use POSIX ":sys_wait_h";
...
#-------------------------------------------------------------------------------------------------------------
#-------------------------------------------------------------------------------------------------------------
sub S_TestForking2 {

    my ($lSleepTime);
    my ($lProcessLabel, @lPidArray);
    my $lFinished = 0;
    my $lStillRunning = 0;
    my $isAlive;
    my $kid;
    my $lpid;
    my $i;
    
    my %lRunningPidHash = ();

    my @lCmdArray;
    my $lCmdIndex;

    # Create a bunch of fake commands that take time
    push (@lCmdArray, "sleep 20");
    push (@lCmdArray, "sleep 25");
    push (@lCmdArray, "sleep 38");
    push (@lCmdArray, "sleep 20");
    push (@lCmdArray, "sleep 17");
    push (@lCmdArray, "sleep 15");
    push (@lCmdArray, "sleep 25");
    push (@lCmdArray, "sleep 30");
    push (@lCmdArray, "sleep 15");


    $lFinished = 0;
    while ($lFinished == 0) {
        
        # Count the running processes using the pid array we filled when we forked the child

        $lStillRunning = 0;
        foreach $lpid (sort keys %lRunningPidHash) {
            waitpid($lpid, WNOHANG);
            if ( $? == -1 ) {
                $lStillRunning++;
            } elsif ($? == 0) {
                # If we ask about this id again  we get -1 forever
                delete $lRunningPidHash{$lpid};
            }
            print "\t$lpid = $?\n";
        }

        print "Running processes: $lStillRunning\n";

        # If our command array is zero and our running processes is zero - we can just exit

        if ( $lStillRunning == 0 and scalar (@lCmdArray) == 0 ) {
            $lFinished = 1;
            last;
        }


        # Pop the commands off the command array so we always have 6 processes running

        for ($i = $lStillRunning; $i < 3; $i++) {
            my $lCmd = pop (@lCmdArray);
            if ( $lCmd ) {
                $lpid = fork;
                die "Couldn't fork: $!" unless defined $lpid;

                if ( $lpid ) {
                    # parent
                    print "Forked off a child: $lCmd - $lpid\n";
                    $lRunningPidHash{$lpid} = 1;
                } else {
                    # child
                    close (STDIN);
                    close (STDOUT);
                    close (STDERR);
        
                    exec ($lCmd) or die ("Error: could not exec command : $lCmd :  $!\n");
                }
            }
        }

        # Sleep a few seconds and re scan
        sleep (5);
                  
    }



    print "Parent exiting\n";


}   # S_TestForking2