[Chicago-talk] A question on threading

[me at heyjay.com]

Hi,

I'm getting unpredictable (at least to me) result.  
If I run the code below, repeatedly, every so often I get:

[o10]:~> ./thread
Invalid value for shared scalar at ./thread line 25.
A thread exited while 2 threads were running.

the other times it works as expected.  I don't see what's
wrong with the code

All I'm trying to do is start a new thread print out a shared value
then stop the thread, and have it stop nicely.

I made an example that demonstrates the problem (should be 
cut/paste runnable as is)

[o10]:~> cat ./thread

#!/usr/bin/perl

package Reader;

use 5.008003;
use strict;
use warnings;

use base qw(Class::Accessor);
use threads;
use threads::shared;

__PACKAGE__->mk_accessors( qw/_run _thread/ );

sub start {

    my $self = shift;

    my $run : shared = 1;
    my $t : shared;

    $self->_run(\$run);

    my $sub = \&loop;
    $t = threads->new($sub, $self);
    $t->detach;
    $self->_thread(\$t);
}

sub stop {
    my $self = shift;
    ${$self->_run} = 0;
    ${$self->_thread}->join;
}

sub loop {

    my $self = shift;

    while (${$self->_run}) {
        print "running: ", ${$self->_run}, " \n";
    }
}

package main;

my $reader = Reader->new();

$reader->start;
$reader->stop;