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Full Discussion: Multi threading - running multiple processes at the same time
Top Forums Shell Programming and Scripting Multi threading - running multiple processes at the same time Post 302978537 by Don Cragun on Sunday 31st of July 2016 07:31:51 PM
Old 07-31-2016
Quote:
Originally Posted by SkySmart
so i've been using this a lot in a lot of my scripts:

Code:
( columnA & columnAPID=$! & columnB & columnBPID=$! & columnC & columnCPID=$! &) &
wait ${columnAPID}
wait ${columnBPID}
wait ${columnCPID}

It seems to work as ive seen it dramatically reduce run time of my scripts.

however, i'm wondering if there's another way to do the above? a better way, maybe? one that' is of course portable and will be faster??

i'm using /bin/sh
You're using an unneeded subshell and running several background jobs that do not need to be in the background. Your script could more simply (and slightly more efficiently) be written as:
Code:
columnA & columnAPID=$!
columnB & columnBPID=$!
columnC & columnCPID=$!
wait ${columnAPID}
wait ${columnBPID}
wait ${columnCPID}

or if you don't have any other background jobs and aren't going to check the exit status of each individual wait command to verify that all three jobs completed successfully:
Code:
columnA &
columnB &
columnC &
wait

This User Gave Thanks to Don Cragun For This Post:
SkySmart
 

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LEARN ABOUT DEBIAN

queuedefs

queuedefs(4)							   File Formats 						      queuedefs(4)

NAME

       queuedefs - queue description file for at, batch, and cron

SYNOPSIS

       /etc/cron.d/queuedefs

DESCRIPTION

       The queuedefs file describes the characteristics of the queues managed by cron(1M). Each non-comment line in this file describes one queue.
       The format of the lines are as follows:

	      q.[njobj][nicen][nwaitw]

       The fields in this line are:

       q	The name of the queue. a is the default queue for jobs started by at(1); b is the default queue for jobs  started  by  batch  (see
		at(1)); c is the default queue for jobs run from a crontab(1) file.

       njob	The  maximum  number of jobs that can be run simultaneously in that queue; if more than njob jobs are ready to run, only the first
		njob jobs will be run, and the others will be run as jobs that are currently running terminate.  The default value is  100.

       nice	The nice(1) value to give to all jobs in that queue that are not run with a user ID of super-user.  The default value is 2.

       nwait	The number of seconds to wait before rescheduling a job that was deferred because more than njob jobs were running in  that  job's
		queue, or because the system-wide limit of jobs executing has been reached.  The default value is 60.

       Lines beginning with # are comments, and are ignored.

EXAMPLES

       Example 1: A sample file.

       #
       #
       a.4j1n
       b.2j2n90w

       This  file  specifies that the a queue, for at jobs, can have up to 4 jobs running simultaneously; those jobs will be run with a nice value
       of 1.  As no nwait value was given, if a job cannot be run because too many other jobs are running cron will wait 60 seconds before  trying
       again to run it.

       The  b  queue, for batch(1) jobs, can have up to 2 jobs running simultaneously; those jobs will be run with a nice(1) value of 2.  If a job
       cannot be run because too many other jobs are running, cron(1M) will wait 90 seconds before trying again to run it. All	other  queues  can
       have up to 100 jobs running simultaneously; they will be run with a nice value of 2, and if a job cannot be run because too many other jobs
       are running cron will wait 60 seconds before trying again to run it.

FILES

       /etc/cron.d/queuedefs	       queue description file for  at, batch, and  cron.

SEE ALSO

       at(1), crontab(1), nice(1), cron(1M)

SunOS 5.10							    1 Mar 1994							      queuedefs(4)
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