Re: libgcj problem in FindClass with shared libraries.

[abhishek desai <abhi00 at gmail dot com>]

OK. It does call the _Jv_RegisterClasses function as soon as the
library gets loaded. Now its loading the library and finding the class
and methods correctly. Thanks.

On Wed, Jun 3, 2009 at 5:23 PM, abhishek desai <abhi00@gmail.com> wrote:
> 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
> dependency.
>
>
> On Wed, Jun 3, 2009 at 4:27 PM, Andrew Haley <aph@redhat.com> 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 <aph@redhat.com> 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 libgcj.so is loaded, and each time a shared library
>>>> is loaded.
>>>>
>>>> Andrew.
>>>>
>>>>
>>
>>
>