I don't understand this part , I think you have too many queues, and you should probably have two, one for files to process , and one for results of that processing

Also the closures don't make sense to me

The meat of the threading code :)

sub create_thread_pool
{
   my $files_to_digest = shift;

   threads->create( threads_progress => $files_to_digest );

   for ( 1 .. $opts->{threads} )
   {
      my $thread_queue = Thread::Queue->new;

      my $worker_thread = threads->create( worker => $thread_queue );

      $worker_queues->{ $worker_thread->tid } = $thread_queue;
   }

   lock $threads_init; $threads_init++;
}

sub get_dup_digests
{
   my $size_dups = shift;
   my $dup_count = 0;
   my $queued = 0;

   $dup_count += @$_ for map { $size_dups->{ $_ } } keys %$size_dups;

   # creates thread pool, passing in as an argument the number of file
+s
   # that the pool needs to digest. this is NOT equivalent to the numb
+er
   # of threads to be created; that is determined in the options ($opt
+s)
   create_thread_pool( $dup_count );

   sub get_tid
   {
      my $tid = $pool_queue->dequeue;

      return $tid;
   }

   my $tid = get_tid();

   SIZESCAN: for my $size ( keys %$size_dups )
   {
      my $group = $size_dups->{ $size };

      for my $file ( @$group )
      {
         $worker_queues->{ $tid }->enqueue( $file ) if !$thread_term;

         $queued++;

         $tid = get_tid() and $queued = 0 if $queued == $opts->{qsize}
+ - 1;

         last SIZESCAN unless defined $tid;
      }
   }

   # wait for threads to finish
   while ( $d_counter < $dup_count )
   {
      usleep 1000; # sleep for 1 millisecond
   }

   # ...tell the threads to exit
   end_wait_thread_pool();

   # get rid of non-dupes
   delete $digests->{ $_ }
      for grep { @{ $digests->{ $_ } } == 1 }
      keys %$digests;

   my $priv_digests = {};

   # sort dup groupings
   for my $digest ( keys %$digests )
   {
      my @group = @{ $digests->{ $digest } };

      $priv_digests->{ $digest } = [ sort { $a cmp $b } @group ];
   }

   undef $digests;

   return $priv_digests;
}
[download]