Lauching a JVM from C and providing interface to C++

Question

Hi
I'm work on a project that launch a JVM using JNI.
I need to provide a interface to a C++ class through JNI in order to allow the launched JVM to access it. The code of this class is in the program that launch the JVM
The problem is that java does not find the given function and fails with:
java.lang.UnsatisfiedLinkError: altitude
The function is present in the database (checked with "nm" against the name given by javah).
I supposed that there is some kind of addressing or kind of "namespace", but don't know how to avoid it.

Answer 1

From a program in a JVM call a routine which has a JNI that launches a new JVM using
C? Why would you want to do this?No it's not what I am doing.
From a C++ program that follows I launch a JVM (that's working, the code have been simplified a bit) and retrieve methods id to store them in attributes (variables names starting with underscore):
      // Create the JVM oine time only
      if (NULL == _env)
        JavaVMInitArgs  vm_args;
        JavaVMOption*   options = NULL;
        char*           char_options = NULL;
        list<string>    user_options;
        _database.getPropertyList("simu.locals.java", "option", &user_options);
        if (0 != user_options.size())
          unsigned long index = 0;
          options = new JavaVMOption[user_options.size()];         
          for (list<string>::iterator   it = user_options.begin();
               user_options.end() != it; it++)
            char_options = strdup(it->c_str());
            options[index++].optionString = char_options;
          vm_args.nOptions = user_options.size();
        vm_args.version = JNI_VERSION_1_4;
        vm_args.options = options;
        vm_args.ignoreUnrecognized = JNI_TRUE;     
        JNI_CreateJavaVM(&_jvm, (void**)&_env, &vm_args);    
      // Retrieve the class and method that will allow to create the
      // planner
      _cls = _env->FindClass(class_name->c_str());
      string*   method =
        _database.getProperty("simu.locals.java.methods.init.name");
      string*   sig =
        _database.getProperty("simu.locals.java.methods.init.signature");
      string*   port =
        _database.getProperty("simu.locals.java.methods.init.argument");
      string            nid = str(format("%d") % id);
      jmethodID         mid =
        _env->GetStaticMethodID(_cls, method->c_str(), sig->c_str());
      jint              arg1 = lexical_cast<unsigned int>(*port);
      jstring           arg2 = _env->NewStringUTF(nid.c_str());
      _planner = _env->CallStaticObjectMethod(_cls, mid, arg1, arg2);
      // Save the method ID we'll need later     
      method =
        _database.getProperty("simu.locals.java.methods.incoming.name");
      sig =
        _database.getProperty("simu.locals.java.methods.incoming.signature");
      _incoming = _env->GetStaticMethodID(_cls, method->c_str(), sig->c_str());
      method =
        _database.getProperty("simu.locals.java.methods.outgoing.name");
      sig =
        _database.getProperty("simu.locals.java.methods.outgoing.signature");
      _outgoing = _env->GetStaticMethodID(_cls, method->c_str(), sig->c_str());Then I call the retrieved static method of the class when needed.
This work perfectly, as far as i have tested.
But now, the java part will need to access some algorithm and datas already existing in the C part. So i made a very simple interface:
** Interface to the environement C++ class
package provided;
public class Environment
    ** Methods implemented in Environment.cc
    public static native double altitude(double lat, double lon);
}I generate the interface with javah and implement it quicly (doing nothing):
#include <iostream>
using namespace std;
** This file implement the interface betwen the C++ class Environment
** (from Environment.h) and the Java class provided.Environment whose
** native method are described in provided_Environment.h.
** It uses jni.h
#include "provided_Environment.h"
#include "Environment.h"
#include "jni.h"
* Class:     provided_Environment
* Method:    altitude
* Signature: (DD)V
extern "C" JNIEXPORT
jdouble JNICALL Java_provided_Environment_altitude(JNIEnv*      env,
                                                   jclass     c,
                                                   jdouble      lat,
                                                   jdouble      lon)
  cout << ARTEMIS::Environment::altitude(lat, lon) << endl; 
  return (ARTEMIS::Environment::altitude(lat, lon));
}nm returns:
nm mms | grep altitude
080aa94c t _GLOBAL__I_Java_provided_Environment_altitude
080aa6e4 T Java_provided_Environment_altitude
080a8778 T _ZN7ARTEMIS11Environment8altitudeEddSo there is no .so . I've tried to have one but there is the same kind of problem as when I load the .so, I have a error because the .so can find the required symbols that are in the program (here the ARTEMIS::Environment::altitude function)
Is it clearer ??