{ 
    my $running : shared = 0;
    local %ENV = %ENV;
    $ENV{ FOO } = 'BAR';
    async{
        my $pid = open ...;
        $running = 1;
        ...
        kill ...
    }->detach;
    ## Wait until the kid is spawned before exiting the scope.
    sleep 1 until $running;
}
## And repeat till done.