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From:	Ken Brown <kbrown AT cornell DOT edu>
To:	"cygwin AT cygwin DOT com" <cygwin AT cygwin DOT com>
Subject:	Re: Regression (last snapshot)
Date:	Mon, 29 Jul 2019 14:26:07 +0000
Message-ID:	<ced2750a-0a52-1396-b6c1-f4228116bde7@cornell.edu>
References:	<265a2749-95b6-38aa-a191-7913bfcc98b6 AT cornell DOT edu> <20190722152016 DOT GE21169 AT calimero DOT vinschen DOT de> <20190722155340 DOT GF21169 AT calimero DOT vinschen DOT de> <20190722164509 DOT GG21169 AT calimero DOT vinschen DOT de> <eb8007691b20df0eb8032ca3d2fa445f AT smtp-cloud8 DOT xs4all DOT net> <b3b04db5-7f03-8281-f376-6cd10207ec01 AT cornell DOT edu> <4b59209a91e8384ec000e2724696791c AT smtp-cloud7 DOT xs4all DOT net> <935d8ce5-fd5c-3010-4664-bb2dc9b7ca2f AT cornell DOT edu> <20190729084552 DOT GL11632 AT calimero DOT vinschen DOT de> <eea273ca-f190-c91a-7892-9407bfcf4326 AT cornell DOT edu> <20190729134700 DOT GO11632 AT calimero DOT vinschen DOT de>
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On 7/29/2019 9:47 AM, Corinna Vinschen wrote:
> On Jul 29 13:18, Ken Brown wrote:
>> On 7/29/2019 4:45 AM, Corinna Vinschen wrote:
>>> On Jul 27 15:24, Ken Brown wrote:
>>>> On 7/27/2019 6:21 AM, Houder wrote:
>>>>> On Fri, 26 Jul 2019 22:12:43, Ken Brown  wrote:
>>>>>
>>>>>> On 7/22/2019 2:47 PM, Houder wrote:
>>>>>
>>>>>>> The specific regression as reported, has gone.
>>>>>>>
>>>>>>> 64-@@ uname -a
>>>>>>> CYGWIN_NT-6.1 Seven 3.1.0s(0.339/5/3) 2019-07-22 16:43 x86_64 Cygwin
>>>>>>> 64-@@ ls -lL <(grep bash .bashrc)
>>>>>>> pr-------- 1 Henri None 0 Jul 22 20:36 /dev/fd/63
>>>>>>
>>>>> Over all the behavior has simularity w/ the error reported by David Karr:
>>>>>
>>>>>        https://cygwin.com/ml/cygwin/2019-07/msg00150.html
>>>>>        ( Piping input from subprocess loses track of temp file )
>>>> [...]
>>>> Repeating this under the 20190722 or 20190725 snapshots gave slightly worse
>>>> results (close to 500 errors).  Using my own unoptimized build of cygwin1.dll,
>>>> the error count went up to about 650.
>>>
>>> I just tried this myself and I can't reproduce the problem.  1000 runs,
>>> no error.
>>
>> Interesting.  And you ran this under X11 in an xterm window?
> 
> I didn't, but I just did and the result is the same, no errors.
> 
>>>> I tried running under gdb, but I couldn't get grep to fail.  More precisely, I
>>>> didn't see an error message from grep.  Every run looked like this:
>>>>
>>>> $ gdb bash
>>>> GNU gdb (GDB) (Cygwin 8.2.1-1) 8.2.1
>>>> [...]
>>>> (gdb) r -c 'ls -lL <(grep bash .bashrc)'
>>>> Starting program: /usr/bin/bash -c 'ls -lL <(grep bash .bashrc)'
>>>> [...]
>>>> pr-------- 1 kbrown None 0 2019-07-27 11:07 /dev/fd/63
>>>> [...]
>>>> [Inferior 1 (process 21712) exited normally]
>>>>
>>>> It would be better to be able to debug ls and/or grep, but I don't know how to
>>>> get to subprocesses in gdb.  And I think I have to start with 'gdb bash' in
>>>> order for the process substitution to happen.
>>>
>>> Yeah, subprocess debugging is a problem in GDB.  Given how this works,
>>> you can at least take grep out of the picture.  Bash is doing all the
>>> lifting, so it's just bash and ls.   Did you try to reproduce this under
>>> strace?
>>
>> Yes, but there I get an error (even under mintty) for a different reason:
>>
>> $ strace -o trace.out ls -lL <(grep bash .bashrc)
>> ls: cannot access '/dev/fd/63': No such file or directory
> 
> No, please run bash:
> 
>    strace -o trace.out bash -c 'ls -lL <(grep bash .bashrc)'
> 
> Otherwise there's no process actually creating the pipe, given the <()
> expression is a bash expression.

Yes, of course.  I should have realized this since it's exactly what I did under 
gdb.  Anyway, the result is the same as it was under gdb: If I run the command 
under strace, I don't see the broken pipe error.

Is it possible that debugging causes an fd to the read end of the pipe to stay 
open longer, thereby preventing the error?

Ken

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