Rémi Forax's Blog

March 2008 Archives

Da Vinci runtime properties

After a week without any internet access point surfing the snow of the Alp, monday, my fingers was eager to touch the keyboard again. Why not finishing my prototype of runtime properties that use the Da Vinci VM (i really love that name).

One ugly thing of the draft v3 of the property spec, is a property object is implemented by a supplementary class generated by the compiler. This means the compiler must create one class by property and so bloat the application with lot of stupid code.
Ok, let's try to do better. No class at compile time means reflection or runtime time generation. In fact, it's not a real choice because reflection since 1.4.1 generates byte-code when a method is often called.

Da Vinci VM

The Da Vinci VM is the prototype implementation of JSR 292, a modified hotspot VM patched with new entry points that help to implement dynamic languages on top of the Java platform.
The first feature available, anonymous class (VM anonymous class not compiler one) allows you to create classes with some interesting features:

1. The class is not referenced by a classloader, so is GCed when there is no more instances of that class
2. Class is like an inner-class of an host class and therefore can access to members of the host class.
3. In order to create the class you can patch an existing class.

How property object works

If you are not familiar with properties, you can read an old blog entry.
A property object stands for a property and permit access to the value of the property of any instance of a Class that declare that property.
By example, the following code:

public class Bean {
  private int x;
  public int getX() {
    return x;
  }
  public void setX(int x) {
    this.x = x;
  }
  
  private String text;
  public String getText() {
    return text;
  }
  public void setText(String text) {
    this.text = text;
  }
    
  public static void main(String[] args) {
      Bean bean = new Bean();
      Property propertyX =
          Property.create(Bean.class, "x");
      bean.setX(0xCAFEBABE);
      System.out.printf(propertyX + " %x\n", propertyX.getValue(bean));
      
      Property propertyText = Property.create(Bean.class, "text");
      propertyText.setValue(bean, "hello property");
      System.out.println(bean.getText());
  }
}

prints:

  int Bean.x cafebabe
  hello property

How to test it ?

If your OS is Windows, Solaris or MacOs you have to compile the VM by yourself, sorry. On linux, you can download the binary of the jdk7 b24 if you haven't already it, download the following zip davinci.zip and unzip it in your JAVA_HOME/jre/lib/i386/
It adds a new server JVM lib named 'davinci' that can be launched using

  java -davinci ...
 

Now download the property runtime support property-runtime.jar, because it adds new classes and overrides some existing classes to the JDK you must prepend the jar to the bootclasspath.
To launch the example above:

  java -davinci -Xbootclasspath/p:property.jar Bean

The source of the property runtime support are available on the kijaro web site here: https://kijaro.dev.java.net/source/browse/kijaro/branches/properties/.

What's the next step, finish to write a new version of the property spec and provide a modified compiler according to that spec. I think i've solved most on the corner cases, so it's just a matter of time.
To be continued...
Rémi

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