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ember-concurrency tasks can be canceled either explicitly (by calling one of the cancel methods on a task or task instance) or implicitly (based on how the task is configured, or because the task's host object was destroyed).

Generally speaking, it is much better to configure your tasks properly (via Task Modifiers) such that they'll be implicitly/automatically canceled at the right time, but there are still some cases where explicit cancelation is the only option.

Explicit Cancelation

There are two ways to explicitly cancel a task:

  1. Call task.cancelAll() on the Task object — this will cancel all running or enqueued Task Instances for that task.
  2. Call taskInstance.cancel() on a Task Instance (the object returned from a prior call to task.perform())


Running tasks: 0

Tip: You can also use the .concurrency property to get the current number of running task instances for a given task, e.g. {{myTask.concurrency}}: 0

<h5>Running tasks: {{count}}</h5>

<button {{action 'performTask'}}>Perform Task</button>
{{#if count}}
  <button {{action 'cancelAll'}}>Cancel All</button>
{{#if mostRecent.isRunning}}
  <button {{action 'cancelMostRecent'}}>Cancel Most Recent</button>
const WAIT_HERE_FOREVER = defer().promise;
export default Controller.extend({
  count: 0,
  mostRecent: null,

  myTask: task(function * () {
    try {
      yield WAIT_HERE_FOREVER;
    } finally {
      // finally blocks always get called,
      // even when the task is being canceled

  actions: {
    performTask() {
      let task = this.get('myTask');
      let taskInstance = task.perform();
      this.set('mostRecent', taskInstance);

    cancelAll() {

    cancelMostRecent() {

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