shared task in route hooks

controllers.application.js

import Ember from 'ember';
import { inject as service } from '@ember/service';

export default Ember.Controller.extend({
	shared: service()
});

router.js

import EmberRouter from '@ember/routing/router';
import config from './config/environment';

const Router = EmberRouter.extend({
  location: 'none',
  rootURL: config.rootURL
});

Router.map(function() {
  this.route('foo');
  this.route('bar');
  this.route('baz');
});

export default Router;

routes.bar.js

import Ember from 'ember';
import { get } from '@ember/object';

export default Ember.Route.extend({
  shared: Ember.inject.service(),
  
  async model() {
    await get(this, 'shared').delay();
    return get(this, 'shared.value');
  }
});

routes.baz.js

import Ember from 'ember';
import { get, set } from '@ember/object';
import { Promise as EmberPromise } from 'rsvp';

export default Ember.Route.extend({
  shared: Ember.inject.service(),
  
  async model() {
    let { value } = get(this, 'shared.value');
    await EmberPromise.resolve({ value });
  },
                                  
  async afterModel() {
    await get(this, 'shared').delay();
  }, 
  
  setupController(controller, model) {
    this._super(controller, model);
    set(controller, 'model', get(this, 'shared.value'));
  }
});

routes.foo.js

import Ember from 'ember';
import { get } from '@ember/object';

export default Ember.Route.extend({
  shared: Ember.inject.service(),
  
  async beforeModel() {
    await get(this, 'shared').delay();
  }, 
  
  model() {
    return get(this, 'shared.value');
  }
});

services.shared.js

import Ember from 'ember';
import { task, timeout } from 'ember-concurrency';
import { get, set } from '@ember/object';
import { reads } from '@ember/object/computed';
import { Promise as EmberPromise } from 'rsvp';

export default Ember.Service.extend({
  delayTask: task(function*() {
    yield timeout(1000);
    return { value: `runs... ${get(this, 'delayTask.performCount')}` };
  }).drop().cancelOn('deactivate').debug(),
  
  async delay() {
    let isRunning = get(this, 'delayTask.isRunning');
    let hasRunOnce = get(this, 'delayTask.performCount') > 0;
    if (isRunning && hasRunOnce) {
      let { value } = get(this, 'value') || { value: null };
      return await EmberPromise.resolve({ value });
    }
    return await get(this, 'delayTask').perform();
  },

  value: reads('delayTask.lastSuccessful.value')
});

styles.app.css

body {
  margin: 12px 16px;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 12pt;
}

a.active {
  color: black;
}

templates.application.hbs

<p>
  Shared task state: {{shared.delayTask.state}}
</p>

<p>
  Transition between the routes before the task finishes, models use shared state from a service's task.
</p>

<p>
  Hit the links below like playing <em>whack-a-mole</em>.
</p>

{{#link-to "foo"}}Foo{{/link-to}} | 
{{#link-to "bar"}}Bar{{/link-to}} |
{{#link-to "baz"}}Baz{{/link-to}}

<br>

{{outlet}}

templates.bar.hbs

<h1>Bar</h1>
<p>
  {{model.value}}
</p>

templates.baz.hbs

<h1>Baz</h1>
<p>
  {{model.value}}
</p>

templates.foo.hbs

<h1>Foo</h1>
<p>
  {{model.value}}
</p>

twiddle.json

{
  "version": "0.15.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.2.2",
    "ember-template-compiler": "3.2.2",
    "ember-testing": "3.2.2"
  },
  "addons": {
    "ember-data": "3.2.0",
    "ember-concurrency": "0.8.19"
  }
}