From: Chet Ramey <chet.ramey@case.edu>
To: Carl Edquist <edquist@cs.wisc.edu>,
Martin D Kealey <martin@kurahaupo.gen.nz>
Cc: chet.ramey@case.edu, Zachary Santer <zsanter@gmail.com>,
bug-bash <bug-bash@gnu.org>,
libc-alpha@sourceware.org
Subject: Re: Examples of concurrent coproc usage?
Date: Sat, 13 Apr 2024 16:10:26 -0400 [thread overview]
Message-ID: <32bd9e76-24bc-4206-aa8a-8bcc817228b1@case.edu> (raw)
In-Reply-To: <e56a7b66-f015-d33c-dbd7-70ce4c71fdd8@cs.wisc.edu>
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On 4/9/24 11:58 AM, Carl Edquist wrote:
> On 4/4/24 7:23 PM, Martin D Kealey wrote:
>
>> I'm somewhat uneasy about having coprocs inaccessible to each other. I
>> can foresee reasonable cases where I'd want a coproc to utilize one or
>> more other coprocs.
>>
>> In particular, I can see cases where a coproc is written to by one
>> process, and read from by another.
>>
>> Can we at least have the auto-close behaviour be made optional, so that
>> it can be turned off when we want to do something more sophisticated?
>
> With support for multiple coprocs, auto-closing the fds to other coprocs
> when creating new ones is important in order to avoid deadlocks.
>
> But if you're willing to take on management of those coproc fds yourself,
> you can expose them to new coprocs by making your own copies with exec
> redirections.
>
> But this only "kind of" works, because for some reason bash seems to close
> all pipe fds for external commands in coprocs, even the ones that the user
> explicitly copies with exec redirections.
>
> (More on that in a bit.)
>
>
> On Mon, 8 Apr 2024, Chet Ramey wrote:
>
>> On 4/4/24 7:23 PM, Martin D Kealey wrote:
>>> I'm somewhat uneasy about having coprocs inaccessible to each other. I
>>> can foresee reasonable cases where I'd want a coproc to utilize one or
>>> more other coprocs.
>>
>> That's not the intended purpose,
The original intent was to allow the shell to drive a long-running process
that ran more-or-less in parallel with it. Look at examples/scripts/bcalc
for an example of that kind of use.
>
> For what it's worth, my experience is that coprocesses in bash (rigged up
> by means other than the coproc keyword) become very fun and interesting
> when you allow for the possibility of communication between coprocesses.
> (Most of my use cases for coprocesses fall under this category, actually.)
Sure, as long as you're willing to take on file descriptor management
yourself. I just don't want to make it a new requirement, since it's never
been one before.
> Now, if you built bash with multiple coproc support, I would have expected
> you could still rig this up, by doing the redirection work explicitly
> yourself. Something like this:
>
> coproc UP { stdbuf -oL tr a-z A-Z; }
> coproc DOWN { stdbuf -oL tr A-Z a-z; }
>
> # make user-managed backup copies of coproc fds
> exec {up_r}<&${UP[0]} {up_w}>&${UP[1]}
> exec {down_r}<&${DOWN[0]} {down_w}>&${DOWN[1]}
>
> coproc THREEWAY { tee /dev/fd/$up_w /dev/fd/$down_w; }
>
>
> But the above doesn't actually work, as it seems that the coproc shell
> (THREEWAY) closes specifically all the pipe fds (beyond 0,1,2), even the
> user-managed ones explicitly copied with exec.
File descriptors the user saves with exec redirections beyond [0-2]
are set to close-on-exec. POSIX makes that behavior unspecified, but
bash has always done it.
Shells don't offer any standard way to modify the state of that flag,
but there is the `fdflags' loadable builtin you can experiment with
to change close-on-exec.
Chet
--
``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:[~2024-04-13 20:10 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
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 [this message]
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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