Named actor

[heyucongtom]

What do these changes do?

Implementing the named-actor issue addressed in #1424, with the API:

# Create named actor.
ray.actors["actor1"] = a

# Get named actor handle (done by a different driver).
a = ray.actors["actor1"]

This is a rough wrapper on the idea of pickling. Would love to talk through it later this week and add some unit test.

Related issue number

#1424

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[robertnishihara]

Thanks a lot @heyucongtom! I think the shortest path to merging this is the following.

1. Let's start off with a non-map API. In particular, can you change this to

   ray.experimental.register_actor(actor_handle, name)
   
   actor_handle = ray.experimental.get_actor(name)

   We can of course iterate on this.

2. As shown above, let's mark this as "experimental", by putting it in something like ray/python/ray/experimental/named_actors.py.

3. Can you add a test for this?

   • In test/actor_test.py e.g., right after testPicklingActorHandle, we can add a test that uses these methods in the same process.
   • In test/multi_node_test.py under MultiNodeTest (which really should be called MultiDriverTest) it would be good to add a test that creates a named actor from one driver and then uses it from another.
   • We should add a test that attempts to get a named actor on a name that was never created and verify that a reasonable exception is raised.

4. Verify that we raise a good error message when no named actor exists.

cc @ericl @richardliaw

[heyucongtom]

Thank you for your reply! Would deal with that soon today.

[robertnishihara]

One more case we should handle is the following. If someone attempts to create an actor with a certain name, but an actor with that name has already been created, we should raise an exception.

[robertnishihara]

Replaced by #2129.