Linux JVM: How to load shared libraries with mutual/circular dependencies

Question

Hi,
I am using the API
System.loadLibrary(String name)
to dynamically link shared libaries to Linux JVM.
The shared libraries has complex circular symbol dependencies among them.
I am not able to load shared libraries due to java.lang.UnsatisfiedLinkError.
Any ideas on how a number of shared libraries with interdependent realtionships
could be successfully linked in to the Linux JVM?
Thanks,
Soumen.
Background
===========
Successful execution of native code within Java virtual machine in a
host platform, has two necessary prerequisites:
Prerequisite 1: The native code is written to the JNI specification
Prerequisite 2: The native code is dynamically linked with Java virtual
machine.
The second step is achieved via simple Java interface, System.loadLibrary:
http://java.sun.com/j2se/1.4.2/docs/api/java/lang/System.html#loadLibrary(java.lang.String)
However, implementation of this interface is highly platform dependent
in regards to exact nature of dynamic linking process.
Tests
=====
I made three shared libraries libfeatureA.so, libfeatureB.so and libfeatureC.so.
Feature A and Feature B are mutually dependent on each other (i.e cicular
dependencies between libfeatureA.so, libfeatureB.so) whereas libfeatureC.so
has no external dependencies.
Case 1
I could link libfeatureC.so with java.
Case 2
Java failed to resolve circular dependency between libfeatureA.so, libfeatureB.so
resulting in linking failure. There may be repackaging workarounds which I have
not yet explored.
Java source code
================
class TestLoadLibrary
static
System.loadLibrary("featureB");
System.loadLibrary("featureA");
System.loadLibrary("featureB");
public static void main(String[] args)
System.out.println("In TestLoadLibrary.main()");
Exception in thread "main" java.lang.UnsatisfiedLinkError: /homes/soumen/work/event/featureB/libfeatureB.so.1.0: /homes/soumen/work/ev B.so.1.0: undefined symbol: featureA_func2
at java.lang.ClassLoader$NativeLibrary.load(Native Method)
at java.lang.ClassLoader.loadLibrary0(ClassLoader.java:1737)
at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1662)
at java.lang.Runtime.loadLibrary0(Runtime.java:817)
at java.lang.System.loadLibrary(System.java:986)
at TestLoadLibrary.<clinit>(TestLoadLibrary.java:5)

Answer 1

The use of "dlopen() application programming" to achieve dynamic link closure works if there are
no circular dependencies. For example, I have the following dependency:
libfeatureD.so ==> libfeatureC.so
Even if I call Java APIs in correct dependency order, i.e.,
System.loadLibrary("featureC");
System.loadLibrary("featureD");
there would be java.lang.UnsatisfiedLinkError for call System.loadLibrary("featureD").
Now, I have a JNI method implementation, which makes native API call in same dependency order:
dlopen("libfeatureC.so", RTLD_LAZY|RTLD_GLOBAL);
dlopen("libfeatureD.so", RTLD_LAZY|RTLD_GLOBAL);
and now System.loadLibrary calls succeed. Note that I had to set environment
variable LD_LIBRARY_PATH so that dlopen call would find libraries to load.
In other words, from a JNI programming point of view, "linking chasm" has been crossed.
I am looking at circular dependency issue, i.e.,
libfeatureA.so <==> libfeatureB.so
There may be library repackaging workaround.
If anybody knows any workaround, please post.
-Soumen Sarkar
JNI code
========
#include <jni.h>
#include "TestLoadLibrary.h"
#include <stdio.h>
#include <string.h>
#include <dlfcn.h>
JNIEXPORT void JNICALL Java_TestLoadLibrary_libLoadNative
(JNIEnv * jenv, jclass class, jobjectArray libNames)
printf("native: In TestLoadLibrary.libLoadNative()\n");
char linuxLibName[1024];
jsize idx = 0;
jsize nLibs = (*jenv)->GetArrayLength(jenv, libNames);
for(idx = 0; idx < nLibs; ++idx)
/* obtain the current object from the object array */
jobject myObject = (*jenv)->GetObjectArrayElement(jenv, libNames, idx);
/* Convert the object just obtained into a String */
const char libName = (jenv)->GetStringUTFChars(jenv,myObject,0);
strcpy(linuxLibName, "lib");
strcat(linuxLibName, libName);
strcat(linuxLibName, ".so");
printf("\nnative: Trying to open lib with name %s\n", linuxLibName);
void* handle = dlopen(linuxLibName, RTLD_LAZY|RTLD_GLOBAL);
if(handle == 0)
fputs ("\nnative: Could not load lib\n", stderr);
fputs (dlerror(), stderr);
else
printf("\nnative: Loaded lib %s\n", linuxLibName);
/* Free up memory to prevent memory leaks */
(*jenv)->ReleaseStringUTFChars(jenv, myObject, libName);
return;