同时使用requests与websockets时Python POST请求挂起问题排查

核心原因 #

requests是同步阻塞式的HTTP库，它的所有IO操作都会直接占用当前线程。而你在asyncio的异步函数make_request里调用s.post()时，会彻底卡住asyncio的事件循环——因为asyncio基于单线程调度，同步阻塞操作会霸占整个线程，导致WebSocket连接的维护、请求本身的网络IO都无法被事件循环调度处理，最终请求超时，服务器甚至没收到完整的请求。

解决方法 #

方法一：改用异步HTTP库（推荐） #

使用专为asyncio设计的aiohttp替代requests，它的异步IO不会阻塞事件循环，能和websockets完美配合：

import asyncio
import aiohttp
import websockets


async def websocket_handler(uri):
    async with websockets.connect(uri) as websocket:
        while True:
            message = await websocket.recv()
            print(f"Received message: {message}")


async def make_request():
    async with aiohttp.ClientSession() as session:
        print(1)
        try:
            async with session.post('http://192.168.1.4/create', timeout=10) as response:
                print(3)
                print(await response.text())
        except asyncio.TimeoutError:
            print("The request timed out")
        except aiohttp.ClientError as e:
            print(f"An error occurred: {e}")


async def main():
    websocket_task = asyncio.create_task(websocket_handler("ws://example.com/websocket"))
    request_task = asyncio.create_task(make_request())
    await asyncio.gather(websocket_task, request_task)


if __name__ == "__main__":
    asyncio.run(main())

方法二：将同步请求放到单独线程执行 #

如果必须保留requests，可以用asyncio.to_thread把同步的POST请求放到独立线程中运行，避免阻塞事件循环：

import asyncio
import requests
import websockets


async def websocket_handler(uri):
    async with websockets.connect(uri) as websocket:
        while True:
            message = await websocket.recv()
            print(f"Received message: {message}")


async def make_request():
    def sync_post():
        s = requests.Session()
        print(1)
        try:
            response = s.post('http://192.168.1.4/create', timeout=10)
            print(3)
            return response.text
        except requests.exceptions.Timeout:
            return "The request timed out"
        except requests.exceptions.RequestException as e:
            return f"An error occurred: {e}"
    
    result = await asyncio.to_thread(sync_post)
    print(result)


async def main():
    websocket_task = asyncio.create_task(websocket_handler("ws://example.com/websocket"))
    request_task = asyncio.create_task(make_request())
    await asyncio.gather(websocket_task, request_task)


if __name__ == "__main__":
    asyncio.run(main())

内容的提问来源于stack exchange，提问作者user23470475