Module registry 

Thread-local actor registry with lifetime-safe access guards.

Design

The actor registry stores actors in thread-local storage and provides access via ActorRef<T> guards. This design addresses several constraints:

• Use-after-free prevention: ActorRef holds an Rc clone, keeping the actor alive even if removed from the registry while the guard exists.
• Re-entrant callbacks: Message handlers frequently call back into the registry to access other actors. Unlike RefCell-style borrow tracking, multiple ActorRef guards can exist simultaneously without panicking.
• No 'static lifetime lie: Previous designs returned &'static mut T, which didn’t reflect actual validity. The guard-based approach ties the borrow to the guard’s lifetime.

Limitations

• Aliasing not prevented: Two guards can exist for the same actor simultaneously, allowing aliased mutable access. This is technically undefined behavior but is required by the re-entrant callback pattern. Higher-level discipline is required.
• Thread-local only: Guards must not be sent across threads.

Structs

ActorRef

A guard providing mutable access to an actor.

ActorRegistry

Registry for storing actors.

Functions

actor_count

Returns the number of registered actors.

actor_exists

Checks if an actor with the id exists in the registry.

get_actor

get_actor_registry

get_actor_unchecked

Returns a guard providing mutable access to the registered actor of type T.

register_actor

Registers an actor.

try_get_actor_unchecked

Attempts to get a guard providing mutable access to the registered actor.