I use Parallel::ForkManager for most of my forking these days.
it setup nice callbacks for Start/wait/finish of children

heres a snipit:

# when a childe spawns
$pm->run_on_start(
    sub {
        my ($pid,$ident)=@_;
        log_report("Parent Starting Child $pid Sending to $ident");
    });

# when a childe finishes
$pm->run_on_finish(
    sub {
        my ($pid, $exit_code, $ident, $error) = @_;
        log_report( "Child at $pid completed on $ident with code:$exit
+_code");
    });

# while we wait.. 
$pm->run_on_wait( sub{log_report( "Waiting for children ..." );} );
[download]

of course this is pretty simplistic :-) read the docs for more info. I imagine you caould build up some sort of execution chain ? for a task then independentl;y walk that chain. assuming you know that task X requires task A and B.