External Events

info

Before you can use an ExternalEventDef in a WfSpec, you need to create the ExternalEventDef metadata object in LittleHorse. You can do that following our metadata management docs.

You can use WorkflowThread#WaitForEvent() to add an EXTERNAL_EVENT Node that causes the WfRun to block until an ExternalEvent arrives. It's simple:

Java

public void workflowLogic(WorkflowThread thread) {
    NodeOutput eventOutput = thread.waitForEvent("my-event-name");
}

Go

func workflowLogic(thread *littlehorse.WorkflowThread) {
    eventOutput := thread.WaitForEvent("my-event-name")
}

Python

def workflow_logic(thread: WorkflowThread) -> None:
    ext_event_output = thread.wait_for_event("my-event-name")

C#

public void WorkflowLogic(WorkflowThread thread) 
{
  NodeOutput eventOutput = thread.WaitForEvent("my-event-name");
}

Accessing Event Content

Lastly, just as with TASK nodes you can use the NodeOutput from WorkflowThread::waitForEvent() to mutate a WfRunVariable:

Java

public void workflowLogic(WorkflowThread thread) {
    WfRunVariable myVar = thread.declareJsonObj("my-var");
    NodeOutput eventOutput = thread.waitForEvent("my-event-name");
    myVar.assign(eventOutput);
}

Go

func workflowLogic(thread *littlehorse.WorkflowThread) {
    myVar := thread.DeclareJsonObj("my-var")
    eventOutput := thread.WaitForEvent("my-event-name")
    myVar.Assign(eventOutput);
}

Python

def workflow_logic(thread: WorkflowThread) -> None:
    my_var = thread.declare_json_obj("my-var")
    event_output = thread.wait_for_event("my-event-name")
    my_var.assign(event_output)

C#

private static void WorkflowLogic(WorkflowThread thread) 
{
  WfRunVariable myVar = thread.DeclareJsonObj("my-var");
  NodeOutput eventOutput = thread.WaitForEvent("my-event-name");
  myVar.Assign(eventOutput);
}

note

If you use an ExternalEventDef for any EXTERNAL_EVENT node as shown in this tutorial, you cannot re-use that ExternalEventDef as a trigger for Interrupts.