Understanding Akka actor framework

Table of Contents

• Actor
• Dispatcher

Actor

An actor is the fundamental unit in the actor model—a computational entity that encapsulates state and behavior. Each actor has a private internal state and a mailbox to receive messages. When an actor processes a message, it can:

Communication between actors is asynchronous. Messages are placed into the actor's mailbox and processed sequentially. To achieve parallelism, multiple actors must be created and distributed accordingly. A collection of actors forms an actor system, and the overall application behavior emerges from the collaboration and message-passing between these actors.

Actors also follow a supervision model. When an actor spawns new actors, it becomes their supervisor. If a child actor fails, the supervisor decides how to handle the failure—by restarting it, ignoring the error, or escalating it to its own supervisor. This structure forms a supervision tree that provides a robust fault-tolerance mechanism, ensuring system resilience through hierarchical error handling.

Dispatcher

In Akka, the ActorSystem.dispatcher is responsible for managing how actors are scheduled and executed. It is the core engine that drives how messages are picked from mailboxes and processed by actors.

The dispatcher plays a critical role in the performance and responsiveness of an Akka system. Here's a breakdown of its main responsibilities:

Scheduling: The dispatcher picks an actor with pending messages in its mailbox, selects the next message, and assigns it to a thread for execution.

Thread Management: It manages a pool of threads (or uses a custom executor) and assigns tasks efficiently to optimize system throughput and resource utilization.

Configuration: Akka allows fine-tuned dispatcher configurations. You can define shared thread pools for groups of actors or assign a dedicated thread to a single actor using a pinned dispatcher.

Default Dispatcher: If no specific dispatcher is defined for an actor, it uses the default dispatcher provided by the ActorSystem, typically a fork-join or thread pool-based executor.

ExecutionContext Integration: Dispatchers also act as ExecutionContexts, meaning they can run asynchronous computations like Futures, enabling seamless integration with other async operations in Akka.