libgcj problem in FindClass with shared libraries.

abhishek desai
Wed Jun 3 11:53:00 GMT 2009

I am a bit confused here.. When does the call to _Jv_RegisterClasses
actually happen ? Is it called the moment the library is loaded by the
linker ? Does this happen for all the classes in the library ?

There is a difference between the way the how libgcj is loaded and how
my library gets loaded. My library is getting loaded using the dlopen
call where as libgcj is getting loaded because of the library

On Wed, Jun 3, 2009 at 4:27 PM, Andrew Haley <> wrote:
> abhishek desai wrote:
>> _Jv_RegisterClasses is called but only initially. Not after we call
>> FindClass.
> Right, which is the cause of your problem.  You need to find out why
> _Jv_RegisterClasses is called by libgcj but not by the shared library
> that you created.
>> Also there is no call happening to dlsym after the library
>> is opened using dlopen in libdl. How are the symbols loaded then ?
> You don't need it.  _Jv_RegisterClasses updates the cache in the class
> loader that is queried to find the class.
> Andrew.
>> On Wed, Jun 3, 2009 at 3:42 PM, Andrew Haley <> wrote:
>>> abhishek desai wrote:
>>>> I am using libgcj version 3.4.6 (I have to use this version of gcc and
>>>> libgcj) .
>>> Well, we can't fix it.  It is ancient history.
>>>> I have shared libraries with precompiled java clases and am
>>>> using JNI function call "(*env)->FindClass" to get the class. Tracing
>>>> through the _Jv_JNI_FIndClass I found that the dynamic library gets
>>>> loaded but the symbols are not loaded into the cache.
>>>> In the function call "jclass
>>>> gnu::gcj::runtime::VMClassLoader::findClass (jstring name)"
>>>> there is a call to "jboolean java::lang::Runtime::loadLibraryInternal
>>>> (jstring lib)" . This does the loading of the library by eventually
>>>> calling dlopen in libtdl.
>>>> After this call there is no call to access the symbol from the library
>>>> or to load it to the cache.
>>>> But the symbol is searched for in the cache using _Jv_FindClassInCache
>>>> which returns NULL. Is this a bug or I am missing something ? Need
>>>> help with getting the symbols loaded.
>>> You need to make sure that _Jv_RegisterClasses is being called when the
>>> shared library is loaded.  If it is, then the classes in the library will
>>> be found; if not, then you need to find out why not.
>>> Put a breakpoint on _Jv_RegisterClasses.  You should see it called once
>>> at startup, again when is loaded, and each time a shared library
>>> is loaded.
>>> Andrew.

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