title: zmq: can multiple threads PUSH in a simple PUSH-PULL pattern
body: <p>I have two processes: a <strong>producer</strong> which pushes messages via <a href="http://www.zeromq.org/" rel="noreferrer">ZMQ</a> to a <strong>consumer</strong> in a simple PULL-PUSH point-to-point pattern. The producer has several internal threads that <code>send()</code> via zmq. However, 0MQ's docs <em>suggest not to share sockets between threads</em>.</p>
  
  <p><strong>Must I use a single thread to send?</strong><br>
  Assuming there is no strict requirement for keeping the sending order between the threads, doesn't the fact that the socket is a one-directional simplex allow multiple threads to use it without introducing locks?</p>