Thursday, July 23 2009, which was Day 4 for me at OSCON 2009, started with keynote by Kirrily Robert, where she she deplored acceptance of women in open source projects. This was followed by lame keynote by Tony Hey from Microsoft, where the presenter showed bits of open source contributions by Microsoft. Finally, Simon Wardley talked about cloud computing that was pretty entertaining. I then proceeded to attend talk on JRuby on Google App Engine, which didn’t quite kept up to its name and a lot of talk focused on persistence. I attended talk on Eucalyptus, which is an open source project for building private EC2 based cloud. This was sort of marketing talk, but I got a couple of things out such as how Amazon throttles network traffic within a datacenter to 500mb/sec and between zones to 200mb/sec.
I then attended A Survey of Concurrency Constructs, which presented common constructs for concurrency such as locks, transactional shared memory, message passing, dataflow, futures, i-structures, etc. I liked dataflow due to its deterministic nature, but is difficult to implement. I-structures is also interesting, but is non-deterministic and requires ports that make it similar to actors. I also like Linda as it can simulate dataflow, actors and CSP. Finally, message-passing and actors model are poplar these days due to their implementation in Erlang and Scala languages. Ted mentioned how most of the solutions are 20-30 years old, you can read history of most of these solutions from his slides. This was bleak talk as none of the options presented satisfactory option, though his bias was towards JVM based technology and he was impressed with Jonas Boner’s work on AKKA.
Next, I attended talk on Clojure: Functional Concurrency for the JVM, which described functional nature of Clojure and brief overview of its features and syntax. I found calling Java code from Clojure a little verbose especially when you are using method chaining, e.g.
factory.newSaxParser().parse(src, handler)
becomes
(.. factory new SaxParser (parse src handler))
Another interesting features of Clojure are its implementation of persistent datastorage and lazy evaluation. Finally, Clojure supports transactional memory for building concurrent applications but there is a little emperical data on its performance and usability. In fact, Ted Sueng mentioned porting some of open source applications to use transactional memory resulted in deadlocks so I am waiting for a little more evidence.
Next, I attended talk on Cassandra: Open Source Bigtable + Dynamo, which is another DHT similar to
Dynomite, Redis, Tokyo Tyrant, Voldemort, HBase, etc. Cassendra is an implementation of DHT based on Amazon Dynamo paper and supports consistent hashing, gossip, failure detection, cluster state, partitioning and replication. I liked the fact that there is no single master as in BigTable so it is easier to scale and uses bloomfilter to keep index of keys. You can read more on its features from the slides.
Last session I attended was “Design Patterns” in Dynamic Languages, where Neal Ford showed how GOF design patterns were created to overcome deficiencies of C++ and he described how dynamic languages like Ruby and Groovy make it trivial to use these patterns without all the ceremony. Neal showed how method_missing can be used to implement builder pattern (though, I prefer not to use method_missing). He showed how each method on array is easier than iterator, how closures can be used to implement command and strategy patterns. Neal then showed, how internel DSLs can be used to implement interpreter pattern. Other examples included decorator and adapter patterns that used invokeMethod feature of Groovy to delegate invocation. Finally, he showed using null object pattern for consistent interface and aridifier to keep your code DRY. You can read more from his slides.