[heap] Add object iterator for OffThreadSpace

Adds an paged space object iterator for OffThreadSpace, and removes
the Heap pointer from the iterator so that it can be used off-thread.

Bug: chromium:1011762
Change-Id: I025edf144f393e61d89cce2485c0ff1fe8c80c56
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1991488
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65658}

src/heap/spaces-inl.h

@@ -5,6 +5,7 @@
 #ifndef V8_HEAP_SPACES_INL_H_
 #define V8_HEAP_SPACES_INL_H_
 
+#include "src/common/globals.h"
 #include "src/heap/spaces.h"
 
 #include "src/base/atomic-utils.h"
@@ -86,8 +87,8 @@ HeapObject PagedSpaceObjectIterator::FromCurrentPage() {
     if (!obj.IsFreeSpaceOrFiller()) {
       if (obj.IsCode()) {
         DCHECK_IMPLIES(
-            space_ != heap_->code_space(),
-            space_ == heap_->read_only_space() && Code::cast(obj).is_builtin());
+            space_->identity() != CODE_SPACE,
+            space_->identity() == RO_SPACE && Code::cast(obj).is_builtin());
         DCHECK_CODEOBJECT_SIZE(obj_size, space_);
       } else {
         DCHECK_OBJECT_SIZE(obj_size);

src/heap/spaces.cc

@@ -53,11 +53,10 @@ PagedSpaceObjectIterator::PagedSpaceObjectIterator(Heap* heap,
                                                    PagedSpace* space)
     : cur_addr_(kNullAddress),
       cur_end_(kNullAddress),
-      heap_(heap),
       space_(space),
       page_range_(space->first_page(), nullptr),
       current_page_(page_range_.begin()) {
-  heap_->mark_compact_collector()->EnsureSweepingCompleted();
+  heap->mark_compact_collector()->EnsureSweepingCompleted();
 }
 
 PagedSpaceObjectIterator::PagedSpaceObjectIterator(Heap* heap,
@@ -65,11 +64,10 @@ PagedSpaceObjectIterator::PagedSpaceObjectIterator(Heap* heap,
                                                    Page* page)
     : cur_addr_(kNullAddress),
       cur_end_(kNullAddress),
-      heap_(heap),
       space_(space),
       page_range_(page),
       current_page_(page_range_.begin()) {
-  heap_->mark_compact_collector()->EnsureSweepingCompleted();
+  heap->mark_compact_collector()->EnsureSweepingCompleted();
 #ifdef DEBUG
   AllocationSpace owner = page->owner_identity();
   DCHECK(owner == RO_SPACE || owner == OLD_SPACE || owner == MAP_SPACE ||
@@ -77,6 +75,13 @@ PagedSpaceObjectIterator::PagedSpaceObjectIterator(Heap* heap,
 #endif  // DEBUG
 }
 
+PagedSpaceObjectIterator::PagedSpaceObjectIterator(OffThreadSpace* space)
+    : cur_addr_(kNullAddress),
+      cur_end_(kNullAddress),
+      space_(space),
+      page_range_(space->first_page(), nullptr),
+      current_page_(page_range_.begin()) {}
+
 // We have hit the end of the page and should advance to the next block of
 // objects.  This happens at the end of the page.
 bool PagedSpaceObjectIterator::AdvanceToNextPage() {

src/heap/spaces.h

@@ -54,6 +54,7 @@ class LocalSpace;
 class MemoryAllocator;
 class MemoryChunk;
 class MemoryChunkLayout;
+class OffThreadSpace;
 class Page;
 class PagedSpace;
 class SemiSpace;
@@ -1619,6 +1620,9 @@ class V8_EXPORT_PRIVATE PagedSpaceObjectIterator : public ObjectIterator {
   PagedSpaceObjectIterator(Heap* heap, PagedSpace* space);
   PagedSpaceObjectIterator(Heap* heap, PagedSpace* space, Page* page);
 
+  // Creates a new object iterator in a given off-thread space.
+  explicit PagedSpaceObjectIterator(OffThreadSpace* space);
+
   // Advance to the next object, skipping free spaces and other fillers and
   // skipping the special garbage section of which there is one per space.
   // Returns nullptr when the iteration has ended.
@@ -1634,7 +1638,6 @@ class V8_EXPORT_PRIVATE PagedSpaceObjectIterator : public ObjectIterator {
 
   Address cur_addr_;  // Current iteration point.
   Address cur_end_;   // End iteration point.
-  Heap* heap_;
   PagedSpace* space_;
   PageRange page_range_;
   PageRange::iterator current_page_;