wireprotoserver: ability to run an SSH server until an event is set It seems useful to be able to start an SSH protocol server that won't run forever and won't call sys.exit() when it stops. This could be used to facilitate intra-process testing of the SSH protocol, for example. We teach the server function to loop until a threading.Event is set and invent a new API to run the server until an event is set. It also won't sys.exit() afterwards. There aren't many callers of serve_forever(). So we could refactor them relatively easily. But I was lazy. threading.Event might be a bit heavyweight. An alternative would be a list whose only elements is changed. We can't use a simple scalar value like a bool or int because those types are immutable. Events are what you use in systems programming for this use case, so the use of threading.Event seems justified. Differential Revision: https://phab.mercurial-scm.org/D2461