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Subject: [Boost-users] [MSM] What happens to MSM if guard returns `false`, mutable events and error recovery?
From: Ovanes Markarian (om_boost_at_[hidden])
Date: 2017-05-28 06:42:46

Hi *,

I am currently reading through the MSM docs and have one question, what
happens to MSM if guard returns `false`. Does the MSM enter an error state
in orthogonal region (
libs/1_64_0/libs/msm/doc/HTML/ch03s02.html#d0e577)? Even internals page
describes, what happens if guard returns `true`, but not a single word on
`false` case.

Regarding the const events: I am programming an MSM to proxy network
traffic and once a message with data was received it'll be analysed and
moved between different states. Message instances implement move semantics.
Currently, the MSM has an initial state `ready` where the `message_in`
event is handled. This event contains the message to be analysed. From my
current understanding I either have to make message field in `message_in`
event mutable or MSM needs to to support r-value references. Can somebody
tell me what's going to happen if the action only accepts r-value reference
to an event instance? Currently, it seems to work, but would like to
understand the implications.

struct some_action_impl {
  template<class Fsm, class Event, class SourceState, class
TargetState> void operator()(Event&& ev, Fsm& fsm, SourceState&
source, TargetState& target) { ... }

My last question relates to multi-threading. I understand that MSM
manages internal states, would it be safe to create MSM as a
thread-local storage and restart the thread-local MSM if the new
request comes in? It's more about, what happens to MSM after an error
state? Is calling stop(), start() members enough?

Many thanks for help,

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