OSGi enabled JavaCPP

[timothyjward]

Following on from discussions in PR #328 this PR does not change the Maven Plugin layout and

1. Adds OSGi metadata to the JavaCPP library
2. Adds an OSGi integration test

Note that the integration test passes because the JavaCPP Loader.load() method is not used, if it is used then the test fails. This demonstrates how the native library loading done by JavaCPP fails in OSGi, and hopefully can be used to design a fix.

[saudet]

If I understand correctly OSGi wants to manage native libraries on its own with Bundle-NativeCode? It looks rather limited in functionality. We probably won't be able to use that. We'll need to figure out the right way to call System.load().

[timothyjward]

If I understand correctly OSGi wants to manage native libraries on its own with Bundle-NativeCode? It looks rather limited in functionality. We probably won't be able to use that. We'll need to figure out the right way to call System.load()

So what OSGi does with Bundle-NativeCode is to allow you to package multiple native binaries for different platforms and have the correct one selected for you automatically. Furthermore it sets up the bundle's class loader properly so that the native library can be found and loaded by the bundle class loader with a call to System.loadLibrary(libName) without any further file extraction required.

I'm currently investigating the feasibility of generating a small Java Helper class to live alongside the class(es) using JavaCPP. This helper can be called to try to load the native library within the correct Class context. If you have another idea about how this could be achieved then I'd be happy to hear it!

[saudet]

Let's see, System.load() looks like this:

    public static void load(String filename) {
        Runtime.getRuntime().load0(getCallerClass(), filename);
    }

https://github.com/openjdk-mirror/jdk7u-jdk/blob/master/src/share/classes/java/lang/System.java#L1058-L1060

Still seems to be the same on the tip:
https://github.com/openjdk/jdk/blob/master/src/java.base/share/classes/java/lang/System.java#L1871

Would you be against trying to call Runtime.load0()? Or is this pretty much guaranteed to fail with OSGi anyway?

[timothyjward]

Would you be against trying to call Runtime.load0()? Or is this pretty much guaranteed to fail with OSGi anyway?

Obviously there are issues with reflectively calling the internals of the JDK (for example this may not work on Eclipse's J9) but there isn't anything that OSGi will do to stop you and it should work. My biggest concern is that this sort of thing may well not work in future versions of Java as the VM is further locked down. When it comes down to it it's your call. I'll create a PR for the "helper class" approach so that you can take a look.

[saudet]

OpenJ9 uses OpenJDK, Android uses OpenJDK, there isn't much of anything that doesn't use OpenJDK these days, well maybe except IBM JDK, but they haven't updated since Java SE 8, so that's not a problem IMO. If OpenJDK ever decides to change that API, or even better, make the equivalent public, then we can always update at that point. There is still nothing to replace Unsafe completely, so people are still using, and the world hasn't ended. Just saying. The alternative is going to be much uglier.

[saudet]

Looks good, but as I pointed out, we don't need to use try to use Runtime.load0(), unless the class loader are not the same. Let's add a check for that?

And could you revert the breaking changes to the manifest as well?

[timothyjward]

Looks good, but as I pointed out, we don't need to use try to use Runtime.load0(), unless the class loader are not the same. Let's add a check for that?

Done

And could you revert the breaking changes to the manifest as well?

Also done, but not as a revert (which results in a broken OSGi bundle and fails the integration test). Instead I have applied the same fix as is on the osgi branch which removes the manifest section and applies the metadata to all the packages.

[timothyjward]

It looks like the Travis build is passing. Are you happy to merge this now?