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From "Weldon Washburn" <weldon...@gmail.com>
Subject [DRLVM] MMTk write barrier -- questions about which writeBarrier() API to use
Date Mon, 05 Jun 2006 19:04:03 GMT

Perhas the MMTk crowd knows the answer to the following questions.

Can I simply not use
org.mmtk.plan.PlanLocal.writeBarrier(ObjectReference src, Address
slot, ObjectReference tgt, Offset metaDataA, int metaDataB, int

Instead, I want to only use writeBarrier(ObjectReference src, Offset
srcOffset, ObjectReference dst, Offset dstOffset, int bytes);.  Will
this be a problem?

Questions about the incoming args:

ObjectReference src
>From the JITs perspective, an ObjectReference is indistinguishable
from a java.lang.Object.  Is this true?  False?

Address slot
When is  "Address slot" argument actually created?  Does this Address
object live long enough such that its "value" field needs to be
updated following a copying GC?  Is the answer the same for both Jikes
and the Rotor ports?

Offset srcOffset

In DRLVM, the classloader resolves a field offset once and it never
changes.  Does it make sense for the classloader to create all the
Offset objects during load time?  Initially, I want to create these
objects _outside_ the formal java heap to have tight control over
object movement and deletion.   Basically, I don't want the Offset
object to ever move or ever be deleted during the initial stages of
MMTk integration.

A question about how jikesrvm-2.4.4/MMTk handles objects that are not
inside the offical heap.  Are these objects simply ignored?  I know
that ECMA CLI spec requires that objects which are not in the official
heap must be ignored.  I simply don't know if this requirement is
incorporated in 2.4.4/MMTk source base.

While it looks like a lot of work to get DRLVM to generate Offset
object properly, it looks like even a bigger job to modify MMTk to
replace Offset class with an "int" that holds a given field's offset.
Any opinions on this statement?

Weldon Washburn
Intel Middleware Products Division

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