Question: pointer to klass

[Andrew Kondratovich]

Yep, you're right.
Simple check shows that pointer is changing the position.
Can anybody give an advise, how to save object class in serialization
in fast way ?)

On 3/10/12, Krystal Mok <rednaxelafx at gmail.com> wrote:
> Hi Andrew,
>
> In normal execution, the klass pointer of an object always points to the
> same klass during its lifetime. But, you shouldn't expect to persist the
> value of a klass pointer and use it later. The klass may move during a full
> GC, so the value of the pointer may change, although it'd still be pointing
> to the same klass. Class redefinition/retransformation doesn't affect the
> klass pointer right now.
>
> Just for fun: if you really want to see what happens when you mess with the
> klass pointer, here's an example [1].
> Do remember that it's just for fun, and the example only works in the
> interpreter, without GC happening in between, or any concurrent access to
> that klass pointer.
>
> HTH,
> Kris Mok
>
> [1]: http://hllvm.group.iteye.com/group/topic/17806
>
> On Sat, Mar 10, 2012 at 5:55 AM, Andrew Kondratovich <
> andrew.kondratovich at gmail.com> wrote:
>
>> Hello.
>>
>> I'm working on object serialization through Unsafe API.
>> Every java object in memory is header + field values. Header contains
>> pointer to klass
>> (
>> http://hg.openjdk.java.net/jdk7/jdk7/hotspot/file/d61c7c22b25c/src/share/vm/oops/klass.hpp
>> ).
>> Can this pointer be changed in Runtime by JVM ? I mean, if I read
>> address to `klass` for some Java Class, does it be the same (the same
>> adress and klass structure for the same Java Class) in 10 minutes, 3
>> hours, 2 days... Or can be changed by JIT for example ?
>>
>> Thanks.
>> --
>> --
>> Andrew
>>
>


-- 
--
Andrew