System.LoadLibrary + dlopen -- callback causes unresolved symbol

Question

Hi guys,
I am currently trying to use the API
System.loadLibrary(String name)in order to dynamically link shared libaries to SOLARIS JVM.
I am facing some unresolved symbol at run-time .
I load a shared library libhello1 (using system.LoadLibary)
and I call from this lib (via JNI interface) a method which
loads a second library libhello2(using dlopen) and invokes hello2().
hello2 will call back a method hello_bug which is implemented in libhello1.
There is the a mutual or cyclic dependence. This dependance is correctly handled if I link the libhello1 to a standard C implemented executable.
But if I load libHello1 via System.Load, the second lib is correctly loaded but the call back is not possible due to unresolved symbol.
It seems like the symbols are not kept in this case(or the dlopen creates a different thread?...)
The workaround to fix the issue is to link explicitely libHello1 to libHello2 when building libHello2.
I don't know if this is clear to everyone so
I have reproduced this on a very simple case.
Basicaly, I have implemented in standard C language 2 shared libraries:
libHelloModule1.so, libHelloModule2.so
one standard executable and one java interface to call the method
Below is the full code for reproduce:
hello1.h:
#include <dlfcn.h>
#include <stdlib.h>
#include <stdio.h>
#include <iostream>
#include <jni.h>
#include "hello_jni.h" [u]//automatically generated by javah -- ref Makefile[/u]
extern "C"  void hello_bug();
hello1.cc :#include "hello1.h"
extern "C" {
JNIEXPORT void JNICALL Java_com_helloworld_Hello_ShowMessage
  (JNIEnv *, jobject, jstring){
void *handle;
const  char *error;
void  (*init) (void);
printf(" load Hello2 \n");
handle = dlopen ("libHelloModule2.so", RTLD_LAZY);
printf (" lib Hello2 onload.. \n");
error = dlerror();
if (!handle) {
      printf ("lib HelloModule2 not loaded correctly %s \n", error);
      exit(1);
   dlerror();
   init =(void(*)())  dlsym(handle, "hello2");
  error = dlerror();
        if(error)
                fprintf(stderr, "Could not find print_hello(): %s\n",
error);
                exit(1);
(*init)();
    dlclose(handle);
void hello_bug()
printf ("Hello bug correctly  invoked : CQFD\n");
}// extern "C"
hello2.cc
#include "hello1.h"
typedef void  ( *PF1) (char *, char *);
extern "C" {
void hello2(){
printf ("Hello2 : ping Hello1\n");
/*simple call work in c not via JNI*/
hello_bug();
Hello.java :
package com.helloworld;
import java.util.*;
import java.io.*;
public class Hello  {
  private native void ShowMessage(String msg);
  public void initialized() {
            System.out.println(" ShowMessage - called");
  try {
          ShowMessage("Generated with JNI");
       } catch (Exception e ) {
            e.printStackTrace();         }
  public Hello(){
  System.loadLibrary("HelloModule1");
            System.out.println(" HelloModule1 loaded");
TestLocal.java :
import java.util.*;
import java.io.*;
import com.helloworld.Hello;
public class TestLocal{
public TestLocal(){
        System.out.println("test local");
public static void main(String[] args) {
        TestLocal test_local = new TestLocal();
        Hello test = new Hello();
        test.initialized();
}THE MOST IMPORTANT IS IN THE MAKEFILE:
Makefile :all: Hello.jar hello_jni.h libHelloModule1.so libHelloModule2.so TestLocal.class dummy
Hello.jar: com/helloworld/Hello.class
jar cvf $@  com/helloworld
com/helloworld/Hello.class: Hello.java
$(JAVAC)  -d . Hello.java
hello_jni.h: Hello.jar
$(JAVAH) -jni -o $@ -classpath ./Hello.jar com.helloworld.Hello
libHelloModule1.so : hello_jni.h hello1.o  
gcc  -G  -o $@ hello1.o -lstdc++
libHelloModule2.so : hello2.o
gcc   -G  -o $@ hello2.o -Wl -lstdc++  -L. -lHelloModule1   [u] # -->CASE  1 :THIS WORKS [/u]
gcc   -G  -o $@ hello2.o -Wl -lstdc++ [u] #-->CASE 2 :THIS  DOES NOT WORK[/u]
dummy : dummy_main.o
gcc  -o $@ dummy_main.o -L. -lHelloModule1 -L/usr/local/lib -lstdc++
hello2.o : hello2.cc
gcc -I. -O -c  hello2.cc
hello1.o : hello1.cc
gcc -I. -O -c  hello1.cc
TestLocal.class : TestLocal.java
$(JAVAC) -classpath  . -d . TestLocal.java
dummy_main.o :  dummy_main.cc
gcc -I. -O -c  dummy_main.cc
clean:
rm -rf com *.o *.so *.class *.jar hello_jni.h dummyCASE 1 : libHelloModule1.so is explicitely linked to libHelloModule2
myhost % dummy
load Hello2
lib Hello2 onload..
Hello2 : ping Hello1
Hello bug correctly invoked : CQFD
myhost % java -cp . TestLocal
test local
HelloModule1 loaded
ShowMessage - called
load Hello2
lib Hello2 onload..
Hello2 : ping Hello1
Hello bug correctly invoked : CQFD
CASE 2 : libHelloModule1.so is not explicitely linked to libHelloModule2
myhost % dummy
load Hello2
lib Hello2 onload..
Hello2 : ping Hello1
Hello bug correctly invoked : CQFD
myhost % java -cp . TestLocal
test local
HelloModule1 loaded
ShowMessage - called
load Hello2
lib Hello2 onload..
lib HelloModule2 not loaded correctly ld.so.1: java: fatal: relocation error: file ./libHelloModule2.so: symbol hello_bug: referenced symbol not found
My concern is to have this working in CASE1 with the JNI interface the same way it does in standard C built runtime.
So does any have encountered this?
Is there something I missed somewhere?
Thanks lot for your help
Youss

Answer 1

Hi,
I have implemented JNative which seems to be close to your problem.
It works under Windows and Linux, and loads libraries via dlopen and dlsym.
You can have a look at it's implementation at http://jnative.cvs.sourceforge.net/jnative/JNativeCpp/
Don't forget to load your libraries before trying to call them with System.load("/path/to/your/lib.so"); if they are not referenced by LD_LIBRARY_PATH.
This post may be false since I know nothing about Solaris. Perhaps JNative may be ported under Solaris ?
--Marc (http://jnative.sf.net)