Hello list,

I need to implement a graceful shutdown procedure for a twistd application.

The application is made up of two services: an internet.TCPClient and an internet.TCPServer.

They're glued together with a MultiService instance, which is in turn set to have 'application' as parent.

The server and the client work together, making a proxy (SMTP server and AMQP client).

My goal is the following:

- intercept a SIGTERM signal

- 'block' on the server side: since it's SMTP I get this by setting a variable that makes the server return tempfails (4xx) for new messages, while keeping current sessions active

- wait until current requests are satisfied (I keep a dictionary of current pending messages)

- shut the whole thing down

What is the best solution for this use case? It's not really clear to me how to catch SIGTERM and handle pending requests *before* the underlying services start to shutdown (i.e. even addSystemEventTrigger('before', 'shutdown', callable) is called too late for my needs).

Thank you very much for your help!

Fabio