my $mw = MainWindow->new();
spawn_child();
$mw->repeat(100,\&read_child);



sub read_child {
  my $rin = "";
  vec($rin, fileno(CHILD), 1) = 1;
  my $err = $rin;
  
  for (0 .. 3) { # try to read from Child this many times before calling it quits
    my ($nfound,$timeleft) = select($rin,undef,$err,0.001);
    print "$nfound." if ($debug > 1);
    while ($nfound) { # there is some data waiting to be read
      my $line = <CHILD>;
      
      ...
      
      ($nfound,$timeleft) = select($rin,undef,$err,0.0001);
      print ":$nfound" if ($debug > 1);
    }
  }
  print "\n" if ($debug > 1);
}

sub spawn_child {
  # parent process does only the GUI stuff all of the tester communication
  # stuff hapens in the child only. The child sits around waiting for the
  # parent to tell it to do something. The child does it, figures out the
  # progress percentage, and informs the parent. The parent, upon receiving
  # this notification, update the GUI.
  
  socketpair(CHILD, PARENT, AF_UNIX, SOCK_STREAM, PF_UNSPEC);
  CHILD->autoflush(1);
  PARENT->autoflush(1);

  die unless defined($childPid=fork());

  if ($childPid){
    close PARENT;
    return;
  }
  
  # child process
  close CHILD;
  my $use_mfg_mode = 0;
  
 Loop:
  while(my $line = <PARENT>){
    my $update = "";
    print "received from parent: $line" if ($debug);
    print PARENT "progress: $update\n";
  }
  print "Child is done!\n" if ($debug);
  exit();
}