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

my $wq = Thread::Queue->new();    # Build a queue where you put work

my $thread_limit = 4;     # how many threads do you want?

my @thr = map {  # create threads and store the handles in @thr
    threads->create(
        sub {
            while (my $item = $wq->dequeue()) { # finish when undef
                # Do something with item
            }
        } );
} 1..$thread_limit;

while (I get $data to process) {
    $wq->enqueue($data);
}

# Tell the threads we are done
$wq->enqueue(undef) for @thr;

# Wait for all the threads to finish
$_->join() for @thr;