Hanging Threads

[WalkingZero]

Need some help. Currently the program is running 4 separate threads, pulling data off a queue to establish it's given task. The sub runs a while loop based off the queue's pending function. The threads all exit their while loops correctly. However after the sub should be done, the joins never occur. I can't quite figure out what's causing the lockup. Any help would be appreciated. Here's the censored version of the code:

sub smtpblast{ 
my $mdq= shift; 
my $pending= $mdq->pending; 
while($pending>0){ 
my $md= $mdq->dequeue_nb; 
my $user= $maildrop{"$md" . "user"}; 
my $pass= $maildrop{"$md". "pass"}; 
print "\n $user \n $pass \n";
my $mailer=Net::SMTP_auth->new('****');
$mailer->auth('Login', $user, $pass);
$mailer->mail("$user");
$mailer->to('****');
my @data=("Subject: Test Messages from $user\n", "E-mail Blast message
+ from $user\n");
$mailer->data(@data);
$mailer->datasend();
$mailer->dataend;
$mailer->quit;
$pending= $mdq->pending;
}
$threadid=threads->self;
print "\n The process for thread $threadid is finished!\n";
}
my $mdqueue=Thread::Queue->new();
$mdqueue->enqueue("md01", "md02", "md03", "md04", "md05", "md06", "md0
+7", "md08", "md09", "md10");
$thr1=threads->new(\&smtpblast, $mdqueue);
$thr2=threads->new(\&smtpblast, $mdqueue);
$thr3=threads->new(\&smtpblast, $mdqueue);
$thr4=threads->new(\&smtpblast, $mdqueue);
$thr1->join;
print "\n Thread $thr1 joined! \n";
$thr2->join;
print "\n Thread $thr2 joined! \n";
$thr3->join;
print "\n Thread $thr3 joined! \n";
$thr4->join;
print "\n Thread $thr4 joined! \n";

The program is for testing mail server latency. I have edited out server information and omitted the has that contains the logins. This is all the relevant pieces of code though.