Pattern: Tree of actors

Example use case

You want to train 3 models at the same time, while being able to checkpoint/inspect its state.

In this pattern, a collection of Ray worker actors is managed by a supervisory Ray actor.

../_images/tree-of-actors.svg

Tree of actors

A single call to the supervisor actor triggers the dispatch of multiple method calls to child actors. The supervisor can process results or update child actors prior to returning.

Notes

  • If the supervisor dies (or the driver), the worker actors are automatically terminated thanks to actor reference counting.

  • Actors can be nested to multiple levels to form a tree.

Code example

@ray.remote(num_cpus=1)
class Worker:
    def work(self):
        return "done"

@ray.remote(num_cpus=1)
class Supervisor:
    def __init__(self):
        self.workers = [Worker.remote() for _ in range(3)]
    def work(self):
        return ray.get([w.work.remote() for w in self.workers])

ray.init()
sup = Supervisor.remote()
print(ray.get(sup.work.remote()))  # outputs ['done', 'done', 'done']