在Pika或RabbitMQ中,如何检查是否有消费者正在消费？

Question

我想检查消费者/工人是否在场消费我即将发送的消息.

如果没有任何工人,我会启动一些工作人员(消费者和发布者都在一台机器上),然后继续发布消息.

如果有类似的函数connection.check_if_has_consumers,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()

但是我无法check_if_has_consumers在pika中找到任何具有功能的功能.

使用鼠兔有没有办法完成这个？或者,通过直接与兔子交谈？

我不能完全肯定,但我真的认为RabbitMQ的是意识的消费者订阅不同的队列数量,因为它派遣的消息,对他们接受的ACK

我刚开始使用RabbitMQ 3小时前...欢迎任何帮助......

这是我写的workers.py代码,如果有任何帮助....

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:

我必须向前迈进,所以这是一个我将采取的解决方法,除非出现更好的方法,

所以,RabbitMQ有这些HTTP管理apis,它们在你打开管理插件后工作,在HTTP apis页面中间有

/ api/connections - 所有打开连接的列表.

/ api/connections/name - 单个连接.删除它将关闭连接.

因此,如果我通过不同的连接名称/用户连接我的Workers和我的Produces,我将能够检查工作者连接是否打开...(当工人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.

所以我可以做点什么,

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功能来做到这一点......

谢谢,

Answer 1

我也只是在研究这个问题.阅读完源代码和文档后,我在channel.py中遇到了以下内容:

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

    :rtype: list

    """
    return self._consumers.keys()

我自己的测试成功了.我使用了以下我的频道对象是self._channel:

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