Docker Java Native Library java.lang.UnsatisfiedLinkError: no vw_jni in java.library.path

[adgaudio]

Hi,

We have a java project that uses VW, and we love it! However, when the java code runs in an Ubuntu 14.04 docker container, it can't load the native bindings. I figured out why this happens and will propose a solution at the bottom of this issue description.

The Error: The following traceback occurs when we run our java program inside a docker container that inherits from Ubuntu:14.04.

[info] java.lang.UnsatisfiedLinkError: no vw_jni in java.library.path
[info]  at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1864)
[info]  at java.lang.Runtime.loadLibrary0(Runtime.java:870)
[info]  at java.lang.System.loadLibrary(System.java:1122)
[info]  at vw.jni.NativeUtils.loadOSDependentLibrary(NativeUtils.java:116)
[info]  at vw.learner.VWLearners.loadNativeLibrary(VWLearners.java:85)
[info]  at vw.learner.VWLearners.initializeVWJni(VWLearners.java:73)
[info]  at vw.learner.VWLearners.create(VWLearners.java:44)

Why this happens:
Looking at VW source code for java/src/main/java/vw/jni/NativeUtils.java, a function named getDistroName directly queries /proc/version (see source). In docker, this returns the host's kernel version, which may not be Ubuntu. (If you use docker-machine, /proc/version returns information about the docker-machine VM that the container runs in). What we actually want it to do, as far as I understand, is query the container OS version, which is Ubuntu 14.04.

Possible Solution:
For better compatibility with VW in docker containers, I suggest we don't query /proc/version. What if, instead, we replace the linux-specific contents of getDistroName with lsb_release -i? Since we already use lsb_release -r for getLinuxVersion, this seems to make quite a bit of sense to me, and I believe it will work in a docker container.

I'd love to get your feedback and would be happy to submit a PR if necessary.

[adgaudio]

A colleague just made me aware of a related issue, #807, which suggests querying /etc/os-release.

Previous attempts linked to #807:
#780
#822

[JohnLangford]

This has been a persistent issue, so it would be nice to get it solved. @jmorra @deaktator have been the primary ones working on the java interface, but if you want to work on a patch for them, that may work well.

[jmorra]

I'm fine with changing this as long as it continues to work on Mac and builds with build.sh I have no problem with any change. @adgaudio is this something you can work on?

[adgaudio]

Sure, I'd love to do it. I plan to submit a PR by next week.