The simplest solution to the memory growth problem is to bound the size of the queue in the writers:

use constant LIMIT => 1000;

sub pause {
    my $delay = shift;
    select '','','', $delay;
}

sub workerSub {
  my ($workerQueue,$outputQueue) = @_;
  while (my $computer = $workerQueue->dequeue()) {
    ## SSH command retrieving grep results and processing

    pause( 0.01 ) while $outputQueue->pending > LIMIT;

    $outputQueue->enqueue($results);
  }
}
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For a slightly more sophisticated approach, take a look at my self-limiting queue implementation:threads::Q