Kata

Create a method called wait_on_threads that accepts an array of threads (can be empty) and waits until all of them finish. For example:

thread1 = Thread.new do
  # do somethng
end
thread2 = Thread.new do
  # do somethng else
end

wait_on_threads( [thread1,thread2] )
# Should wait inside the method until both thread1 and thread2 
# finish whatever they were doing and exit. 

You can read more about threads in wikipedia: http://en.wikipedia.org/wiki/Thread_(computing)