Actor Model

The actor model addresses the problem of organizing concurrent computation around isolated, addressable participants that communicate by message passing.

Cohesive Formulation

In Cohesive terms, actors are a realization pattern for addressable observers. An actor address gives other observers a delivery path to a receiving observer boundary.

Actors can also realize entities when actor identity aligns with entity identity and the actor hosts that entity's transition boundary.

Concurrent sends introduce reception-order indeterminacy: local transport, arbitration, and scheduling determine which message is interpreted next. The architecture is least sensitive to that order when handlers commute or form confluent paths. Fairness and delivery guarantees remain explicit runtime and protocol obligations.

In the Model

The practice is useful when correctness depends on serializing interpretation and commit for a subject. A mailbox turn can align observer, state access, transition interpretation, and commit.

Failure Modes

Actor serialization only proves transition correctness when the actor owns the transition boundary. A router, cache, shard, or forwarding actor may be addressable without being the semantic owner of the entity transition.

External References

Carl Hewitt, Actor Model of Computation: Scalable Robust Information Systems, 2010.