Eclipse Goes Native
Currently, we don't compile Eclipse directly from source to object code. Instead, we compile to bytecode and then compile the jar files to shared libraries. This is done for two reasons. First, a few bugs in the GCJ source compiler haven't been fixed. Second, Eclipse comes with its own build scripts that compile from source to bytecode. Reworking the Eclipse build system to allow building directly from source to binary seemed like a much larger divergence from the upstream sources than we were willing to maintain.
Also, we currently don't precompile all the jar files to shared libraries—some remain as jar files and are interpreted at runtime. This is done because the class libraries still are incomplete, and these jar files refer to classes that have not been implemented yet.
One of our patches is unsuitable for the public GCJ. We had to disable the compile-time bytecode verifier, as it was too buggy to compile some of the Eclipse jar files. We're in the process of replacing this verifier with a more robust one.
In addition, one limitation of natively compiled Eclipse deserves mention. You can't use natively compiled Eclipse to debug a GCJ-compiled application, because JDWP, the Java Debug Wire Protocol used by Eclipse, hasn't been implemented in libgcj yet.
The achievement of the native compilation of Eclipse is a strong indication that open-source Java based on GCJ and libgcj/classpath has reached the point of being commercially useful. That said, it's still not complete. Some fairly substantial gaps still need to be filled in before open-source Java can be a proper drop-in substitute for proprietary JVMs.
One of the major areas that needs work is the development/integration of a JIT compiler. JIT would allow a GCJ-based open-source Java environment to be used in a manner similar to a conventional JVM, meaning that native compilation and platform-specific binaries would not be necessary for performance reasons.
The other major piece that needs work also is, by far, the most visible missing piece—Swing. Work on an open-source implementation of Swing is coming along nicely as part of the GNU Classpath Project, but Swing is a huge undertaking and the GNU Classpath implementation is still not quite usable.
A full-featured and completely open-source Java environment is an attractive alternative to proprietary JVMs, and it's now within reach. During the past six months, Red Hat has more than doubled the number of engineers working in support of the Open Source Java solution and community. Eclipse is a large, complicated piece of software, and natively compiling and running it was an excellent test of and testament to the progress being made on open-source Java. The power of open source lies in its communities, so please consider joining the open-source Java community and contributing to the GCJ and GNU Classpath Projects in any way that interests you.
Resources for this article: /article/7549.
John Healy is the manager of Red Hat's Eclipse Engineering group, based in Toronto (people.redhat.com/jhealy). In the past he's worked on custom open-source toolchains for embedded processors as well as CRM and computer-telephony applications.
Andrew Haley has been a programmer for longer than he cares to remember. He is one of the maintainers of GCJ. He works for Red Hat, which supports him in this task.
Tom Tromey has worked on free software since the early 1990s. Patches of his appear in GCC, Emacs, GNOME, Autoconf, GDB and probably other packages he has forgotten about. He works at Red Hat as the technical lead of the Eclipse Engineering team. He can be reached at email@example.com.
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