使用multiprocessing生成子进程导致Socket未关闭的HTTP请求异常

启动子进程后遇到以下异常情况：

• 当uvicorn的timeout_keep_alive超时后，点击浏览器的“stop”按钮会出现无限加载，且无HTTP连接日志输出
• 点击其他按钮或刷新页面能正常工作，但会收到两次响应
• Netstat显示端口60862的Socket处于绑定打开状态，但uvicorn日志中却有TRACE: 127.0.0.1:60862 - HTTP connection lost的记录

相关代码 #

import multiprocessing
import os
import time

import uvicorn
from fastapi import FastAPI

app = FastAPI()
processes = []


def keep_alive_process():
    while True:
        print(f"process {os.getpid()} is alive")
        time.sleep(1)


@app.post("/start")
async def start_processes():

    for i in range(4):
        process = multiprocessing.Process(target=keep_alive_process,
                                          args=())
        processes.append(process)
        process.start()

    return {'status': 'started'}


@app.post("/stop")
async def stop_processes():

    for process in processes:
        process.kill()
    processes.clear()

    return {'status': 'stopped'}


if __name__ == '__main__':
    uvicorn.run('main:app', timeout_keep_alive=10, log_level='trace')

日志信息 #

TRACE:    127.0.0.1:60862 - HTTP connection made
TRACE:    127.0.0.1:60862 - ASGI [2] Started scope={'type': 'http', 'asgi': {'version': '3.0', 'spec_version': '2.3'}, 'http_version': '1.1', 'server': ('127.0.0.1', 8010), 'client': ('127.0.0.1', 60862), 'scheme': 'http', 'root_path': '', 'headers': '<...>', 'method': 'POST', 'path': '/start', 'raw_path': b'/start', 'query_string': b''}
TRACE:    127.0.0.1:60862 - ASGI [2] Send {'type': 'http.response.start', 'status': 200, 'headers': '<...>'}
TRACE:    127.0.0.1:60862 - ASGI [2] Send {'type': 'http.response.body', 'body': '<20 bytes>'}
TRACE:    127.0.0.1:60862 - ASGI [2] Completed
process 63912 is alive
process 63913 is alive
process 63914 is alive
process 63915 is alive
INFO:     127.0.0.1:60862 - "POST /start HTTP/1.1" 200 OK
process 63912 is alive
process 63913 is alive
TRACE:    127.0.0.1:60862 - HTTP connection lost

....

process 63912 is alive
INFO:     127.0.0.1:59092 - "POST /stop HTTP/1.1" 200 OK
INFO:     127.0.0.1:59092 - "POST /stop HTTP/1.1" 200 OK
TRACE:    127.0.0.1:59092 - HTTP connection made
TRACE:    127.0.0.1:59092 - ASGI [3] Started scope={'type': 'http', 'asgi': {'version': '3.0', 'spec_version': '2.3'}, 'http_version': '1.1', 'server': ('127.0.0.1', 8010), 'client': ('127.0.0.1', 59092), 'scheme': 'http', 'root_path': '', 'headers': '<...>', 'method': 'POST', 'path': '/stop', 'raw_path': b'/stop', 'query_string': b''}
TRACE:    127.0.0.1:59092 - ASGI [3] Send {'type': 'http.response.start', 'status': 200, 'headers': '<...>'}
TRACE:    127.0.0.1:59092 - ASGI [3] Send {'type': 'http.response.body', 'body': '<20 bytes>'}
TRACE:    127.0.0.1:59092 - ASGI [3] Completed
TRACE:    127.0.0.1:59092 - ASGI [4] Started scope={'type': 'http', 'asgi': {'version': '3.0', 'spec_version': '2.3'}, 'http_version': '1.1', 'server': ('127.0.0.1', 8010), 'client': ('127.0.0.1', 59092), 'scheme': 'http', 'root_path': '', 'headers': '<...>', 'method': 'POST', 'path': '/stop', 'raw_path': b'/stop', 'query_string': b''}
TRACE:    127.0.0.1:59092 - ASGI [4] Send {'type': 'http.response.start', 'status': 200, 'headers': '<...>'}
TRACE:    127.0.0.1:59092 - ASGI [4] Send {'type': 'http.response.body', 'body': '<20 bytes>'}
TRACE:    127.0.0.1:59092 - ASGI [4] Completed
TRACE:    127.0.0.1:59092 - HTTP connection lost

Swagger界面截图 #

内容的提问来源于stack exchange，提问作者Xavatu