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I want to learn the internals of JVM. For this purpose I chose Jikes RVM to work with, but the problem is that I am not able to debug the source code as it doesn't support it. My question is that is there some open source JVM which can be debugged to see how it works with class files. I am in real need of some good information about it.

Thanks

Pankaj Sejwal
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2 Answers2

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Well, since the Oracle JDK is open source, this might be a good place to start: http://openjdk.java.net/

Tim Büthe
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  • ya I am aware of it but is it debuggable via breakpoints ?? that's my concern !! Moreover I see that during the native calls it just does nothing...is it possible to see the native methods ?? – Pankaj Sejwal Jul 11 '12 at 09:19
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The internals of the JVM is different between JVM's and knowledge gained from one may not be usable for other JVM's.

If you want to see how the runtime library (all the java.* classes) is implemented, there is a src.zip in most JDK distributions (not the JRE ones). If you use Eclipse, set it up to use that JDK as the JRE and you can navigate directly around in the various classes starting from your own program.

Thorbjørn Ravn Andersen
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  • I am using it for openjdk but it does nothing at native methods...as if nothing happened..so in a sense I am not seeing object allocation or garbage collection. I tried simple threading class, all I saw was thread being initialized and run but object allocation inside run() doesn't show up. Just happens in the background !! tha's where I want to reach . – Pankaj Sejwal Jul 11 '12 at 09:22
  • The smallest but fully capable JVM I know of is JamVM. http://jamvm.sourceforge.net/ – Thorbjørn Ravn Andersen Jul 11 '12 at 10:56