Server.wait_closed() currently does two checks:

1. if _sockets is None -- means that Server.close() was called
2. if self._waiters is None -- means that Server._wakeup() was called

if (1) *or* (2) is true, wait_closed() just returns without waiting on anything.

However, when Server.close() is called there might be still active transports serving requests.  Server.wait_closed() should wait until all of them are detached, even if Server._sockets is already reset.

So the below implementation:

    async def wait_closed(self):
        if self._sockets is None or self._waiters is None:
            return
        waiter = self._loop.create_future()
        self._waiters.append(waiter)
        await waiter

should be changed to:

    async def wait_closed(self):
        if self._waiters is None:
            assert self._active_count == 0
            return
        waiter = self._loop.create_future()
        self._waiters.append(waiter)
        await waiter

I believe this is by design: the documentation says:

> The sockets that represent existing incoming client connections are left open.

`Server` doesn't keep track of active transports serving requests.

(That said, I haven't figured out what _waiters is here so I could be wrong.)

I ran into this while working on an asyncio application using
asyncio.start_server.

From the documentation, I expected the combination of `close` and `wait_closed`
to wait until all connection handlers have finished. Instead, handlers remaining
running with open connections as background tasks. I wanted to be able to
"gracefully" close the server, with all processing done, so I could inspect some
results for a test case.

Could there be a method for this? One suggestion would be:

*   Clarify the current behaviour of `close` and `wait_closed`
    (https://bugs.python.org/issue34852)
*   Add new coro `wait_finished` which waits until all handler tasks are done

I'm afraid I'm not familiar with low-level asyncio APIs like transports and
protocols, so I don't know how/if this fits in with those.