From: Chet Ramey <chet.ramey@case.edu>
To: Carl Edquist <edquist@cs.wisc.edu>, Zachary Santer <zsanter@gmail.com>
Cc: chet.ramey@case.edu, bug-bash <bug-bash@gnu.org>,
libc-alpha@sourceware.org
Subject: Re: Examples of concurrent coproc usage?
Date: Mon, 1 Apr 2024 15:31:19 -0400 [thread overview]
Message-ID: <1878a356-3eb4-4818-85d9-96531bd35bc9@case.edu> (raw)
In-Reply-To: <d498e418-c501-45a1-aff3-8194929c8bc9@case.edu>
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On 4/1/24 3:24 PM, Chet Ramey wrote:
> On 3/14/24 5:58 AM, Carl Edquist wrote:
>
>
>> But you can create a deadlock without doing anything fancy.
>>
>>
>> Well, *without multi-coproc support*, here's a simple wc example; first
>> with a single coproc:
>>
>> $ coproc WC { wc; }
>> $ exec {WC[1]}>&-
>> $ read -u ${WC[0]} X
>> $ echo $X
>> 0 0 0
>>
>> This works as expected.
>>
>> But if you try it with a second coproc (again, without multi-coproc
>> support), the second coproc will inherit copies of the shell's read and
>> write pipe fds to the first coproc, and the read will hang (as described
>> above), as the first coproc doesn't see EOF:
>>
>> $ coproc WC { wc; }
>> $ coproc CAT { cat; }
>> $ exec {WC[1]}>&-
>> $ read -u ${WC[0]} X
>>
>> # HANGS
>>
>>
>> But, this can be observed even before attempting the read that hangs.
>
> Let's see if we can tackle these one at a time. This seems like it would be
> pretty easy to fix if a coproc closed the fds corresponding to an existing
> coproc in the child after the fork. That wouldn't really change anything
> regarding how scripts have to manually manage multiple coprocs, but it
> will prevent the shell from hanging.
>
I sent this before I was ready. This would be equivalent to changing the
commands to use
coproc CAT { exec {WC[0]}<&- {WC[1]}>&- ; cat; }
but the script writer wouldn't have to manage it.
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU chet@case.edu http://tiswww.cwru.edu/~chet/
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next prev parent reply other threads:[~2024-04-01 19:31 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CABkLJULa8c0zr1BkzWLTpAxHBcpb15Xms0-Q2OOVCHiAHuL0uA@mail.gmail.com>
[not found] ` <9831afe6-958a-fbd3-9434-05dd0c9b602a@draigBrady.com>
2024-03-10 15:29 ` RFE: enable buffering on null-terminated data Zachary Santer
2024-03-10 20:36 ` Carl Edquist
2024-03-11 3:48 ` Zachary Santer
2024-03-11 11:54 ` Carl Edquist
2024-03-11 15:12 ` Examples of concurrent coproc usage? Zachary Santer
2024-03-14 9:58 ` Carl Edquist
2024-03-17 19:40 ` Zachary Santer
2024-04-01 19:24 ` Chet Ramey
2024-04-01 19:31 ` Chet Ramey [this message]
2024-04-02 16:22 ` Carl Edquist
2024-04-03 13:54 ` Chet Ramey
2024-04-03 14:32 ` Chet Ramey
2024-04-03 17:19 ` Zachary Santer
2024-04-08 15:07 ` Chet Ramey
2024-04-09 3:44 ` Zachary Santer
2024-04-13 18:45 ` Chet Ramey
2024-04-14 2:09 ` Zachary Santer
2024-04-04 12:52 ` Carl Edquist
2024-04-04 23:23 ` Martin D Kealey
2024-04-08 19:50 ` Chet Ramey
2024-04-09 14:46 ` Zachary Santer
2024-04-13 18:51 ` Chet Ramey
2024-04-09 15:58 ` Carl Edquist
2024-04-13 20:10 ` Chet Ramey
2024-04-14 18:43 ` Zachary Santer
2024-04-15 18:55 ` Chet Ramey
2024-04-15 17:01 ` Carl Edquist
2024-04-17 14:20 ` Chet Ramey
2024-04-20 22:04 ` Carl Edquist
2024-04-22 16:06 ` Chet Ramey
2024-04-27 16:56 ` Carl Edquist
2024-04-28 17:50 ` Chet Ramey
2024-04-08 16:21 ` Chet Ramey
2024-04-12 16:49 ` Carl Edquist
2024-04-16 15:48 ` Chet Ramey
2024-04-20 23:11 ` Carl Edquist
2024-04-22 16:12 ` Chet Ramey
2024-04-17 14:37 ` Chet Ramey
2024-04-20 22:04 ` Carl Edquist
2024-03-12 3:34 ` RFE: enable buffering on null-terminated data Zachary Santer
2024-03-14 14:15 ` Carl Edquist
2024-03-18 0:12 ` Zachary Santer
2024-03-19 5:24 ` Kaz Kylheku
2024-03-19 12:50 ` Zachary Santer
2024-03-20 8:55 ` Carl Edquist
2024-04-19 0:16 ` Modify buffering of standard streams via environment variables (not LD_PRELOAD)? Zachary Santer
2024-04-19 9:32 ` Pádraig Brady
2024-04-19 11:36 ` Zachary Santer
2024-04-19 12:26 ` Pádraig Brady
2024-04-19 16:11 ` Zachary Santer
2024-04-20 16:00 ` Carl Edquist
2024-04-20 20:00 ` Zachary Santer
2024-04-20 21:45 ` Carl Edquist
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