A generic state machine
The module provides tools for defining and tracking generic state machines. For a more specific implementation that specifically defines finite state machines, see the FSM module, that provides additional tools on top of the generic machines defined here
State machines:
- Receive Events
- Modify State
- Take further actions based on new state, possibly generating more events
A state machine is defined in terms of a Planner.
It has the following signature:
type Planner func(events []Event, user interface{}) (nextActions interface{}, eventsProcessed uint64, err error)A planner receives a series of events and a pointer to the current state (represented by user)
The planner generally:
- processes one or more events that mutate state
- constructs a function that will perform additional actions based on the new state
It returns:
- The next actions handler-- should have the signature func(ctx Context, st ) error), where is the typeOf(user) param
- The number of events processed
- An error if occured
As a general rule, you mutate inside the planner function, while you perform side effects outside the planner in the return handler, which only receives a value for state and cannot mutate it (but can dispatch more events).
The go-statemachine is designed to be used with a list of data structures, persisted to a datastore through the go-statestore module. When working with statemachines this way, you define a StateHandler with a Plan function that works like a Planner.
You initialize a new set of statemachines for a given type of state as follows:
var ds datastore.Batching
var stateHandler StateHandler
var stateMachines = statemachine.New(ds, stateHandler, StateType{})This creates a machine for the given data store that will process data of type StateType with the given stateHandler.
You can now dispatch events to a state machine with:
var id interface{} // some identifier of a tracked state
var evt Event // some event type
stateMachines.Send(id, evt)The state machine group will initialize a new statemachine if it is not already tracking data for the given identifier
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