Use the first sister message as a Heartbeat, too #93
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A practical example where this can happen is when a nodelet is unloaded very shortly after being loaded. |
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Could this please get a review? |
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I've noticed that when the sister is killed quickly after being started, there is (very much repeatable) chance to deadlock the other Bond. Consider this sequence:
AwaitingSister->SisterAlive()which callsConnect().Connect()stops the connection timer.Alivestate. However,Heartbeat()has not yet been called (that would be done by the second message which did not come), soheartbeat_timer_is still off and does not trigger the timeout event.The fix I sent fixes it on the C++ side. I'm not sure about the Python side, and not sure about the SM source code. The
Heartbeat()needs to be called already in theAlivestate (it is undefined inAwaitingSister). Quickly skimming through the SM syntax, it doesn't seem to me it would support calling some functions before the transition and some after it.If that would be the case, I'd suggest calling
Heartbeatin theAwaitingSisterstate (right after callingConnected()) and defining it forAwaitingSisterstate to do the same as for theAlivestate. That would require no additional changes to the SM definition, so it might be preferred.I'll let the maintainers decide which approach would be better.