v8/test/unittests/heap/cppgc/marker-unittest.cc

// Copyright 2020 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 "src/heap/cppgc/marker.h"

#include <memory>

#include "include/cppgc/allocation.h"
#include "include/cppgc/ephemeron-pair.h"
#include "include/cppgc/internal/pointer-policies.h"
#include "include/cppgc/member.h"
#include "include/cppgc/persistent.h"
#include "include/cppgc/trace-trait.h"
#include "src/heap/cppgc/heap-object-header.h"
#include "src/heap/cppgc/marking-visitor.h"
#include "src/heap/cppgc/object-allocator.h"
#include "src/heap/cppgc/stats-collector.h"
#include "test/unittests/heap/cppgc/tests.h"
#include "testing/gtest/include/gtest/gtest.h"

namespace cppgc {
namespace internal {

namespace {
class MarkerTest : public testing::TestWithHeap {
 public:
  using MarkingConfig = Marker::MarkingConfig;

  void DoMarking(MarkingConfig::StackState stack_state) {
    const MarkingConfig config = {MarkingConfig::CollectionType::kMajor,
                                  stack_state};
    auto* heap = Heap::From(GetHeap());
    InitializeMarker(*heap, GetPlatformHandle().get(), config);
    marker_->FinishMarking(stack_state);
    // Pretend do finish sweeping as StatsCollector verifies that Notify*
    // methods are called in the right order.
    heap->stats_collector()->NotifySweepingCompleted(
        GarbageCollector::Config::SweepingType::kAtomic);
  }

  void InitializeMarker(HeapBase& heap, cppgc::Platform* platform,
                        MarkingConfig config) {
    marker_ = std::make_unique<Marker>(heap, platform, config);
    marker_->StartMarking();
  }

  Marker* marker() const { return marker_.get(); }

  void ResetMarker() { marker_.reset(); }

 private:
  std::unique_ptr<Marker> marker_;
};

class GCed : public GarbageCollected<GCed> {
 public:
  void SetChild(GCed* child) { child_ = child; }
  void SetWeakChild(GCed* child) { weak_child_ = child; }
  GCed* child() const { return child_.Get(); }
  GCed* weak_child() const { return weak_child_.Get(); }
  void Trace(cppgc::Visitor* visitor) const {
    visitor->Trace(child_);
    visitor->Trace(weak_child_);
  }

 private:
  Member<GCed> child_;
  WeakMember<GCed> weak_child_;
};

template <typename T>
V8_NOINLINE T access(volatile const T& t) {
  return t;
}

}  // namespace

TEST_F(MarkerTest, PersistentIsMarked) {
  Persistent<GCed> object = MakeGarbageCollected<GCed>(GetAllocationHandle());
  HeapObjectHeader& header = HeapObjectHeader::FromObject(object);
  EXPECT_FALSE(header.IsMarked());
  DoMarking(MarkingConfig::StackState::kNoHeapPointers);
  EXPECT_TRUE(header.IsMarked());
}

TEST_F(MarkerTest, ReachableMemberIsMarked) {
  Persistent<GCed> parent = MakeGarbageCollected<GCed>(GetAllocationHandle());
  parent->SetChild(MakeGarbageCollected<GCed>(GetAllocationHandle()));
  HeapObjectHeader& header = HeapObjectHeader::FromObject(parent->child());
  EXPECT_FALSE(header.IsMarked());
  DoMarking(MarkingConfig::StackState::kNoHeapPointers);
  EXPECT_TRUE(header.IsMarked());
}

TEST_F(MarkerTest, UnreachableMemberIsNotMarked) {
  Member<GCed> object = MakeGarbageCollected<GCed>(GetAllocationHandle());
  HeapObjectHeader& header = HeapObjectHeader::FromObject(object);
  EXPECT_FALSE(header.IsMarked());
  DoMarking(MarkingConfig::StackState::kNoHeapPointers);
  EXPECT_FALSE(header.IsMarked());
}

TEST_F(MarkerTest, ObjectReachableFromStackIsMarked) {
  GCed* object = MakeGarbageCollected<GCed>(GetAllocationHandle());
  EXPECT_FALSE(HeapObjectHeader::FromObject(object).IsMarked());
  DoMarking(MarkingConfig::StackState::kMayContainHeapPointers);
  EXPECT_TRUE(HeapObjectHeader::FromObject(object).IsMarked());
  access(object);
}

TEST_F(MarkerTest, ObjectReachableOnlyFromStackIsNotMarkedIfStackIsEmpty) {
  GCed* object = MakeGarbageCollected<GCed>(GetAllocationHandle());
  HeapObjectHeader& header = HeapObjectHeader::FromObject(object);
  EXPECT_FALSE(header.IsMarked());
  DoMarking(MarkingConfig::StackState::kNoHeapPointers);
  EXPECT_FALSE(header.IsMarked());
  access(object);
}

TEST_F(MarkerTest, WeakReferenceToUnreachableObjectIsCleared) {
  {
    WeakPersistent<GCed> weak_object =
        MakeGarbageCollected<GCed>(GetAllocationHandle());
    EXPECT_TRUE(weak_object);
    DoMarking(MarkingConfig::StackState::kNoHeapPointers);
    EXPECT_FALSE(weak_object);
  }
  {
    Persistent<GCed> parent = MakeGarbageCollected<GCed>(GetAllocationHandle());
    parent->SetWeakChild(MakeGarbageCollected<GCed>(GetAllocationHandle()));
    EXPECT_TRUE(parent->weak_child());
    DoMarking(MarkingConfig::StackState::kNoHeapPointers);
    EXPECT_FALSE(parent->weak_child());
  }
}

TEST_F(MarkerTest, WeakReferenceToReachableObjectIsNotCleared) {
  // Reachable from Persistent
  {
    Persistent<GCed> object = MakeGarbageCollected<GCed>(GetAllocationHandle());
    WeakPersistent<GCed> weak_object(object);
    EXPECT_TRUE(weak_object);
    DoMarking(MarkingConfig::StackState::kNoHeapPointers);
    EXPECT_TRUE(weak_object);
  }
  {
    Persistent<GCed> object = MakeGarbageCollected<GCed>(GetAllocationHandle());
    Persistent<GCed> parent = MakeGarbageCollected<GCed>(GetAllocationHandle());
    parent->SetWeakChild(object);
    EXPECT_TRUE(parent->weak_child());
    DoMarking(MarkingConfig::StackState::kNoHeapPointers);
    EXPECT_TRUE(parent->weak_child());
  }
  // Reachable from Member
  {
    Persistent<GCed> parent = MakeGarbageCollected<GCed>(GetAllocationHandle());
    WeakPersistent<GCed> weak_object(
        MakeGarbageCollected<GCed>(GetAllocationHandle()));
    parent->SetChild(weak_object);
    EXPECT_TRUE(weak_object);
    DoMarking(MarkingConfig::StackState::kNoHeapPointers);
    EXPECT_TRUE(weak_object);
  }
  {
    Persistent<GCed> parent = MakeGarbageCollected<GCed>(GetAllocationHandle());
    parent->SetChild(MakeGarbageCollected<GCed>(GetAllocationHandle()));
    parent->SetWeakChild(parent->child());
    EXPECT_TRUE(parent->weak_child());
    DoMarking(MarkingConfig::StackState::kNoHeapPointers);
    EXPECT_TRUE(parent->weak_child());
  }
  // Reachable from stack
  {
    GCed* object = MakeGarbageCollected<GCed>(GetAllocationHandle());
    WeakPersistent<GCed> weak_object(object);
    EXPECT_TRUE(weak_object);
    DoMarking(MarkingConfig::StackState::kMayContainHeapPointers);
    EXPECT_TRUE(weak_object);
    access(object);
  }
  {
    GCed* object = MakeGarbageCollected<GCed>(GetAllocationHandle());
    Persistent<GCed> parent = MakeGarbageCollected<GCed>(GetAllocationHandle());
    parent->SetWeakChild(object);
    EXPECT_TRUE(parent->weak_child());
    DoMarking(MarkingConfig::StackState::kMayContainHeapPointers);
    EXPECT_TRUE(parent->weak_child());
    access(object);
  }
}

TEST_F(MarkerTest, DeepHierarchyIsMarked) {
  static constexpr int kHierarchyDepth = 10;
  Persistent<GCed> root = MakeGarbageCollected<GCed>(GetAllocationHandle());
  GCed* parent = root;
  for (int i = 0; i < kHierarchyDepth; ++i) {
    parent->SetChild(MakeGarbageCollected<GCed>(GetAllocationHandle()));
    parent->SetWeakChild(parent->child());
    parent = parent->child();
  }
  DoMarking(MarkingConfig::StackState::kNoHeapPointers);
  EXPECT_TRUE(HeapObjectHeader::FromObject(root).IsMarked());
  parent = root;
  for (int i = 0; i < kHierarchyDepth; ++i) {
    EXPECT_TRUE(HeapObjectHeader::FromObject(parent->child()).IsMarked());
    EXPECT_TRUE(parent->weak_child());
    parent = parent->child();
  }
}

TEST_F(MarkerTest, NestedObjectsOnStackAreMarked) {
  GCed* root = MakeGarbageCollected<GCed>(GetAllocationHandle());
  root->SetChild(MakeGarbageCollected<GCed>(GetAllocationHandle()));
  root->child()->SetChild(MakeGarbageCollected<GCed>(GetAllocationHandle()));
  DoMarking(MarkingConfig::StackState::kMayContainHeapPointers);
  EXPECT_TRUE(HeapObjectHeader::FromObject(root).IsMarked());
  EXPECT_TRUE(HeapObjectHeader::FromObject(root->child()).IsMarked());
  EXPECT_TRUE(HeapObjectHeader::FromObject(root->child()->child()).IsMarked());
}

namespace {

class GCedWithCallback : public GarbageCollected<GCedWithCallback> {
 public:
  template <typename Callback>
  explicit GCedWithCallback(Callback callback) {
    callback(this);
  }

  template <typename Callback>
  GCedWithCallback(Callback callback, GCed* gced) : gced_(gced) {
    callback(this);
  }

  void Trace(Visitor* visitor) const { visitor->Trace(gced_); }

  GCed* gced() const { return gced_; }

 private:
  Member<GCed> gced_;
};

}  // namespace

TEST_F(MarkerTest, InConstructionObjectIsEventuallyMarkedEmptyStack) {
  static const Marker::MarkingConfig config = {
      MarkingConfig::CollectionType::kMajor,
      MarkingConfig::StackState::kMayContainHeapPointers};
  InitializeMarker(*Heap::From(GetHeap()), GetPlatformHandle().get(), config);
  GCedWithCallback* object = MakeGarbageCollected<GCedWithCallback>(
      GetAllocationHandle(), [marker = marker()](GCedWithCallback* obj) {
        Member<GCedWithCallback> member(obj);
        marker->Visitor().Trace(member);
      });
  EXPECT_FALSE(HeapObjectHeader::FromObject(object).IsMarked());
  marker()->FinishMarking(MarkingConfig::StackState::kMayContainHeapPointers);
  EXPECT_TRUE(HeapObjectHeader::FromObject(object).IsMarked());
}

TEST_F(MarkerTest, InConstructionObjectIsEventuallyMarkedNonEmptyStack) {
  static const Marker::MarkingConfig config = {
      MarkingConfig::CollectionType::kMajor,
      MarkingConfig::StackState::kMayContainHeapPointers};
  InitializeMarker(*Heap::From(GetHeap()), GetPlatformHandle().get(), config);
  MakeGarbageCollected<GCedWithCallback>(
      GetAllocationHandle(), [marker = marker()](GCedWithCallback* obj) {
        Member<GCedWithCallback> member(obj);
        marker->Visitor().Trace(member);
        EXPECT_FALSE(HeapObjectHeader::FromObject(obj).IsMarked());
        marker->FinishMarking(
            MarkingConfig::StackState::kMayContainHeapPointers);
        EXPECT_TRUE(HeapObjectHeader::FromObject(obj).IsMarked());
      });
}

namespace {

// Storage that can be used to hide a pointer from the GC. Only useful when
// dealing with the stack separately.
class GCObliviousObjectStorage final {
 public:
  GCObliviousObjectStorage()
      : storage_(std::make_unique<const void*>(nullptr)) {}

  template <typename T>
  void set_object(T* t) {
    *storage_.get() = TraceTrait<T>::GetTraceDescriptor(t).base_object_payload;
  }

  const void* object() const { return *storage_; }

 private:
  std::unique_ptr<const void*> storage_;
};

V8_NOINLINE void RegisterInConstructionObject(
    AllocationHandle& allocation_handle, Visitor& v,
    GCObliviousObjectStorage& storage) {
  // Create deeper stack to avoid finding any temporary reference in the caller.
  char space[500];
  USE(space);
  MakeGarbageCollected<GCedWithCallback>(
      allocation_handle,
      [&visitor = v, &storage](GCedWithCallback* obj) {
        Member<GCedWithCallback> member(obj);
        // Adds GCedWithCallback to in-construction objects.
        visitor.Trace(member);
        EXPECT_FALSE(HeapObjectHeader::FromObject(obj).IsMarked());
        // The inner object GCed is only found if GCedWithCallback is processed.
        storage.set_object(obj->gced());
      },
      // Initializing store does not trigger a write barrier.
      MakeGarbageCollected<GCed>(allocation_handle));
}

}  // namespace

TEST_F(MarkerTest,
       InConstructionObjectIsEventuallyMarkedDifferentNonEmptyStack) {
  static const Marker::MarkingConfig config = {
      MarkingConfig::CollectionType::kMajor,
      MarkingConfig::StackState::kMayContainHeapPointers};
  InitializeMarker(*Heap::From(GetHeap()), GetPlatformHandle().get(), config);

  GCObliviousObjectStorage storage;
  RegisterInConstructionObject(GetAllocationHandle(), marker()->Visitor(),
                               storage);
  EXPECT_FALSE(HeapObjectHeader::FromObject(storage.object()).IsMarked());
  marker()->FinishMarking(MarkingConfig::StackState::kMayContainHeapPointers);
  EXPECT_TRUE(HeapObjectHeader::FromObject(storage.object()).IsMarked());
}

TEST_F(MarkerTest, SentinelNotClearedOnWeakPersistentHandling) {
  static const Marker::MarkingConfig config = {
      MarkingConfig::CollectionType::kMajor,
      MarkingConfig::StackState::kNoHeapPointers,
      MarkingConfig::MarkingType::kIncremental};
  Persistent<GCed> root = MakeGarbageCollected<GCed>(GetAllocationHandle());
  auto* tmp = MakeGarbageCollected<GCed>(GetAllocationHandle());
  root->SetWeakChild(tmp);
  InitializeMarker(*Heap::From(GetHeap()), GetPlatformHandle().get(), config);
  while (!marker()->IncrementalMarkingStepForTesting(
      MarkingConfig::StackState::kNoHeapPointers)) {
  }
  // {root} object must be marked at this point because we do not allow
  // encountering kSentinelPointer in WeakMember on regular Trace() calls.
  ASSERT_TRUE(HeapObjectHeader::FromObject(root.Get()).IsMarked());
  root->SetWeakChild(kSentinelPointer);
  marker()->FinishMarking(MarkingConfig::StackState::kNoHeapPointers);
  EXPECT_EQ(kSentinelPointer, root->weak_child());
}

namespace {

class SimpleObject final : public GarbageCollected<SimpleObject> {
 public:
  void Trace(Visitor*) const {}
};

class ObjectWithEphemeronPair final
    : public GarbageCollected<ObjectWithEphemeronPair> {
 public:
  explicit ObjectWithEphemeronPair(AllocationHandle& handle)
      : ephemeron_pair_(MakeGarbageCollected<SimpleObject>(handle),
                        MakeGarbageCollected<SimpleObject>(handle)) {}

  void Trace(Visitor* visitor) const {
    // First trace the ephemeron pair. The key is not yet marked as live, so the
    // pair should be recorded for later processing. Then strongly mark the key.
    // Marking the key will not trigger another worklist processing iteration,
    // as it merely continues the same loop for regular objects and will leave
    // the main marking worklist empty. If recording the ephemeron pair doesn't
    // as well, we will get a crash when destroying the marker.
    visitor->Trace(ephemeron_pair_);
    visitor->TraceStrongly(ephemeron_pair_.key);
  }

 private:
  const EphemeronPair<SimpleObject, SimpleObject> ephemeron_pair_;
};

}  // namespace

TEST_F(MarkerTest, MarkerProcessesAllEphemeronPairs) {
  static const Marker::MarkingConfig config = {
      MarkingConfig::CollectionType::kMajor,
      MarkingConfig::StackState::kNoHeapPointers,
      MarkingConfig::MarkingType::kAtomic};
  Persistent<ObjectWithEphemeronPair> obj =
      MakeGarbageCollected<ObjectWithEphemeronPair>(GetAllocationHandle(),
                                                    GetAllocationHandle());
  InitializeMarker(*Heap::From(GetHeap()), GetPlatformHandle().get(), config);
  marker()->FinishMarking(MarkingConfig::StackState::kNoHeapPointers);
  ResetMarker();
}

// Incremental Marking

class IncrementalMarkingTest : public testing::TestWithHeap {
 public:
  using MarkingConfig = Marker::MarkingConfig;

  static constexpr MarkingConfig IncrementalPreciseMarkingConfig = {
      MarkingConfig::CollectionType::kMajor,
      MarkingConfig::StackState::kNoHeapPointers,
      MarkingConfig::MarkingType::kIncremental};

  void FinishSteps(MarkingConfig::StackState stack_state) {
    while (!SingleStep(stack_state)) {
    }
  }

  void FinishMarking() {
    GetMarkerRef()->FinishMarking(
        MarkingConfig::StackState::kMayContainHeapPointers);
    // Pretend do finish sweeping as StatsCollector verifies that Notify*
    // methods are called in the right order.
    GetMarkerRef().reset();
    Heap::From(GetHeap())->stats_collector()->NotifySweepingCompleted(
        GarbageCollector::Config::SweepingType::kIncremental);
  }

  void InitializeMarker(HeapBase& heap, cppgc::Platform* platform,
                        MarkingConfig config) {
    GetMarkerRef() = std::make_unique<Marker>(heap, platform, config);
    GetMarkerRef()->StartMarking();
  }

  MarkerBase* marker() const { return Heap::From(GetHeap())->marker(); }

 private:
  bool SingleStep(MarkingConfig::StackState stack_state) {
    return GetMarkerRef()->IncrementalMarkingStepForTesting(stack_state);
  }
};

constexpr IncrementalMarkingTest::MarkingConfig
    IncrementalMarkingTest::IncrementalPreciseMarkingConfig;

TEST_F(IncrementalMarkingTest, RootIsMarkedAfterMarkingStarted) {
  Persistent<GCed> root = MakeGarbageCollected<GCed>(GetAllocationHandle());
  EXPECT_FALSE(HeapObjectHeader::FromObject(root).IsMarked());
  InitializeMarker(*Heap::From(GetHeap()), GetPlatformHandle().get(),
                   IncrementalPreciseMarkingConfig);
  EXPECT_TRUE(HeapObjectHeader::FromObject(root).IsMarked());
  FinishMarking();
}

TEST_F(IncrementalMarkingTest, MemberIsMarkedAfterMarkingSteps) {
  Persistent<GCed> root = MakeGarbageCollected<GCed>(GetAllocationHandle());
  root->SetChild(MakeGarbageCollected<GCed>(GetAllocationHandle()));
  HeapObjectHeader& header = HeapObjectHeader::FromObject(root->child());
  EXPECT_FALSE(header.IsMarked());
  InitializeMarker(*Heap::From(GetHeap()), GetPlatformHandle().get(),
                   IncrementalPreciseMarkingConfig);
  FinishSteps(MarkingConfig::StackState::kNoHeapPointers);
  EXPECT_TRUE(header.IsMarked());
  FinishMarking();
}

TEST_F(IncrementalMarkingTest,
       MemberWithWriteBarrierIsMarkedAfterMarkingSteps) {
  Persistent<GCed> root = MakeGarbageCollected<GCed>(GetAllocationHandle());
  InitializeMarker(*Heap::From(GetHeap()), GetPlatformHandle().get(),
                   IncrementalPreciseMarkingConfig);
  root->SetChild(MakeGarbageCollected<GCed>(GetAllocationHandle()));
  FinishSteps(MarkingConfig::StackState::kNoHeapPointers);
  HeapObjectHeader& header = HeapObjectHeader::FromObject(root->child());
  EXPECT_TRUE(header.IsMarked());
  FinishMarking();
}

namespace {
class Holder : public GarbageCollected<Holder> {
 public:
  void Trace(Visitor* visitor) const { visitor->Trace(member_); }

  Member<GCedWithCallback> member_;
};
}  // namespace

TEST_F(IncrementalMarkingTest, IncrementalStepDuringAllocation) {
  Persistent<Holder> holder =
      MakeGarbageCollected<Holder>(GetAllocationHandle());
  InitializeMarker(*Heap::From(GetHeap()), GetPlatformHandle().get(),
                   IncrementalPreciseMarkingConfig);
  const HeapObjectHeader* header;
  MakeGarbageCollected<GCedWithCallback>(
      GetAllocationHandle(), [this, &holder, &header](GCedWithCallback* obj) {
        header = &HeapObjectHeader::FromObject(obj);
        holder->member_ = obj;
        EXPECT_FALSE(header->IsMarked());
        FinishSteps(MarkingConfig::StackState::kMayContainHeapPointers);
        EXPECT_FALSE(header->IsMarked());
      });
  FinishSteps(MarkingConfig::StackState::kNoHeapPointers);
  EXPECT_TRUE(header->IsMarked());
  FinishMarking();
}

TEST_F(IncrementalMarkingTest, MarkingRunsOutOfWorkEventually) {
  InitializeMarker(*Heap::From(GetHeap()), GetPlatformHandle().get(),
                   IncrementalPreciseMarkingConfig);
  FinishSteps(MarkingConfig::StackState::kNoHeapPointers);
  FinishMarking();
}

}  // namespace internal
}  // namespace cppgc