问题描述

我在新 Python asyncio 模块的 asyncio.Protocol.data_received 回调中执行异步操作时遇到问题.

I am having a problem doing asynchronous stuff in the asyncio.Protocol.data_received callback of the new Python asyncio module.

考虑以下服务器:

class MathServer(asyncio.Protocol):

   @asyncio.coroutine
   def slow_sqrt(self, x):
      yield from asyncio.sleep(1)
      return math.sqrt(x)

   def fast_sqrt(self, x):
      return math.sqrt(x)

   def connection_made(self, transport):
      self.transport = transport

   #@asyncio.coroutine
   def data_received(self, data):
      print('data received: {}'.format(data.decode()))
      x = json.loads(data.decode())
      #res = self.fast_sqrt(x)
      res = yield from self.slow_sqrt(x)
      self.transport.write(json.dumps(res).encode('utf8'))
      self.transport.close()

用于以下客户端:

class MathClient(asyncio.Protocol):

   def connection_made(self, transport):
      transport.write(json.dumps(2.).encode('utf8'))

   def data_received(self, data):
      print('data received: {}'.format(data.decode()))

   def connection_lost(self, exc):
      asyncio.get_event_loop().stop()

调用 self.fast_sqrt 后，一切正常.

With self.fast_sqrt being called, everything works as expected.

使用 self.slow_sqrt，它不起作用.

它也不适用于 self.fast_sqrt 和 data_received 上的 @asyncio.coroutine 装饰器.

It also does not work with self.fast_sqrt and the @asyncio.coroutine decorator on data_received.

我觉得我在这里遗漏了一些基本的东西.

I feel I am missing something fundamental here.

完整代码在这里:

• 服务器
• 客户端

测试:

• Python 3.4.0b1 (Windows)
• Python 3.3.3 + asyncio-0.2.1 (FreeBSD)

两者的问题是相同的:使用 slow_sqrt，客户端/服务器将无所事事地挂起.

The issue is the same on both: with slow_sqrt, the client/server will just hang doing nothing.

推荐答案

看来，这需要通过 Future 来解耦——尽管我仍然不确定这是否是正确的方法.

It seems, this needs to be decoupled via a Future - though I am still not sure if this is the right way.

class MathServer(asyncio.Protocol):

   @asyncio.coroutine
   def slow_sqrt(self, x):
      yield from asyncio.sleep(2)
      return math.sqrt(x)

   def fast_sqrt(self, x):
      return math.sqrt(x)

   def consume(self):
      while True:
         self.waiter = asyncio.Future()
         yield from self.waiter
         while len(self.receive_queue):
            data = self.receive_queue.popleft()
            if self.transport:
               try:
                  res = self.process(data)
                  if isinstance(res, asyncio.Future) or 
                     inspect.isgenerator(res):
                     res = yield from res
               except Exception as e:
                  print(e)

   def connection_made(self, transport):
      self.transport = transport
      self.receive_queue = deque()
      asyncio.Task(self.consume())

   def data_received(self, data):
      self.receive_queue.append(data)
      if not self.waiter.done():
         self.waiter.set_result(None)
      print("data_received {} {}".format(len(data), len(self.receive_queue)))

   def process(self, data):
      x = json.loads(data.decode())
      #res = self.fast_sqrt(x)
      res = yield from self.slow_sqrt(x)
      self.transport.write(json.dumps(res).encode('utf8'))
      #self.transport.close()

   def connection_lost(self, exc):
      self.transport = None

这是 Guido van 的答案罗森:

Here is an answer by Guido van Rossum:

解决方案很简单:将该逻辑编写为标记为单独的方法使用 @coroutine，并在 data_received() 中使用async()(在本例中为 == Task()).不建这个的原因进入协议的是，如果是，则需要备用事件处理协程的循环实现.

The solution is simple: write that logic as a separate method marked with @coroutine, and fire it off in data_received() using async() (== Task(), in this case). The reason why this isn't built into the protocol is that if it was, it would require alternate event loop implementations to deal with coroutines.

def data_received(self, data):
    asyncio.ensure_future(self.process_data(data))

@asyncio.coroutine
def process_data(self, data):
    # ...stuff using yield from...

完整代码在这里:- 客户端- 服务器

Full code is here: - Client - Server

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