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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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  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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