TaskCluster Task Scheduler (Prototype)

This is a simple scheduler that schedules dependent tasks. This is done by listening for all task-defined messages, load tasks and read the task.extra.waitFor property. If the property is a list of taskIds, the task will be scheduled when the tasks referenced have been completed.

Tasks are created on the queue using the queue.defineTask method. Notice, that if task.extra.waitFor is an empty list it will be scheduled immediately by taskcluster-scheduler; task that doesn't specify the task.extra.waitFor property will be ignored.

Example below how for to create two dependent tasks:

var queue = new taskcluster.Queue(...);

// Create two taskIds
var taskIdA = slugid.nice();
var taskIdB = slugid.nice();

// Define taskA (which is scheduled by taskcluster-scheduler)
queue.defineTask(taskIdA, {
  provisionerId:    '...',
  workerType:       '...',
  created:          taskcluster.fromNowJSON(),
  deadline:         taskcluster.fromNowJSON('12 hours'),
  payload:          {...},
  metadata:         {...},
  extra: {
    waitFor:        []  // empty-set means it'll be scheduled immediately
  }
});

// Define taskB (which is scheduled by taskcluster-scheduler) after taskA
queue.defineTask(taskIdB, {
  provisionerId:    '...',
  workerType:       '...',
  created:          taskcluster.fromNowJSON(),
  deadline:         taskcluster.fromNowJSON('12 hours'),
  payload:          {...},
  metadata:         {...},
  extra: {
    waitFor:        [taskIdA]  // schedule when taskA is completed
  }
});

The order in which you define the tasks on the queue is not important to the scheduler. If you create taskB referencing taskA, before you create taskA, someone else can technically listen for the task-defined messages, get the taskId for taskA and define this before you do so. For this reason it is strongly encouraged that the task graph is constructed in a top-down manner.

If your tasks download artifacts from dependent tasks, failing to construct the graph in a top-down manner may be a security issue.