boost msm - boost msm multiple deferred events

Question

Let's say I have 2 states, an Active state and an Idle state. If I receive some events in Active state I would like to defer them and execute them when I go back to Idle state.

But when I go back to Idle State is there a way to chose which previously deferred event to process? or is there a way to prioritize them or even ignore few of them?

Thanks,

Answer 1

I see that the basic capability of deferred events is covered in the documentation provided on the project, which I have found helpful in general. In the section titled Orthogonal regions, terminate state, event deferring look for the text "UML defines event deferring as a state property. To accommodate this, MSM lets you specify this in states by providing a deferred_events type..." Note that there are two different methods described there for implementing the deferred events.

Without testing an example, I cannot say whether or not the referenced material on Conflicting transitions and guards will allow you to establish the priority you are seeking on deferred events. You could post your problem or a simplified example.

Answer 2

I am not aware of a solution native to boost MSM. I have heard that the author Christophe Henry is quite responsive to this kind of question on the Mailing list.

If your situation really is that trivial (only two states) nothing is stopping you from implementing your own deferred event queue, passing "defferred events" to it in Active. You can implement an internal transition for each event type with an action that pushes them into your custom queue. Upon entering Idle you can reorder them however you want and post them all back to the SM. This solution doesn't scale all that well though and its a bit of a hack.