Question: pointer to klass

[David Holmes]

On 10/03/2012 8:54 AM, Andrew Kondratovich wrote:
> 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 ?)

What do you mean? The type of the object serialized is part of the 
serialization information. You can't just save a pointer as the Class 
may have to be loaded as part of de-serialization.

David

> 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
>>>
>>
>
>