Re: Prompt expansion, multi-job for

[Andre Pang <andrep-ml@vjolnir.org>]

On Thu, Jan 06, 2000 at 12:03:09PM +0000, Oliver Kiddle wrote:

> Andre Pang wrote:
> 
> >     2) Is there any way to emulate make's -jn option in the for command?
> > This would be *really* useful for SMP systems.  Currently, doing something
> > like "for i in ***/***.wav; do l3enc $i; done" doesn't take advantage of
> > multiple CPUs (on a Linux system, at least); hacking the for command to
> > accept a 'make -j'-like parameter (eg: for -j2 i in *; do l3enc $i; done)
> > would allow us lucky ones who have SMP systems to do many things similar to
> > the above without going mad and writing silly Makefiles simply so we can
> > utilise make -j.  If someone's written a function to do this already (Bart?
> > ;) it'd be *very* cool.
> 
> If I'm not mistaken, you should be able to do this by running l3enc as a
> background process, i.e. for i in *.wav; do l3enc $i& done. I haven't
> got an SMP system available to me to test but I'd assume that it would
> allocate different l3enc processes to different processors. Putting the

    Yes, you're right there.  I've done this a few times when I've had < 15
jobs to run, but today, I did a 'for i in ***/***.wav; do shorten $i; done',
and I have easily >200 .wavs which I wanted to compress.  Running 200
background processes isn't my idea of fun :).

> a maximum of 4 l3encs at once. This would be a bit messy to implement in
> Zsh (compared to something like Ada) but can be done.

    Which brings me back to my original question - if someone has a function
to do this already, I'll be most happy.  I'm just not sure whether it's
possible to make a function which can emulate the behaviour of the for
command perfectly, because it's treated as a complex command and not as a
function.  I'm thinking that the only way to implement this gracefully would
be to either (a) change the syntax of the new function, thus having a for
command with a different syntax - annoying[1], or (b) modify the zsh source
to deal with it, which I would love to do, but I lack the skill for.

    Suggestions, guys?

    [1] Perhaps the closest you'd get is ``jfor -2 i in * do 'l3enc -q $i;
echo done $i' done'' -- note the lack of semicolons and the single quotes
around the commands to run.  Even then, the syntax is different from normal
for.  Syntax change == bad.


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