Re: Interface gcj-compiled library with Java programs in a runtime (other than gij)?

[Bryce McKinlay <bmckinlay@gmail.com>]

On Tue, Feb 14, 2012 at 11:26 AM, Yi Lin <qinsoon@gmail.com> wrote:
>
> Thank you all for the answers. I think I have some clue about CNI/JNI on the interface.
>
> But I still have doubt about how a shared library compiled from Java can be used by a) c/c++, b) Java code running on other JVM (not libgcj interpreter). I think b) is straightforwad if a) is possible.
>
> So for a), is calling a shared library of compiled java code any different than calling a shared library from normal c/c++ code? I have been spending two days exploring this and trying different approaches. My expectation is to load the compiled Java lib and use its method via dlopen, dlsym, etc. I guess another possibility is to use JvCreateVM(), and do everything in Java fashion. I don't have any success in either yet. Any hint would be very helpful so I could stop wasting time on a wrong track.


a) is certainly possible, using either JNI or CNI. Whichever one you
use, you need to call a couple of functions to initialize the Java VM
before you start calling your Java classes. You just need to make sure
libgcj gets loaded somehow, either using -lgcj or dlopen.
See here for a CNI example:
http://gcc.gnu.org/onlinedocs/gcj/Invocation.html#Invocation

b) "Should" work, but maybe you'd get conflicts with things like
signal handlers since you effectively have 2 Java runtimes running in
the same process.