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IKVM 0.46.0.1 hacked to work with MonoTouch

branch: master
README.md

IKVM MonoTouch

This code is based on release 0.46.0.1 of IKVM and is modified to allow operation with MonoTouch. The two big challenges in supporting MonoTouch are:

  • MonoTouch uses AOT compilation to deploy to iOS, and thus cannot support dynamic code generation. IKVM uses dynamic code generation extensively to support fast reflection.

  • MonoTouch only provides the Silverlight runtime profile, which lacks a substantial number of the features of the desktop profile, on which IKVM relies.

These challenges have largely been overcome:

  • Reflection is supported through standard CLR reflection (which is slower than code generation, but at least it works).

  • The Silverlight profile is accommodated by aggressive pruning of the JDK with which IKVM operates. This means that the vast majority of the "enterprisey" features of OpenJDK are not available via IKVM MonoTouch.

Building

IKVM MonoTouch can (naturally) only be built on a Mac which has MonoTouch installed. You also need to install NAnt (as it's no longer bundled with MonoTouch). Once you've installed NAnt, you need to patch your bin/NAnt.exe.config file using the NAnt.exe.config.patch in the top-level directory of ikvm-monotouch.

In addition to this project, you need to check out the ikvm-openjdk repository in the same directory that contains the ikvm-monotouch checkout. The IKVM build will use the Java source in the ikvm-openjdk directory during its build.

Once you have created your symlink and checked out ikvm-openjdk, you can build everything using the build.sh script:

./build.sh

This will generate all of the IKVM dlls and exes in the ikvm-monotouch/bin directory. This version of IKVM can then be used in the normal manner to convert Java bytecode to a dll that can be included in a MonoTouch project.

JNI is supported by including the bin/libikvm-natives.a file in your MonoTouch project. The file needs to be copied, not linked, otherwise MonoTouch does not pick it up. You have to add the following arguments to IPhone Build -> Additional mtouch arguments:

-nosymbolstrip -nostrip -cxx -gcc_flags "-L${ProjectDir} -likvm-natives -force_load ${ProjectDir}/libikvm-natives.a"

Your JNI code must use the jni.h file found in native/. Setup an XCode static library project, add your JNI files plus a reference to native/jni.h. Then add the static library just like you add the libikvm-native.a file (including the mtouch arguments to force link all symbols).

It is not necessary to use this custom project to convert C# dlls to Java stub classes (via ikvmstub.exe), but you can use it, and save yourself the trouble of installing a standard IKVM distribution.

Limitations

There are numerous limitations, too many to enumerate. However, this project is successfully enabling the PlayN game development library to convert Java game projects into iOS binaries.

One known limitation that can probably be overcome is the lack of java.net support. The aggressive pruning of the OpenJDK to remove all of the enterprise functionality that could not be supported on Silverlight resulted in java.net being cut out due non-trivial internal dependencies on JNDI and from there into a bunch of enterprise crap.

I strongly suspect that the JNDI and other enterprise crap can be surgically removed, leaving a functional java.net which supports basic DNS and TCP/UDP. However, that will take more time and effort than I have thus far been able to muster.

Distribution

See LICENSE for license information on IKVM.

Contact

Questions, comments, and suchlike can be directed to the Three Rings Libraries Google Group.

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