title: python pool doesn't work
body: <p>I'm trying to use multithreading and in order to keep it simple at first, i'm running the following code:</p>
  
  <pre><code>import multiprocessing as mp
  
  pool = mp.Pool(4)
  
  def square(x):
  
      return x**2
  
  results=pool.map(square,range(1,20))
  </code></pre>
  
  <p>As i understand, results should be a list containig the squares from 1 to 20.
  However, the code does not seem to terminate.(doing the same  without pool finishes in a blink, this ran for several minutes, before i stopped it manually).</p>
  
  <p>Additional information: task manager tells me, that the additional python processes have been launched and are running, but are using zero % of my cpu; still other unrelated processes like firefox skyrocket in their cpu usage, while the programm is running. 
  I'm using windows 8 and a i5-4300U cpu (pooling to 2 instead of 4 doesn't help either)</p>
  
  <p>What am i doing wrong?
  Are there any good ressources on the Pool class, which could help me understand what is wrong with my code?</p>