foreach my $node (@nodes) {
        chomp $node;
        wait_for_a_kid() if keys %pid_to_node > 4;
        if (my $pid = fork) {
                ## parent does...
                $pid_to_node{$pid} = $node;
        }
        else {
                local $SIG {ALRM} = sub {
                        kill -15, $pid or die "kill: $!";
                        print "Killed PID $pid\n"};
                eval {
                        unless ($pid) {
                                ## child does...
                                setpgrp(0,0);
                                exit !&NODE($node);
                        }
                        alarm 15;
                        waitpid $pid => 0;
                };
        }
}
## final reap:
1 while wait_for_a_kid();

sub wait_for_a_kid {
        my $pid = wait;
        return 0 if $pid < 0;
        my $node = delete $pid_to_node{$pid} or warn("Why did I see $pid ($?)\n"), next;
1;
}

##</code><code>##

#!/bin/perl
for ($i=0; $i<=10; $i++) {
        wait_for_a_kid() if keys %pid_to_node > 3;
        $pid = fork;
        if ($pid) {
                ## parent does...
                $pid_to_node{$pid} = $i;
        }
        else {
                print "$i $$\n";
                local $SIG {ALRM} = sub {
                kill -15, $$ or die "kill: $!";
                print "\tKilled PID $$\n"}; # Just SIGTERM.
                eval {
                        ## child does...
                        setpgrp(0,0);
                        exit !&Test;
                        alarm 1;
                        waitpid $pid => 0;
                };
        }
}
## final reap:
1 while wait_for_a_kid();

sub wait_for_a_kid {
        my $pid = wait;
        return 0 if $pid < 0;
        my $node = delete $pid_to_node{$pid} or warn("Why did I see $pid ($?)\n"), next;
}

sub Test {
        sleep 10;
}