"RuntimeError: Lost reference to actor" when using get_actor directly (i.e. not storing in a temporary variable)

I’ve encountered a super puzzling lifecycle/scope(?) issue that took a long time to debug so wanted to share and gather some ideas form the community.

In my project I have a very basic setup (like this) with an actor that I converted into a named one so I don’t need to pass it though multiple layers of my code.

Doing so triggered this bizarre error:

>>> ray.get_actor("CounterActor").read.remote()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "###\envs\ray\lib\site-packages\ray\actor.py", line 111, in remote
    return self._remote(args, kwargs)
  File "###\envs\ray\lib\site-packages\ray\actor.py", line 152, in _remote
    return invocation(args, kwargs)
  File "###\envs\ray\lib\site-packages\ray\actor.py", line 140, in invocation
    raise RuntimeError("Lost reference to actor")
RuntimeError: Lost reference to actor

I’ve confirmed that my agent is still around because the same one passed via a variable was still happily accepting calls, and even tried to use “detached” lifecycle, just in case, with no effect.

Turned out that as long as I do something like this:

f = ray.get_actor('CounterActor')

everything works, but converting this to a oneliner doesn’t


so if anyone has ideas on what is going on, I would be happy for any clues :slight_smile:

You can reproduce this issue without named actors as follows.

import ray


class Foo:
    def method(self):


The issue is tracked here Lost reference to actor exception for seemingly valid code. · Issue #6265 · ray-project/ray · GitHub.

Right now it’s a limitation that we have because the natural fix would introduce performance issues. There’s probably a good way to get around this though. We can probably also improve the error message in the short term.

Thank you, Robert!

I’ve missed the bug, which is embarrassing given that it’s the first Google result :slight_smile:

A better error message (or perhaps a warning in the docs) would be super helpful.

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