trap "echo USR1 received" USR1
stub() {
    echo "sleeping for $1 sec"
    sleep $1
    echo "$1 sec passed, sending USR1 to parent"
    kill -USR1 $$
}
stub 2 &
stub 1 &
until { echo "Waiting"; wait; } do
    echo "Wait exit code: $?"
done
echo "Wait returned 0"