Listing 2: The do_stats() function is responsible for launching the timing tests

sub do_stats {
    my $doit = shift;
    my $start = time();

    # open a pipe so that child processes can send results to parent.
    my $pipe = IO::Pipe->new || die "Can't pipe: $!";

    # spawn correct number of children
    for (my $i=0; $i<$COPIES; $i++) {
	die "Can't fork: $!" unless defined (my $pid = fork());
	# if parent, continue spawning children
	next if $pid > 0;  

	# otherwise we're a child, so we run the test once and exit
	$pipe->writer; select $pipe;
	run_test($doit);
	exit 0;
    }

    # otherwise, parent reads and tallies the results
    $SIG{CHLD} = sub { do {} while waitpid(-1,WNOHANG) > 0; };

    # open pipe for reading
    $pipe->reader;
    my $stats = tally_results($pipe);
    $stats->{elapsed} = time() - $start;
    return $stats;
}