Re: Regression (last snapshot)

[Ken Brown <kbrown@cornell.edu>]

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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 )
>>
>> Thanks, I hadn't noticed that.
>>
>> The situation is more complicated than what I reported.  First, it happens even
>> in cygwin-3.0.7, as David Karr's report suggests.  Second, it's true that I can
>> only reproduce it under X11, but the pattern is not as regular as I thought.  I
>> just ran the ls command 1000 times in an xterm window under cygwin-3.0.7, and I
>> got the "Broken pipe" error 390 times, with a varying number of consecutive
>> successful runs between the errors.
>>
>> 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 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

The strace output shows a call to fhandler_process::exists on /proc/45036/fd/63; 
here 45036 is the PID of 'ls'.  And then I see an EBADF error.  But I think 
what's happening here might be that bash is parsing '<(grep bash .bashrc)' too 
soon, so that '/dev/fd/63' isn't related to the 'ls' command.

By the way, I've just tried a different experiment, in which I simplify the ls 
command to 'ls <(grep bash .bashrc)'.  When I run this under xterm, I get the 
broken pipe error 98% of the time or more.  But it's fine under mintty.

Ken
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