sem
is part of GNU Parallel and is made for this kind of situation.
for i in "${list[@]}"
do
for j in "${other[@]}"
do
# some processing in here - 20-30 lines of almost pure bash
sem -j 4 dolong task
done
done
If you like the function better GNU Parallel can do the dual for loop in one go:
dowork() {
echo "Starting i=$1, j=$2"
sleep 5
echo "Done i=$1, j=$2"
}
export -f dowork
parallel dowork ::: "${list[@]}" ::: "${other[@]}"