# Thursday, April 17, 2008
Invalid Casting Goodness

Yesterday Miguel blogged about a nice new feature in Mono. I added the IKVM_VERBOSE_CAST environment variable to IKVM to do something similar a while ago.

public class test {
  public static void main(String[] args) {

C:\j>\ikvm-\bin\ikvm test
Exception in thread "main" java.lang.ClassCastException
        at test.main(test.java)


C:\j>\ikvm-\bin\ikvm test
Exception in thread "main" java.lang.ClassCastException: Object of type "System.String[], mscorlib, Version=1.0.5000.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" cannot be cast to "System.String, mscorlib, Version=1.0.5000.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
        at test.main(test.java)

Note that the assembly qualified type names are displayed, as I believe this feature is particularly useful when trying to debug issues that arise from having loaded multiple assemblies that contain the "same" types.

While writing this I discovered that both JDK 1.6 and .NET 2.0 always generate descriptive exception messages for invalid casts:

C:\j>\jdk1.6\bin\java test
Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.String; can not be cast to java.lang.String
        at test.main(test.java:5)

C:\j>\ikvm\bin\ikvm test
Exception in thread "main" java.lang.ClassCastException: Unable to cast object of type 'System.String[]' to type 'System.String'.
        at test.main(test.java:5)

This last result is my local ikvm development version running on .NET 2.0 with a patch to enable taking the exception message from the .NET InvalidCastException, which I didn't previously do because on .NET 1.1 this message didn't contain any useful information.

Thursday, April 17, 2008 8:51:38 AM (W. Europe Daylight Time, UTC+02:00)  #    Comments [2]
# Monday, April 14, 2008
New Development Snapshot

It's been quite a while since the last development snapshot. I'm still working on integrating .NET 2.0 features, but I'm also doing random fixes/improvements here and there as I come across them. The biggest visible change in this snapshot is the support for defining .NET properties as Java fields. The main motivation was that I wanted to handle the System.in/out/err fields more cleanly. They are now implemented like this:

public final static InputStream in;

static { in = null; }

private static InputStream get_in()
    return StdIO.in;

This defines a .NET property called "in" and associates the getter method of the property with the get_in() method. Note that we're only specifying the getter here in the Property annotation because the field is final, but you can also specify a setter method. The static initializer that initializes the property to null is necessary to keep javac happy, but it doesn't actually do anything. The ikvm bytecode compiler will ignore any assignments to read-only properties. Another thing to note is that the get_in() will automatically be made public (because the field is public), but from Java it will still appear private.

Changes since previous development snapshot:

  • Fixed regression in return value annotation value.
  • Forked Class, Constructor and Field.
  • Made class annotation handling lazy and bypass encode/decode.
  • Fixed ReflectionOnly referenced assembly loading order (ikvmstub).
  • Initialize class library in JVM_CreateJavaVM.
  • Reintroduced guard against recursive FinishCore invocations.
  • Implemented support for annotations on .NET fields/methods/parameters.
  • Hide ikvmc generated GetEnumerator() method from Java.
  • Simplified annotation handling.
  • Added support to Class.forName() for assembly qualified Java type names.
  • Replaced notion of DynamicOnly types with Fake types. Fake types are implemented as generic type instances and can have DynamicOnly methods.
  • Changed System.nanoTime() implementation to use Stopwatch.GetTimestamp().
  • Ripped out annotation/constant pool support that is no longer needed.
  • Added support for defining unloadable (i.e. missing) types to use as custom modifiers in signatures.
  • Use custom modifiers to make sure constructor signature is unique (if necessary).
  • Restructured code to remove compiler warnings.
  • Updated FlushFileBuffers p/invoke to use SafeFileHandle.
  • Forked OpenJDK sources that are going to be modified to refactor the library initialization.
  • Made __Fields nested class abstract (it was already sealed) and removed the constructor.
  • Restored the special case for interface .cctor methods to fix bug #1930303
  • Added ikvm/internal/MonoUtils.java. A new helper class to contain Mono specific methods.
  • Added Mac OS X platform detection.
  • Fixed System.mapLibraryName() to use platform detection instead of os.name property.
  • Improved java.library.path for Windows, Linux and Mac OS X.
  • Added support for setting os.name and os.ver on Mac OS X.
  • Try to guess os.arch based on IntPtr.Size.
  • Set sun.nio.MaxDirectMemorySize to -1 to allow "unlimited" direct byte buffers.
  • Fixed memory mapped file bug that caused mapping at non-zero file position to fail.
  • Close mapping handle using the Close() method on SafeFileHanlde instead of p/invoking the Win32 API directly.
  • Added support for filenames/paths with colons in them to Win32FileSystem.CanonicalizePath().
  • Added support for turning Java fields into .NET properties with an annotation.
  • Implemented System.in/out/err as .NET properties (explicitly).


Development snapshots are intended for evaluating and keeping track of where the project is going, not for production usage. The binaries have not been extensively tested and are not strong named.

If you want to run this version on Mono, you'll need a Mono version built from recent svn, it does not work on Mono 1.9.

Binaries available here: ikvmbin-0.37.3026.zip

Monday, April 14, 2008 7:40:06 AM (W. Europe Daylight Time, UTC+02:00)  #    Comments [0]
# Monday, April 7, 2008
IKVM 0.36 Update 1 Released

When I released IKVM 0.36 I said I intended to support 0.36 for a longer period since it is the last version that runs on .NET 1.1. Today I've released the first update release of 0.36 to SourceForge. For those who have been tracking the release candidates, this release is identical to release candidate 5.

Changes since IKVM

  • Changed version to IKVM
  • Fix for reflection bug on .NET generic nested types that caused this.
  • Fix for bug #1865922.
  • java.awt.image.Raster fix.
  • Fix bug in DynamicMethod based serialization for fields typed as ghost interfaces.
  • Fixed ikvmc to support referencing assemblies that contain .NET type named java.lang.Object.
  • Improved error handling for ikvmc -reference option.
  • Optimized codegen for lcmp, fcmp, dcmp and shift opcodes.
  • Added support to Class.forName() for loading Java types with assembly qualified type names.
  • Implemented field/method/parameter annotation support for .NET types.
  • Added workaround for .NET 1.1 bug in Directory.CreateDirectory(). (bug #1902154)
  • Added -removeassertions optimization option to ikvmc.
  • Added -removeassertions to IKVM.OpenJDK.ClassLibrary.dll build.
  • Fixed JVM_CreateJavaVM to initialize the class library.
  • Fixed ikvmc to include zero length resource files.
  • Implemented SocketOptions.IP_MULTICAST_IF and SocketOptions.IP_MULTICAST_IF2.
  • Fixed assembly class loader to ignore codebase for dynamic assemblies (previously it would throw an exception).
  • Fixed exception stack trace code to return the .NET name of a type when a method in a primitive type is on the stack.
  • Fixed JNI reflection to filter out HideFromReflection members.
  • Fixed java.net.NetworkInterface to work on pre-Win2K3 systems.
  • Fixed java.lang.Thread to set context class loader for threads started from .NET.

If you want to build from source, you need ikvm-0.36.11.zip, classpath-0.95-stripped.zip, openjdk-b13-stripped.zip and the java.awt.image.Raster fix.

Monday, April 7, 2008 6:15:18 AM (W. Europe Daylight Time, UTC+02:00)  #    Comments [0]