# Monday, 30 November 2009
IKVM 0.42 Release Candidate 3

A new release candidate is available.

Changes since previous release candidate:

  • Changed version to
  • Fix for bug #2887316.
  • Eyal Alaluf fixed a massive performance bug that caused IKVM.OpenJDK.Core.dll to be 1.4 MB too big and allocate a couple of MB of unnecessary strings on initialization.
  • Fixed JNI to use system class loader instead of bootstrap class loader when no Java code is on the stack.
  • Fixed JNI method lookup algorithm.

Binaries available here: ikvmbin-

Sources: ikvm-, openjdk6-b16-stripped.zip

Monday, 30 November 2009 07:00:02 (W. Europe Standard Time, UTC+01:00)  #    Comments [4]
# Wednesday, 25 November 2009
Running Eclipse with NGEN

In the weeks before PDC I've been working on compiling Eclipse with ikvmc. This works was triggered by Mainsoft's Eyal Alaluf who asked me to work on this and also provided a desperately needed starting point. I had wanted to do this for ages, but didn't feel like struggling with the Eclipse build system to figure out how to get started.

A couple of the changes in the most recent development snapshot are specifically related to this. In particular the ability for custom assembly class loaders to be called when the module initializer is run. This enables the statically compiled Eclipse OSGi bundles to be lazily activated on first use.


Here are the steps needed to compile Eclipse 3.4.2 x86 on Windows:

  1. Download eclipse-SDK-3.4.2-win32.zip
  2. Download ikvmbin-0.43.3595.zip
  3. Download ikvm-eclipse-0.1.zip
  4. Unzip eclipse-SDK-3.4.2-win32.zip
  5. Open a Command Prompt in the just unzipped eclipse directory
  6. Unzip ikvmbin-0.43.3595.zip in that directory
  7. Unzip ikvm-eclipse-0.1.zip in that directory
  8. Create a directory for the compiled plugins:
    md plugins-compiled
  9. Run ikvmc to compile the eclipse plugins:
    ikvm\bin\ikvmc @response0.txt
    ikvm\bin\ikvmc @response1.txt
    (Ignore the warnings and note that this takes a while and requires a lot of memory. I haven't tested this on a 32 bit machine, it may well run out of address space there.)
  10. You can now run "eclipse-clr.exe" to start Eclipse. Note that if you compare startup times, the first time that Eclipse starts it does some initial configuration, so don't compare the first startup with the subsequent ones.
  11. Optionally you can run ngen-all.bat to compile all assemblies to native code. Make sure that you have the x86 version of ngen.exe in your path. Note that this also takes a while.

Source Code

The sources for eclipse-clr.exe are in this Visual Studio 2008 solution. It's pretty small and most of what it does is configure and hook OSGi to change the bundle loading and initialization. If you want to build eclipse-clr.exe, you first have to run ikvmc on response0.txt, then build eclipse-clr.exe (it depends on the OSGi assembly built with response0.txt) and after that you can run ikvmc on response1.txt (it depends on eclipse-clr.exe, because that contains the custom assembly class loader used for the bundles).

The response0.txt and response1.txt files were generated from the OSGi manifests and if there is interest I can publish the source to that as well, but is pretty hacky.


When compiled to native with ngen, Eclipse starts up faster than with JDK 1.6 on my systems. In theory the private working set should also be significantly less, allowing multiple Eclipse instances to use far less memory.


This is just a technology demonstration, not production code and has not been extensively tested.

Wednesday, 25 November 2009 06:32:30 (W. Europe Standard Time, UTC+01:00)  #    Comments [20]
# Tuesday, 10 November 2009
Going Crazy with Generics, or The Story of ThreadLocal(Of T)

Jon Skeet recently blogged about the performance of [ThreadStatic] versus the new .NET 4.0 ThreadLocal<T>. I was surprised to see that ThreadLocal<T> was faster than [ThreadStatic], because ThreadLocal<T> uses [ThreadStatic] as the underlying primitive.

How do you go from a static field to a per instance field? It's simple, once you think of it. You (ab)use generic types. Here's a simplified ThreadLocal<T>:

public class ThreadLocal<T>
  HolderBase holder;
  static int count;
  static Type[] types = new Type[] { typeof(C1), typeof(C2), typeof(C3) };

  abstract class HolderBase
    internal abstract T Value { get; set; }

  class C1 { }
  class C2 { }
  class C3 { }

  class Holder : HolderBase
    static T val;

    internal override T Value
      get { return val; }
      set { val = value; }

  public ThreadLocal()
    holder = MakeHolder(Interlocked.Increment(ref count) - 1);

  HolderBase MakeHolder(int index)
    Type t1 = types[index % 3];
    Type t2 = types[(index / 3) % 3];
    Type t3 = types[index / 9];
    Type type = typeof(Holder<,,>).MakeGenericType(typeof(T), t1, t2, t3);
    return (HolderBase)Activator.CreateInstance(type);

  public T Value
    get { return holder.Value; }
    set { holder.Value = value; }

The real ThreadLocal<T> type in .NET 4.0 beta 2 is much more complex, because it has to deal with recycling the types and protecting against returning a value from a recycled type. It also uses a higher base counting system  to number the types, the maximum number of types generated (per T) is 4096 in beta 2. After you allocate more than that, it falls back to using a holder type that uses Thread.SetData().

I'm not sure what to make of this. It's a clever trick, but I think it ultimately is too clever. I benchmarked a simpler approach using arrays (where each ThreadLocal<T> simply allocated an index in the [ThreadStatic] array) and it was a little bit faster and doesn't suffer from the downsides of creating a gazillion types (which probably take more memory and those types stay around until the AppDomain is destroyed).

Finally a tip for Microsoft, move the Cn types out of ThreadLocal, because currently they are also generic (due to the fact that C# automatically makes nested types generic based on the outer type's generic type parameters) and that is unnecessarily wasteful.

Tuesday, 10 November 2009 07:03:31 (W. Europe Standard Time, UTC+01:00)  #    Comments [6]
# Wednesday, 04 November 2009
New Development Snapshot

While the 0.42 release is still baking, a new development snapshot is available.


  • Nat worked on clipboard and drag-and-drop support.
  • Volker worked on print support.
  • Various awt fixes/improvements.
  • Code cleanup/refactoring to prepare for IKVM.Reflection (replacement of IKVM.Reflection.Emit).
  • Fixed ikvmstub to ignore private interfaces.
  • Removed .NET 4.0 beta 1 workarounds.
  • Simplified the obj1.getClass() == obj2.getClass() intrinsic to avoid requiring full trust on .NET 4.0.
  • Optimized field reflection. We now delay creating the dynamic methods to access the field until after the field has been accessed a couple of times, this saves a lot of memory for fields that are only usused a few times.
  • Added -publicpackage:<pkg> option to ikvmc. Contributed by Eyal Alaluf of Mainsoft.
  • Added public API to get ClassLoader from Assembly.
  • Added (optional) per-module initialization to custom assembly class loaders.
  • Added ikvmc option -nopeercrossreference and the ability to use -r with peer assemblies.

Binaries available here: ikvmbin-0.43.3595.zip

Wednesday, 04 November 2009 15:23:41 (W. Europe Standard Time, UTC+01:00)  #    Comments [5]