3. This one is my fault and might be a problem for you as you seek performance. I think we discussed this but I forgot it in the doc. Pseudo exits require the message queue and you deactivated it with: typedef int no_message_queue;
Thinking again about it, as you have the newest MSM version (time for a bit of advertisement for the new version ;-) ), there is now a way around the queue. The exit point needs the queue because it will process an event4 during processing of event3, so that MSM has time to update its current state before processing event4. But this is only because MSM does this after the transition (the UML standard "forgot" to specify this point). The newest version allows you to override this and decide that this updating job will be done for example before the transition is taken (after the guard chooses the transition of course), or after the exit action, etc. To do this, add into every state machine: typedef msm::active_state_switch_before_transition active_state_switch_policy; Now you don't need the queue. Doc is there: http://svn.boost.org/svn/boost/trunk/libs/msm/doc/HTML/ch03s05.html#backend-... Regards, Christophe