Limit bash script to one running instance, while keeping it open to other calls

lockfile_pid_tpl.sh

#!/bin/bash

user_id_num=$(id -u)
pid_file="/tmp/foobar-$user_id_num/foobar-$user_id_num.pid"
lock_file="/tmp/foobar-$user_id_num/running.lock"
ps_id=$$

function alertRunningPS () {
	local PID=$(cat "$pid_file" 2> /dev/null)
	echo "Lockfile present. ps id file: $PID"
	echo "Checking if process is actually running or something left over from crash..."
	if kill -0 $PID 2> /dev/null; then
		echo "Already running, exiting"
		exit 1
	else
		echo "Not running, removing lock and continuing"
		rm -f "$lock_file"
		lockfile -r 0 "$lock_file"
	fi
}

echo "Hello, checking some stuff before locking stuff"

# Lock further operations to one process
mkdir -p /tmp/foobar-$user_id_num
lockfile -r 0 "$lock_file" || alertRunningPS

# Do stuff here
echo -n $ps_id > "$pid_file"
echo "Running stuff in ONE ps"

sleep 30s

rm -f "$lock_file"
rm -f "$pid_file"
exit 0