Jelatine JVM

16/10/2009: Jelatine 0.9.4 has been released, you can find it on SourceForge's download area. This is mostly a bug-fix release, a lot of nasty bugs have been quashed and the machine is now much more robust, especially when using multi-threading. Jelatine is licensed under the GPLv3.

Jelatine is a new Java Virtual Machine which targets the Java 2 Micro Edition Connected Limited Device Configuration (J2ME CLDC). The machine was designed to work on very small embedded systems and requires as little as 32 KiB of RAM for running non-trivial Java code (provided that the executable is stored in ROM). It also provides an (almost) CLDC compliant classpath which has been obtained by modifying and reusing parts of the GNU/Classpath project.

To build the machine you will need a C99 compiler, Sun's javac compiler available from Java developer kit and the zziplib library if you for JAR file support. For thread support you either need POSIX threads support or GNU/Pth. To build the source code documentation you will need Doxygen. If you want to try out Jelatine's mainline you can now find it through Sourceforge's subversion service. You can check it out with the following command:

svn checkout http://svn.code.sf.net/p/jelatine/code/trunk jelatine

The Jelatine JVM is currently functional and was tested with non-trivial code but it still lacks a lot of features (mainly bytecode verification and an basic profile implementation) so consider it a work in progress. Feedback is welcome, bug reports, advices, suggestions and requests should be sent to the e-mail address provided below or through Sourceforge's tracker.

Features

• Runs in as little as 32 KiB of RAM
• Provides both a portable interpreter written in plain C and a faster one using GNU C compiler extensions
• Uses a custom memory manager which allocates C and Java objects from the same unified heap with an hybrid best-fit/first-fit policy
• True single word header for Java objects and C allocations minimizes per-object overhead
• Permanent C allocations (i.e. objects which will live until the machine quits) do not have any additional allocation overhead
• Unified constant pool for sharing data among classes this minimizing memory usage
• Compact bytecode layout, bytecode optimizations and fine grained lazy binding enable fast interpreted execution in a very small memory footprint
• Robust mark-and-sweep garbage-collector implemented using a pointer-reversal technique which does not require any additional memory and implements the mark phase using an iterative algorythm
• Support for multi-threading either through POSIX threads and GNU/Pth software threads or single-threaded operation
• Support for the KNI native interface
• Support for Weak references
• Supports 16-, 32- and 64-bit machines
• Support for JAR files and resources

Todo

• Implement the bytecode verifier
• Implement an accurate/precies mark-sweep-compact garbage collector
• Rewrite the preverifier tool and make it a separate package

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