Pika Exchange\u声明回调中的Exchange名称

Question

我尝试在回调中使用exchange名称。我在Pika中使用SelectConnection适配器处理异步请求。

我的想法是首先在我的程序中构建交换、队列和绑定的列表。然后，我将多个交换和队列声明分派给Pika，并在每个绑定所需的队列和交换收到DeclareOK消息后立即创建绑定。

这意味着我需要知道回调中交换和队列的名称，以便我可以将它们与要创建的绑定相关联。

类似这样：

print "Create A"
channel.exchange_declare(callback=on_exchange, exchange="exchangeA")
print "Create B"
channel.exchange_declare(callback=on_exchange, exchange="exchangeB")

def on_exchange(response):
  # How do I know if this was exchangeA or exchangeB ?
  print "Exchange declared"
  print response

这将给出以下输出，清楚地表明首先声明交换，然后触发回调（如预期的那样）：

Create A
Create B
Exchange declared
<METHOD(['method=<Exchange.DeclareOk>', 'channel_number=1', 'frame_type=1'])>
Exchange declared
<METHOD(['method=<Exchange.DeclareOk>', 'channel_number=1', 'frame_type=1'])>

我已经弄明白，反应属于皮卡类型。框架但我如何从那里开始呢？交易所是否保证按顺序申报？

Answer 1

似乎无法读取回调中的exchange名称。相反，您需要做的是保留一个计数器，以便知道何时创建了所有交易所：

class ...:
  def __init__(self):
    self.exchangestocreate = 2

  #...

  def declare_exchanges(self):
    channel.exchange_declare(callback=self.on_exchange, exchange="exchangeA")
    channel.exchange_declare(callback=self.on_exchange, exchange="exchangeB")

  def on_exchange(self, response):
    self.exchangestocreate -= 1
    if self.exhangestocreate == 0:
      # Declare bindings here

这将有效地使接口在exchange声明步骤中同步。

Answer 2

您可以相应地链接回调以控制安装过程。只需逐步建立您的交易所和队列。这更为冗长，但您可以控制。

class ChatServer(object):
    def __init__(self):
        self.channel_in = None
        self.channel_out = None
        cred = pika.PlainCredentials('guest','guest')
        param = pika.ConnectionParameters(host='localhost',
                                          port=5672,
                                          virtual_host='/',
                                          credentials=cred)
        self.connection = pika.SelectConnection(param,self.on_connected)


    def on_connected(self, connection):
        self.connection.channel(self.on_channel_out_open)

    def on_channel_out_open(self,channel):
        self.channel_out = channel
        self.channel_out.exchange_declare(exchange='chatserver_out',
                                          type='direct',
                                          auto_delete=False,
                                          callback=self.on_exchange_declare_out)
    def on_exchange_declare_out(self,method_frame):
        self.channel_out.exchange_declare(exchange='cmd',
                                          type='direct',
                                          auto_delete=False,
                                          callback=self.on_exchange_declare_cmd_out)
    def on_exchange_declare_cmd_out(self,method_frame):
        # now all exchanges are defined.
        # Let's create the queues.
        # ...

Answer 3

闭包是保持代码异步的解决方案：

def declare_exchanges(self):
    exchange = "exchangeA"
    callback = self.on_exchange(exchange)
    channel.exchange_declare(callback=callback, exchange=exchange)

    exchange = "exchangeB"
    callback = self.on_exchange(exchange)
    channel.exchange_declare(callback=callback, exchange=exchange)

def on_exchange(self, exchange):
    def callback(response):
        print(exchange)

    return callback

PS：我在上游开了一个问题，https://github.com/pika/pika/issues/898