Sync producer fails when required_acks == 0

[cscheffler]

pykafka version: 2.0.0

Behaviour: producing a message fails when a producer is created with sync=True and required_acks=0. This does not happen with required_acks=1 (default) or sync=False (default).

To reproduce:

from pykafka import KafkaClient
kafka_client = KafkaClient(hosts=HOSTS)
topic = kafka_client.topics[TOPIC]
message = 'test'
with topic.get_producer(sync=True, required_acks=0) as producer:
    producer.produce(message)

Exception:

Traceback (most recent call last):
  File "test.py", line 11, in <module>
    producer.produce(message)
  File "/home/ubuntu/carl/kafka-tests/venv/local/lib/python2.7/site-packages/pykafka/producer.py", line 169, in __exit__
    self.stop()
  File "/home/ubuntu/carl/kafka-tests/venv/local/lib/python2.7/site-packages/pykafka/producer.py", line 219, in stop
    self._wait_all()
  File "/home/ubuntu/carl/kafka-tests/venv/local/lib/python2.7/site-packages/pykafka/producer.py", line 359, in _wait_all
    self._raise_worker_exceptions()
  File "/home/ubuntu/carl/kafka-tests/venv/local/lib/python2.7/site-packages/pykafka/producer.py", line 154, in _raise_worker_exceptions
    raise ex
AttributeError: 'NoneType' object has no attribute 'topics'

[yungchin]

Thanks, this one's confirmed too. Additionally, it's even worse on the producer-futures branch, #269 - there we'd simply block forever (great!).

[yungchin]

Quick update: this is also a problem when sync=False, it's just that the error doesn't surface in the main thread as readily.