ros2_control shutdown protocol

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I'm working on implementing a ros2_control hardware abstraction for a robot, and am having difficulties implementing the shutdown protocol.

What is the difference between implementing the "on_deactivate" and "on_shutdown" methods, and under what conditions are those methods executed? Right now I have both of those methods implemented, but cannot seem to get them to execute. On startup, the "on_init" and "on_activate" methods are run automatically in turn, I would have expected the deactivation methods to run automatically when a SIGINT is sent with CTRL-C.