Hello kikuchiyo,

The thread Non-blocking Reads from Pipe Filehandle from 10 years ago is a good read. Thank you for posting the link. Queues typically have non-blocking capabilities. Thus, the reason for taking MCE::Hobo and MCE::Shared for a drive.

I've added a $poll variable to have the timer code leave early unless awaiting a reply.

#!/usr/bin/perl
##
#   Gtk2 app on Windows, driving a background process:
#   http://www.perlmonks.org/?node_id=1191637
#
#   Gtk2 and MCE::Hobo demonstration base on:
#   http://www.perlmonks.org/?node_id=1191649
##
use strict;
use warnings;

use Gtk2 -init;
use IPC::Open2;
use MCE::Hobo ();
use MCE::Shared ();

my $cmd  = $^O eq 'MSWin32' ? 'bc.exe' : 'bc';
my $qjob = MCE::Shared->queue();
my $qres = MCE::Shared->queue();

sub background {
    my $pid = open2( my $reader, my $writer, $cmd );
    print STDERR "=== pid hobo : $$\n";
    print STDERR "=== pid bc   : $pid\n";
    while ( defined ( my $text = $qjob->dequeue() ) ) {
        print $writer $text;
        $qres->enqueue(scalar <$reader>);
    }
    kill 'TERM', $pid;
    waitpid $pid, 0;
}

my $hobo = MCE::Hobo->create(\&background);

my $w = Gtk2::Window->new();
my $vbox = Gtk2::VBox->new();
my $l = Gtk2::Label->new();
my $i = Gtk2::Entry->new();
my $poll = 0;

$w->signal_connect(destroy => \&cleanup);
$i->signal_connect(activate => sub {
    my $text = $i->get_text();
    $qjob->enqueue("$text\n"), $poll = 1;
    print STDERR ">>> $text\n";
    $i->set_text('');
});

Glib::Timeout->add(60, \&update_label);

# Emulated fork on Windows returns a negative pid.
# The hobo worker can send the bc pid if desired.
# E.g.: $qres->enqueue($pid); from inside hobo
#       my $bc_pid = $qres->dequeue;

$l->set_text( "init ".$hobo->pid() );

$vbox->add($i);
$vbox->add($l);
$w->add($vbox);
$w->show_all();

Gtk2->main();

sub update_label {
    return Glib::SOURCE_CONTINUE unless $poll;
    my $read = $qres->dequeue_nb();
    if (length $read) {
        $poll = 0, chomp $read;
        chop $read if $^O eq 'MSWin32';
        print STDERR "<<< $read\n";
        $l->set_text($read);
    }
    return Glib::SOURCE_CONTINUE;
}

sub cleanup {
    $qjob->end(), $hobo->join();
    Gtk2->main_quit();
}
[download]

Regards, Mario.