Re: Examples of concurrent coproc usage?

[Chet Ramey <chet.ramey@case.edu>]

On 4/15/24 1:01 PM, Carl Edquist wrote:
> On Sat, 13 Apr 2024, Chet Ramey wrote:
> 
>> 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.
> 
> Thanks for mentioning this example.  As you understand, this model use case 
> does not require closing the coproc fds when finished, because they will be 
> closed implicitly when the shell exits.  (As bcalc itself admits.)
> 
> And if the coproc is left open for the lifetime of the shell, the alternate 
> behavior of deferring the coproc deallocation (until both coproc fds are 
> closed) would not require anything extra from the user.
> 
> The bcalc example does close both coproc fds though - both at the end, and 
> whenever it resets.  And so in this example (which as you say, was the 
> original intent), the user is already explicitly closing both coproc fds 
> explicitly; so the alternate deferring behavior would not require anything 
> extra from the user here either.
> 
> ...
> 
> Yet another point brought to light by the bcalc example relates to the 
> coproc pid variable.  The reset() function first closes the coproc pipe 
> fds, then sleeps for a second to give the BC coproc some time to finish.
> 
> An alternative might be to 'wait' for the coproc to finish (likely faster 
> than sleeping for a second). 

If the coproc has some problem and doesn't exit immediately, `wait' without
options will hang. That's why I opted for the sleep/kill-as-insurance
combo.

(And before you ask why I didn't use `wait -n', I wrote bcalc in 30 minutes
after someone asked me a question about doing floating point math with awk
in a shell script, and it worked.)

-- 
``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/