Things to *not* do in ruby that will break ruby threads.  This list 
isn't complete, but it's things I've noticed while working on stuff:

- select with no timeout
  This will make a blocking select call that will block all other 
  threads.

  I'm going to write a select wrapper that will reduce timeouts to
  lower values and just keep looping on select until the timeout
  expires.

- use sleep
  This will block all threads.

  I'll probably write a wrapper around this too.