cppgc: Fix data race ObjectSizeTrait

Fix benign race in
  https://clusterfuzz.com/testcase-detail/5203237072076800

Change-Id: I558b230e4905a48342d8e7cf70d39be5a1b7fdb8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3306375
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Auto-Submit: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78121}

src/heap/cppgc/heap-base.cc

@@ -36,7 +36,7 @@ class ObjectSizeCounter : private HeapVisitor<ObjectSizeCounter> {
 
  private:
   static size_t ObjectSize(const HeapObjectHeader& header) {
-    return ObjectView(header).Size();
+    return ObjectView<>(header).Size();
   }
 
   bool VisitHeapObjectHeader(HeapObjectHeader& header) {

src/heap/cppgc/marking-verifier.cc

@@ -124,7 +124,7 @@ bool MarkingVerifierBase::VisitHeapObjectHeader(HeapObjectHeader& header) {
   }
 
   verifier_found_marked_bytes_ +=
-      ObjectView(header).Size() + sizeof(HeapObjectHeader);
+      ObjectView<>(header).Size() + sizeof(HeapObjectHeader);
 
   verification_state_.SetCurrentParent(nullptr);
 

src/heap/cppgc/object-size-trait.cc

@@ -14,8 +14,8 @@ namespace internal {
 // static
 size_t BaseObjectSizeTrait::GetObjectSizeForGarbageCollected(
     const void* object) {
-  return ObjectView(HeapObjectHeader::FromObject(object))
-      .Size<AccessMode::kAtomic>();
+  return ObjectView<AccessMode::kAtomic>(HeapObjectHeader::FromObject(object))
+      .Size();
 }
 
 // static

src/heap/cppgc/object-view.h

@@ -15,13 +15,13 @@ namespace internal {
 
 // ObjectView allows accessing a header within the bounds of the actual object.
 // It is not exposed externally and does not keep the underlying object alive.
+template <AccessMode = AccessMode::kNonAtomic>
 class ObjectView final {
  public:
   V8_INLINE explicit ObjectView(const HeapObjectHeader& header);
 
   V8_INLINE Address Start() const;
   V8_INLINE ConstAddress End() const;
-  template <AccessMode = AccessMode::kNonAtomic>
   V8_INLINE size_t Size() const;
 
  private:
@@ -30,25 +30,30 @@ class ObjectView final {
   const bool is_large_object_;
 };
 
-ObjectView::ObjectView(const HeapObjectHeader& header)
+template <AccessMode access_mode>
+ObjectView<access_mode>::ObjectView(const HeapObjectHeader& header)
     : header_(header),
       base_page_(
           BasePage::FromPayload(const_cast<HeapObjectHeader*>(&header_))),
-      is_large_object_(header_.IsLargeObject()) {
+      is_large_object_(header_.IsLargeObject<access_mode>()) {
   DCHECK_EQ(Start() + Size(), End());
 }
 
-Address ObjectView::Start() const { return header_.ObjectStart(); }
+template <AccessMode access_mode>
+Address ObjectView<access_mode>::Start() const {
+  return header_.ObjectStart();
+}
 
-ConstAddress ObjectView::End() const {
+template <AccessMode access_mode>
+ConstAddress ObjectView<access_mode>::End() const {
   return is_large_object_ ? LargePage::From(base_page_)->PayloadEnd()
                           : header_.ObjectEnd();
 }
 
-template <AccessMode mode>
-size_t ObjectView::Size() const {
+template <AccessMode access_mode>
+size_t ObjectView<access_mode>::Size() const {
   return is_large_object_ ? LargePage::From(base_page_)->ObjectSize()
-                          : header_.ObjectSize<mode>();
+                          : header_.ObjectSize<access_mode>();
 }
 
 }  // namespace internal

src/heap/cppgc/visitor.cc

@@ -32,7 +32,7 @@ namespace {
 
 void TraceConservatively(ConservativeTracingVisitor* conservative_visitor,
                          const HeapObjectHeader& header) {
-  const auto object_view = ObjectView(header);
+  const auto object_view = ObjectView<>(header);
   Address* object = reinterpret_cast<Address*>(object_view.Start());
   for (size_t i = 0; i < (object_view.Size() / sizeof(Address)); ++i) {
     Address maybe_ptr = object[i];

test/unittests/heap/cppgc/workloads-unittest.cc

@@ -207,7 +207,7 @@ class ObjectSizeCounter final : private HeapVisitor<ObjectSizeCounter> {
 
  private:
   static size_t ObjectSize(const HeapObjectHeader& header) {
-    return ObjectView(header).Size();
+    return ObjectView<>(header).Size();
   }
 
   bool VisitHeapObjectHeader(HeapObjectHeader& header) {