Your queue handling is fatally flawed.

Why are you exiting your queue reading loop if there is nothing pending?

do {
   ...
} while ($worker->pending());
[download]

If (for example), some other process decides to hammer the disk drive, then your queue population code might stall waiting for access to the disk, at which point your queue will empty and all your worker threads will terminate despite that there are still files to be read from disk.

Also, why are you calling (pullDataFromDbWithDirectory(), bith in your main thread and in all your worker threads. That's very confused.

The normal way to do this is:

1. Have your queue worker thread queue reading loops terminate when they see undef:

   sub doOperation () {
       my $ithread = threads->tid();
   
       while( my $folder = $worker->dequeue() ) {
           print "Read $folder from queue with thread $ithread\n" if $deb
   +ug;
           ## Do something useful here...
       }
   }
   [download]

2. Start your threads before you populate the queue:

   They will all block on the dequeue() until something is made available.

3. Populate your queue from you main thread (*ONLY*);

   The threads will start doing work as soon as your main thread gives them something to work on.

4. Once the main thread has finished populating the queue, it then queues one undef per worker thread to cause the worker loops to terminate and thus the worker threads to end.

   You are queing undefs, but you're not doing it until you've already seen that your threads have ended, at which point it serves no purpose.

5. Finally, loop over the thread handles calling join() to ensure all the threads have finished before you exit the program.

This way, the whole process becomes self-managing and you don;t have to poll to count threads.