works as expected on Linux.

You need to add code to detect HUP | IN - hup is never being called separately so the second watch is never being fired

<?php

function out($pipe) {
       echo "STDOUT\n";
       echo stream_get_contents($pipe);
}

function hupin($pipe){
       echo "STDOUT\n";
       echo stream_get_contents($pipe);
       echo "HUP\n";
       Gtk::main_quit();
       return false;
}

function hup($pipe){
       echo "HUP\n";
       Gtk::main_quit();
       return false;
}

$pipes = null;
$descriptor = array(
       0 => array("pipe", "r"),  // stdin
       1 => array("pipe", "w"),  // stdout is a pipe that the child will write to
       2 => array("pipe", "w")   // stderr
);
$cmd = 'dir';
$p = proc_open($cmd, $descriptor, $pipes);
Gtk::io_add_watch($pipes[1],GTK::IO_IN, 'out');
Gtk::io_add_watch($pipes[1],GTK::IO_HUP, 'hup');
Gtk::io_add_watch($pipes[1],GTK::IO_HUP | GTK::IO_IN, 'hupin');

Gtk::main();
echo "EXIT\n";
fclose($pipes[0]);
fclose($pipes[1]);
fclose($pipes[2]);
?>

@auroraeosrose
Using Windows binary with Gtk+ 2.10 with GTK::IO_HUP | GTK::IO_IN the script doesn't hang anymore but shows the content partially. For example sometimes only the first lines, others only the last, and regularly there's no output at all.

If you use the second argument of the watch :

function hupin($pipe, $condition)

Only IO_IN (integer 1) is fired, in few cases both IO_IN| IO_HUP (integer 17). In previous version (2.0.0 alpha) IO_HUP worked correctly.

This only is a toy example, but my main application uses this behavior avoiding the 'busy-wait' effect in several long running tasks (wrapping svn commands for example), and currently it's loosing functionality in Windows.