#!/usr/bin/perl -w
use feature 'say';
use IO::Handle;

my $total=0.0;
@waitlist = qw(0 200 400 800 1000);

foreach $item (@waitlist) {
  pipe(*{$item},RETHAND);
  *{$item}->autoflush(1);
  RETHAND->autoflush(1);
  unless (my $pid = fork()) {
    my $h = 1.0 /1200.0;
    my $sum = 0.0;
    for (my $i = $item; $i < ($item+200); $i++){        
    my $x = $h * ($i - 0.5);
    $sum += 4.0 / (1.0 + $x*$x);
    }
    my $ret=$sum*$h;
    print RETHAND "$ret";
    exit; 
  }else{
    close RETHAND
  }
}

foreach $item (@waitlist) {
  $response = <$item>;
  $total+= ($response+0.0);
  print "$total\n";
}  


1 while (wait() != -1);
print " $total\n";
print "All done!\n";