"Andreas Huber" <ah2003@gmx.net> writes:
Please have a look at the state chart at
Let us assume that the lower orthogonal region is entered first (in boost::fsm this would be region 0). When we initiate this state machine, The states are entered in the following sequence: A, B, (exception is thrown while trying to enter C). When that exception is thrown then, as you rightly point out, we have a state machine that is in an invalid state. To bring this machine back into a stable state, boost::fsm now does the following: 1. The outermost unstable state (see definitions.html) is determined. In this example this is A, because the state machine never had the chance to enter the second orthogonal region. 2. An exception_thrown event is allocated on the stack 3. The state machine searches for a reaction for the exception_thrown event. It starts by examining the outermost unstable state. If that state does not have an appropriate reaction, it works its way outward. 4. Since A does have a reaction for the exception_thrown event, that reaction is executed. 5. The execution of said reaction leads to the exit of B, the exit of A and finally to the entry of E.
Do we agree that the state machine is now in a valid (stable) state (assuming that the entry action of E did not throw)?
Sure, if every state whose entry action can fail has a superstate, you can bail out and leave the machine in the superstate. Are you requiring that? Is that superstate always a reasonable place to end up upon failure? FWIW, I don't know what an orthogonal region is, and I don't have time to learn right now, so I'm probably missing a lot. If you're still convinced you have everything right, I'll assume I'm missing something important and stop poking at this design decision. -- Dave Abrahams Boost Consulting http://www.boost-consulting.com