AFUnixSender crash (EEXIST)

During a random test:
evan@zeno ~/code/zygote (master) $ PYTHONPATH=.:$PYTHONPATH testify tests.test  ZygoteTests.test_hup
[5823] 2011-07-04 21:50:39,137 :: INFO    :: zygote.master - main started
[5823] 2011-07-04 21:50:39,139 :: INFO    :: zygote.master - started zygote 5828 pointed at base '/data/code/zygote/example'
[5823] 2011-07-04 21:50:39,140 :: INFO    :: zygote.master - Attempted to transition 0 workers from 0 zygotes
[5828] 2011-07-04 21:50:39,141 :: INFO    :: zygote.worker.zygote_process - new zygote started
[5829] 2011-07-04 21:50:39,242 :: DEBUG   :: zygote.worker.worker_process - new worker started
[5830] 2011-07-04 21:50:39,244 :: DEBUG   :: zygote.worker.worker_process - new worker started
[5823] 2011-07-04 21:50:39,245 :: DEBUG   :: zygote.master - received message of type MessageWorkerStart from pid 5829
[5831] 2011-07-04 21:50:39,245 :: DEBUG   :: zygote.worker.worker_process - new worker started
[5823] 2011-07-04 21:50:39,246 :: DEBUG   :: zygote.master - received message of type MessageWorkerStart from pid 5830
[5832] 2011-07-04 21:50:39,247 :: DEBUG   :: zygote.worker.worker_process - new worker started
[5823] 2011-07-04 21:50:39,248 :: DEBUG   :: zygote.master - received message of type MessageWorkerStart from pid 5831
[5823] 2011-07-04 21:50:39,249 :: DEBUG   :: zygote.master - received message of type MessageWorkerStart from pid 5832
[5823] 2011-07-04 21:50:40,018 :: INFO    :: zygote.master - started zygote 5833 pointed at base '/data/code/zygote/example'
[5823] 2011-07-04 21:50:40,019 :: INFO    :: zygote.master - Attempted to transition 4 workers from 1 zygotes
[5832] 2011-07-04 21:50:40,019 :: INFO    :: zygote.worker.worker_process - received SIGTERM, exiting
[5829] 2011-07-04 21:50:40,019 :: INFO    :: zygote.worker.worker_process - received SIGTERM, exiting
[5830] 2011-07-04 21:50:40,020 :: INFO    :: zygote.worker.worker_process - received SIGTERM, exiting
[5833] 2011-07-04 21:50:40,020 :: INFO    :: zygote.worker.zygote_process - new zygote started
[5831] 2011-07-04 21:50:40,021 :: INFO    :: zygote.worker.worker_process - received SIGTERM, exiting
[5828] 2011-07-04 21:50:40,052 :: INFO    :: zygote.worker.zygote_process - reaped worker 5829, status 0
[5828] 2011-07-04 21:50:40,052 :: INFO    :: zygote.worker.zygote_process - reaped worker 5831, status 0
[5828] 2011-07-04 21:50:40,054 :: INFO    :: zygote.worker.zygote_process - reaped worker 5830, status 0
Traceback (most recent call last):
  File "zygote/main.py", line 51, in <module>
    main()
  File "zygote/main.py", line 48, in main
    zygote.master.main(opts, args)
  File "/data/code/zygote/zygote/master.py", line 283, in main
    master.start()
  File "/data/code/zygote/zygote/master.py", line 243, in start
    z = self.create_zygote()
  File "/data/code/zygote/zygote/master.py", line 234, in create_zygote
    z.loop()
  File "/data/code/zygote/zygote/worker.py", line 120, in loop
    self.io_loop.start()
  File "/usr/lib/python2.7/site-packages/tornado/ioloop.py", line 261, in start
    event_pairs = self._impl.poll(poll_timeout)
  File "/data/code/zygote/zygote/worker.py", line 117, in reap_child
    notify(self.notify_socket, MessageWorkerExit, '%d %d' % (pid, status_code))
  File "/data/code/zygote/zygote/worker.py", line 35, in notify
    sock.send(msg_cls.emit(str(body)))
  File "/data/code/zygote/zygote/util.py", line 166, in send
    self._sendall()
  File "/data/code/zygote/zygote/util.py", line 161, in _sendall
    self.io_loop.add_handler(self.socket.fileno(), sender, self.io_loop.WRITE)
  File "/usr/lib/python2.7/site-packages/tornado/ioloop.py", line 164, in add_handler
    self._impl.register(fd, events | self.ERROR)
IOError: [Errno 17] File exists
This doesn't happen reliably, and I couldn't reproduce it, but there's a bug lurking somewhere in this code.
Yelp / zygote

AFUnixSender crash (EEXIST) #7
