation.
>>>>>
>>>>> Anything triggering a race or deadlock will depend on so many other
>>>>> things that it really is no surprise to see seemingly unrelated changes
>>>>> making the bug appear or disappear.  There are certainly races left in
>>>>> Cygwin, I see them from time to time in various Perl modules, just never
>>>>> reproducible enough to give anyone an idea of where to look.
>>>>
>>>> That makes sense.
>>>>
>>>> In the meantime, I've already discovered another problem, within an hour of
>>>> posting my claim that everything was working fine: If I start emacs-X11 with
>>>> cygserver running, I can't fork any subprocesses within emacs.  I get
>>>>
>>>> 0 [main] emacs 2689 dofork: child 2693 - died waiting for dll loading, errno 11
>>>>
>>>> Back to the drawing board....  I've never looked at the cygserver code, but
>>>> maybe it will turn out to be something easy.
>>>
>>> Good news (for me): This isn't related to my pipe code.  The same problem occurs
>>> if I build the master branch.  I'll bisect when I get a chance (probably
>>> tomorrow).  In the meantime, all I can say is that strace shows a
>>> STATUS_ACCESS_VIOLATION at shm.cc:125.
>>
>> A bisection shows that the problem starts with the following commit:
> 
> Thanks for bisecting!
> 
>> commit f03ea8e1c57bd5cea83f6cd47fa02870bdfeb1c5
>> Author: Michael Haubenwallner <michael.haubenwallner@ssi-schaefer.com>
>> Date:   Thu May 2 12:12:44 2019 +0200
>>
>>      Cygwin: fork: Remember child not before success.
>>
>>      Do not remember the child before it was successfully initialized, or we
>>      would need more sophisticated cleanup on child initialization failure,
>>      like cleaning up the process table and suppressing SIGCHILD delivery
>>      with multiple threads ("waitproc") involved.  Compared to that, the
>>      potential slowdown due to an extra yield () call should be negligible.
> 
> Please revert the patch for the time being.  Michael, this needs some
> more work, apparently.

Because of https://cygwin.com/ml/cygwin/2019-06/msg00110.html:
Is there still some problem related to that commit I need to figure out?

/haubi/



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