synchronous startup function blocking on a future hangs when TestClient is used as a context manager

[cjw296]

Here's a brief reproducer:

def test_async_startup_hangs():

    async def foo():
        pass

    def blocking_foo():
        coro = foo()
        loop = asyncio.get_event_loop()
        future = asyncio.run_coroutine_threadsafe(coro, loop)
        return future.result()

    app = Starlette(on_startup=[blocking_foo])

    with TestClient(app) as client:
        pass

The test hangs on entering the context inside the blocking stuff inside future.result.

If I just do:

app = Starlette(on_startup=[foo])

...then foo isn't run at all by the with TestClient block.

[cjw296]

Right, so it seems like the intention is to support async startup callables, so this issue becomes much more of an edge case. I've filed the more important problem under #886

[florimondmanca]

I think this can be closed, since as you mentioned async startup callables should be called directly, without any thread wrapping.

[cjw296]

Not so sure, it's definitely not important, but there's still an edge case here where blocking on a future doesn't appear to work in a startup function.

[Kludex]

At the time this issue was created, Starlette was still didn't have anyio as dependency. Today, you can run blocking code with anyio.to_thread.