Bash script with concurrency control

gistfile1.txt

#!/usr/bin/env bash

MAX_CONCURRENCY=10 # max task slots

sub_task() {
    sleep $(( ( RANDOM % 10 )  + 1 ))
    echo "Task $1 finished at $(date)"
}

mkfifo testfifo
exec 10<>testfifo && rm -f testfifo
for _ in $(seq 1 ${MAX_CONCURRENCY}); do { echo >&10; } done
for T in {01..30}; do
    read -r -u10
    {
        ### do something
        sub_task $T
        echo "finish: $T with $?"

        echo >&10
    } &
done
wait
exec 10>&-
exec 10<&-