serve_connection should handle panic?

[tisonkun]

poem/poem/src/server.rs

Lines 168 to 197 in c66d78a

	tokio::spawn(async move {
	let serve_connection = serve_connection(socket, local_addr, remote_addr, scheme, ep, server_graceful_shutdown_token.clone(), idle_timeout);
	if timeout.is_some() {
	tokio::select! {
	_ = serve_connection => {}
	_ = timeout_token.cancelled() => {}
	}
	} else {
	serve_connection.await;
	}
	if alive_connections.fetch_sub(1, Ordering::Acquire) == 1 {
	// notify only if shutdown is initiated, to prevent notification when server is active.
	// It's a valid state to have 0 alive connections when server is not shutting down.
	if server_graceful_shutdown_token.is_cancelled() {
	notify.notify_one();
	}
	}
	});
	}
	}
	}
	}
	drop(acceptor);
	if alive_connections.load(Ordering::Acquire) > 0 {
	tracing::info!(name = name, "wait for all connections to close.");
	notify.notified().await;
	}

We have a situation that serve_connection.await panic and thus alive_connections.fetch_sub doesn't execute, so that outer notify.notified().await blocks forever.

We should either handle panic, or do a timeout for waiting connections to close.