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Understanding actor concurrency, Part 1: Actors in Erlang
A new way to think about structuring concurrent applications
Page 6 of 6
Because of Erlang's focus on messaging, it seems to be a good fit for these kinds of systems. The ejabberd daemon is a highly-regarded Jabber/XMPP implementation that has been used in some large implementations such as jabber.org. Similarly, RabbitMQ is a high-performance AMQP server written in Erlang that can reportedly handle 400,000 messages per second.
Several so-called Web 2.0 companies have also had success building parts of their systems in Erlang. Facebook Chat uses a combination of C++ and an Erlang Web server to handle 70,000 concurrent users. Delicious 2.0 relaunched in 2008 and is primarily based on C++ but uses Erlang in several subsystems such as data migrations, rolling migrations, and algorithmic analysis. CouchDB, which has gotten a lot of press lately as a document-centric Web database, is written entirely in Erlang. Reportedly the Amazon SimpleDB service also uses Erlang internally.
In short, Erlang can boast a number of high-profile successes, and these users consistently tout Erlang's strengths for writing distributed, concurrent, fault-tolerant software. It's clear that the actor model is a valid alternative for addressing concurrency without shared state and locks.
You may be thinking, "This sounds cool, but there's no way my manager will let me start deploying software in Erlang." Don't you wish you could use the actor model on the JVM? Well, stay tuned for Part 2.
About the author
Alex Miller is a tech lead at Terracotta Inc, the makers of the open-source Java clustering product Terracotta. Previously, Alex worked at BEA Systems on the AquaLogic product line and was Chief Architect at MetaMatrix. Alex blogs at Pure Danger Tech and speaks at user groups, conferences, and the No Fluff Just Stuff tour. He has an enduring love for his wife and three children, music, and nachos.
Read more about Core Java in JavaWorld's Core Java section.
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More from JavaWorld
Resources
- Hardware trends:
- Concurrent applications no longer get a free ride from increasing chip speeds, according to "The Free Lunch is Over: A Fundamental Turn Toward Concurrency in Software" (Herb Sutter, Dr. Dobb's Journal, March 2005).
- Read Wikipedia's entries on Amdahl's Law, CPU speed trends, and Transistor count trends.
- Background on the actor model:
- Check out Wikipedia's entries on the Actor model and its history.
- The c2 wiki has an entry on the Actors model.
- The actor model has its foundations in the classic book Communicating Sequential Processes (C.A.R. Hoare, Prentice Hall International, 1985), now available in a free electronic version.
- More information on Erlang and actors in Erlang:
- The erlang.org site hosts the Erlang source code and supporting libraries.
- Read about "Concurrency in Erlang & Scala: The Actor Model" (Ruben Vermeersch, January 2009).
- Erlang Message Passing Concurrency, For the Win and Concurrency Oriented Programming in Erlang are both slide presentations.
- Watch video of a presentation by Andre Pang on Concurrency and Erlang
- "Concurrent programming with Erlang" (Bruce Tate, IBM developerWorks, April 2006) explores Erlang and compares its concurrency features to Java's.
- Erlang success stories:
- Facebook engineer Eugene Letuchy discusses Erlang at Facebook.
- Nick Gerakines and Mark Zweifel talk about developing with Erlang at Yahoo in Erlang at Yahoo.
- Apache vs. YAWS compares the Apache HTTP server's performance to that of Yaws, a Web server written entirely in Erlang.
- Multicore and concurrency topics on JavaWorld
- "Multicore processing for client-side Java applications" (Kirill Grouchnikov, September 2007) introduces a parallel programming implementation for collection sorting.
- "Hyper-threaded Java" (Randall Scarberry, November 2006) introduces the Java concurrency API.
- "Better monitors for Java" (Theodore S. Norvell, October 2007) introduces a Hoare-style monitor package for multithreaded programming in Java.
- "Java.next: Immutability" (Stuart Halloway, JW Blogs, September 2008) concludes a series of blog posts looking at the future of concurrent programming on the JVM.
- Ted Neward on why Java developers need Scala (JW Podcast, June 2008).
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