invoke

README

Invoked Services

This example models a service manager that spawns asynchronous work when it enters a loading state. The goroutine is started via Invoke and is automatically cancelled when the state exits — whether that happens because the work finished or because a CANCEL event forced a transition. This tight coupling between a goroutine's lifetime and the state lifecycle prevents resource leaks without any manual cleanup.

State Diagram

---
title: Service Manager
config:
    theme: default
    maxTextSize: 50000
    maxEdges: 500
    fontSize: 16
---
stateDiagram-v2
    state "error" as error
    state "idle" as idle
    state "loading" as loading
    state "success" as success
	error --> [*]
	success --> [*]
	[*] --> loading
	loading --> idle: CANCEL
	loading --> success: done.invoke
	loading --> error: error

SCXML

<?xml version="1.0" encoding="UTF-8"?>
<scxml xmlns="http://www.w3.org/2005/07/scxml" version="1.0" name="service_manager" initial="loading">
  <final id="error"></final>
  <state id="idle"></state>
  <state id="loading">
    <transition event="CANCEL" target="idle"></transition>
    <transition event="done.invoke.loading" target="success"></transition>
    <transition event="error.platform" target="error"></transition>
    <invoke id="loading"></invoke>
  </state>
  <final id="success"></final>
</scxml>

What Happens

Case 1 — Completion. The machine starts in loading, which spawns a goroutine that simulates 100 ms of work. After the work finishes the goroutine returns nil, triggering the onDone path. The machine transitions to success, a final state.

Case 2 — Cancellation. The machine again starts in loading and spawns the same goroutine. After only 20 ms a CANCEL event is sent. The machine exits loading and moves to idle. Exiting the state cancels the goroutine's context.Context, so the goroutine sees ctx.Done(), prints a cancellation message, and exits cleanly.

When To Use This

• API calls — enter a loading state that fetches data; transition to success or error on completion, and cancel the request automatically on timeout or user action.
• File uploads — an uploading state with a cancel button; pressing cancel exits the state and aborts the upload goroutine.
• Background jobs — a processing state that cleans up automatically if the user navigates away or the parent state is exited.

Output

--- Test Case 1: Completion ---
  [Invoke] Starting async work...
  [Invoke] Task successfully completed!
Final State: success

--- Test Case 2: Cancellation ---
  [Invoke] Starting async work...
Action: Sending CANCEL event...
  [Invoke] Task was cancelled by state exit!
Final State: idle

--- Conclusion ---
Invoked services allow for clean async logic that is
tightly bound to the state lifecycle, preventing resource leaks.

Running

go run .