parallel.sh

#!/bin/bash

# Shamelessly borrowed from
# https://pebblesinthesand.wordpress.com/2008/05/22/a-srcipt-for-running-processes-in-parallel-in-bash/

# SYNTAX: "bash parallel.sh -j 8 ./main 8.dcm"
NUM=0
QUEUE=""
MAX_NPROC=2 # default
REPLACE_CMD=0 # no replacement by default
USAGE="A simple wrapper for running processes in parallel.
Usage: `basename $0` [-h] [-r] [-j nb_jobs] command arg_list
    -h      Shows this help
    -r      Replace asterix * in the command string with argument
    -j nb_jobs  Set number of simultanious jobs [2]
 Examples:
    `basename $0` somecommand arg1 arg2 arg3
    `basename $0` -j 3 \"somecommand -r -p\" arg1 arg2 arg3
    `basename $0` -j 6 -r \"convert -scale 50% * small/small_*\" *.jpg"
 
function queue {
    QUEUE="$QUEUE $1"
    NUM=$(($NUM+1))
}
 
function regeneratequeue {
    OLDREQUEUE=$QUEUE
    QUEUE=""
    NUM=0
    for PID in $OLDREQUEUE
    do
        if [ -d /proc/$PID  ] ; then
            QUEUE="$QUEUE $PID"
            NUM=$(($NUM+1))
        fi
    done
}
 
function checkqueue {
    OLDCHQUEUE=$QUEUE
    for PID in $OLDCHQUEUE
    do
        if [ ! -d /proc/$PID ] ; then
            regeneratequeue # at least one PID has finished
            break
        fi
    done
}
 
# parse command line
if [ $# -eq 0 ]; then #  must be at least one arg
    echo "$USAGE" >&2
    exit 1
fi
 
while getopts j:rh OPT; do # "j:" waits for an argument "h" doesnt
    case $OPT in
    h)  echo "$USAGE"
        exit 0 ;;
    j)  MAX_NPROC=$OPTARG ;;
    r)  REPLACE_CMD=1 ;;
    \?) # getopts issues an error message
        echo "$USAGE" >&2
        exit 1 ;;
    esac
done
 
# Main program
echo Using $MAX_NPROC parallel threads
shift `expr $OPTIND - 1` # shift input args, ignore processed args
COMMAND=$1
shift
 
for INS in $* # for the rest of the arguments
do
    # DEFINE COMMAND
    if [ $REPLACE_CMD -eq 1 ]; then
        CMD=${COMMAND//"*"/$INS}
    else
        CMD="$COMMAND $INS" #append args
    fi
    echo "Running $CMD"
 
    $CMD &
    # DEFINE COMMAND END
 
    PID=$!
    queue $PID
 
    while [ $NUM -ge $MAX_NPROC ]; do
        checkqueue
        sleep 0.4
    done
done
wait # wait for all processes to finish before exit