[cppgc] expose wrapper descriptor on CppHeap

This makes it possible for embedders to: 1. Avoid creating wrapper objects that happen to have a layout that leads V8 to consider the object cppgc-managed while it's not. Refs: nodejs/node#43521 2. Create cppgc-managed wrapper objects when they do not own the CppHeap. Refs: nodejs/node#45704 Bug: v8:13960 Change-Id: If31f4d56c5ead59dc0d56f937494d23d631f7438 Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/4598833 Reviewed-by: Michael Lippautz <mlippautz@chromium.org> Commit-Queue: Michael Lippautz <mlippautz@chromium.org> Cr-Commit-Position: refs/heads/main@{#88490}

Author: joyeecheung

include/v8-cppgc.h

@@ -177,6 +177,11 @@ class V8_EXPORT CppHeap {
  void CollectGarbageInYoungGenerationForTesting(
  cppgc::EmbedderStackState stack_state);
 
+ /**
+ * \returns the wrapper descriptor of this CppHeap.
+ */
+ v8::WrapperDescriptor wrapper_descriptor() const;
+
  private:
  CppHeap() = default;
 

src/heap/cppgc-js/cpp-heap.cc

@@ -147,6 +147,10 @@ void CppHeap::CollectGarbageInYoungGenerationForTesting(
  internal::CppHeap::CollectionType::kMinor, stack_state);
 }
 
+v8::WrapperDescriptor CppHeap::wrapper_descriptor() const {
+ return internal::CppHeap::From(this)->wrapper_descriptor();
+}
+
 namespace internal {
 
 namespace {

test/unittests/heap/cppgc-js/unified-heap-unittest.cc

@@ -710,4 +710,45 @@ TEST_F(UnifiedHeapTest, TracedReferenceHandlesDoNotLeak) {
  EXPECT_EQ(initial_count, final_count + 1);
 }
 
+namespace {
+class Wrappable2 final : public cppgc::GarbageCollected<Wrappable2> {
+ public:
+ static size_t destructor_call_count;
+ void Trace(cppgc::Visitor* visitor) const {}
+ ~Wrappable2() { destructor_call_count++; }
+};
+
+size_t Wrappable2::destructor_call_count = 0;
+} // namespace
+
+TEST_F(UnifiedHeapTest, WrapperDescriptorGetter) {
+ v8::Isolate* isolate = v8_isolate();
+ v8::HandleScope scope(isolate);
+ auto* wrappable_object =
+ cppgc::MakeGarbageCollected<Wrappable2>(allocation_handle());
+ v8::WrapperDescriptor descriptor =
+ isolate->GetCppHeap()->wrapper_descriptor();
+ v8::Local<v8::ObjectTemplate> tmpl = v8::ObjectTemplate::New(isolate);
+ int size = std::max(descriptor.wrappable_type_index,
+ descriptor.wrappable_instance_index) +
+ 1;
+ tmpl->SetInternalFieldCount(size);
+ v8::Local<v8::Object> api_object =
+ tmpl->NewInstance(isolate->GetCurrentContext()).ToLocalChecked();
+ api_object->SetAlignedPointerInInternalField(
+ descriptor.wrappable_type_index,
+ &descriptor.embedder_id_for_garbage_collected);
+ api_object->SetAlignedPointerInInternalField(
+ descriptor.wrappable_instance_index, wrappable_object);
+
+ Wrappable2::destructor_call_count = 0;
+ EXPECT_EQ(0u, Wrappable2::destructor_call_count);
+ CollectGarbageWithoutEmbedderStack(cppgc::Heap::SweepingType::kAtomic);
+ EXPECT_EQ(0u, Wrappable2::destructor_call_count);
+ api_object->SetAlignedPointerInInternalField(
+ descriptor.wrappable_instance_index, nullptr);
+ CollectGarbageWithoutEmbedderStack(cppgc::Heap::SweepingType::kAtomic);
+ EXPECT_EQ(1u, Wrappable2::destructor_call_count);
+}
+
 } // namespace v8::internal