Implement HeapIterator that skips over unreachable objects.

Implement HeapIterator that skips over unreachable objects.

I'm using it when creating heap snapshots. I decided that it will
be more convenient to have it as a separate piece of code, instead
of embedding into the snapshot generator.

Committed: http://code.google.com/p/v8/source/detail?r=6091

[Søren Thygesen Gjesse, 2010-12-21 09:04:44]

LGTM

http://codereview.chromium.org/6014004/diff/1/src/heap.cc
File src/heap.cc (right):

http://codereview.chromium.org/6014004/diff/1/src/heap.cc#newcode4965
src/heap.cc:4965: class UnreachableObjectsFilter : public HeapObjectsFilter {
Regarding the marking of unreachable objects - can't you just re-use the GC-code
for marking of all live objects and then skip the un-marked ones insteadm?

[mnaganov (inactive), 2010-12-21 10:48:00]

http://codereview.chromium.org/6014004/diff/1/src/heap.cc
File src/heap.cc (right):

http://codereview.chromium.org/6014004/diff/1/src/heap.cc#newcode4965
src/heap.cc:4965: class UnreachableObjectsFilter : public HeapObjectsFilter {
On 2010/12/21 09:04:44, Søren Gjesse wrote:
> Regarding the marking of unreachable objects - can't you just re-use the
GC-code
> for marking of all live objects and then skip the un-marked ones insteadm?

The problem is: once an object is marked, it doesn't appear as a valid heap
object (you need to get its map_word, unmark it, etc.) That's why I mark those
objects that are to be skipped by the iterator.