Sunday Sep 30, 2012

The Java Specialist: An Interview with Java Champion Heinz Kabutz

Dr. Heinz Kabutz is well known for his Java Specialists’ Newsletter, initiated in November 2000, where he displays his acute grasp of the intricacies of the Java platform for an estimated 70,000 readers; for his work as a consultant; and for his workshops and trainings at his home on the Island of Crete where he has lived since 2006 -- where he is known to curl up on the beach with his laptop to hack away, in between dips in the Mediterranean.

Kabutz was born of German parents and raised in Cape Town, South Africa, where he developed a love of programming in junior high school through his explorations on a ZX Spectrum computer. He received a B.S. from the University of Cape Town, and at 25, a Ph.D., both in computer science.

He will be leading a two-hour hands-on lab session, HOL6500 – “Finding and Solving Java Deadlocks,” at this year’s JavaOne that will explore what causes deadlocks and how to solve them.

Q: Tell us about your JavaOne plans.

A: I am arriving on Sunday evening and have just one hands-on-lab to do on Monday morning. This is the first time that a non-Oracle team is doing a HOL at JavaOne under Oracle's stewardship and we are all a bit nervous about how it will turn out. Oracle has been immensely helpful in getting us set up. I have a great team helping me: Kirk Pepperdine, Dario Laverde, Benjamin Evans and Martijn Verburg from jClarity, Nathan Reynolds from Oracle, Henri Tremblay of OCTO Technology and Jeff Genender of Savoir Technologies.

Monday will be hard work, but after that, I will hopefully get to network with fellow Java experts, attend interesting sessions and just enjoy San Francisco. Oh, and my kids have already given me a shopping list of things to get, like a GoPro Hero 2 dive housing for shooting those nice videos of Crete. (That's me at the beginning diving down.)

Q: What sessions are you attending that we should know about?

A: Sometimes the most unusual sessions are the best. I avoid the "big names". They often are spread too thin with all their sessions, which makes it difficult for them to deliver what I would consider deep content. I also avoid entertainers who might be good at presenting but who do not say that much.

In 2010, I attended a session by Vladimir Yaroslavskiy where he talked about sorting. Although he struggled to speak English, what he had to say was spectacular. There was hardly anybody in the room, having not heard of Vladimir before. To me that was the highlight of 2010. Funnily enough, he was supposed to speak with Joshua Bloch, but if you remember, Google cancelled. If Bloch has been there, the room would have been packed to capacity.

Q: Give us an update on the Java Specialists’ Newsletter.

A: The Java Specialists' Newsletter continues being read by an elite audience around the world. The apostrophe in the name is significant.  It is a newsletter for Java specialists. When I started it twelve years ago, I was trying to find non-obvious things in Java to write about. Things that would be interesting to an advanced audience.

As an April Fool's joke, I told my readers in Issue 44 that subscribing would remain free, but that they would have to pay US$5 to US$7 depending on their geographical location. I received quite a few angry emails from that one. I would have not earned that much from unsubscriptions. Most readers stay for a very long time.

After Oracle bought Sun, the Java community held its breath for about two years whilst Oracle was figuring out what to do with Java. For a while, we were quite concerned that there was not much progress shown by Oracle. My newsletter still continued, but it was quite difficult finding new things to write about. We have probably about 70,000 readers, which is quite a small number for a Java publication. However, our readers are the top in the Java industry. So I don't mind having "only" 70000 readers, as long as they are the top 0.7%.

Java concurrency is a very important topic that programmers think they should know about, but often neglect to fully understand. I continued writing about that and made some interesting discoveries. For example, in Issue 165, I showed how we can get thread starvation with the ReadWriteLock. This was a bug in Java 5, which was corrected in Java 6, but perhaps a bit too much. Whereas we could get starvation of writers in Java 5, in Java 6 we could now get starvation of readers. All of these interesting findings make their way into my courseware to help companies avoid these pitfalls.

Another interesting discovery was how polymorphism works in the Server HotSpot compiler in Issue 157 and Issue 158. HotSpot can inline methods from interfaces that have only one implementation class in the JVM. When a new subclass is instantiated and called for the first time, the JVM will undo the previous optimization and re-optimize differently.

Here is a little memory puzzle for your readers:

public class JavaMemoryPuzzle {
  private final int dataSize =
      (int) (Runtime.getRuntime().maxMemory() * 0.6);

  public void f() {
    {
      byte[] data = new byte[dataSize];
    }
    byte[] data2 = new byte[dataSize];
  }

  public static void main(String[] args) {
    JavaMemoryPuzzle jmp = new JavaMemoryPuzzle();
    jmp.f();
  }
}


When you run this you will always get an OutOfMemoryError, even though the local variable data is no longer visible outside of the code block.

So here comes the puzzle, that I'd like you to ponder a bit. If you very politely ask the VM to release memory, then you don't get an OutOfMemoryError:

public class JavaMemoryPuzzlePolite {
  private final int dataSize =
      (int) (Runtime.getRuntime().maxMemory() * 0.6);

  public void f() {
    {
      byte[] data = new byte[dataSize];
    }

    for(int i=0; i<10; i++) {
      System.out.println("Please be so kind and release memory");
    }
    byte[] data2 = new byte[dataSize];
  }

  public static void main(String[] args) {
    JavaMemoryPuzzlePolite jmp = new JavaMemoryPuzzlePolite();
    jmp.f();
    System.out.println("No OutOfMemoryError");
  }
}


Why does this work? When I published this in my newsletter, I received over 400 emails from excited readers around the world, most of whom sent me the wrong explanation. After the 300th wrong answer, my replies became unfortunately a bit curt. Have a look at Issue 174 for a detailed explanation, but before you do, put on your thinking caps and try to figure it out yourself.

Q: What do you think Java developers should know that they currently do not know?

A: They should definitely get to know more about concurrency. It is a tough subject that most programmers try to avoid. Unfortunately we do come in contact with it. And when we do, we need to know how to protect ourselves and how to solve tricky system errors.

Knowing your IDE is also useful. Most IDEs have a ton of shortcuts, which can make you a lot more productive in moving code around. Another thing that is useful is being able to read GC logs. Kirk Pepperdine has a great talk at JavaOne that I can recommend if you want to learn more. It's this: CON5405 – “Are Your Garbage Collection Logs Speaking to You?”

Q: What are you looking forward to in Java 8?

A: I'm quite excited about lambdas, though I must confess that I have not studied them in detail yet. Maurice Naftalin's Lambda FAQ is quite a good start to document what you can do with them. I'm looking forward to finding all the interesting bugs that we will now get due to lambdas obscuring what is really going on underneath, just like we had with generics.

I am quite impressed with what the team at Oracle did with OpenJDK's performance. A lot of the benchmarks now run faster.

Hopefully Java 8 will come with JSR 310, the Date and Time API. It still boggles my mind that such an important API has been left out in the cold for so long.

What I am not looking forward to is losing perm space. Even though some systems run out of perm space, at least the problem is contained and they usually manage to work around it. In most cases, this is due to a memory leak in that region of memory. Once they bundle perm space with the old generation, I predict that memory leaks in perm space will be harder to find. More contracts for us, but also more pain for our customers.

Originally published on blogs.oracle.com/javaone.

Talking JavaOne with Rock Star Kirk Pepperdine

Kirk Pepperdine is not only a JavaOne Rock Star but a Java Champion and a highly regarded expert in Java performance tuning who works as a consultant, educator, and author. He is the principal consultant at Kodewerk Ltd. He speaks frequently at conferences and co-authored the Ant Developer's Handbook. In the rapidly shifting world of information technology, Pepperdine, as much as anyone, keeps up with what's happening with Java performance tuning.

Pepperdine will participate in the following sessions:

  • CON5405 - Are Your Garbage Collection Logs Speaking to You?
  • BOF6540 - Java Champions and JUG Leaders Meet Oracle Executives (with Jeff Genender, Mattias Karlsson, Henrik Stahl, Georges Saab)
  • HOL6500 - Finding and Solving Java Deadlocks (with Heinz Kabutz, Ellen Kraffmiller Martijn Verburg, Jeff Genender, and Henri Tremblay)


I asked him what technological changes need to be taken into account in performance tuning. “The volume of data we're dealing with just seems to be getting bigger and bigger all the time,” observed Pepperdine. “A couple of years ago you'd never think of needing a heap that was 64g, but today there are deployments where the heap has grown to 256g and tomorrow there are plans for heaps that are even larger. Dealing with all that data simply requires more horse power and some very specialized techniques. In some cases, teams are trying to push hardware to the breaking point. Under those conditions, you need to be very clever just to get things to work -- let alone to get them to be fast. We are very quickly moving from a world where everything happens in a transaction to one where if you were to even consider using a transaction, you've lost."

When asked about the greatest misconceptions about performance tuning that he currently encounters, he said, “If you have a performance problem, you should start looking at code at the very least and for that extra step, whip out an execution profiler. I'm not going to say that I never use execution profilers or look at code. What I will say is that execution profilers are effective for a small subset of performance problems and code is literally the last thing you should look at.

And what is the most exciting thing happening in the world of Java today? “Interesting question because so many people would say that nothing exciting is happening in Java. Some might be disappointed that a few features have slipped in terms of scheduling. But I'd disagree with the first group and I'm not so concerned about the slippage because I still see a lot of exciting things happening. First, lambda will finally be with us and with lambda will come better ways.”

For JavaOne, he is proctoring for Heinz Kabutz's lab. “I'm actually looking forward to that more than I am to my own talk,” he remarked. “Heinz will be the third non-Sun/Oracle employee to present a lab and the first since Oracle began hosting JavaOne. He's got a great message. He's spent a ton of time making sure things are going to work, and we've got a great team of proctors to help out. After that, getting my talk done, the Java Champion's panel session and then kicking back and just meeting up and talking to some Java heads."

Finally, what should Java developers know that they currently do not know? “’Write Once, Run Everywhere’ is a great slogan and Java has come closer to that dream than any other technology stack that I've used. That said, different hardware bits work differently and as hard as we try, the JVM can't hide all the differences. Plus, if we are to get good performance we need to work with our hardware and not against it. All this implies that Java developers need to know more about the hardware they are deploying to.”

Originally published on blogs.oracle.com/javaone.

Talking JavaOne with Rock Star Charles Nutter

JavaOne Rock Stars, conceived in 2005, are the top rated speakers from the JavaOne Conference. They are awarded by their peers who through conference surveys recognize them for their outstanding sessions and speaking ability. Over the years many of the world’s leading Java developers have been so recognized.

We spoke with distinguished Rock Star, Charles Nutter.

A JRuby Update from Charles Nutter

Charles Nutter of Red Hat is well known as a lead developer of JRuby, a Ruby implementation of Java that is tightly integrated with Java to allow for the embedding of the interpreter into any Java application with full two-way access between the Java and the Ruby code.

Nutter is giving the following sessions at this year’s JavaOne:

  • CON7257 – “JVM Bytecode for Dummies (and the Rest of Us Too)”
  • CON7284 – “Implementing Ruby: The Long, Hard Road”
  • CON7263 – “JVM JIT for Dummies”
  • BOF6682 – “I’ve Got 99 Languages, but Java Ain’t One”
  • CON6575 – “Polyglot for Dummies” (Both with Thomas Enebo)


I asked Nutter, to give us the latest on JRuby. “JRuby seems to have hit a tipping point this past year,” he explained, “moving from ‘just another Ruby implementation’ to ‘the best Ruby implementation for X,’ where X may be performance, scaling, big data, stability, reliability, security, and a number of other features important for today's applications. We're currently wrapping up JRuby 1.7, which improves support for Ruby 1.9 APIs, solves a number of user issues and concurrency challenges, and utilizes invokedynamic to outperform all other Ruby implementations by a wide margin. JRuby just gets better and better.”

When asked what he thought about the rapid growth of alternative languages for the JVM, he replied, “I'm very intrigued by efforts to bring a high-performance JavaScript runtime to the JVM. There's really no reason the JVM couldn't be the fastest platform for running JavaScript with the right implementation, and I'm excited to see that happen.”

And what is Nutter working on currently? “Aside from JRuby 1.7 wrap-up,” he explained, “I'm helping the Hotspot developers investigate invokedynamic performance issues and test-driving their new invokedynamic code in Java 8. I'm also starting to explore ways to improve the general state of dynamic languages on the JVM using JRuby as a guide, and to help the JVM become a better platform for all kinds of languages.”

Originally published on blogs.oracle.com/javaone.


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