Using Graal in JDK 9 EA Builds

JRuby+Truffle is designed to be run with a JVM that has the Graal compiler. The easiest way to get this is by downloading the [GraalVM](Downloading GraalVM), but it also possible to use Graal with JDK 9 EA (early access) builds.

The JDK EA builds lag behind Graal development a bit so the interfaces are not always compatible. This will stabilise over time. I believe at the moment they are unfortunately incompatible. When they are compatible in the future, this is how it should work. You'll need to download a JDK 9 EA build.

https://jdk9.java.net/download/

You will also need a copy of graal.jar. You can [build this yourself](Building Graal) or get it from [a download of GraalVM](Downloading GraalVM).

To use the EA build of Java to run JRuby+Truffle, set the JAVACMD environment variable. You will also need to pass several other command line options.

$ JAVACMD=path/to/jdk9/bin/java bin/jruby.bash -X+T \
  -J-XX:+UnlockExperimentalVMOptions -J-XX:+EnableJVMCI \
  -J-Djvmci.compiler=graal \
  -J-Xbootclasspath/p:graal.jar \
  ...

• -J-XX:+UnlockExperimentalVMOptions -J-XX:+EnableJVMCI enables JVMCI - the interface that Graal uses
• -J-Djvmci.compiler=graal tells JVMCI to use Graal
• -J-Xbootclasspath/p:graal.jar puts Graal on the boot classpath, where it needs to be in order to be used by JVMCI