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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 NETBSD

wait

WAIT(1) 						    BSD General Commands Manual 						   WAIT(1)

NAME

     wait -- await process completion

SYNOPSIS

     wait [pid]

DESCRIPTION

     If invoked with no arguments, the wait utility waits until all existing child processes in the background have terminated.

     Available operands:

     pid     If a pid operand is specified, and it is the process ID of a background child process that still exists, the wait utility waits until
	     that process has completed and consumes its status information, without consuming the status information of any other process.

	     If a pid operand is specified that is not the process ID of a child background process that still exists, wait exits without waiting
	     for any processes to complete.

     The wait utility exits with one of the following values:

     0	     The wait utility was invoked with no operands and all of the existing background child processes have terminated, or the process
	     specified by the pid operand exited normally with 0 as its exit status.

     >0      The specified process did not exist and its exit status information was not available, or the specified process existed or its exit
	     status information was available, and it terminated with a non-zero exit status.

     If the specified process terminated abnormally due to the receipt of a signal, the exit status information of wait contains that termination
     status as well.

STANDARDS

     The wait command is expected to be IEEE Std 1003.2 (``POSIX.2'') compatible.

BSD
								   June 5, 1993 							       BSD
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