5.5.2.1.9. Join Node

Join Node

A Join Node synchronizes incoming flows before allowing its outgoing flow to continue. In UML, the bar-shaped join waits for the required incoming control/object flows; it is distinct from a Merge Node, which passes alternative arrivals through without synchronization.

flowchart LR
    start@{ shape: circle, label: " " }
    start --> item(Load items)
    start --> address(Validate address)
    item --> sync
    address --> sync
    sync[ ]:::bar
    sync --> ship(Dispatch order)
    classDef bar fill:#000,stroke:#000

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Mermaid approximation: this diagram shows the model's routing, not a complete UML Activity notation. Rounded boxes represent actions; edge labels identify token types or guards. The black rectangle approximates a UML fork/join bar; its exact proportions depend on Mermaid rendering.

Definition

.AddInitial(node => node
    .AddControlFlow("LoadItems")
    .AddControlFlow("ValidateAddress"))
.AddAction(
    "LoadItems",
    async c => c.OutputRange(await orders.LoadItemsAsync(orderId, c.CancellationToken)),
    node => node.AddFlow<Item, JoinNode>())
.AddAction(
    "ValidateAddress",
    async c => c.Output(await addresses.ValidateAsync(orderId, c.CancellationToken)),
    node => node.AddFlow<AddressCheck, JoinNode>())
.AddJoin(join => join
    .AddFlow<Item>("DispatchOrder")
    .AddFlow<AddressCheck>("DispatchOrder"))
.AddAction("DispatchOrder", async c =>
    await shipping.DispatchAsync(
        c.GetTokensOfType<Item>(),
        c.GetTokensOfType<AddressCheck>().Single(),
        c.CancellationToken))

Configure each incoming flow explicitly so the Join receives the required arrivals. The Join forwards tokens onward; the target can read the input token types after synchronization. Do not substitute a Join where every arriving branch should proceed independently: use a Merge Node for that. See also Implicit Fork and Join.