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Subject: Re: Sv: Sv: open descriptor to named pipes sometimes fail
To: sten DOT kristian DOT ivarsson AT gmail DOT com
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From: Ken Brown via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Ken Brown <kbrown AT cornell DOT edu>
Cc: cygwin <cygwin AT cygwin DOT com>
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On 4/8/2020 8:53 AM, Ken Brown via Cygwin wrote:
> On 4/8/2020 4:52 AM, sten DOT kristian DOT ivarsson AT gmail DOT com wrote:
>>> On 4/7/2020 2:38 PM, sten DOT kristian DOT ivarsson AT gmail DOT com wrote:
>>>>> On 4/7/2020 11:10 AM, Kristian Ivarsson via Cygwin wrote:
>>>>>> Opening a (second) descriptor for (blocking) write sometimes fail
>>>>>>
>>>>>> The provided test case sometimes succeed, but quite often fail with
>>>>>> ENOENT (in various indexes)
>>>>>>
>>>>>> I haven't dug deeper to find the underlaying cause yet
>>>>>>
>>>>>> Have anyone experienced this before ?
>>>>>
>>>>> I can't reproduce this on my system.  I changed 1000 to 10000 and
>>>>> then ran your test case 10 times, and it never failed.  I tested both
>>>>> cygwin-3.1.4 and the HEAD of the topic/fifo branch (which I recently
>>>>> force-pushed in case you want to try it).
>>>>>
>>>>> Can you run your test under strace and see if that provides a clue?
>>>>
>>>> I'm running things on a few year old laptop, perhaps with less muscles
>>>> ;-)
>>>>
>>>> With strace it was harder to reproduce, but I could reproduce it (and
>>>> it happen to be the first iteration this time)
>>>
>>> Does this help?
>>>
>>> --- a/winsup/cygwin/fhandler_fifo.cc
>>> +++ b/winsup/cygwin/fhandler_fifo.cc
>>> @@ -624,7 +624,8 @@ fhandler_fifo::open (int flags, mode_t)
>>>                     else
>>>                       goto success;
>>>                   }
>>> -             else if (STATUS_PIPE_NO_INSTANCE_AVAILABLE (status))
>>> +             else if (STATUS_PIPE_NO_INSTANCE_AVAILABLE (status)
>>> +                      | status == STATUS_OBJECT_NAME_NOT_FOUND)
>>>                   continue;
>>>                 else
>>>                   {
>>
>> Did you mean to use the bit-or-operator or the or-operator ?
> 
> The or-operator.  Thanks for catching that.
> 
>> I did
>> ...
>>     else if (STATUS_PIPE_NO_INSTANCE_AVAILABLE (status) || status ==
>> STATUS_OBJECT_NAME_NOT_FOUND)
>> ...
>> and with that change I cannot reproduce the error in the test-program
> 
> Great.  I'll push it to the topic/fifo branch.  For the record, that patch was 
> motivated by your strace output, which showed NtOpenFile failing with status 
> 0xC0000034, which is STATUS_OBJECT_NAME_NOT_FOUND.

This was not a well-thought-out change.  It creates a drastic slow-down.  I'll 
have to find a better solution.

Ken
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