title: task_done() called too many times
body: <p>Hi stack overflow folks!</p>
  
  <p>I'm currently getting this error every once and awhile in my Flask/Socketio app and I haven't a clue where to begin debugging or what it means:</p>
  
  <pre><code>Traceback (most recent call last):
    File "/lib/python2.7/site-packages/gevent/greenlet.py", line 536, in run
    File "/lib/python2.7/site-packages/engineio/socket.py", line 167, in writer
    File "/lib/python2.7/site-packages/engineio/socket.py", line 37, in poll
    File "/lib/python2.7/site-packages/gevent/queue.py", line 470, in task_done
  ValueError: task_done() called too many times
  </code></pre>
  
  <p>There seems to be no rhyme or reason to when it happens either.</p>