[Twisted-Python] Correct pattern to do SSH forwarding in a GUI

[Luper Rouch]

I am using twisted in a GUI application to do port forwarding over an 
SSH connection. All the network connections of the application 
(database, etc...) are routed through this connection, to simplify 
server configuration and secure things.

My first attempt was to run the reactor in the main thread, but the 
application was "freezing" when e.g. doing a SELECT with 
SQLAlchemy/psycopg2 (I guess because psycopg2 just waits for data and 
blocks the twisted reactor). So I put reactor.run() in a thread and it 
works, but I'm getting strange issues on some platforms (for example I 
can't connect at all on *some* OSX computers, getting a "reactor 
stopping" log from twisted without any further error), and I feel I'm 
doing the whole thing terribly wrong.

So my question is, how to do proper SSH port forwarding with conch in an 
application that also uses the tunnels not the asynchronous way ? If 
running the reactor in a thread is OK, are there particular things to 
watch out for ?