while (1) {
    $pm->start and next;
    ...
    # do child tasks here
    ...
    $pm->finish;
}

##</code><code>##

    $pm->wait_all_children;

##</code><code>##

$pmgr->run_on_finish(
    sub {
        my ($pid, $exit_code, $ident) = @_;
        waitpid $pid, 0;
    }
);