[Twisted-Python] Graceful shutdown of Twisted daemon

[Chris Miles]

I have a Twisted app that is often waiting for child processes (calls  
to external commands).

I'd like to make the app gracefully shutdown by default.  As in, when  
the app is killed I want to make sure that any currently running  
child processes can complete and the results of their work can be  
processed before the daemon dies.

What would be the best way to achieve this?

Can I override the SIGTERM signal handler so that it waits for other  
events to complete before allowing the app to die?

Cheers
Chris Miles