JavaOne 2009 from my perspective

It has been a week since I got back to Sweden after my trip to San Francisco for what I am sad to say was my worst JavaOne so far. Don't get me wrong, JavaOne was good. There were a lot of good sessions, and as always it was nice to meet my friends in the community. But the two previous years were better. Much of it can be blamed on the economy. And the rest can be blamed on me. To a large extent the reason I didn't get the JavaOne experience I would have liked to was because I was too busy. I had a deadline waiting for me on a project at work when I got home, and had to work quite a lot during my JavaOne week. But the fact stands, JavaOne was a lot smaller this year, only about 9000 attendees, and you notice that.

These are the highlight from the sessions I attended at CommunityOne and then JavaOne:

• Beyond impossible: How JRuby has evolved the Java Platform by Charles Nutter. Charles is a kickass developer and has become a really good speaker as well. It's amazing what he has done with JRuby, and this talk was a summary of the highlights from that. Including things such as the fact that the JRuby team have implemented their own regular expressions library and posix layer for doing system calls from the JVM. All of which adds up to making JRuby the fastest complete implementation of Ruby.
• Return of the Puzzlers: Schlock and Awe by Joshua Bloch and Neal Gafter. All I can say is that all the digging around on the low levels of the JVM that I have done has payed off, I had the right answer for 7 out of 7 Puzzlers, much better than the first time I attended a Java Puzzlers session.
• Toward a Renaissance VM by John Rose. John talked about Invokedynamic and Method Handles. It was all familiar stuff, but a good introduction for the odd people who do not spend most of their time implementing languages for the JVM.
• Meet the Java Posse. I've known the guys of the Java Posse for a while, but this is the first time that I was not doing something completely different during their BoF at JavaOne. Not much to say, listen to the podcast.
• JSR 292 Cookbook mostly by John Rose. This is what I think was the eye opening session about Invokedynamic and MethodHandles for most people. Hands on examples, showing all of the JSR 292 goodness in action. More people should have attended. Everyone not familiar with JSR 292 on beforehand that I talked to after the session realized that it is useful for far more things than just implementing languages.
• How to write a distributed garbage collector by Ari Zilka and Saravanan Subbiah from Terracotta. This was the last session of the last day and probably the best session at JavaOne this year. Ari and Saravanan talked about how garbage is detected and collected in the distributed environment that is Terracotta when all references to an object could be from a different node. Very interesting stuff, I need to take a deeper look at Terracotta at some point soon.

There were also some noteworthy sessions that I missed while I was working:

• Java Platform Concurrency Gotchas by Alex Miller. A smart guy talking about interesting stuff, too bad I missed that one.
• The Ghost in the Virtual Machine: A Reference to References by Bob Lee. I have a feeling that there are still a few things that can be done using Weak, Soft and Phantom references, that I don't know about yet. I would also have liked to hear what he had to say about Ephemerons. Are they coming to the JVM soon btw?

Then there are the two presentations I gave. A BoF on Interface Injection entitled "Language Interoperability on the JVM Made Simple" and a Technical session entitled "Exploiting Concurrency with Dynamic Languages".

Language Interoperability on the JVM Made Simple

Since this was a Birds of a Feather session I divided it into two main sections: The first half I gave an introduction to interface injection, the status of the implementation and some ideas as to what you can do with it. The second half of the session was spent on discussions about what people want from interface injection, how they want to use it and how it should work.

The short summary is:

• I have implemented the injection mechanism.
• I have designed a proposal API for how the injection process should work on the Java level.
• I have wired up interface injection to invokeinterface, there are still a few more places that would need to be able to call the injection mechanism.
• The Reflection API for injected interfaces is still unspecified.
• A lot of people want only explicit injection of interfaces. That is for interfaces to only be injected when an inject() method is invoked in some API. This can be emulated by setting a flag in the injector when this method is invoked, and unset it at the end of this method.
• There was also some concern about the fact that methods on an injected interface gets implemented automatically by methods with the same name and signature that exist in the target class. I agree that it would be better if interface implementations could be separate for each interface in the class file format. But I don't think this problem will be as big as people might fear since the methods have to match exactly on return type as well as parameter types.

The staff in room 102/103 was really helpful, they offered to rearrange the chairs and tables to better host the discussion I wanted to encourage about interface injection. This can not be said about the staff in room 104 where I had my second presentation. Although being very friendly, they were not very professional. First of all my session was supposed to be recorded, but after the session I was informed that they had forgotten to record the slides, and transitions. I gave them my slides on a memory stick and they said that they were going to match it to the best of their ability then send it to me for review, I have yet to hear from them. On top of that some members of the staff were constantly talking behind the stage, leaving me very distracted. Highly unprofessional of them. I was so surprised by this that I didn't even tell them to shut up.

Exploiting Concurrency with Dynamic Languages

I spent too much time at JavaOne preparing for my second talk about how languages other than the Java Programming Language on the JVM lend themselves better to expressing concurrent programs. I really should have prepared the talk much more before I left Sweden. I believe that I could have done a better presentation. The staff in the room is to blame to a large extent for the fact that I didn't feel satisfied by my performance, but half of the blame is on me. Although, the few reviews that I've heard have been good. Basically that the topic was good, that I had interesting ideas and made good points, but that it was too short, although with good Q&A. A fair review in my opinion, it will be interesting to see the review cards when they get sent out to the speakers.

What is more interesting however is what I was able to conclude in my talk. It should come as a surprise to no one that closures make it much easier to express concurrent programs, and to encapsulate best practices and patterns in libraries. Other higher level constructs are helpful here as well, please have a look at my slides for reference. I also found that Jython has a lot of room for improvement, but more on that in another blog post.