title: why is concurrent_queue non-blocking?
body: <p>In the concurrency runtime introduced in VS2010, there is a concurrent_queue class. It has a non blocking try_pop() function.<br>
  Similar in Intel Thread Building Blocks (TBB), the blocking pop() call was removed when going from version 2.1 to 2.2.</p>
  
  <p>I wonder what the problem is with a blocking call. Why was it removed from TBB? And why is there no blocking concurrent_queue?</p>
  
  <p>I'm in a situation where I need a blocking concurrent queue, and I don't want a busy wait.
  Apart from writing a queue myself, is there another possibility in the concurrency runtime?</p>