The actor model is a novel approach to writing concurrent software. It is based on the concept of small computational units communicating through asynchronous message passing, thus allowing concurrency and scalability while negating a lot of the problems of concurrent programming. Though the actor model got some adoption with the Erlang language and the Akka framework, it remained a rather niche approach and has not become a commonly used practice. But this may be changing now with the introduction of “Virtual Actors” - a new abstraction for writing distributed applications. This abstraction was introduced with the Orleans framework by Microsoft and adopted to Java by EA with their Orbit framework. This talk will include a short introduction to the actor model. We will then explore the Virtual Actors model, how it’s different from the classic model, and why it makes distributed application programming a lot simpler.

1. Rotem Hermon
@margolis20
Actors, Evolved
#dmconf15

2. Not THAT
kind of actors.

3. Multithreading

4. The problem with multi-threaded concurrency
• Shared memory and state
• Race conditions
• Locks and deadlocks
• Blocking calls
• Hard to understand and maintain
• Not easily distributed

5. Threads are EVIL!

6. There has to be a
better way…

7. The Actor Model
• Formalized in 1973 (Carl Hewitt)
• Concurrency by Message Passing
• Avoids problems of threading and locking

8. An Actor, Carl Hewitt definition
• The fundamental unit of computation that embodies:
• Processing
• Storage
• Communication
• An actor can:
• Create new Actors
• Send messages to Actors
• Designate how to handle the next message

9. An Actor
• Lightweight
• Never shares state
• Communicates through asynchronous messages
• Mailbox buffers incoming messages
• Processes one message at a time

10. An Actor
• Lightweight
• Never shares state
• Communicates through asynchronous messages
• Mailbox buffers incoming messages
• Processes one message at a time
• Single threaded

11. The Actor Model
• Higher abstraction level
• Simpler concurrent programming model
• Write single-threaded code (easier to understand)
• Concurrency and scale via actor instances
• Maximizes CPU utilization
• Easy to distribute

12. (Actors are actually
Nanoservices)

13. Leading Classic Actor Implementations
• Erlang
• Developed in the late 90s by Ericsson for HA telecom exchanges
• Actors are a core language feature
• Akka
• A JVM (Scala/Java) Actor framework library
• Started by Jonas Bonér in 2009
• Became part of Typesafe (company behind Scala)
• .NET port in progress since 2014 (Akka.NET)

14. Akka Fundamentals
Actors Contains:
• State
• Behavior
• An actor can “switch” its internal behavior
• Mailbox
• Several types of mailboxes
• Children
• An actor is “responsible” for other actors it creates - Supervisor

15. Akka Fundamentals
• Actors form an hierarchical structure

16. Akka Fundamentals
• Actor Lifecycle
• Actors needs to be created
and destroyed
• Fault handling is done via
supervision hierarchies
• Several available supervision
strategies

17. Akka Fundamentals
• Location Transparency
• Actors can be created remotely
• Actors are called via an actor reference, same for local and remote
• Akka Clustering for additional features

18. Akka Fundamentals
• Dispatchers
• Schedules the message delivery to actors (code execution)
• Can be shared across actors
• Several types of dispatchers and configurations

19. Akka Fundamentals
• Routers
• An actor that routes messages to other actors
• Several routing strategies

21. There has to be a
better way…

22. Virtual Actors
• A simplified Actors implementation with a higher abstraction
level
• Introduced by Microsoft Research – Project Orleans
• Goals:
• Make distributed application programming easier
• Prefer developer productivity and transparent scalability
• “A programming model and runtime for building cloud native
services”

23. Virtual Actors
• A Virtual Actor:
always exists
and
never fails

24. Virtual Actors
Actor types:
• Worker
• An auto-scaling processing unit – multiple instances created by
framework as needed

25. Virtual Actors
Actor types:
• Single Activation
• Guaranteed to have a single active instance in the cluster

26. Virtual Actors
Actor types:
• Single Activation
• Guaranteed to have a single active instance in the cluster
• A Stateful application middle-tier!

27. Virtual Actor Framework
• A runtime providing virtual “actor space”, analogues to
virtual memory
• Handles Actor placement, activation and GC when needed
• Balances resources across the cluster, provides elastic
scalability

28. Virtual Actor Framework
Node
Node
Node
Node
Node
Node

29. Virtual Actor Framework

30. Virtual Actor Framework
User
#21
User
#73
Game
#254 Game
#33

31. Virtual Actor Framework
Auto Scaling

32. Virtual Actor Framework
Auto Scaling

33. Virtual Actor Framework
Auto Scaling

34. Virtual Actor Framework
Auto Scaling

35. Virtual Actor Framework
Failure Recovery

36. Virtual Actor Framework
Failure Recovery

37. Virtual Actor Framework
Failure Recovery

38. Simplified Programming Model
• An Actor is a class, implementing an interface with
asynchronous methods
• The caller of an Actor uses the actor interface via a proxy
• Messaging is transparent and handled by the runtime.
Programmers deal with interfaces and methods

39. Simplified Programming Model

40. Simplified Programming Model

41. Use Cases
• Stateful Services
• Smart Cache
• Modeling objects at scale (games, IoT)
• Protecting resources / Aggregations

42. Virtual Actor Implementations
• Orleans (.NET)
• Started by Microsoft Research in 2011, in production since 2012
• Service high scale services on Azure (Halo 4 cloud services)
• Open sourced in January 2015, active community
• Orbit (Java)
• Developed by BioWare (division of Electronic Arts)
• Inspired by Orleans (“not a port but a re-write”)
• Powering online game services
• Azure Service Fabric (Reliable Actors)

44. Virtual Actors (Orleans)
• Focus on simplicity and
productivity
• Implicit lifecycle, handled by
runtime
• Automatic clustering and load
balancing
• No hierarchy, all actors are
directly accessible
• Actor interfaces are regular
interfaces (standard OOP)
Classic Actors (Akka)
• Provide full power (exposing
complexity)
• Explicit lifecycle, handled by
programmer
• Clustering and load balancing
available (but more complex)
• Actors are hierarchical and
accessible by path
• Actors communicates via explicit
message classes

45. Virtual Actors (Orleans)
Choose if:
• Need a simple model for
distributed applications
• Automatic and straightforward
scaling
• Development team with varied
levels of experience
Classic Actors (Akka)
Choose if:
• Need full power – complex
topologies, fine grain failure
handling, dynamic changing of
behavior, explicit message
handling
• Experienced development team

46. Thank You!
Rotem Hermon
@margolis20
VP Architecture @ Gigya