Re: [boost] [statechart] Documentation update suggestion.

From: Andreas Huber (ahd6974-spamboostorgtrap_at_[hidden])
Date: 2007-11-01 06:29:45

Hi Jurko

Thanks for your feedback.

>    Just an idea: update the documentation to explicitly note that 
> statechart using code should synchronize both processEvent() and 
> terminate() calls when using a single statechart from multiple threads.

The fact that none of the state_machine methods are reentrant (and therefore 
also not thread-safe) is mentioned in the turtorial:

<http://www.boost.org/libs/statechart/doc/tutorial.html#AsynchronousStateMachine
s>

>    We just solved a bug in one of our projects using the statechart 
> library where we forgot to synchronize the terminate() call. Was causing
> non-reproducible assertion failures in the termination code. 

Note that you'd have to synchronize access to *all* state_machine member 
functions.
Moreover, it's usually suboptimal to just protect access to a state_machine 
subtype object with a mutex. This approach scales badly when events for the 
same state machine originate in multiple different threads (as they seem in 
your application).
Also, if you happen to have multiple cores a lot of the processing that could 
be parallelized is not and thus leads to even worse performance.
Both problems can be overcome with a scheduler, which is essentially a 
combination of an event queue with a dedicated worker thread (see link above).

Regards,

Andreas