# Tuesday, 30 May 2006
java.util.concurrent.atomic.AtomicInteger

Last week Tom Tromey posted a proposal for a patch to the Classpath patches mailing list for JSR-166 support. Triggered by this I did some preliminary investigation to see how much work it will be to support this in IKVM.

The reference implementation uses the sun.misc.Unsafe class to calculate the offset of a field in a class and to directly access this field using the appropriate memory model semantics. HotSpot has intrinsic support for the performance cricitical methods in sun.misc.Unsafe. Unfortunately, this model isn't very suitable for IKVM, because the CLI does not specify a way to portably obtain the offset of a field in a class (and it even allows the offset to change over time). I've implemented all the required methods in sun.misc.Unsafe based on reflection, but obviously this is very slow (preliminary measurements show a 10x to 100x slowdown compared to JDK 1.5).

The good news is that some important classes can easily be ported to a more CLI friendly approach. As an example I've modified the reference implementation of AtomicInteger to use System.Threading.Interlocked.CompareExchange() instead of sun.misc.Unsafe.compareAndSwapInt(). This is a small change and allows for good performance. Here is the benchmark I used:

import java.util.concurrent.atomic.*;

public class test {
static AtomicInteger foo = new AtomicInteger(0);
public static void main(String[] args) {
long start = System.currentTimeMillis();
for (int i = 0; i < 100000000; i++) {
foo.incrementAndGet();
}
long end = System.currentTimeMillis();
System.out.println(end - start);
System.out.println(foo);
}
}

Here are the timings (IKVM and C# timings on Microsoft .NET Framework 1.1):

  Time (ms)
JDK 1.5 HotSpot Server VM

861

JDK 1.5 HotSpot Client VM

1312

IKVM

1543

C#

1452


I included the C# version for comparision. Here is the source for it:

using System;
using System.Threading;

public class test {
static int foo;
static void Main() {
int start = Environment.TickCount;
for (int i = 0; i < 100000000; i++) {
Interlocked.Increment(ref foo);
}
int end = Environment.TickCount;
Console.WriteLine(end - start);
Console.WriteLine(foo);
} }

Note how much easier the C# programming model is. Given support for managed by ref arguments, there is no need for an extra indirection or hacks like sun.misc.Unsafe.

Tuesday, 30 May 2006 12:27:17 (W. Europe Daylight Time, UTC+02:00)  #    Comments [1]
# Tuesday, 23 May 2006
IKVM 0.28 Released

I released 0.28 (same bits as last week's release candidate) to SourceForge.

Tuesday, 23 May 2006 13:30:32 (W. Europe Daylight Time, UTC+02:00)  #    Comments [1]
# Tuesday, 16 May 2006
Using foreach to enumerate Java collections in C# 3.0
A long standing feature request for IKVM has been to make Java collections implement System.IEnumerable and I've always resisted doing that for various reasons.

I while ago -- while discussing this with Stuart Ballard -- I realised that with the proposed C# 3.0 language extensions, in particular "extension methods" it should be possible to make Java collections foreach-able with little effort:

namespace java.util
{
  public static class CollectionExtensionMethods
  {
    public static IEnumerator GetEnumerator(this java.util.Collection col)
    {
       return new CollectionEnumerator(col);
    }
  }
}

For those who don't know how extension methods work, basically the above code (note the this keyword before the argument type) adds a method to java.util.Collection that feels like an instance method.

Given the way foreach works, I had expected that it too would recognize this GetEnumerator method and therefore work on all Java collections, but alas that is not the case.
If you want to see this changed before C# 3.0 is released, please vote. Alternatively, if you're Miguel and on the ECMA C# committee, it should be obvious what to do ;-)

Tuesday, 16 May 2006 15:03:28 (W. Europe Daylight Time, UTC+02:00)  #    Comments [4]
IKVM 0.28 rc1

A new release candidate based on GNU Classpath 0.91. I did some perf work and a fair bit of restructuring in the way class loaders work, to better support ikvmc and ikvmstub on assemblies loaded in the ReflectionOnly context (on .NET 2.0). The perf work resulted in a significantly improved startup time for Eclipse (IKVM 0.26: 1 minute 23 seconds, IKVM 0.28: 55 seconds).

Updated japi results are available here. The comparison is against JDK 1.5 now and ignores the generics metadata.

Changes:

  • Integrated GNU Classpath 0.91 plus one patch.
  • Added explicit null check for return value of GetEntryAssembly() in VMSystemProperties.
  • Implemented socket timeout by using Socket.Poll() instead of setting the timeout on the underlying socket (because .NET 2.0 considers the socket broken after a Read timed out).
  • Removed classLoader field from TypeWrapper and made GetClassLoader() abstract (to enable subclasses to use a more efficient way to store the class loader).
  • Moved creation of java.lang.Class object from TypeWrapper constructor (because it would trigger a call to GetClassLoader before that was ready to return meaningful data and also because it wasn't semantically correct to expose the TypeWrapper instance before it was fully constructed).
  • Added ikvm.lang.Internal annotation to mark types and members as internal to the assembly (supported by ikvmc only, not in dynamic mode.) Note that ikvm.lang.Internal should only be applied to public types and members. Note also that to reflection these internal types and members will appears as package private.
  • Removed map.xml hacks to work around cross package accessibility issues (now done by marking the appropriate types/members public and annotating them with @ikvm.lang.Internal).
  • Added map.xml implementation of Class.newInstance (to support @ikvm.lang.Internal).
  • Changed ClassFile to pack major version and flags together to reduce the size of the object.
  • Changed ClassFile.FieldOrMethod to pack flags together.
  • Simplified (and made more consistent) member access checking in reflection.
  • Added -privatepackage option to ikvmc (to mark all classes in a package tree as internal).
  • Fixed object model remapping to add methods inherited from Object to Throwable.
  • Fixed some edge cases in method override resolution.
  • Added optimization to compiler to devirtualize method calls on this reference when it is safe to do so.
  • Added volatile opcode prefix to remapper.
  • Added support for specifying .NET types in catch block to remapper.
  • Made 1.5 support part of the standard build.
  • Restructed ikvmc.exe and IKVM.Runtime.dll.
  • Centralized caching of ByteCodeHelper MethodInfos in ByteCodeHelperMethods.
  • Fixed Thread.join() bug that caused join to spin for large timeouts.
  • Added optimization to not emit linenumbertable for methods that cannot throw exceptions.
  • Much improved annotation support.
  • Fixed ikvmc to only generate corresponding .NET attributes for annotations that have RetentionPolicy.RUNTIME.
  • Fixed ikvmc to add AttributeUsageAttribute to annotation attributes (based on the Target annotation).
  • Optimized verifier a little by making InstructionState use copy-on-write strategy.
  • Changed string comparisons to ReferenceEquals when possible (identifiers are interned, so this is usually possible).
  • Improved VMStackWalker.getCalling[Class|ClassLoader] performance by removing the unnecessary check for HideFromJava/HideFromReflection attributes.
  • Almost completely removed usage of custom attributes for dynamically compiled code (because defining custom attributes is slow).
  • Fixed race condition when two threads define the same class name in two different class loaders at the same time.
  • Fixed possible deadlock while finishing dynamically loaded types.
  • Fixed bug in Class.getModifiers() for statically compiled anonymous inner classes.
  • Moved loading .NET types by their assembly qualified names from the class loader to Class.forName.
  • Fixed class loader not to load Java classes, by their .NET array, pointer or reference name.
  • Moved hack to return system class loader for .NET and statically compiled types from [Compiled|DotNet]TypeWrapper to Class.getClassLoader.

Files are available here: ikvm-0.28.0.0.zip (sources + binaries), ikvmbin-0.28.0.0.zip (binaries), ikvmbin-generics-0.28.0.0.zip (binaries built from generics branch)

Tuesday, 16 May 2006 11:06:10 (W. Europe Daylight Time, UTC+02:00)  #    Comments [0]