StateMachine

Create State Machine

Create either a passive or an active state machine:

The above sample uses the enums States and Events that define the available states and events.

Define Transitions

A simple transition

If the state machine is in state A and receives event B then it performs a transition to state B.

Transition with action

Actions are defined with Execute. Multiple actions can be defined on a single transition. The actions are performed in the same order as they are defined. An action is defined as a delegate. Therefore, you can use lambda expressions or normal delegates. The following signatures are supported:

Actions can use the event argument that were passed to the Fire method of the state machine. If the type you specify as the generic parameter type does not match the argument passed with the event, an exception is thrown.

Transition with guard

Guards are used to decide which transition to take if there are multiple transitions defined for a single event on a state. Guards can use the event argument that was passed to the Fire method of the state machine. The first transition with a guard that returns true is taken.

The signature of guards is as follows:

Entry and Exit Actions

When a transition is executed, the exit action of the current state is executed first. Then the transition action is executed. Finally, the entry action of the new current state is executed.

The signature of entry and exit actions are as follows:

Internal and Self Transitions

Internal and Self transitions are transitions from a state to itself.

When an internal transition is performed then the state is not exited, i.e. no exit or entry action is performed. When an self transition is performed then the state is exited and re-entered, i.e. exit and entry actions, if any, are performed.

Define Hierarchies

The following sample defines that B1, B2 and B3 are sub states of state B. B1 is defined to be the initial sub state of state B.

History Types

When defining hierarchies then you can define which history type is used when a state is re-entered:

• None:
  The state enters into its initial sub state. The sub state itself enters its initial sub state and so on until the innermost nested state is reached.
• Deep:
  The state enters into its last active sub state. The sub state itself enters into its last active state and so on until the innermost nested state is reached.
• Shallow:
  The state enters into its last active sub state. The sub state itself enters its initial sub state and so on until the innermost nested state is reached.

Initialize, Start and Stop State Machine

Once you have defined your state machine then you can start using it.

First you have to initialize the state machine to set the first state (A in the sample):

Afterward, you start the state machine:

Events are processed only if the state machine is started. However, you can queue up events before starting the state machine. As soon as you start the state machine, it will start performing the events.

To suspend event processing, you can stop the state machine:

If you want, you can then start the state machine again, then stop it, start again and so on.

Fire Events

To get the state machine to do its work, you send events to it:

This fires the event B on the state machine and it will perform the corresponding transition for this event on its current state.

You can also pass an argument to the state machine that can be used by transition actions and guards:

Another possibility is to send a priority event:

In this case, the event B is enqueued in front of all queued events. This is especially helpful in error scenarios to go to the error state immediately without performing any other already queued events first.

That’s it for the tutorial. See rest of documentation for more details on specific topics.

Sample State Machine

This is a sample state machine.

Definition

The above state machine uses these actions and guards:

Run the State Machine

This is a small sample to show how to interact with the state machine:

Log

If you add the log4net log extensions available in the Appccelerate.SourceTemplate package:

to the above code then these are the log messages (if all are enabled – see log4net documentation on how to configure log messages). Note how the state exits and enters are logged, especially for hierarchical transitions.

You can write your own extension for different logging.

Reports

yEd Report

csv Report

Textual Report

Elevator: initial state = OnFloor
    Healthy: initial state = OnFloor history type = Deep
        entry action: 
        exit action: 
        ErrorOccured -> Error actions:  guard: 
        OnFloor: initial state = DoorClosed history type = None
            entry action: AnnounceFloor
            exit action: Beep, Beep
            CloseDoor -> DoorClosed actions:  guard: 
            OpenDoor -> DoorOpen actions:  guard: 
            GoUp -> MovingUp actions:  guard: CheckOverload
            GoUp -> internal actions: AnnounceOverload, Beep guard: 
            GoDown -> MovingDown actions:  guard: CheckOverload
            GoDown -> internal actions: AnnounceOverload guard: 
            DoorClosed: initial state = None history type = None
                entry action: 
                exit action: 
            DoorOpen: initial state = None history type = None
                entry action: 
                exit action: 
        Moving: initial state = MovingUp history type = Shallow
            entry action: 
            exit action: 
            Stop -> OnFloor actions:  guard: 
            MovingUp: initial state = None history type = None
                entry action: 
                exit action: 
            MovingDown: initial state = None history type = None
                entry action: 
                exit action: 
    Error: initial state = None history type = None
        entry action: 
        exit action: 
        Reset -> Healthy actions:  guard: 
        ErrorOccured -> internal actions:  guard: