How to run given function in Bash in parallel?

Question

There have been some similar questions, but my problem is not \"run several programs in parallel\" - which can be trivially done with parallel or xargs

Answer 1

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[@]}"