Using Threads and XML::LibXML appears to cause a memory allocation bug.

libxml_threads.pl

use strict;
use warnings;
use threads;
use Thread::Queue;

my $q = Thread::Queue->new();    # A new empty queue
my $q2 = Thread::Queue->new();    # A new empty queue

use XML::LibXML qw(:threads_shared);
my $parser = XML::LibXML->new;
my @docs = 
	map { $parser->parse_string(qq{<root><foo id="$_">bar</foo></root>}) } 
	1..10
	;

# Worker threads
my $getter = threads->create(
	sub {
		# Thread will loop until no more work
		while (defined(my $item = $q->dequeue())) {
			# $q2->enqueue($item);
			$q2->enqueue( $item->documentElement->findvalue('//foo/@id'));
		}
		$q2->enqueue (undef);
	}
);

my $printer = threads->create(
	sub {
		# Thread will loop until no more work
		while (defined(my $item = $q2->dequeue())) {
			print "\n".$item;
		}
	}
);

$q->enqueue(@docs);
$q->enqueue(undef);

$printer->join();
$getter->join();