Preventing Class Definitions from Compacting At GC Cycle

David Holmes david.holmes at
Mon Nov 4 01:52:02 UTC 2013

On 4/11/2013 11:40 AM, 姜善林 wrote:
> Hi all,
> I'm sorry if this email bothers you. Just one question, is there any way
> to determine precisely the regression test scope for java development
> and testing?

I have no idea what you mean by that but it doesn't sound related to 
Serkan's query so please start your own email thread - perhaps on 
hotspot-dev if it is a general hotspot question.


> Many thanks!
> 2013/11/4 David Holmes <david.holmes at
> <mailto:david.holmes at>>
>     Adding hotspot-gc and (hopefully) bcc'ing the discuss list.
>     David
>     On 3/11/2013 5:18 AM, serkan özal wrote:
>         Hi all,
>         I am not sure that target of mail is this group or not but I
>         don't know better one for asking :)
>         I am currently working on an OffHeap solution and I have a
>         problem with "Compact" phase of GC.As I see at "Compact" phase,
>         location of classes these not loaded by bootloader may be
>         changed. However, location of classes these loaded by bootloader
>         (classloaders are null) are not changed.Changing memory location
>         of class definition fails my OffHeap solution.
>         Compacting can be disabled by VM arguments but I don't want to
>         use these arguments. Because disabling compaction for all
>         objects causes increasing of fragmentation. In addition, I tried
>         class pinning with JNI by "NewGlobalRef" method but it doesn't
>         prevent compacting. As I understood, it only hides object from
>         garbage collected.
>         In brief, is there any way to prevent compacting of any specific
>         class defition (or object) at GC cycle?Is there any bit, offset
>         or field (such as mark_oop) in object header to prevent
>         compacting of fully from GC for any specific object or class?
>         Thanks in advance.
>         --
>         Serkan ÖZAL
> --
> 姜善林

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