Package io.vlingo.xoom.stepflow

Interface Kernel

  • All Known Implementing Classes:
    KernelActor
    public interface Kernel

    Kernels implement state machines and validate state mutations by comparing the current state of an object to a desired state. Kernels do not tightly couple themselves to event messages. Event messages do not directly inform the state of an entity, rather, handlers are responsible for accepting or rejecting a state-carried transfer. The kernel is a consumer and producer of state mutations that are subscribed to by a collection of handlers.

    A kernel has a collection of input states that map to output states. When a state transfer is received by a kernel, it can either accept or reject the request. A state transfer is applied to the underlying adapter during validation by the kernel. If the underlying storage reflects a different state of an entity than the input state, the state transfer will be rejected as a part of a transactional guarantee provided by the storage implementation.

    Kernels do not tightly couple to storage implementations. The processor must provide a transactional function to the kernel. The transaction will compare the input state (stale read) to the actual state. This guarantees that any stale reads are rejected.

    Kernels implement state machines that version an entity as mutations are applied. All state mutations are applied in a linear order, and are guaranteed to replicate the state of an entity. Versions of an entity are incremented whenever a state mutation is accepted by the kernel. Output states can equal their input states. A field update to an entity may not require a logical state transition. A valid input state could be a list or none. When no input state is provided, the logical state will remain the same while the versioned state will be incremented.

    • Method Detail

      • getName

        io.vlingo.common.Completes<java.lang.String> getName()

      • setName

        void setName​(java.lang.String name)

      • registerStates

        void registerStates​(State<? extends State>... states)

      • getStates

        io.vlingo.common.Completes<java.util.List<State<? extends State>>> getStates()

      • getStateTransitions

        io.vlingo.common.Completes<java.util.List<StateTransition>> getStateTransitions()

      • getTransitionMap

        io.vlingo.common.Completes<java.util.Map<java.lang.String,​TransitionHandler>> getTransitionMap()

      • applyEvent

        <T extends Event> io.vlingo.common.Completes<StateTransition> applyEvent​(T event)