Terminating Actors#

Actor processes will be terminated automatically when all copies of the actor handle have gone out of scope in Python, or if the original creator process dies.

Note that automatic termination of actors is not yet supported in Java or C++.

Manual termination via an actor handle#

In most cases, Ray will automatically terminate actors that have gone out of scope, but you may sometimes need to terminate an actor forcefully. This should be reserved for cases where an actor is unexpectedly hanging or leaking resources, and for detached actors, which must be manually destroyed.

Python

import ray

@ray.remote
class Actor:
    pass

actor_handle = Actor.remote()

ray.kill(actor_handle)
# This will not go through the normal Python sys.exit
# teardown logic, so any exit handlers installed in
# the actor using ``atexit`` will not be called.

Java

actorHandle.kill();
// This will not go through the normal Java System.exit teardown logic, so any
// shutdown hooks installed in the actor using ``Runtime.addShutdownHook(...)`` will
// not be called.

C++

actor_handle.Kill();
// This will not go through the normal C++ std::exit
// teardown logic, so any exit handlers installed in
// the actor using ``std::atexit`` will not be called.

This will cause the actor to immediately exit its process, causing any current, pending, and future tasks to fail with a RayActorError. If you would like Ray to automatically restart the actor, make sure to set a nonzero max_restarts in the @ray.remote options for the actor, then pass the flag no_restart=False to ray.kill.

For named and detached actors, calling ray.kill on an actor handle destroys the actor and allow the name to be reused.

Use ray list actors --detail from State API to see the death cause of dead actors:

# This API is only available when you download Ray via `pip install "ray[default]"`
ray list actors --detail

---
-   actor_id: e8702085880657b355bf7ef001000000
    class_name: Actor
    state: DEAD
    job_id: '01000000'
    name: ''
    node_id: null
    pid: 0
    ray_namespace: dbab546b-7ce5-4cbb-96f1-d0f64588ae60
    serialized_runtime_env: '{}'
    required_resources: {}
    death_cause:
        actor_died_error_context: # <---- You could see the error message w.r.t why the actor exits.
            error_message: The actor is dead because `ray.kill` killed it.
            owner_id: 01000000ffffffffffffffffffffffffffffffffffffffffffffffff
            owner_ip_address: 127.0.0.1
            ray_namespace: dbab546b-7ce5-4cbb-96f1-d0f64588ae60
            class_name: Actor
            actor_id: e8702085880657b355bf7ef001000000
            never_started: true
            node_ip_address: ''
            pid: 0
            name: ''
    is_detached: false
    placement_group_id: null
    repr_name: ''

Manual termination within the actor#

If necessary, you can manually terminate an actor from within one of the actor methods. This will kill the actor process and release resources associated/assigned to the actor.

Python

@ray.remote
class Actor:
    def exit(self):
        ray.actor.exit_actor()

actor = Actor.remote()
actor.exit.remote()

This approach should generally not be necessary as actors are automatically garbage collected. The ObjectRef resulting from the task can be waited on to wait for the actor to exit (calling ray.get() on it will raise a RayActorError).

Java

Ray.exitActor();

Garbage collection for actors haven’t been implemented yet, so this is currently the only way to terminate an actor gracefully. The ObjectRef resulting from the task can be waited on to wait for the actor to exit (calling ObjectRef::get on it will throw a RayActorException).

C++

ray::ExitActor();

Note that this method of termination waits until any previously submitted tasks finish executing and then exits the process gracefully with sys.exit.

You could see the actor is dead as a result of the user’s exit_actor() call:

# This API is only available when you download Ray via `pip install "ray[default]"`
ray list actors --detail

---
-   actor_id: 070eb5f0c9194b851bb1cf1602000000
    class_name: Actor
    state: DEAD
    job_id: '02000000'
    name: ''
    node_id: 47ccba54e3ea71bac244c015d680e202f187fbbd2f60066174a11ced
    pid: 47978
    ray_namespace: 18898403-dda0-485a-9c11-e9f94dffcbed
    serialized_runtime_env: '{}'
    required_resources: {}
    death_cause:
        actor_died_error_context:
            error_message: 'The actor is dead because its worker process has died.
                Worker exit type: INTENDED_USER_EXIT Worker exit detail: Worker exits
                by an user request. exit_actor() is called.'
            owner_id: 02000000ffffffffffffffffffffffffffffffffffffffffffffffff
            owner_ip_address: 127.0.0.1
            node_ip_address: 127.0.0.1
            pid: 47978
            ray_namespace: 18898403-dda0-485a-9c11-e9f94dffcbed
            class_name: Actor
            actor_id: 070eb5f0c9194b851bb1cf1602000000
            name: ''
            never_started: false
    is_detached: false
    placement_group_id: null
    repr_name: ''