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Re: [rvm-research] Add metadata to each field of an object?
by Michael Bond
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On Fri, 11 Sep 2009, Colin(Du Li) wrote:
> Which project did you use the MiscHeader? I would like to know more
> detail about the project.
> I also have two questions as follows.
> 1. If we use MiscHeader to expand the object size, can GC automatically
> adapt to this changes, that is, can GC trace and collect objects using the
> new object size?
Hi Du Li,
I'm currently using MiscHeader for metadata for race detection, but I
don't think I've used it in any patches that are on the Research Archive.
Fortunately, GC and the rest of the VM will automatically use the new
object size if you add a word via MiscHeader. You do need to modify the
GC if you want the header word traced as a reference.
> 2. Is that possible to expand header for part of objects (to save
> space), or all the objects should expand header?
Yeah, that's possible. For example, Maria Jump added header words to a
dynamically chosen subset of objects for dynamic object sampling work from
ISMM 2004. That's implemented in an older version of Jikes, though.
Does anyone know of or have a recent Jikes patch that does non-uniform
extra header words?
You might look at how Jikes does address-based hashing: for objects that
are copied after their Object.hashCode() method has been called, an extra
word is added to the object to store the old object address. The extra
word is added either at the start or end of the object, depending on the
value of JavaHeaderConstants.DYNAMIC_HASH_OFFSET.
Mike
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> Which project did you use the MiscHeader? I would like to know more
> detail about the project.
> I also have two questions as follows.
> 1. If we use MiscHeader to expand the object size, can GC automatically
> adapt to this changes, that is, can GC trace and collect objects using the
> new object size?
Hi Du Li,
I'm currently using MiscHeader for metadata for race detection, but I
don't think I've used it in any patches that are on the Research Archive.
Fortunately, GC and the rest of the VM will automatically use the new
object size if you add a word via MiscHeader. You do need to modify the
GC if you want the header word traced as a reference.
> 2. Is that possible to expand header for part of objects (to save
> space), or all the objects should expand header?
Yeah, that's possible. For example, Maria Jump added header words to a
dynamically chosen subset of objects for dynamic object sampling work from
ISMM 2004. That's implemented in an older version of Jikes, though.
Does anyone know of or have a recent Jikes patch that does non-uniform
extra header words?
You might look at how Jikes does address-based hashing: for objects that
are copied after their Object.hashCode() method has been called, an extra
word is added to the object to store the old object address. The extra
word is added either at the start or end of the object, depending on the
value of JavaHeaderConstants.DYNAMIC_HASH_OFFSET.
Mike
------------------------------------------------------------------------------
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trial. Simplify your report design, integration and deployment - and focus on
what you do best, core application coding. Discover what's new with
Crystal Reports now. http://p.sf.net/sfu/bobj-july
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