我需要使用 AWS IoT MQTT 服务。我正在用 https://github.com/aws/aws-iot-device-sdk-python 做一些试验目前。
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。
这个库是否可能会阻止代码执行？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 AWSIoTMQTTClient来自上面的库。
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))
请您参考如下方法:
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包含长时间运行的阻塞(同步)代码。它会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
如果您需要在协程中运行阻塞代码，您应该在执行器中执行(read here 关于它)。
在编写协程时应该牢记这一点，但如果启用 debug mode，asyncio 通常会警告您此错误。 :
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()
你会看到警告:
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
