Memory leak when replacing listbox contents - Perl

On 24 Oct 2005 00:32:28 -0700, "Stephen" <stephenpage@hotmail.com>
wrote:

>Hello,
>
>In one of my perl/tk programs I refresh the contents of a listbox with
>new data by deleting the current values and inserting new ones. A few
>bytes of memory seem to be leaked by the Listbox->insert() function
>that are not recovered by the Listbox->delete() function. Given time,
>a program refreshing a listbox in this way can consume a lot of memory.
>
>I have observed the problem under both Linux and Windows. Under Linux,
>I am using perl 5.8.5 with perl-Tk version 804.27.
>
>A short piece of example code follows at the end of this message.
>Despite its simplicity, it will gradually consume more and more memory.
>
>I would appreciate any advice that anyone could offer. Am I doing
>something wrong, or is there a bug in the tk modules?
>
>Kind regards,
>
>Stephen
>

It's a pretty small leak in the code you shown. In the following,
I get a 32k increase every 6000 cycles.

#!/usr/bin/perl
use warnings;
use strict;
use Tk;

# Create main window containing a listbox
my $main_window = new MainWindow;
my $listbox = $main_window->Listbox->pack;

my $count = 0;
while(1){
$count++;

# Delete all entries in listbox
$listbox->delete(0, "end");

# Insert an entry into listbox (memory leak here!)
$listbox->insert("end", "test");

# Refresh window
$main_window->update;

my $index = $listbox->index('end');
print "$index->$count\n";

}
# EOF
###############################################

The only solution I have found is to store your data in an array,
and use the listbox only to display the array.

#!/usr/bin/perl
use warnings;
use strict;
use Tk;

#no leaks, but watch out for @array being empty...crash
#make sure @array has at least a '';

my $mw = Tk::MainWindow->new(-title => 'Listbox Leak');
my @array = (1..1000);

my $lb = $mw->Listbox(
-listvariable=> \@array,
)->pack();

my $b = $mw->Button(-text => 'Leak Test',
-command => \&leak
)->pack();

MainLoop;

sub leak {
my $count = 0;
while(1){
$count++;
@array = map{"$_.$count"}(1..1000);
$lb->update;
}
}
__END__



--
I'm not really a human, but I play one on earth.
http://zentara.net/japh.html

Hello,

Thank you for the suggestion. I will try switching to using an array
as a listvariable to see whether that fixes the problem in my case.

I don't think there was anything fundamentally wrong with the way I was
doing things though and this modification seems to sidestep a possible
bug rather than solving it (unless I misunderstood something).
Eventually the leak causes a considerable amount of memory to be
consumed in my case (though I am looping at ~1Hz in my program rather
than continuously as in the example).

Should a Listbox->delete not clear up after a Listbox->insert?

Thank you very much for your advice.

Stephen

Tk::Listbox does indeed have a memory leak.

This has been reported as CPAN bug #12466 :
http://rt.cpan.org/NoAuth/Bug.html?id=12466

Hopefully we will get a new version of Tk soon that fixes this.

Ken

Thanks Zentara, using listvariables as you suggested stopped the leak
in my program.

Cheers,

Stephen

Hello Ken,

Thank you for the information.

Cheers,

Stephen