Binding forked subtask to a parent task

[aikoven]

Suppose I have a parent task that forks another task inside its executor at some point.
Is there a suggested way to bind the forked task to the parent's execution, so that when the parent is resolved, rejected or canceled, that task is canceled?

The use case for this is this:
The parent task acquires some external lock and runs the substask while it owns the lock. When canceled, parent task releases the lock. When the lock is forcibly released from outside, or on connectivity problems, parent task is rejected. I'd like the subtask to be canceled automatically in these cases, similarly to how it happens redux-saga.

[Andarist]

I don't think that's possible right now without writing custom abstraction over avenir. redux-saga uses internally a forkQueue structure to implement this.

[yelouafi]

yeah actually there is no automatic management for child forks.

The above use case could be solved manually (but less elegantly)

const subtask = ...

const task = Task.from((resolve, reject, cancel) => {
  const lock = acquireLock()
  lock.onRelease(() => {
     reject(...)
     cleanup()
  })
  ...
  const subtaskFuture = subtask.run(...)
  ...
  // When canceled, parent task releases the lock
  return cleanup

  /**
     operations in cleanup should be idempotent (ie calling a second time is noop)
  **/
  function cleanup() {
    lock.release()
    subtaskFuture.cancel()
  }
})

Assuming we have some auto-management of child tasks. Could be solved by this code

const acquireLockTask = Task.from((resolve, reject) => {
  const lock = acquireLock()
   /*
     In a fork model like we have in redux-saga this 
     would cause the parent task to reject as well 
  */
  lock.onRelease(reject)
})

const task = Task.do(function*() {
  const lock = yield acquireLockTask
  try {
    ...
    // rejecting of cancelling parent task should cancel this if active
    yield subTask 
    ...
  }
  finally {
    lock.release()
  }  
})