v8/test/cctest/heap/test-embedder-tracing.cc

// Copyright 2017 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <unordered_map>
#include <vector>

#include "include/v8.h"
#include "src/api/api-inl.h"
#include "src/heap/heap-inl.h"
#include "src/objects/module.h"
#include "src/objects/objects-inl.h"
#include "src/objects/script.h"
#include "src/objects/shared-function-info.h"
#include "test/cctest/cctest.h"
#include "test/cctest/heap/heap-utils.h"

namespace v8 {

// See test below: TracedGlobalNoDestructor.
template <>
struct TracedGlobalTrait<v8::TracedGlobal<v8::Value>> {
  static constexpr bool kRequiresExplicitDestruction = false;
};

namespace internal {
namespace heap {

namespace {

v8::Local<v8::Object> ConstructTraceableJSApiObject(
    v8::Local<v8::Context> context, void* first_field, void* second_field) {
  v8::EscapableHandleScope scope(context->GetIsolate());
  v8::Local<v8::FunctionTemplate> function_t =
      v8::FunctionTemplate::New(context->GetIsolate());
  v8::Local<v8::ObjectTemplate> instance_t = function_t->InstanceTemplate();
  instance_t->SetInternalFieldCount(2);
  v8::Local<v8::Function> function =
      function_t->GetFunction(context).ToLocalChecked();
  v8::Local<v8::Object> instance =
      function->NewInstance(context).ToLocalChecked();
  instance->SetAlignedPointerInInternalField(0, first_field);
  instance->SetAlignedPointerInInternalField(1, second_field);
  CHECK(!instance.IsEmpty());
  i::Handle<i::JSReceiver> js_obj = v8::Utils::OpenHandle(*instance);
  CHECK_EQ(i::JS_API_OBJECT_TYPE, js_obj->map().instance_type());
  return scope.Escape(instance);
}

enum class TracePrologueBehavior { kNoop, kCallV8WriteBarrier };

class TestEmbedderHeapTracer final : public v8::EmbedderHeapTracer {
 public:
  TestEmbedderHeapTracer() = default;
  TestEmbedderHeapTracer(TracePrologueBehavior prologue_behavior,
                         v8::Global<v8::Array> array)
      : prologue_behavior_(prologue_behavior), array_(std::move(array)) {}

  void RegisterV8References(
      const std::vector<std::pair<void*, void*>>& embedder_fields) final {
    registered_from_v8_.insert(registered_from_v8_.end(),
                               embedder_fields.begin(), embedder_fields.end());
  }

  void AddReferenceForTracing(v8::TracedGlobal<v8::Object>* global) {
    to_register_with_v8_.push_back(global);
  }

  bool AdvanceTracing(double deadline_in_ms) final {
    for (auto global : to_register_with_v8_) {
      RegisterEmbedderReference(global->As<v8::Value>());
    }
    to_register_with_v8_.clear();
    return true;
  }

  bool IsTracingDone() final { return to_register_with_v8_.empty(); }

  void TracePrologue(EmbedderHeapTracer::TraceFlags) final {
    if (prologue_behavior_ == TracePrologueBehavior::kCallV8WriteBarrier) {
      auto local = array_.Get(isolate());
      local->Set(local->CreationContext(), 0, v8::Object::New(isolate()))
          .Check();
    }
  }

  void TraceEpilogue() final {}
  void EnterFinalPause(EmbedderStackState) final {}

  bool IsRegisteredFromV8(void* first_field) const {
    for (auto pair : registered_from_v8_) {
      if (pair.first == first_field) return true;
    }
    return false;
  }

  void ConsiderTracedGlobalAsRoot(bool value) {
    consider_traced_global_as_root_ = value;
  }

  bool IsRootForNonTracingGC(const v8::TracedGlobal<v8::Value>& handle) final {
    return consider_traced_global_as_root_;
  }

 private:
  std::vector<std::pair<void*, void*>> registered_from_v8_;
  std::vector<v8::TracedGlobal<v8::Object>*> to_register_with_v8_;
  bool consider_traced_global_as_root_ = true;
  TracePrologueBehavior prologue_behavior_ = TracePrologueBehavior::kNoop;
  v8::Global<v8::Array> array_;
};

}  // namespace

TEST(V8RegisteringEmbedderReference) {
  // Tests that wrappers are properly registered with the embedder heap
  // tracer.
  ManualGCScope manual_gc;
  CcTest::InitializeVM();
  v8::Isolate* isolate = CcTest::isolate();
  TestEmbedderHeapTracer tracer;
  heap::TemporaryEmbedderHeapTracerScope tracer_scope(isolate, &tracer);
  v8::HandleScope scope(isolate);
  v8::Local<v8::Context> context = v8::Context::New(isolate);
  v8::Context::Scope context_scope(context);

  void* first_field = reinterpret_cast<void*>(0x2);
  v8::Local<v8::Object> api_object =
      ConstructTraceableJSApiObject(context, first_field, nullptr);
  CHECK(!api_object.IsEmpty());
  CcTest::CollectGarbage(i::OLD_SPACE);
  CHECK(tracer.IsRegisteredFromV8(first_field));
}

TEST(EmbedderRegisteringV8Reference) {
  // Tests that references that are registered by the embedder heap tracer are
  // considered live by V8.
  ManualGCScope manual_gc;
  CcTest::InitializeVM();
  v8::Isolate* isolate = CcTest::isolate();
  TestEmbedderHeapTracer tracer;
  heap::TemporaryEmbedderHeapTracerScope tracer_scope(isolate, &tracer);
  v8::HandleScope scope(isolate);
  v8::Local<v8::Context> context = v8::Context::New(isolate);
  v8::Context::Scope context_scope(context);

  v8::TracedGlobal<v8::Object> g;
  {
    v8::HandleScope inner_scope(isolate);
    v8::Local<v8::Object> o =
        v8::Local<v8::Object>::New(isolate, v8::Object::New(isolate));
    g.Reset(isolate, o);
  }
  tracer.AddReferenceForTracing(&g);
  CcTest::CollectGarbage(i::OLD_SPACE);
  CHECK(!g.IsEmpty());
}

namespace {

void ResurrectingFinalizer(
    const v8::WeakCallbackInfo<v8::Global<v8::Object>>& data) {
  data.GetParameter()->ClearWeak();
}

}  // namespace

TEST(TracingInRevivedSubgraph) {
  // Tests that wrappers are traced when they are contained with in a subgraph
  // that is revived by a finalizer.
  ManualGCScope manual_gc;
  CcTest::InitializeVM();
  v8::Isolate* isolate = CcTest::isolate();
  TestEmbedderHeapTracer tracer;
  heap::TemporaryEmbedderHeapTracerScope tracer_scope(isolate, &tracer);
  v8::HandleScope scope(isolate);
  v8::Local<v8::Context> context = v8::Context::New(isolate);
  v8::Context::Scope context_scope(context);

  v8::Global<v8::Object> g;
  void* first_field = reinterpret_cast<void*>(0x4);
  {
    v8::HandleScope inner_scope(isolate);
    v8::Local<v8::Object> api_object =
        ConstructTraceableJSApiObject(context, first_field, nullptr);
    CHECK(!api_object.IsEmpty());
    v8::Local<v8::Object> o =
        v8::Local<v8::Object>::New(isolate, v8::Object::New(isolate));
    o->Set(context, v8_str("link"), api_object).FromJust();
    g.Reset(isolate, o);
    g.SetWeak(&g, ResurrectingFinalizer, v8::WeakCallbackType::kFinalizer);
  }
  CcTest::CollectGarbage(i::OLD_SPACE);
  CHECK(tracer.IsRegisteredFromV8(first_field));
}

TEST(TracingInEphemerons) {
  // Tests that wrappers that are part of ephemerons are traced.
  ManualGCScope manual_gc;
  CcTest::InitializeVM();
  v8::Isolate* isolate = CcTest::isolate();
  TestEmbedderHeapTracer tracer;
  heap::TemporaryEmbedderHeapTracerScope tracer_scope(isolate, &tracer);
  v8::HandleScope scope(isolate);
  v8::Local<v8::Context> context = v8::Context::New(isolate);
  v8::Context::Scope context_scope(context);

  v8::Local<v8::Object> key =
      v8::Local<v8::Object>::New(isolate, v8::Object::New(isolate));
  void* first_field = reinterpret_cast<void*>(0x8);
  i::Isolate* i_isolate = reinterpret_cast<i::Isolate*>(isolate);
  Handle<JSWeakMap> weak_map = i_isolate->factory()->NewJSWeakMap();
  {
    v8::HandleScope inner_scope(isolate);
    v8::Local<v8::Object> api_object =
        ConstructTraceableJSApiObject(context, first_field, nullptr);
    CHECK(!api_object.IsEmpty());
    Handle<JSObject> js_key =
        handle(JSObject::cast(*v8::Utils::OpenHandle(*key)), i_isolate);
    Handle<JSReceiver> js_api_object = v8::Utils::OpenHandle(*api_object);
    int32_t hash = js_key->GetOrCreateHash(i_isolate).value();
    JSWeakCollection::Set(weak_map, js_key, js_api_object, hash);
  }
  CcTest::CollectGarbage(i::OLD_SPACE);
  CHECK(tracer.IsRegisteredFromV8(first_field));
}

TEST(FinalizeTracingIsNoopWhenNotMarking) {
  ManualGCScope manual_gc;
  CcTest::InitializeVM();
  v8::Isolate* isolate = CcTest::isolate();
  Isolate* i_isolate = CcTest::i_isolate();
  TestEmbedderHeapTracer tracer;
  heap::TemporaryEmbedderHeapTracerScope tracer_scope(isolate, &tracer);

  // Finalize a potentially running garbage collection.
  i_isolate->heap()->CollectGarbage(OLD_SPACE,
                                    GarbageCollectionReason::kTesting);
  CHECK(i_isolate->heap()->incremental_marking()->IsStopped());

  int gc_counter = i_isolate->heap()->gc_count();
  tracer.FinalizeTracing();
  CHECK(i_isolate->heap()->incremental_marking()->IsStopped());
  CHECK_EQ(gc_counter, i_isolate->heap()->gc_count());
}

TEST(FinalizeTracingWhenMarking) {
  ManualGCScope manual_gc;
  CcTest::InitializeVM();
  v8::Isolate* isolate = CcTest::isolate();
  Isolate* i_isolate = CcTest::i_isolate();
  TestEmbedderHeapTracer tracer;
  heap::TemporaryEmbedderHeapTracerScope tracer_scope(isolate, &tracer);

  // Finalize a potentially running garbage collection.
  i_isolate->heap()->CollectGarbage(OLD_SPACE,
                                    GarbageCollectionReason::kTesting);
  if (i_isolate->heap()->mark_compact_collector()->sweeping_in_progress()) {
    i_isolate->heap()->mark_compact_collector()->EnsureSweepingCompleted();
  }
  CHECK(i_isolate->heap()->incremental_marking()->IsStopped());

  i::IncrementalMarking* marking = i_isolate->heap()->incremental_marking();
  marking->Start(i::GarbageCollectionReason::kTesting);
  // Sweeping is not runing so we should immediately start marking.
  CHECK(marking->IsMarking());
  tracer.FinalizeTracing();
  CHECK(marking->IsStopped());
}

TEST(GarbageCollectionForTesting) {
  ManualGCScope manual_gc;
  i::FLAG_expose_gc = true;
  CcTest::InitializeVM();
  v8::Isolate* isolate = CcTest::isolate();
  Isolate* i_isolate = CcTest::i_isolate();
  TestEmbedderHeapTracer tracer;
  heap::TemporaryEmbedderHeapTracerScope tracer_scope(isolate, &tracer);

  int saved_gc_counter = i_isolate->heap()->gc_count();
  tracer.GarbageCollectionForTesting(EmbedderHeapTracer::kUnknown);
  CHECK_GT(i_isolate->heap()->gc_count(), saved_gc_counter);
}

namespace {

void ConstructJSObject(v8::Isolate* isolate, v8::Local<v8::Context> context,
                       v8::TracedGlobal<v8::Object>* global) {
  v8::HandleScope scope(isolate);
  v8::Local<v8::Object> object(v8::Object::New(isolate));
  CHECK(!object.IsEmpty());
  *global = v8::TracedGlobal<v8::Object>(isolate, object);
  CHECK(!global->IsEmpty());
}

void ConstructJSApiObject(v8::Isolate* isolate, v8::Local<v8::Context> context,
                          v8::TracedGlobal<v8::Object>* global) {
  v8::HandleScope scope(isolate);
  v8::Local<v8::Object> object(
      ConstructTraceableJSApiObject(context, nullptr, nullptr));
  CHECK(!object.IsEmpty());
  *global = v8::TracedGlobal<v8::Object>(isolate, object);
  CHECK(!global->IsEmpty());
}

enum class SurvivalMode { kSurvives, kDies };

template <typename ModifierFunction, typename ConstructTracedGlobalFunction>
void TracedGlobalTest(v8::Isolate* isolate,
                      ConstructTracedGlobalFunction construct_function,
                      ModifierFunction modifier_function, void (*gc_function)(),
                      SurvivalMode survives) {
  v8::HandleScope scope(isolate);
  v8::Local<v8::Context> context = v8::Context::New(isolate);
  v8::Context::Scope context_scope(context);

  v8::TracedGlobal<v8::Object> global;
  construct_function(isolate, context, &global);
  CHECK(InYoungGeneration(isolate, global));
  modifier_function(global);
  gc_function();
  CHECK_IMPLIES(survives == SurvivalMode::kSurvives, !global.IsEmpty());
  CHECK_IMPLIES(survives == SurvivalMode::kDies, global.IsEmpty());
}

}  // namespace

TEST(TracedGlobalReset) {
  CcTest::InitializeVM();
  v8::Isolate* isolate = CcTest::isolate();
  v8::HandleScope scope(isolate);

  v8::TracedGlobal<v8::Object> traced;
  ConstructJSObject(isolate, isolate->GetCurrentContext(), &traced);
  CHECK(!traced.IsEmpty());
  traced.Reset();
  CHECK(traced.IsEmpty());
}

TEST(TracedGlobalInStdVector) {
  ManualGCScope manual_gc;
  CcTest::InitializeVM();
  v8::Isolate* isolate = CcTest::isolate();
  v8::HandleScope scope(isolate);

  std::vector<v8::TracedGlobal<v8::Object>> vec;
  {
    v8::HandleScope scope(isolate);
    vec.emplace_back(isolate, v8::Object::New(isolate));
  }
  CHECK(!vec[0].IsEmpty());
  InvokeMarkSweep();
  CHECK(vec[0].IsEmpty());
}

TEST(TracedGlobalInStdUnorderedMap) {
  ManualGCScope manual_gc;
  CcTest::InitializeVM();
  v8::Isolate* isolate = CcTest::isolate();
  v8::HandleScope scope(isolate);

  std::unordered_map<int, v8::TracedGlobal<v8::Object>> map;
  {
    v8::HandleScope scope(isolate);
    map.emplace(std::piecewise_construct, std::forward_as_tuple(1),
                std::forward_as_tuple(isolate, v8::Object::New(isolate)));
  }
  CHECK(!map[1].IsEmpty());
  InvokeMarkSweep();
  CHECK(map[1].IsEmpty());
}

TEST(TracedGlobalToUnmodifiedJSObjectDiesOnMarkSweep) {
  CcTest::InitializeVM();
  TracedGlobalTest(
      CcTest::isolate(), ConstructJSObject,
      [](const TracedGlobal<v8::Object>& global) {}, InvokeMarkSweep,
      SurvivalMode::kDies);
}

TEST(TracedGlobalToUnmodifiedJSObjectSurvivesMarkSweepWhenHeldAliveOtherwise) {
  CcTest::InitializeVM();
  v8::Isolate* isolate = CcTest::isolate();
  v8::Global<v8::Object> strong_global;
  TracedGlobalTest(
      CcTest::isolate(), ConstructJSObject,
      [isolate, &strong_global](const TracedGlobal<v8::Object>& global) {
        v8::HandleScope scope(isolate);
        strong_global = v8::Global<v8::Object>(isolate, global.Get(isolate));
      },
      InvokeMarkSweep, SurvivalMode::kSurvives);
}

TEST(TracedGlobalToUnmodifiedJSObjectSurvivesScavenge) {
  ManualGCScope manual_gc;
  CcTest::InitializeVM();
  TracedGlobalTest(
      CcTest::isolate(), ConstructJSObject,
      [](const TracedGlobal<v8::Object>& global) {}, InvokeScavenge,
      SurvivalMode::kSurvives);
}

TEST(TracedGlobalToUnmodifiedJSObjectSurvivesScavengeWhenExcludedFromRoots) {
  ManualGCScope manual_gc;
  CcTest::InitializeVM();
  v8::Isolate* isolate = CcTest::isolate();
  TestEmbedderHeapTracer tracer;
  heap::TemporaryEmbedderHeapTracerScope tracer_scope(isolate, &tracer);
  tracer.ConsiderTracedGlobalAsRoot(false);
  TracedGlobalTest(
      CcTest::isolate(), ConstructJSObject,
      [](const TracedGlobal<v8::Object>& global) {}, InvokeScavenge,
      SurvivalMode::kSurvives);
}

TEST(TracedGlobalToUnmodifiedJSApiObjectSurvivesScavengePerDefault) {
  ManualGCScope manual_gc;
  CcTest::InitializeVM();
  v8::Isolate* isolate = CcTest::isolate();
  TestEmbedderHeapTracer tracer;
  heap::TemporaryEmbedderHeapTracerScope tracer_scope(isolate, &tracer);
  tracer.ConsiderTracedGlobalAsRoot(true);
  TracedGlobalTest(
      CcTest::isolate(), ConstructJSApiObject,
      [](const TracedGlobal<v8::Object>& global) {}, InvokeScavenge,
      SurvivalMode::kSurvives);
}

TEST(TracedGlobalToUnmodifiedJSApiObjectDiesOnScavengeWhenExcludedFromRoots) {
  ManualGCScope manual_gc;
  CcTest::InitializeVM();
  v8::Isolate* isolate = CcTest::isolate();
  TestEmbedderHeapTracer tracer;
  heap::TemporaryEmbedderHeapTracerScope tracer_scope(isolate, &tracer);
  tracer.ConsiderTracedGlobalAsRoot(false);
  TracedGlobalTest(
      CcTest::isolate(), ConstructJSApiObject,
      [](const TracedGlobal<v8::Object>& global) {}, InvokeScavenge,
      SurvivalMode::kDies);
}

TEST(TracedGlobalWrapperClassId) {
  ManualGCScope manual_gc;
  CcTest::InitializeVM();
  v8::Isolate* isolate = CcTest::isolate();
  v8::HandleScope scope(isolate);
  TestEmbedderHeapTracer tracer;
  heap::TemporaryEmbedderHeapTracerScope tracer_scope(isolate, &tracer);

  v8::TracedGlobal<v8::Object> traced;
  ConstructJSObject(isolate, isolate->GetCurrentContext(), &traced);
  CHECK_EQ(0, traced.WrapperClassId());
  traced.SetWrapperClassId(17);
  CHECK_EQ(17, traced.WrapperClassId());
}

namespace {

class TracedGlobalVisitor final
    : public v8::EmbedderHeapTracer::TracedGlobalHandleVisitor {
 public:
  ~TracedGlobalVisitor() override = default;
  void VisitTracedGlobalHandle(const TracedGlobal<Value>& value) final {
    if (value.WrapperClassId() == 57) {
      count_++;
    }
  }

  size_t count() const { return count_; }

 private:
  size_t count_ = 0;
};

}  // namespace

TEST(TracedGlobalIteration) {
  ManualGCScope manual_gc;
  CcTest::InitializeVM();
  v8::Isolate* isolate = CcTest::isolate();
  v8::HandleScope scope(isolate);
  TestEmbedderHeapTracer tracer;
  heap::TemporaryEmbedderHeapTracerScope tracer_scope(isolate, &tracer);

  v8::TracedGlobal<v8::Object> traced;
  ConstructJSObject(isolate, isolate->GetCurrentContext(), &traced);
  CHECK(!traced.IsEmpty());
  traced.SetWrapperClassId(57);
  TracedGlobalVisitor visitor;
  {
    v8::HandleScope scope(isolate);
    tracer.IterateTracedGlobalHandles(&visitor);
  }
  CHECK_EQ(1, visitor.count());
}

namespace {

void FinalizationCallback(const WeakCallbackInfo<void>& data) {
  v8::TracedGlobal<v8::Object>* traced =
      reinterpret_cast<v8::TracedGlobal<v8::Object>*>(data.GetParameter());
  CHECK_EQ(reinterpret_cast<void*>(0x4), data.GetInternalField(0));
  CHECK_EQ(reinterpret_cast<void*>(0x8), data.GetInternalField(1));
  traced->Reset();
}

}  // namespace

TEST(TracedGlobalSetFinalizationCallbackScavenge) {
  ManualGCScope manual_gc;
  CcTest::InitializeVM();
  v8::Isolate* isolate = CcTest::isolate();
  v8::HandleScope scope(isolate);
  TestEmbedderHeapTracer tracer;
  tracer.ConsiderTracedGlobalAsRoot(false);
  heap::TemporaryEmbedderHeapTracerScope tracer_scope(isolate, &tracer);

  v8::TracedGlobal<v8::Object> traced;
  ConstructJSApiObject(isolate, isolate->GetCurrentContext(), &traced);
  CHECK(!traced.IsEmpty());
  {
    v8::HandleScope scope(isolate);
    auto local = traced.Get(isolate);
    local->SetAlignedPointerInInternalField(0, reinterpret_cast<void*>(0x4));
    local->SetAlignedPointerInInternalField(1, reinterpret_cast<void*>(0x8));
  }
  traced.SetFinalizationCallback(&traced, FinalizationCallback);
  heap::InvokeScavenge();
  CHECK(traced.IsEmpty());
}

TEST(TracedGlobalSetFinalizationCallbackMarkSweep) {
  ManualGCScope manual_gc;
  CcTest::InitializeVM();
  v8::Isolate* isolate = CcTest::isolate();
  v8::HandleScope scope(isolate);
  TestEmbedderHeapTracer tracer;
  heap::TemporaryEmbedderHeapTracerScope tracer_scope(isolate, &tracer);

  v8::TracedGlobal<v8::Object> traced;
  ConstructJSApiObject(isolate, isolate->GetCurrentContext(), &traced);
  CHECK(!traced.IsEmpty());
  {
    v8::HandleScope scope(isolate);
    auto local = traced.Get(isolate);
    local->SetAlignedPointerInInternalField(0, reinterpret_cast<void*>(0x4));
    local->SetAlignedPointerInInternalField(1, reinterpret_cast<void*>(0x8));
  }
  traced.SetFinalizationCallback(&traced, FinalizationCallback);
  heap::InvokeMarkSweep();
  CHECK(traced.IsEmpty());
}

TEST(TracePrologueCallingIntoV8WriteBarrier) {
  // Regression test: https://crbug.com/940003
  ManualGCScope manual_gc;
  CcTest::InitializeVM();
  v8::Isolate* isolate = CcTest::isolate();
  v8::HandleScope scope(isolate);
  v8::Global<v8::Array> global;
  {
    v8::HandleScope scope(isolate);
    auto local = v8::Array::New(isolate, 10);
    global.Reset(isolate, local);
  }
  TestEmbedderHeapTracer tracer(TracePrologueBehavior::kCallV8WriteBarrier,
                                std::move(global));
  heap::TemporaryEmbedderHeapTracerScope tracer_scope(isolate, &tracer);
  SimulateIncrementalMarking(CcTest::i_isolate()->heap());
}

TEST(TracedGlobalWithDestructor) {
  ManualGCScope manual_gc;
  CcTest::InitializeVM();
  v8::Isolate* isolate = CcTest::isolate();
  v8::HandleScope scope(isolate);
  TestEmbedderHeapTracer tracer;
  heap::TemporaryEmbedderHeapTracerScope tracer_scope(isolate, &tracer);
  i::GlobalHandles* global_handles = CcTest::i_isolate()->global_handles();

  const size_t initial_count = global_handles->handles_count();
  auto* traced = new v8::TracedGlobal<v8::Object>();
  {
    v8::HandleScope scope(isolate);
    v8::Local<v8::Object> object(ConstructTraceableJSApiObject(
        isolate->GetCurrentContext(), nullptr, nullptr));
    CHECK(traced->IsEmpty());
    *traced = v8::TracedGlobal<v8::Object>(isolate, object);
    CHECK(!traced->IsEmpty());
    CHECK_EQ(initial_count + 1, global_handles->handles_count());
  }
  static_assert(TracedGlobalTrait<
                    v8::TracedGlobal<v8::Object>>::kRequiresExplicitDestruction,
                "destructor expected");
  delete traced;
  CHECK_EQ(initial_count, global_handles->handles_count());
  // GC should not need to clear the handle.
  heap::InvokeMarkSweep();
  CHECK_EQ(initial_count, global_handles->handles_count());
}

TEST(TracedGlobalNoDestructor) {
  ManualGCScope manual_gc;
  CcTest::InitializeVM();
  v8::Isolate* isolate = CcTest::isolate();
  v8::HandleScope scope(isolate);
  TestEmbedderHeapTracer tracer;
  heap::TemporaryEmbedderHeapTracerScope tracer_scope(isolate, &tracer);
  i::GlobalHandles* global_handles = CcTest::i_isolate()->global_handles();

  const size_t initial_count = global_handles->handles_count();
  char* memory = new char[sizeof(v8::TracedGlobal<v8::Value>)];
  auto* traced = new (memory) v8::TracedGlobal<v8::Value>();
  {
    v8::HandleScope scope(isolate);
    v8::Local<v8::Value> object(ConstructTraceableJSApiObject(
        isolate->GetCurrentContext(), nullptr, nullptr));
    CHECK(traced->IsEmpty());
    *traced = v8::TracedGlobal<v8::Value>(isolate, object);
    CHECK(!traced->IsEmpty());
    CHECK_EQ(initial_count + 1, global_handles->handles_count());
  }
  static_assert(!TracedGlobalTrait<
                    v8::TracedGlobal<v8::Value>>::kRequiresExplicitDestruction,
                "no destructor expected");
  traced->~TracedGlobal<v8::Value>();
  CHECK_EQ(initial_count + 1, global_handles->handles_count());
  // GC should clear the handle.
  heap::InvokeMarkSweep();
  CHECK_EQ(initial_count, global_handles->handles_count());
  delete[] memory;
}

}  // namespace heap
}  // namespace internal
}  // namespace v8