Re: [rvm-research] Regarding Address of Object Reference in Field section of Object

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The MMTk plan "poisoned" unconditionally sets and clears the low-order
bit of all object references - this is the regression test for object
read and write barriers.

cheers

On 14/01/14 15:53, Hari Krishnan wrote:
> Robin,
> 
> The process is basically to mark the references as I trace the
> objects. Since I want to mark the instance field references in each
> object, I want to mutate a single bit indicating the reference is
> processed.  So yes to question (you want to add a single bit of
> metadata to each object reference ?).Thank you for your help. I
> want to try Read Barriers. I appreciate your quick response. Is
> there any code that  already overrides read barrier?
> 
> Cheers Hari Krishnan.
> 
> 
> On Mon, Jan 13, 2014 at 10:45 PM, Robin Garner
> <[email protected] <mailto:[email protected]>> wrote:
> 
> Hari,
> 
> Just to clarify, you want to add a single bit of metadata to each 
> object reference ?
> 
> The "simplest"[1] solution is to use one of the two low-order bits
> of each object reference (objects are always (at least) 4-byte
> aligned). In order to do this you'll need a read barrier that masks
> out this bit so that the mutator always sees aligned pointers, and
> a write barrier that reinstates the metadata.
> 
> Alternatively, if this is too expensive, I'd suggest adding
> additional space to the object via the classloader - how easy this
> is depends on how you want to use the data, how much space you're
> prepared to use etc.
> 
> cheers
> 
> [1] Read barriers are never simple :-/
> 
> On 14/01/14 12:01, Hari Krishnan wrote:
>> Hi ,
> 
>> I want to set a bit, toggle a bit and test a bit in the section 
>> where each address of the instance field (object references)
>> saved in objects. Is there any bit that I can use in each object
>> fields for this purpose?
> 
>> Cheers Hari Krishnan
> 
> 
> 
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