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Top Forums Shell Programming and Scripting Waiting for an arbitrary background process (limiting number of jobs running) Post 302390712 by p.f.moore on Thursday 28th of January 2010 06:11:38 PM
Old 01-28-2010
Waiting for an arbitrary background process (limiting number of jobs running)

Hi,
I'm trying to write a script to decompress a directory full of files. The decompression commands can run in the background, so that many can run at once. But I want to limit the number running at any one time, so that I don't overload the machine.

Something like this:

Code:
n=0
for i in *.gz
do
    gzip -d $i &
    n=$((n+1))
    if [ $n -ge 10 ]; then
        # XXX Not sure what to do here
    fi
done

At the marked spot, I want to wait for one of my background processes to complete. I don't mind which one, but I do want to wait for just one.

wait doesn't work, as it waits for all jobs to complete. On the other hand, wait N doesn't work, because I don't know which job will finish first.

I could use trap "..." 20, but I'd need to be able to pause my script at the XXX line and be able to resume it via the "..." from the trap command. I can't think of a way of doing this ("suspend" in bash might work, but really I need this to work in ksh - I'm not sure the server this will ultimately run on has bash installed).

Can anyone suggest an approach that I could use?

Thanks,
Paul.
 

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wait(1) 						      General Commands Manual							   wait(1)

NAME
wait - await process completion SYNOPSIS
[pid] DESCRIPTION
If no argument is specified, waits until all processes (started with of the current shell have completed, and reports on abnormal termina- tions. If a numeric argument pid is given and is the process ID of a background process, waits until that process has completed. Other- wise, if pid is not a background process, exits without waiting for any processes to complete. Because the system call must be executed in the parent process, the shell itself executes without creating a new process (see wait(2)). Command-Line Arguments supports the following command line arguments: The unsigned decimal integer process ID of a command, whose termination is to wait for. WARNINGS
Some processes in a 2-or-more-stage pipeline may not be children of the shell, and thus cannot be waited for. SEE ALSO
csh(1), ksh(1), sh-posix(1), sh(1), wait(2). STANDARDS CONFORMANCE
wait(1)
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