AWS IoT Python SDK 和 asyncio

Question

我需要使用 AWS IoT MQTT 服务。我目前正在对 https://github.com/aws/aws-iot-device-sdk-python 进行一些试验。

我的应用程序将使用 websockets 与其他服务通信，然后发布/订阅 MQTT 主题以转发/接收消息。

这个库可能会阻止代码执行吗？我仍然试图了解 asyncio，但不确定我应该注意什么。我怎么知道它是否会引起问题？

我相信我只需要使用上面库中的AWSIoTMQTTClient。

这是我的工作代码的摘录：

class AWSIoTClient:

    def __init__():
        ...
        self.client = AWSIoTMQTTClient(...)

    def subscribe(self, callback):
        self.client.subscribe(f'{self.TOPIC}/subscribe/', 0, callback)

    def publish(self, message):
        self.client.publish(self.TOPIC, message, 0)


class MyWSProtocol(WebSocketClientProtocol):

    def set_aws_client(self, client: AWSIoTClient):
        client.subscribe(self.customCallback)
        self.client = client

    def customCallback(self, client, userdata, message):
        # This will be called when we send message from AWS
        if message.payload:
            message = json.loads(message.payload.decode('utf-8').replace("'", '"'))
            message['id'] = self.next_id()
            self.sendMessage(json.dumps(message).encode('utf-8'))

    def onMessage(self, payload, isBinary):
        message = json.loads(payload)

        # This will forward message to AWS
        self.client.publish(str(payload))

Answer 1

Is it likely that this library will be blocking code execution?

How do I know if it will cause problems?

您不应允许在任何协程中使用长运行宁阻塞（同步）代码。它将导致阻塞你的全局事件循环并进一步阻塞你所有的协程。

async def main():
    await asyncio.sleep(3)  # async sleeping, it's ok

    time.sleep(3)           # synchronous sleeping, this freezes event loop 
                            # and all coroutines for 3 seconds, 
                            # you should avoid it!
    
    await asyncio.sleep(3)  # async sleeping, it's ok

如果您需要运行在协程中阻塞代码，您应该在执行程序中执行（）。

你在编写协程时应该牢记这一点，但如果你启用 debug mode:

，asyncio 通常会警告你这个错误

import asyncio
import time


async def main():
    await asyncio.sleep(3)
    time.sleep(3)
    await asyncio.sleep(3)


loop = asyncio.get_event_loop()
loop.set_debug(True)  # debug mode
try:
    loop.run_until_complete(main())
finally:
    loop.run_until_complete(loop.shutdown_asyncgens())
    loop.close()

您将看到警告：

Executing <Handle <TaskWakeupMethWrapper object at 0x000002063C2521F8>(<Future finis...events.py:275>) created at C:\Users\gmn\AppData\Local\Programs\Python\Python36\Lib\asyncio\futures.py:348> took 3.000 seconds

AWS IoT Python SDK 和 asyncio

AWS IoT Python SDK and asyncio

python

amazon-web-services

mqtt

python-asyncio

aws-iot