[vmkit-commits] Breaking change for openjdk

[Will Dietz]

On Fri, Dec 2, 2011 at 11:54 AM, Nicolas Geoffray
<nicolas.geoffray at gmail.com> wrote:
> Yes, I believe that's possible. Depends if openjdk needs fancy things when
> creating a WeakHashMap.

How right you were (see commits involving hardcoding the
java.lang.Reference's clinit as to not spawn its own thread....) but
seems to be working fine now :).

> This is great news! Does that mean precompilation and GC work on the openjdk
> port? That's awesome. Can't wait to try it out!

Precompilation has worked for some time (the speedups it provides
makes it a high priority :)), and I believe the GC works.  It
certainly "mostly" works, but for example the limiting factor in
specjvm2008 presently is that memory isn't being freed when it should,
so I'm running out of memory when trying to do a full run--running
individual benchmarks works much better.  In general the bugs I'm
seeing seem to be more of a "memory not freed" variety not a "memory
freed that shouldn't be", which is some comfort.

Also, I've almost exclusively tested with the default MarkSweep mmtk
plan, although the others seem to work in much more limited testing.

As for trying this out yourself, here's a rough guide:

** Install an OpenJDK JDK6 (not Sun, not JRE, not 1.7).
This should be available in your linux distribution's package manager,
otherwise I've had great success with locally built copies of icedtea6
(what I use for most my testing, actually).

** Replace the GNU Classpath-related configure arguments with
"--with-classpath-impl=openjdk --with-openjdk-path=$JDK_HOME".
JDK_HOME is in surprisingly different places on different
distributions, but it should contain "bin/javac" as well as a "jre"
subdirectory.  The configure script's checks on the path should tell
you if you've got the right path.

** "make"
Might want to cross your fingers first :).


Some caveats when testing this on the various systems I have access to:

* When precompiling, in particular building BootstrapClasses.s,
sometimes gcc (at least with 4.4.5 on one particular system) barfs
claiming invalid assembly.  Other versions of gcc build the same
assembly fine, and "make CC=clang CXX=clang++" avoids this as well.
FYI
* Many recent OpenJDK versions seem to work (1.9 and later), although
I've encountered one ("OpenJDK Runtime Environment (IcedTea6 1.9.10)
(rhel-1.40.1.9.10.el6_1-x86_64)" from Scientific Linux 6.1) that has
some dlopen/dlclose issue (of all things) that makes accessing fonts
segfault.  Previous version from same distribution works as does
building from scratch via IcedTea, so I've mostly given up on this.

The abbreviated version of the above is that "some configurations
don't work" and I don't have a particularly great handle on that due
to lack of time and testing :).  So YMMV.

If you do get to trying it please let me know how it goes/if you have
problems/etc :).  Once it seems to work well for you, then I can work
towards writing a more formal set of instructions for the website as
you previously mentioned :).

Good luck and happy holidays! :)

~Will