SimpleActionState.execute will block when "ctrl+c" pressed

[developer-yj]

1, if "ctrl+c" pressed, "done_cb" will never be called by SimpleActionClient because rospy was shutdown, action client cannot receive action server's state message. So, it will be blocked by the code:"self._done_cond.wait()".

2, in multi-thread mode, run "SimpleActionState.execute()" in child thread, after "ctrl+c" pressed, call "SimpleActionState.request_preempt()" in main thread is not working because that, rospy was shutdown, call SimpleActionClient.cancel_goal() will be failed, So, it will be blocked by the code:"self._done_cond.wait()" again.

Suggestion：
check rospy's state in SimpleAction.request_preempt() function, if rospy is shutdown, call self._done_cond.notify() to notify SimpleAction.execute() function to return "preempted" state.

[sjhansen3]

I just rewrote the class without threading and it no longer blocks a signal.sigint. It seems the issue is related to signals behavior pre python 3.3

https://stackoverflow.com/questions/25676835/signal-handling-in-multi-threaded-python

[sjhansen3]

Is there interest for a PR on this?

[sjhansen3]

I spoke more about my issue and solution here: #52