Master
boot up workers
listen for worker messages
add worker messages to message queue
process message queue
"reply" to a message allows sending a message back down to worker

When worker asks for file but no files left, send shutdown message to worker
when worker connection breaks, end thread
wait on all threads
when all threads are done, all workers must be done



when a runner asks for file but master responds with shutdown, mark self
  as terminated, shut down runners. Any runner that asks for a file is
  auto-terminated
wait for runner threads to finish
then exit, breaking master connection

Test individual messages? Ensure they handle the right method? May not be worth it.