我有一个pika消费者客户端的类，它基于pika的TornadoConnection示例代码。我正在尝试从主题队列中消费。问题是，由于连接是以异步方式建立的，因此我无法知道通道何时建立或何时声明队列。我的班级：
class PikaClient(object):
""" Based on:
http://pika.readthedocs.org/en/latest/examples/tornado_consumer.html
https://reminiscential.wordpress.com/2012/04/07/realtime-notification-delivery-using-rabbitmq-tornado-and-websocket/
"""
def __init__(self, exchange, exchange_type):
self._connection = None
self._channel = None
self._closing = False
self._consumer_tag = None
self.exchange = exchange
self.exchange_type = exchange_type
self.queue = None
self.event_listeners = set([])
def connect(self):
logger.info('Connecting to RabbitMQ')
cred = pika.PlainCredentials('guest', 'guest')
param = pika.ConnectionParameters(
host='localhost',
port=5672,
virtual_host='/',
credentials=cred,
)
return pika.adapters.TornadoConnection(param,
on_open_callback=self.on_connection_open)
def close_connection(self):
logger.info('Closing connection')
self._connection.close()
def on_connection_closed(self, connection, reply_code, reply_text):
self._channel = None
if not self._closing:
logger.warning('Connection closed, reopening in 5 seconds: (%s) %s',
reply_code, reply_text)
self._connection.add_timeout(5, self.reconnect)
def on_connection_open(self, connection):
logger.info('Connected to RabbitMQ')
self._connection.add_on_close_callback(self.on_connection_closed)
self._connection.channel(self.on_channel_open)
def reconnect(self):
if not self._closing:
# Create a new connection
self._connection = self.connect()
def on_channel_closed(self, channel, reply_code, reply_text):
logger.warning('Channel %i was closed: (%s) %s',
channel, reply_code, reply_text)
self._connection.close()
def on_channel_open(self, channel):
logger.info('Channel open, declaring exchange')
self._channel = channel
self._channel.add_on_close_callback(self.on_channel_closed)
self._channel.exchange_declare(self.on_exchange_declareok,
self.exchange,
self.exchange_type,
passive=True,
)
def on_exchange_declareok(self, unused_frame):
logger.info('Exchange declared, declaring queue')
self._channel.queue_declare(self.on_queue_declareok,
exclusive=True,
auto_delete=True,
)
def on_queue_declareok(self, method_frame):
self.queue = method_frame.method.queue
def bind_key(self, routing_key):
logger.info('Binding %s to %s with %s',
self.exchange, self.queue, routing_key)
self._channel.queue_bind(self.on_bindok, self.queue,
self.exchange, routing_key)
def add_on_cancel_callback(self):
logger.info('Adding consumer cancellation callback')
self._channel.add_on_cancel_callback(self.on_consumer_cancelled)
def on_consumer_cancelled(self, method_frame):
logger.info('Consumer was cancelled remotely, shutting down: %r',
method_frame)
if self._channel:
self._channel.close()
def on_message(self, unused_channel, basic_deliver, properties, body):
logger.debug('Received message # %s from %s',
basic_deliver.delivery_tag, properties.app_id)
#self.notify_listeners(body)
def on_cancelok(self, unused_frame):
logger.info('RabbitMQ acknowledged the cancellation of the consumer')
self.close_channel()
def stop_consuming(self):
if self._channel:
logger.info('Sending a Basic.Cancel RPC command to RabbitMQ')
self._channel.basic_cancel(self.on_cancelok, self._consumer_tag)
def start_consuming(self):
logger.info('Issuing consumer related RPC commands')
self.add_on_cancel_callback()
self._consumer_tag = self._channel.basic_consume(self.on_message, no_ack=True)
def on_bindok(self, unused_frame):
logger.info('Queue bound')
self.start_consuming()
def close_channel(self):
logger.info('Closing the channel')
self._channel.close()
def open_channel(self):
logger.info('Creating a new channel')
self._connection.channel(on_open_callback=self.on_channel_open)
def run(self):
self._connection = self.connect()
def stop(self):
logger.info('Stopping')
self._closing = True
self.stop_consuming()
logger.info('Stopped')
使用它的代码示例（在WebSocketHandler.open中）：
self.pc = PikaClient('agents', 'topic')
self.pc.run()
self.pc.bind_key('mytopic.*')
尝试运行此命令时，bind_key会抛出异常，因为_channel仍为None。但是，在建立通道和队列之前，我还没有找到阻止的方法。是否有任何方法可以使用动态主题列表（在消费者开始运行后可能会改变）？
答案 0 :(得分：0)
您确实有办法知道队列何时建立 - 方法on_queue_declareok()。一旦self.queue_declare方法完成，将执行该回调，self.queue_declare完成后执行_channel.exchance_declare等。您可以一直关注链接到您的run方法：
run - ＆gt; connect - ＆gt; on_connection_open - ＆gt; _connection.channel - ＆gt; on_channel_open - ＆gt; _channel.exchange_declare - ＆gt; on_exchange_declareok - ＆gt; _channel.queue_declare - ＆gt; on_queue_declareok
因此，您只需将您的通话添加到bind_key至on_queue_declareok，这将触发对on_bindok的调用，该调用将调用start_consuming。此时，您的客户端实际上正在侦听消息。如果您希望能够动态提供主题，只需将它们放在PikaClient的构造函数中即可。然后，您可以在每个bind_key内拨打on_queue_declareok。您还需要添加一个标记，表明您已经开始消费，因此您不要尝试两次。
这样的事情（假设下面未显示的所有方法保持不变）：
def __init__(self, exchange, exchange_type, topics=None):
self._topics = [] if topics is None else topics
self._connection = None
self._channel = None
self._closing = False
self._consumer_tag = None
self._consuming = False
self.exchange = exchange
self.exchange_type = exchange_type
self.queue = None
self.event_listeners = set([])
def on_queue_declareok(self, method_frame):
self.queue = method_frame.method.queue
for topic in self._topics:
self.bind_key(topic)
def start_consuming(self):
if self._consuming:
return
logger.info('Issuing consumer related RPC commands')
self.add_on_cancel_callback()
self._consumer_tag = self._channel.basic_consume(self.on_message, no_ack=True)
self._consuming = True