This is nice. I made some small modifications. I always wanted to use threads in perl. I have a great application and might reuse this code :)

One mod was to print the key when the batch was finished. Since L already know the key I an tell if the code works or not. In this case, the key is never incremented and is always A. The map function does not seem to work.

It was nice to see that each thread processes about 1666 iterations per second. It was not a good idea to shell for date. I actually know better than that. Thanks