Saturday, August 14, 2010

Ctrl-C and the NServiceBus generic host

Ten posts and almost a whole year later, my very first post about NServiceBus is still by far my most popular. So here is some more NServiceBus-y goodness.

Last week a coworker came to me asking for help with a self-hosted NServiceBus application. He had a small console application set up to test NServiceBus and it worked beautifully in all but one case. When he killed the application with Ctrl-C, the message being processed was always lost. At first I thought maybe the application was not using a transactional endpoint, but it was configured to do so. I did not see the same behavior with the generic host running in console mode, so I figured the generic host was handling Ctrl-C somehow. A quick search turned up the CancelKeyPress event. I opened up the generic host in reflector, and, on a hunch, navigated to the TopShelf.Internal.Hosts namespace (the generic host internalizes another excellent open source project called TopShelf). Sure enough, the TopShelf console host handles the CancelKeyPress event, and ultimately allows all of the worker threads in NServiceBus to finish handling messages before shutting down.

One question this brought up is what happens if someone pulls the plug on my machine after a message has been received, but before it has been processed? My impression was that a transactional endpoint would take care of this, but now I'm not so sure.

1 comment:

  1. The host can't influence these outcomes, regardless of what it does to the threads, either the message will complete processing successfully, or it'll be rolled back to the queue.