code: def _on_context_disconnect(self, context):
          
          self._lock.acquire()
          try:
              LOG.info('%r: Forgetting %r due to stream disconnect', self, context)
              self._forget_context_unlocked(context)
          finally:
              self._lock.release()
docs: Respond to Context disconnect event by deleting any record of the no
          longer reachable context.  This method runs in the Broker thread and
          must not to block.