Shell Programming and Scripting

Hi.

The Linux xargs has a feature to perform this kind of task:

Code:

       --max-procs=max-procs
       -P max-procs
              Run up to max-procs processes at a time; the default is  1.   If
              max-procs  is 0, xargs will run as many processes as possible at
              a time.

See man xargs for details ... cheers, drl

BTW, ksh93t has built-in support for automatically limiting the number of background jobs that run at the same time. See the MAXJOBS parameter. You can also use the SIGCHLD trap to find out which background job has completed and get it's exit status.

Thanks! A small correction: I think it is ksh93t+ and higher and the variable is call JOBMAX. It works nicely. If you do:

Code:

#!/bin/ksh
JOBMAX=10  # works in ksh93t+
for i in *
do
  sleep 10 &
done
wait

ps will show 11 processes at every moment including the parent.

My mistake. It was late. I took it from a Dave Korn email without checking the sources.

https://mailman.research.att.com/pip...q2/002931.html

For completeness, here is the ksh93 release note on JOBMAX.

08-12-04 +SHOPT_BGX enables background job extensions. Noted by "J" in
the version string when enabled. (1) JOBMAX=n limits the number
of concurrent & jobs to n; the n+1 & job will block until a
running background job completes. (2) SIGCHLD traps are queued
so that each completing background job gets its own trap; $! is
set to the job pid and $? is set to the job exit status at the
beginning of the trap. (3) sleep -s added to sleep until the time
expires or until a signal is delivered.