python - 在 Pika 或 RabbitMQ 中，如何检查当前是否有消费者正在消费？

Question

我想检查是否存在 Consumer/Worker 来消费我将要发送的 Message。

如果没有任何 Worker，我会启动一些 worker(消费者和发布者都在一台机器上)然后开始发布消息。 p>

如果有像 connection.check_if_has_consumers 这样的函数，我会像这样实现它 -

import pika
import workers

# code for publishing to worker queue
connection = pika.BlockingConnection(pika.ConnectionParameters(host='localhost'))
channel = connection.channel()

# if there are no consumers running (would be nice to have such a function)
if not connection.check_if_has_consumers(queue="worker_queue", exchange=""):
    # start the workers in other processes, using python's `multiprocessing`
    workers.start_workers()

# now, publish with no fear of your queues getting filled up
channel.queue_declare(queue="worker_queue", auto_delete=False, durable=True)
channel.basic_publish(exchange="", routing_key="worker_queue", body="rockin",
                            properties=pika.BasicProperties(delivery_mode=2))
connection.close()

但我无法在 pika 中找到具有 check_if_has_consumers 功能的任何函数。

有什么方法可以使用 pika 来完成这个任务吗？或者，通过直接与兔子交谈？

我不完全确定，但我真的认为 RabbitMQ 会知道订阅不同队列的消费者数量，因为它会向他们发送消息并接受确认

我 3 小时前才开始使用 RabbitMQ...欢迎任何帮助...

这是我写的workers.py代码，如果有帮助的话....

import multiprocessing
import pika


def start_workers(num=3):
    """start workers as non-daemon processes"""
    for i in xrange(num):    
        process = WorkerProcess()
        process.start()


class WorkerProcess(multiprocessing.Process):
    """
    worker process that waits infinitly for task msgs and calls
    the `callback` whenever it gets a msg
    """
    def __init__(self):
        multiprocessing.Process.__init__(self)
        self.stop_working = multiprocessing.Event()

    def run(self):
        """
        worker method, open a channel through a pika connection and
        start consuming
        """
        connection = pika.BlockingConnection(
                              pika.ConnectionParameters(host='localhost')
                     )
        channel = connection.channel()
        channel.queue_declare(queue='worker_queue', auto_delete=False,
                                                    durable=True)

        # don't give work to one worker guy until he's finished
        channel.basic_qos(prefetch_count=1)
        channel.basic_consume(callback, queue='worker_queue')

        # do what `channel.start_consuming()` does but with stopping signal
        while len(channel._consumers) and not self.stop_working.is_set():
            channel.transport.connection.process_data_events()

        channel.stop_consuming()
        connection.close()
        return 0

    def signal_exit(self):
        """exit when finished with current loop"""
        self.stop_working.set()

    def exit(self):
        """exit worker, blocks until worker is finished and dead"""
        self.signal_exit()
        while self.is_alive(): # checking `is_alive()` on zombies kills them
            time.sleep(1)

    def kill(self):
        """kill now! should not use this, might create problems"""
        self.terminate()
        self.join()


def callback(channel, method, properties, body):
    """pika basic consume callback"""
    print 'GOT:', body
    # do some heavy lifting here
    result = save_to_database(body)
    print 'DONE:', result
    channel.basic_ack(delivery_tag=method.delivery_tag)

编辑:

我必须继续前进，所以这是我要采取的解决方法，除非出现更好的方法，

所以，RabbitMQ 有这些 HTTP management apis ，它们在您打开 management plugin 后工作在 HTTP api 页面的中间有

/api/connections - A list of all open connections.

/api/connections/name - An individual connection. DELETEing it will close the connection.

因此，如果我通过不同的Connection 名称/用户连接我的Workers 和我的Produces，我将能够检查是否Worker Connection 已打开...(当 worker 死亡时可能会出现问题...)

将等待更好的解决方案...

编辑:

刚刚在 rabbitmq 文档中找到了这个，但是在 python 中这样做会很麻烦:

shobhit@oracle:~$ sudo rabbitmqctl -p vhostname list_queues name consumers
Listing queues ...
worker_queue    0
...done.

所以我可以做类似的事情，

subprocess.call("echo password|sudo -S rabbitmqctl -p vhostname list_queues name consumers | grep 'worker_queue'")

hacky...仍然希望 pika 有一些 python 函数来做到这一点...

谢谢，

Answer 1

我也在研究这个。阅读源代码和文档后，我在 channel.py 中发现了以下内容:

@property
def consumer_tags(self):
    """Property method that returns a list of currently active consumers

    :rtype: list

    """
    return self._consumers.keys()

我自己测试成功了。我在 channel 对象为 self._channel 的地方使用了以下内容:

if len(self._channel.consumer_tags) == 0:
        LOGGER.info("Nobody is listening.  I'll come back in a couple of minutes.")
        ...