Re: [boost] [msm] state machine construction / destruction

Subject: Re: [boost] [msm] state machine construction / destruction
From: Christophe Henry (christophe.j.henry_at_[hidden])
Date: 2011-10-21 02:18:48

Hi,

> MSM enthusiasts,
>
> I have done a performance profiling with a simple parser with 3
> implementations, plain C++, SMC and Boost MSM.  I was happy to learn that
> the MSM implementation was very efficient.

:)

> I'm having some questions about MSM space allocation, please let me know 
> if
> my understanding of things are wrong (very likely).
>
> I work in a high performance computing environment so I will try to 
> minimize
> unnecessary object constructions.
>
> Is it possible for the data in the state machine backend live somewhere 
> else
> external to the state machine?  If that's possible then I can put the 
> state
> machine's internal states close to the data that needs to be manipulated 
> and
> the state machine itself is data-less and I can have a single copy of the
> state machine and each data item carries everything.  I know this breaks
> encapsulation but I'm just wondering.

No, all the states are constructed at the same time (fsm creation) and live 
together in a fusion set. I'm thinking about allowing different construction 
schemes but it's not going to be in the short-term.
You can of course have in the states a pointer to the data but it's probably 
not what you're looking for. Sorry, at the moment it's not doable.

> The state machine has a events queue (std::deque?), can I choose to not 
> have
> this and other data structures I don't think I will need?

You can do 2 things:
- replace the queue by something more efficient (like a 
boost::circular_buffer) if you need the queue but are stuck with a bad deque 
implementation 
(http://www.boost.org/doc/libs/1_47_0/libs/msm/doc/HTML/ch03s05.html#d0e2678)
- remove the queue if you don't need it (meaning no posting of events during 
transition processing, no exit pseudo-states). To do this, provide a 
no_message_queue typedef.  See: 
http://www.boost.org/doc/libs/1_47_0/libs/msm/doc/HTML/ch03s02.html#d0e1197. 
If you didn't use this yet, you might still not be getting the best speed 
out of msm. Providing also no_exception_thrown will get you a tick more 
speed.

Please let me know whether the performance inproves (with compiler / target 
system if possible), I'm very interested in msm performance.

> Thanks,
> -jh

HTH,
Christophe