process watching?

process watching?

[Joe Fouche]

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A few times lately, I've had need of a way to watch for a certain process to
exit. I think it'd be a nice addition to zsh. For example, suppose I want to
be notified when the process "foo" terminates.  I'd like to be able to do

% watch $(pidof foo)

and continue about my business, and later zsh would say something like

foo exited at 8:10AM.
%

Is this feasible? :)
-- 
    _ ____  Joe Fouche (jf@ugcs.caltech.edu)  
 ___| |---       Deranged College Student    

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Re: process watching?

[Zefram]

Joe Fouche wrote:
>A few times lately, I've had need of a way to watch for a certain process to
>exit. I think it'd be a nice addition to zsh. For example, suppose I want to
>be notified when the process "foo" terminates.  I'd like to be able to do
>
>% watch $(pidof foo)
>
>and continue about my business, and later zsh would say something like
>
>foo exited at 8:10AM.
>%
>
>Is this feasible? :)

Very feasible, in much the same way as the current $WATCH system, and I
for one would find it useful.  Perhaps you'd like to write it as a module?
All the necessary hooks already exist -- look at the sched module to
see how it runs code before each prompt.  (Of course, it could be done
in user code, using $PERIODIC, but that's a rather messy mechanism and
not entirely appropriate.)

(I would implement this tonight, but I'm very busy with real life
right now.)

-zefram

Re: process watching?

[Zoltan T. Hidvegi]

Zefram wrote:
> see how it runs code before each prompt.  (Of course, it could be done
> in user code, using $PERIODIC, but that's a rather messy mechanism and
> not entirely appropriate.)

Why?  What's wrong with the user code implementation?  kill -0 pid can be
used to test for the presence of the process.  It can be put either to
precmd or to periodic (periodic is the function name which is executed in
every $PERIOD seconds, just before a prompt).

Zoltan

Re: process watching?

[Zefram]

Zoltan T. Hidvegi wrote:
>Why?  What's wrong with the user code implementation?  kill -0 pid can be
>used to test for the presence of the process.  It can be put either to
>precmd or to periodic (periodic is the function name which is executed in
>every $PERIOD seconds, just before a prompt).

There's nothing inherently wrong with doing it that way.  It will work,
and be tolerably efficient.  It's fine for a one-off.  However, there is
the problem that there can only be one periodic function, so if the user
wants to do two periodic things, they must both have the same period
and both be invoked in the periodic function.  For something that is
to be used regularly, it would be nice to extend sched to do periodic
execution of this nature, or otherwise allow multiple independent
periodic functions.

-zefram