[Core] Decrement lineage ref count of an actor when the actor task return object reference is deleted

[jjyao]

Why are these changes needed?

std::vector<rpc::ObjectReference> TaskManager::AddPendingTask(..) {
   if (spec.IsActorTask()) {
    const auto actor_creation_return_id = spec.ActorCreationDummyObjectId();
    task_deps.push_back(actor_creation_return_id);
   }
}

When an actor method is called, the actor lineage ref count increments as it's seen as a dependency of the actor task.

However, when we know that the actor task won't be retried (i.e. the return object is out of scope), we forget to decrement the actor lineage ref count.

This PR fixes this so that we have a matching pair of increment and decrement.

Also removed some dead code.

Related issue number

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  • This PR is not tested :(

[jjyao]

Actual fix

[stephanie-wang]

Was this just unused?

[jjyao]

Yes, dead code

[farmer00317558]

@jjyao Hello, I would like to ask, what phenomenon will this issue cause? Will it only affect the scenario where the Actor fails and retries? Or could it potentially lead to memory leaks during the execution of the Actor tasks?

I want to determine whether an upgrade to the latest version is necessary.

Thanks.