Hi, I'm making a lib so that cpp apps can communicate with the JVM. Suppose that the JVM has already started how can I make a cpp binary communicate with the JVM? I think the best solution is to store the JNI env variable in the shared object (so) so I can include it on the cpp and use later.
Is that possible?
EDIT ----
I want to get the JavaVM Interface outside of the JVM, something like this method:
No, I don't think so. The JVM gets the environment at the time of its starting, and it can't be changed from an outside process during the program's runtime.
Standard procedure these days is for programs to communicate using TCP/IP and sockets. For a simple and cheap solution, you could consider using files in a directory (though there are performance and concurrency problems with this, of course).
I just noticed the "I'm making a lib" statement. If your lib is for "public" consumption, it should be cross-platform, and then I think socket I/O would be the thing to do.
You could possibly hijack JMX to do what you're asking for, but I'm not very knowledgeable on that.
Your question is unclear: it sounds like you want a C++ application to communicate with a JVM running as a separate process. In which case you need to use some form of inter-process communication such as pipes, sockets, CORBA, whatever. The JNIEnv pointer, like all pointers, is only valid within the process in which it's used.
The only case that I think fits your question is if you start a Java program, call into a native method, then that native method starts up separate threads. In which case, no, you can't share the JNIEnv pointer, because it's tied to a thread. However, you can use the JNI invocation API to access the Java VM from your C++ thread.
How many processes are you in here? If this is all inside one process, then the answer is 'yes'. C++ can call the GetEnv API from jni.h.