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From "Xiao-Feng Li" <xiaofeng...@gmail.com>
Subject [DRLVM] what's the purpose to set NEXT_TO_HIGH_BIT_SET_MASK in object size?
Date Wed, 21 Mar 2007 05:24:57 GMT
Hi, the source code for class preparation calls
set_instance_data_size_constraint_bit() for three situations: special
alignment requirement, having finalizer, and to be pinned. And the
comments there say the constraint bit is for GC to understand.

But current GC actually doesn't care about this bit, and simply masks
it off. Does anybody know what are the situations for the size
constraint bit to be set for allocation?

I recall this kind of constraint bit was ORP legacy, when the
intention was for gc_alloc_fast to be really fast, avoiding any
special allocation treatment. So once the big flag is set,
gc_alloc_fast will simply return NULL, and the VM will invoke gc_alloc
to accomplish the allocation.

Now DRLVM has different processing, and the GC doesn't use the flag in
size for allocation. I wonder what is the real purpose of this size
flag in allocation.


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