Actor Frameworks in .NET

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.

The actor model has been gaining adoption with the Erlang language and the Akka framework for JVM languages. But up until now, the .NET landscape lacked a truly robust and production ready actor framework. This changed dramatically this year with the release of not one but two open-source actor frameworks for .NET - Akka.NET (a port of the JVM Akka), and Orleans by Microsoft.

Presented at the Gigya Meetup group, June 2015.

Transcript

1. Rotem Hermon Actor Frameworks in .NET
2. Not THAT kind of actors.
3. The problem with multi-threaded concurrency • Shared memory and state • Locks and deadlocks • Race conditions • Blocking calls • Not easily distributed • Hard to understand and maintain
4. Threads are EVIL!
5. The Actor Model • Formalized in 1973 (Carl Hewitt) • Concurrency by Message Passing • Avoids problems of threading and locking
6. 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
7. An Actor • Lightweight • Never shares state • Communicates through asynchronous messages • Mailbox buffers incoming messages • Processes one message at a time • Single threaded
8. (Actors are actually Nanoservices)
9. The Actor Model • Simpler concurrent programming model • Higher abstraction level • Write single-threaded code (easier to understand) • Scale via actor instances • Maximize CPU utilization • Easy to distribute
10. Leading 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)
11. Actors in .NET Before 2015
12. Actors in .NET After 2015
13. Akka.NET MS Orleans
14. Akka.NET • A port of Akka to .NET. • Started Jan 2014 by Roger Alsing and Aaron Stannard • V1.0 – March 2015 • Some modules still in beta (Persistence, Clustering) • Founded Petabridge as an OS company behind Akka.NET (cooperating with Typesafe)
15. Akka.NET 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
16. Akka.NET Fundamentals • Actors form an hierarchical structure • Actor Lifecycle • Actors needs to be created and destroyed • Fault handling is done via supervision hierarchies • Several available supervision strategies • Location Transparency • Actors can be created remotely • Actors are called via an actor reference, same for local and remote • Akka Clustering for additional features
17. Akka.NET Fundamentals • Dispatchers • Schedules the message delivery to actors (code execution) • Can be shared across actors • Several types of dispatchers and configurations • Routers • An actor that routes messages to other actors • Several routing strategies
19. Orleans • A project by Microsoft Research • Started at 2011, in production since 2012 • Serving high scale Microsoft services on Azure (Halo 4 cloud services) • Open sourced in January 2015
20. Orleans • Project goal: a simplified Actors implementation to make distributed application programming easier • Prefer developer productivity and transparent scalability • Provides a higher abstraction level for actors: Virtual Actors
21. Orleans – Virtual Actors • A virtual “actor space”, analogues to virtual memory • An Actor “always exists” • Orleans runtime handles Actor placement, activation and GC when needed • Orleans balances resources across the cluster, provides elastic scalability
22. Orleans – Programming Model • An Actor is a .NET class, implementing an interface with asynchronous methods • Orleans uses code generation to create Actor proxies • The caller of an Actor uses the actor interface via the proxy • Messaging is transparent and handled by Orleans. Programmers deal with interfaces and methods
23. Orleans (Virtual Actors) • Focus on simplicity and productivity • Implicit lifecycle, handled by runtime • Automatic clustering and load balancing • Actor interfaces are regular interfaces (standard OOP) • No hierarchy, all actors are directly accessible Akka (Classic Actors) • Provide full power (exposing complexity) • Explicit lifecycle, handled by programmer • Clustering and load balancing available (but more complex) • Actors communicates via explicit message classes • Actors are ordered in hierarchies and accessible by path
25. Orleans or Akka ? • Choose Akka if • Need full power – complex topologies, fine grain failure handling, dynamic changing of behavior, explicit message handling • Experienced development team • Choose Orleans if • Need a simple model for distributed applications • Automatic and straightforward scaling • Development team with varied levels of experience
26. Thank You! We’re hiring! http://gigya.com/careers/ Rotem Hermon VP Architecture @ Gigya