Re: problem with Gtk2::Helper & STDOUT


I don't think this is a Gtk issue - isn't STDOUT essentially a
write-only file handle?

Even if it's not, think of where the current position is. It will
start at eof, and when you write out to it it will stay at eof (after
anything you just wrote). So unless you seek backwards (which I don't
think you can do on STDOUT) there's never anything after the current
position, so there's never anything to read, so the watch never gets

If you mapped STDOUT to a seekable read/write filehandle and made sure
you seek'd backwards every time you wrote to it, that _might_ trigger
a watch on that file handle (and you'd have to make sure you truncate
it in the watch or you'd end up repeating everything over and over
again). That sounds incredibly flaky though.


2009/9/10 Landry Breuil <landry rhaalovely net>:

i'm asking here after turning around a strange problem for days...
i can't get to make Gtk2::Helper watch the STDOUT of the current program
(not from a forked child or whatever). The idea is to do smth like 'tail' but
in a Gtk Widget or VTE Widget, but showing current process STDOUT.

I think i tried everything so far, all supposed (from my understanding
of the docs) to catch the 'FOO'
printed on STDOUT :

Glib::IO->add_watch (fileno (STDOUT), 'in', sub {
       my $fd = shift;
       print STDERR "received \"$_\"\n" while (<$fd>);
       return TRUE;
print "FOO\n";

same thing with an anonymous file handler :

open my $fh, "+>", undef or die "blaaah : $!";
select $fh;
my $id = Glib::IO->add_watch (fileno $fh, 'in', sub {
       my $fd = shift;
       print STDERR "received \"$_\"\n" while (<$fd>);
       return TRUE;
print "FOO\n";

With those examples, 'FOO' is dropped.

Is there a way to realize this ? I'd really appreciate some help,
because this is turning me mad since days. Apparently, bare glib allows
io channels to be created with stdout.. maybe the problem lies in the
fact that i want to _read_ on  STDOUT. I also tried :

pipe ($read,$fh);
select $fh;
Gtk2::Helper->add_watch (fileno($read), 'in', sub {cbk($fh)});

With no luck.

Thanks for any pointers/insights.


Ps: here's the whole test program :

#!/usr/bin/perl -w

use strict;
use Glib 1.040, qw(TRUE FALSE);
use Gtk2;
use Data::Dumper;
use Gtk2::Helper;


my $window = Gtk2::Window->new;
$window->signal_connect (delete_event => sub {exit});
$window->set_default_size (400, 300);
my $vbox = Gtk2::VBox->new;
$window->add ($vbox);
my $scroller = Gtk2::ScrolledWindow->new;
$vbox->add ($scroller);
my $textview = Gtk2::TextView->new;
my $buffer = $textview->get_buffer;
$buffer->create_mark ('end', $buffer->get_end_iter, FALSE);
$buffer->signal_connect (insert_text => sub { $textview->scroll_to_mark ($buffer->get_mark ('end'), 0.0, 
TRUE, 0, 0.5);});
$scroller->add ($textview);
my $button = Gtk2::Button->new ('go');
$button->signal_connect (clicked => \&button_handler);
$vbox->pack_start ($button, FALSE, FALSE, 0);

sub button_handler {
       $button->set_sensitive (FALSE);
       my $fh;
       open ($fh, "+>", undef) or die "PROTCH:$!";
       select $fh;
       Gtk2::Helper->add_watch (fileno($fh), 'in', sub {cbk($fh)});
       print STDERR "FOO1\n";
       print "FOO2\n";
       sleep 1;
       print $fh "FOO3\n";
       $buffer->insert ($buffer->get_end_iter, "done");
       $button->set_sensitive (TRUE);
sub cbk {
       my $fd = shift;
       my $buf;
       print STDERR Dumper($fd).fileno($fd)."!\n";
       while (sysread ($fd,$buf,1028)) {
               print STDERR "received \"$buf\"\n";
               $buffer->insert ($buffer->get_end_iter, $buf);
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