使用 websockets 优雅地关闭 uvicorn starlette 应用程序

Question

鉴于此示例 Starlette 应用程序具有开放的 websocket 连接，您如何关闭 Starlette 应用程序？我在 uvicorn 运行。每当我按 Ctrl+C 时，输出都是 Waiting for background tasks to complete.，它永远挂起。

from starlette.applications import Starlette

app = Starlette()

@app.websocket_route('/ws')
async def ws(websocket):
    await websocket.accept()

    while True:
        # How to interrupt this while loop on the shutdown event?
        await asyncio.sleep(0.1)

    await websocket.close()

我尝试在关闭事件中切换一个 bool 变量，但该变量从未更新。它总是 False.

例如

app.state.is_shutting_down = False


@app.on_event('shutdown')
async def shutdown():
    app.state.is_shutting_down = True


@app.websocket_route('/ws')
async def ws(websocket):
    await websocket.accept()

    while app.state.is_shutting_down is False:

Answer 1

我无法真正重现问题，我明白了

INFO: Started server process [31]
INFO: Waiting for application startup.
INFO: Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
^CINFO: Shutting down
INFO: Waiting for application shutdown.
INFO: Finished server process [31]

但我在自己的异步应用程序中正常关闭的做法是：

import signal

async def shutdown(signal: signal):
    """
    try to shut down gracefully
    """
    logger.info("Received exit signal %s...", signal.name)
    tasks = [t for t in asyncio.all_tasks() if t is not asyncio.current_task()]
    [task.cancel() for task in tasks]
    logging.info("Canceling outstanding tasks")
    await asyncio.gather(*tasks)


if __name__ == "__main__":

    loop = asyncio.get_event_loop()
    signals = (signal.SIGHUP, signal.SIGTERM, signal.SIGINT)
    for s in signals:
        loop.add_signal_handler(
            s, lambda s=s: asyncio.create_task(shutdown(s))
        )

您可能必须将 await websocket.close() 移动到 shutdown 方法中。

Answer 2

你的变量没有改变的原因是因为 "shutdown" 事件的处理程序是在所有任务执行完后执行的（即无限循环）。

在 asyncio 事件循环上设置一个信号处理程序可能不会起作用，因为我相信只允许一个信号处理程序，uvicorn 已经为它自己的关闭过程设置了。
相反，您可以通过 Monkey Patch uvicorn 信号处理程序来检测应用程序关闭并在该新函数中设置您的控制变量。

import asyncio
from starlette.applications import Starlette
from uvicorn.main import Server

original_handler = Server.handle_exit

class AppStatus:
    should_exit = False

    @staticmethod
    def handle_exit(*args, **kwargs):
        AppStatus.should_exit = True
        original_handler(*args, **kwargs)

Server.handle_exit = AppStatus.handle_exit

app = Starlette()

@app.websocket_route('/ws')
async def ws(websocket):
    await websocket.accept()

    while AppStatus.should_exit is False:

        await asyncio.sleep(0.1)

    await websocket.close()
    print('Exited!')

使用 websockets 优雅地关闭 uvicorn starlette 应用程序

Graceful shutdown of uvicorn starlette app with websockets

python

python-asyncio

asgi

starlette

uvicorn