hot spot optimization techniques?

[stephan schweitzer]

Hi,
I am searching for some information about the techniques used
in the hotspot vm. No general informations. What I really
need are informations about the techniques used in the virtual
machine and which preconditions must be fulfilled so that the
techniques are applicable.
thanks stephan

[Ilja Preuss]

What do you need this for? I do ask because this is a quite general (and possibly hard to answer) question, so knowing more about your needs might help us helping you...

[Ernest Friedman-Hill]

Note that if you license the Java source from Sun (you can do this at no cost), then you can see the HotSpot code for yourself.

[Howard Kushner]

Hello Stephan,
Do you google? A quick google turns up:

http://java.sun.com/products/hotspot/whitepaper.html

http://www.javaworld.com/javaworld/jw-03-1998/jw-03-hotspot.html

I came across a JavaOne presentation once, but I can't seem to find it right now.
Hope this help.
Regards,

[stephan schweitzer]

Originally posted by Ilja Preuss:
What do you need this for? I do ask because this is a quite general (and possibly hard to answer) question, so knowing more about your needs might help us helping you...

Thanks for your reply. Here are my questions about the optimization techniques:
[list]First Problem:
It seems to me that at least in the client version of the VM the following two source codes have a different performance (Source 2 seems to be better).
Source 1:

[/list]
class A 
{
  Iterator iterator()
  {
    return new Iterator()
    {
     ...
    };
  }
}
class B 
{
  public void method(A a) 
  {
    Iterator i = a.iterator();
 
    ...
  }
}

Source 2:

class A 
{
  public static class Iter implements Iterator
  {
  ...
  }
  Iter iterator()
  {
    return new Iter();
  }
}
class B
{
  public void method(A a) 
  {
    A.Iter i = a.iterator();
 
    ...
  }
}

Am I right or completely wrong? If I am right does this depend on the
method inlining technique used in the VM?
Anyway: Which methods are inlined and when are they inlined?

Second Problem:
I have read that it is not advicable to use object pools with the

Java Hotspot VM. But I have used an iterator pool in my application
and the performance has increased by 10 percent. To be more precise the
code looks like this:

class IteratorReleasable implements Iterator
{
   private static IteratorReleasable buffer[] = new IteratorReleasable[20];
   private static int count = 0;
   ...
   public static ReleasableInstance instance(...)
   {
      ReleasableInstance inst;
      ...
     
      if (count > 0)
        inst = buffer[--count];
      else inst = new ReleasableIterator();
   }
   public releaseInstance()
   {
     if (count < 20)
       buffer[count++] = this;
   }
}

and the classes which uses this iterator looks like this:

class MyObject
{
  ...
  public ReleasableIterator iteratorReleasable()
  {
    return ReleasableIterator.create(...); 
  }
  ...
}
class PreorderIterator
{
  private ReleasableIterator[] buffer;
  private int cursor;
  
  ...
  protected Object nextStep()
  {
    while (cursor >= 0)
      if (buffer[cursor].hasNext())    
      {
        MyObject current = (MyObject) buffer[cursor].next();
        buffer[++cursor] = current.iteratorReleasable();
        ...
      }
      else 
      {
        buffer[cursor].releaseInstance();
        buffer[cursor--] = null; 
      }
    return null;
  }
  
  public void releaseInstance()
  {
    while (cursor >= 0)
      buffer[cursor--].releaseInstance();
  }
}

Question: Is the increased performance dued to the not local life-time of the iterator objects or is this iterator pool also applicable to normal
for-loops?

Third problem:

Because the cast-operators and the instanceof-operator may also
decrease the performance I was wondering if there exists an optimization
technique to optimistically eliminate these operators?

Thanks Stephan
[ October 27, 2003: Message edited by: stephan schweitzer ]