Activity Nodes

Activity Nodes

Nodes are the vertices of a UML Activity graph. A node performs work, routes tokens, accepts an event, or defines an execution boundary. Flows connect the nodes and determine when and with what data a target can execute.

Node definition styles

Lambda-defined nodes use a string name and callbacks:

.AddAction(
    "Produce",
    async c => c.Output(42),
    node => node.AddFlow<int>("Handle"))
.AddAction("Handle", async c =>
{
    var value = c.GetTokensOfType<int>().Single();
    await processor.HandleAsync(value, c.CancellationToken);
})

Action nodes can also be defined as classes implementing IActionNode. Such actions can receive services and declared input/output token interfaces through constructor injection; see Action Node. Built-in UML node types such as FinalNode and DecisionNode<TToken> can be referenced with typed builder overloads instead of string names.

Node roles

Role	Nodes
Entry, exit, and boundary	Initial, Final, Input, Output
Executable work and event acceptance	Action, Accept Event, Send Event, Publish Event, Time Event
Routing and synchronization	Decision, Merge, Fork, Join
Data retention and nested execution	Data Store, Structured, Iterative, Parallel Activity Nodes

Nodes are uniquely identified within their containing Activity scope. Nested nodes belong to their structured Activity, not to the containing graph's top-level namespace. Node defaults and how they affect activation and token reuse are described in Implicit Fork and Join.

Executable nodes and structured Activity nodes can also register exception handlers. See Activity Exception Handling for exception routing, matching, and examples.