runParallel.sh

runParallel() {
  local batchSize=1
  if [ "$1" == "--batch" ]; then
    batchSize="$2"
    shift 2
  fi
  local concurrency="$1"
  shift
  local tasks=()
  local exitCode=0
  local elemExitCode=0
  [[ $- = *e* ]]; local setE=$?
  set +e
  while IFS= read -r elem; do
    while (( ${#tasks[@]} >= $concurrency )); do
      for i in ${!tasks[@]}; do
        if ! [ -d /proc/"${tasks[$i]}"/ ]; then
          wait "${tasks[$i]}" || exitCode="$?"
          unset tasks[$i]
        fi
      done
      if (( ${#tasks[@]} >= $concurrency )); then
        sleep 0.01
      fi
    done
    local elems=( "$elem" )
    if (( $batchSize > 1 )); then
      mapfile -t -O 1 -n "$(( $batchSize - 1 ))" elems
    fi
    {
      exitCode=0
      for elem in "${elems[@]}"; do
        (
          (( $setE )) && set -e
          "$@" "$elem"
        )
        elemExitCode="$?"
        (( $elemExitCode )) && exitCode="$elemExitCode"
      done
      exit "$exitCode"
    } &
    tasks=( "${tasks[@]}" "${!}" )
  done
  for task in "${tasks[@]}"; do
    wait "$task" || exitCode="$?"
  done
  (( $setE )) && set -e
  return "$exitCode"
}