bash parallel execution

parallel.sh

#!/bin/bash

pause() { read -p "Press any key to continue..." -n1 -r; }

# func <min> <max>
randnum() {
    local min=$1
    local max=$[ $2 - $min + 1 ]
    local num=$(cat /dev/urandom 2>/dev/null | head -n 8 | cksum | cut -f1 -d' ')
    echo $[ $num % $max + $min ]
}

# func <fdnum>
tmpfd() {
	local tmpfifo=/tmp/pid$$fd$1.fifo
	trap "exec $1>&-;exec $1<&-;exit 0" 2
	mkfifo $tmpfifo
	eval "exec $1<>$tmpfifo"
	rm -rf $tmpfifo
}

NPROC=16; total=200; arr=($(seq 1 $total))


time=$($DATE -u +%s%3N)
tmpfd 6; for i in $(seq 1 $NPROC); do echo >&6; done # Generate $NPROC tokens
for i in $(seq 0 $[$total -1 ]); do
	read -u6 # Take token, will wait when no token is available
	{
		sleep 2
		#sleep $(randnum 1 3)
		if [ $i -ne 30 -a $i -ne 69 -a $i -ne 99 -a $i -ne 199 ]; then
			echo "$i ${arr[$i]}"
		fi
		echo >&6 # Release token
	} &
done
wait
time=$[ $($DATE -u +%s%3N) - $time ]
echo "Total time: $[ $time / 60000 ]m$[ $time / 1000 % 60 ].$[ $time % 1000 ]s."
pause


time=$($DATE -u +%s%3N)
for i in $(seq 0 $[$total -1 ]); do
	while [ $(jobs -p|wc -l) -ge $NPROC ]; do wait -n; done
	{
		sleep 2
		#sleep $(randnum 1 3)
		echo "$i ${arr[$i]}"
		# Variables from subshell cannot be passed to parent shell
	} &
done
wait
time=$[ $($DATE -u +%s%3N) - $time ]
echo "Total time: $[ $time / 60000 ]m$[ $time / 1000 % 60 ].$[ $time % 1000 ]s."

ref: https://superuser.com/questions/153630/running-commands-in-parallel-with-a-limit-of-simultaneous-number-of-commands