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// 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.

#ifndef INCLUDE_CPPGC_INTERNAL_WRITE_BARRIER_H_
#define INCLUDE_CPPGC_INTERNAL_WRITE_BARRIER_H_

#include <cstddef>
#include <cstdint>

#include "cppgc/heap-handle.h"
#include "cppgc/heap-state.h"
#include "cppgc/internal/api-constants.h"
#include "cppgc/internal/atomic-entry-flag.h"
#include "cppgc/internal/base-page-handle.h"
#include "cppgc/internal/member-storage.h"
#include "cppgc/platform.h"
#include "cppgc/sentinel-pointer.h"
#include "cppgc/trace-trait.h"
#include "v8config.h"  // NOLINT(build/include_directory)

#if defined(CPPGC_CAGED_HEAP)
#include "cppgc/internal/caged-heap-local-data.h"
#include "cppgc/internal/caged-heap.h"
#endif

namespace cppgc {

class HeapHandle;

namespace internal {

#if defined(CPPGC_CAGED_HEAP)
class WriteBarrierTypeForCagedHeapPolicy;
#else   // !CPPGC_CAGED_HEAP
class WriteBarrierTypeForNonCagedHeapPolicy;
#endif  // !CPPGC_CAGED_HEAP

class V8_EXPORT WriteBarrier final {
 public:
  enum class Type : uint8_t {
    kNone,
    kMarking,
    kGenerational,
  };

  enum class GenerationalBarrierType : uint8_t {
    kPreciseSlot,
    kPreciseUncompressedSlot,
    kImpreciseSlot,
  };

  struct Params {
    HeapHandle* heap = nullptr;
#if V8_ENABLE_CHECKS
    Type type = Type::kNone;
#endif  // !V8_ENABLE_CHECKS
#if defined(CPPGC_CAGED_HEAP)
    uintptr_t slot_offset = 0;
    uintptr_t value_offset = 0;
#endif  // CPPGC_CAGED_HEAP
  };

  enum class ValueMode {
    kValuePresent,
    kNoValuePresent,
  };

  // Returns the required write barrier for a given `slot` and `value`.
  static V8_INLINE Type GetWriteBarrierType(const void* slot, const void* value,
                                            Params& params);
  // Returns the required write barrier for a given `slot` and `value`.
  template <typename MemberStorage>
  static V8_INLINE Type GetWriteBarrierType(const void* slot, MemberStorage,
                                            Params& params);
  // Returns the required write barrier for a given `slot`.
  template <typename HeapHandleCallback>
  static V8_INLINE Type GetWriteBarrierType(const void* slot, Params& params,
                                            HeapHandleCallback callback);
  // Returns the required write barrier for a given  `value`.
  static V8_INLINE Type GetWriteBarrierType(const void* value, Params& params);

#ifdef CPPGC_SLIM_WRITE_BARRIER
  // A write barrier that combines `GenerationalBarrier()` and
  // `DijkstraMarkingBarrier()`. We only pass a single parameter here to clobber
  // as few registers as possible.
  template <WriteBarrierSlotType>
  static V8_NOINLINE void V8_PRESERVE_MOST
  CombinedWriteBarrierSlow(const void* slot);
#endif  // CPPGC_SLIM_WRITE_BARRIER

  static V8_INLINE void DijkstraMarkingBarrier(const Params& params,
                                               const void* object);
  static V8_INLINE void DijkstraMarkingBarrierRange(
      const Params& params, const void* first_element, size_t element_size,
      size_t number_of_elements, TraceCallback trace_callback);
  static V8_INLINE void SteeleMarkingBarrier(const Params& params,
                                             const void* object);
#if defined(CPPGC_YOUNG_GENERATION)
  template <GenerationalBarrierType>
  static V8_INLINE void GenerationalBarrier(const Params& params,
                                            const void* slot);
#else  // !CPPGC_YOUNG_GENERATION
  template <GenerationalBarrierType>
  static V8_INLINE void GenerationalBarrier(const Params& params,
                                            const void* slot){}
#endif  // CPPGC_YOUNG_GENERATION

#if V8_ENABLE_CHECKS
  static void CheckParams(Type expected_type, const Params& params);
#else   // !V8_ENABLE_CHECKS
  static void CheckParams(Type expected_type, const Params& params) {}
#endif  // !V8_ENABLE_CHECKS

  // The FlagUpdater class allows cppgc internal to update
  // |write_barrier_enabled_|.
  class FlagUpdater;
  static bool IsEnabled() { return write_barrier_enabled_.MightBeEntered(); }

 private:
  WriteBarrier() = delete;

#if defined(CPPGC_CAGED_HEAP)
  using WriteBarrierTypePolicy = WriteBarrierTypeForCagedHeapPolicy;
#else   // !CPPGC_CAGED_HEAP
  using WriteBarrierTypePolicy = WriteBarrierTypeForNonCagedHeapPolicy;
#endif  // !CPPGC_CAGED_HEAP

  static void DijkstraMarkingBarrierSlow(const void* value);
  static void DijkstraMarkingBarrierSlowWithSentinelCheck(const void* value);
  static void DijkstraMarkingBarrierRangeSlow(HeapHandle& heap_handle,
                                              const void* first_element,
                                              size_t element_size,
                                              size_t number_of_elements,
                                              TraceCallback trace_callback);
  static void SteeleMarkingBarrierSlow(const void* value);
  static void SteeleMarkingBarrierSlowWithSentinelCheck(const void* value);

#if defined(CPPGC_YOUNG_GENERATION)
  static CagedHeapLocalData& GetLocalData(HeapHandle&);
  static void GenerationalBarrierSlow(const CagedHeapLocalData& local_data,
                                      const AgeTable& age_table,
                                      const void* slot, uintptr_t value_offset,
                                      HeapHandle* heap_handle);
  static void GenerationalBarrierForUncompressedSlotSlow(
      const CagedHeapLocalData& local_data, const AgeTable& age_table,
      const void* slot, uintptr_t value_offset, HeapHandle* heap_handle);
  static void GenerationalBarrierForSourceObjectSlow(
      const CagedHeapLocalData& local_data, const void* object,
      HeapHandle* heap_handle);
#endif  // CPPGC_YOUNG_GENERATION

  static AtomicEntryFlag write_barrier_enabled_;
};

template <WriteBarrier::Type type>
V8_INLINE WriteBarrier::Type SetAndReturnType(WriteBarrier::Params& params) {
  if constexpr (type == WriteBarrier::Type::kNone)
    return WriteBarrier::Type::kNone;
#if V8_ENABLE_CHECKS
  params.type = type;
#endif  // !V8_ENABLE_CHECKS
  return type;
}

#if defined(CPPGC_CAGED_HEAP)
class V8_EXPORT WriteBarrierTypeForCagedHeapPolicy final {
 public:
  template <WriteBarrier::ValueMode value_mode, typename HeapHandleCallback>
  static V8_INLINE WriteBarrier::Type Get(const void* slot, const void* value,
                                          WriteBarrier::Params& params,
                                          HeapHandleCallback callback) {
    return ValueModeDispatch<value_mode>::Get(slot, value, params, callback);
  }

  template <WriteBarrier::ValueMode value_mode, typename HeapHandleCallback,
            typename MemberStorage>
  static V8_INLINE WriteBarrier::Type Get(const void* slot, MemberStorage value,
                                          WriteBarrier::Params& params,
                                          HeapHandleCallback callback) {
    return ValueModeDispatch<value_mode>::Get(slot, value, params, callback);
  }

  template <WriteBarrier::ValueMode value_mode, typename HeapHandleCallback>
  static V8_INLINE WriteBarrier::Type Get(const void* value,
                                          WriteBarrier::Params& params,
                                          HeapHandleCallback callback) {
    return GetNoSlot(value, params, callback);
  }

 private:
  WriteBarrierTypeForCagedHeapPolicy() = delete;

  template <typename HeapHandleCallback>
  static V8_INLINE WriteBarrier::Type GetNoSlot(const void* value,
                                                WriteBarrier::Params& params,
                                                HeapHandleCallback) {
    const bool within_cage = CagedHeapBase::IsWithinCage(value);
    if (!within_cage) return WriteBarrier::Type::kNone;

    // We know that |value| points either within the normal page or to the
    // beginning of large-page, so extract the page header by bitmasking.
    BasePageHandle* page =
        BasePageHandle::FromPayload(const_cast<void*>(value));

    HeapHandle& heap_handle = page->heap_handle();
    if (V8_UNLIKELY(heap_handle.is_incremental_marking_in_progress())) {
      return SetAndReturnType<WriteBarrier::Type::kMarking>(params);
    }

    return SetAndReturnType<WriteBarrier::Type::kNone>(params);
  }

  template <WriteBarrier::ValueMode value_mode>
  struct ValueModeDispatch;
};

template <>
struct WriteBarrierTypeForCagedHeapPolicy::ValueModeDispatch<
    WriteBarrier::ValueMode::kValuePresent> {
  template <typename HeapHandleCallback, typename MemberStorage>
  static V8_INLINE WriteBarrier::Type Get(const void* slot,
                                          MemberStorage storage,
                                          WriteBarrier::Params& params,
                                          HeapHandleCallback) {
    if (V8_LIKELY(!WriteBarrier::IsEnabled()))
      return SetAndReturnType<WriteBarrier::Type::kNone>(params);

    return BarrierEnabledGet(slot, storage.Load(), params);
  }

  template <typename HeapHandleCallback>
  static V8_INLINE WriteBarrier::Type Get(const void* slot, const void* value,
                                          WriteBarrier::Params& params,
                                          HeapHandleCallback) {
    if (V8_LIKELY(!WriteBarrier::IsEnabled()))
      return SetAndReturnType<WriteBarrier::Type::kNone>(params);

    return BarrierEnabledGet(slot, value, params);
  }

 private:
  static V8_INLINE WriteBarrier::Type BarrierEnabledGet(
      const void* slot, const void* value, WriteBarrier::Params& params) {
    const bool within_cage = CagedHeapBase::AreWithinCage(slot, value);
    if (!within_cage) return WriteBarrier::Type::kNone;

    // We know that |value| points either within the normal page or to the
    // beginning of large-page, so extract the page header by bitmasking.
    BasePageHandle* page =
        BasePageHandle::FromPayload(const_cast<void*>(value));

    HeapHandle& heap_handle = page->heap_handle();
    if (V8_LIKELY(!heap_handle.is_incremental_marking_in_progress())) {
#if defined(CPPGC_YOUNG_GENERATION)
      if (!heap_handle.is_young_generation_enabled())
        return WriteBarrier::Type::kNone;
      params.heap = &heap_handle;
      params.slot_offset = CagedHeapBase::OffsetFromAddress(slot);
      params.value_offset = CagedHeapBase::OffsetFromAddress(value);
      return SetAndReturnType<WriteBarrier::Type::kGenerational>(params);
#else   // !CPPGC_YOUNG_GENERATION
      return SetAndReturnType<WriteBarrier::Type::kNone>(params);
#endif  // !CPPGC_YOUNG_GENERATION
    }

    // Use marking barrier.
    params.heap = &heap_handle;
    return SetAndReturnType<WriteBarrier::Type::kMarking>(params);
  }
};

template <>
struct WriteBarrierTypeForCagedHeapPolicy::ValueModeDispatch<
    WriteBarrier::ValueMode::kNoValuePresent> {
  template <typename HeapHandleCallback>
  static V8_INLINE WriteBarrier::Type Get(const void* slot, const void*,
                                          WriteBarrier::Params& params,
                                          HeapHandleCallback callback) {
    if (V8_LIKELY(!WriteBarrier::IsEnabled()))
      return SetAndReturnType<WriteBarrier::Type::kNone>(params);

    HeapHandle& handle = callback();
#if defined(CPPGC_YOUNG_GENERATION)
    if (V8_LIKELY(!handle.is_incremental_marking_in_progress())) {
      if (!handle.is_young_generation_enabled()) {
        return WriteBarrier::Type::kNone;
      }
      params.heap = &handle;
      // Check if slot is on stack.
      if (V8_UNLIKELY(!CagedHeapBase::IsWithinCage(slot))) {
        return SetAndReturnType<WriteBarrier::Type::kNone>(params);
      }
      params.slot_offset = CagedHeapBase::OffsetFromAddress(slot);
      return SetAndReturnType<WriteBarrier::Type::kGenerational>(params);
    }
#else   // !defined(CPPGC_YOUNG_GENERATION)
    if (V8_UNLIKELY(!handle.is_incremental_marking_in_progress())) {
      return SetAndReturnType<WriteBarrier::Type::kNone>(params);
    }
#endif  // !defined(CPPGC_YOUNG_GENERATION)
    params.heap = &handle;
    return SetAndReturnType<WriteBarrier::Type::kMarking>(params);
  }
};

#endif  // CPPGC_CAGED_HEAP

class V8_EXPORT WriteBarrierTypeForNonCagedHeapPolicy final {
 public:
  template <WriteBarrier::ValueMode value_mode, typename HeapHandleCallback>
  static V8_INLINE WriteBarrier::Type Get(const void* slot, const void* value,
                                          WriteBarrier::Params& params,
                                          HeapHandleCallback callback) {
    return ValueModeDispatch<value_mode>::Get(slot, value, params, callback);
  }

  template <WriteBarrier::ValueMode value_mode, typename HeapHandleCallback>
  static V8_INLINE WriteBarrier::Type Get(const void* slot, RawPointer value,
                                          WriteBarrier::Params& params,
                                          HeapHandleCallback callback) {
    return ValueModeDispatch<value_mode>::Get(slot, value.Load(), params,
                                              callback);
  }

  template <WriteBarrier::ValueMode value_mode, typename HeapHandleCallback>
  static V8_INLINE WriteBarrier::Type Get(const void* value,
                                          WriteBarrier::Params& params,
                                          HeapHandleCallback callback) {
    // The slot will never be used in `Get()` below.
    return Get<WriteBarrier::ValueMode::kValuePresent>(nullptr, value, params,
                                                       callback);
  }

 private:
  template <WriteBarrier::ValueMode value_mode>
  struct ValueModeDispatch;

  WriteBarrierTypeForNonCagedHeapPolicy() = delete;
};

template <>
struct WriteBarrierTypeForNonCagedHeapPolicy::ValueModeDispatch<
    WriteBarrier::ValueMode::kValuePresent> {
  template <typename HeapHandleCallback>
  static V8_INLINE WriteBarrier::Type Get(const void*, const void* object,
                                          WriteBarrier::Params& params,
                                          HeapHandleCallback callback) {
    // The following check covers nullptr as well as sentinel pointer.
    if (object <= static_cast<void*>(kSentinelPointer)) {
      return SetAndReturnType<WriteBarrier::Type::kNone>(params);
    }
    if (V8_LIKELY(!WriteBarrier::IsEnabled())) {
      return SetAndReturnType<WriteBarrier::Type::kNone>(params);
    }
    // We know that |object| is within the normal page or in the beginning of a
    // large page, so extract the page header by bitmasking.
    BasePageHandle* page =
        BasePageHandle::FromPayload(const_cast<void*>(object));

    HeapHandle& heap_handle = page->heap_handle();
    if (V8_LIKELY(heap_handle.is_incremental_marking_in_progress())) {
      return SetAndReturnType<WriteBarrier::Type::kMarking>(params);
    }
    return SetAndReturnType<WriteBarrier::Type::kNone>(params);
  }
};

template <>
struct WriteBarrierTypeForNonCagedHeapPolicy::ValueModeDispatch<
    WriteBarrier::ValueMode::kNoValuePresent> {
  template <typename HeapHandleCallback>
  static V8_INLINE WriteBarrier::Type Get(const void*, const void*,
                                          WriteBarrier::Params& params,
                                          HeapHandleCallback callback) {
    if (V8_UNLIKELY(WriteBarrier::IsEnabled())) {
      HeapHandle& handle = callback();
      if (V8_LIKELY(handle.is_incremental_marking_in_progress())) {
        params.heap = &handle;
        return SetAndReturnType<WriteBarrier::Type::kMarking>(params);
      }
    }
    return WriteBarrier::Type::kNone;
  }
};

// static
WriteBarrier::Type WriteBarrier::GetWriteBarrierType(
    const void* slot, const void* value, WriteBarrier::Params& params) {
  return WriteBarrierTypePolicy::Get<ValueMode::kValuePresent>(slot, value,
                                                               params, []() {});
}

// static
template <typename MemberStorage>
WriteBarrier::Type WriteBarrier::GetWriteBarrierType(
    const void* slot, MemberStorage value, WriteBarrier::Params& params) {
  return WriteBarrierTypePolicy::Get<ValueMode::kValuePresent>(slot, value,
                                                               params, []() {});
}

// static
template <typename HeapHandleCallback>
WriteBarrier::Type WriteBarrier::GetWriteBarrierType(
    const void* slot, WriteBarrier::Params& params,
    HeapHandleCallback callback) {
  return WriteBarrierTypePolicy::Get<ValueMode::kNoValuePresent>(
      slot, nullptr, params, callback);
}

// static
WriteBarrier::Type WriteBarrier::GetWriteBarrierType(
    const void* value, WriteBarrier::Params& params) {
  return WriteBarrierTypePolicy::Get<ValueMode::kValuePresent>(value, params,
                                                               []() {});
}

// static
void WriteBarrier::DijkstraMarkingBarrier(const Params& params,
                                          const void* object) {
  CheckParams(Type::kMarking, params);
#if defined(CPPGC_CAGED_HEAP)
  // Caged heap already filters out sentinels.
  DijkstraMarkingBarrierSlow(object);
#else   // !CPPGC_CAGED_HEAP
  DijkstraMarkingBarrierSlowWithSentinelCheck(object);
#endif  // !CPPGC_CAGED_HEAP
}

// static
void WriteBarrier::DijkstraMarkingBarrierRange(const Params& params,
                                               const void* first_element,
                                               size_t element_size,
                                               size_t number_of_elements,
                                               TraceCallback trace_callback) {
  CheckParams(Type::kMarking, params);
  DijkstraMarkingBarrierRangeSlow(*params.heap, first_element, element_size,
                                  number_of_elements, trace_callback);
}

// static
void WriteBarrier::SteeleMarkingBarrier(const Params& params,
                                        const void* object) {
  CheckParams(Type::kMarking, params);
#if defined(CPPGC_CAGED_HEAP)
  // Caged heap already filters out sentinels.
  SteeleMarkingBarrierSlow(object);
#else   // !CPPGC_CAGED_HEAP
  SteeleMarkingBarrierSlowWithSentinelCheck(object);
#endif  // !CPPGC_CAGED_HEAP
}

#if defined(CPPGC_YOUNG_GENERATION)

// static
template <WriteBarrier::GenerationalBarrierType type>
void WriteBarrier::GenerationalBarrier(const Params& params, const void* slot) {
  CheckParams(Type::kGenerational, params);

  const CagedHeapLocalData& local_data = CagedHeapLocalData::Get();
  const AgeTable& age_table = local_data.age_table;

  // Bail out if the slot (precise or imprecise) is in young generation.
  if (V8_LIKELY(age_table.GetAge(params.slot_offset) == AgeTable::Age::kYoung))
    return;

  // Dispatch between different types of barriers.
  // TODO(chromium:1029379): Consider reload local_data in the slow path to
  // reduce register pressure.
  if constexpr (type == GenerationalBarrierType::kPreciseSlot) {
    GenerationalBarrierSlow(local_data, age_table, slot, params.value_offset,
                            params.heap);
  } else if constexpr (type ==
                       GenerationalBarrierType::kPreciseUncompressedSlot) {
    GenerationalBarrierForUncompressedSlotSlow(
        local_data, age_table, slot, params.value_offset, params.heap);
  } else {
    GenerationalBarrierForSourceObjectSlow(local_data, slot, params.heap);
  }
}

#endif  // !CPPGC_YOUNG_GENERATION

}  // namespace internal
}  // namespace cppgc

#endif  // INCLUDE_CPPGC_INTERNAL_WRITE_BARRIER_H_

	// 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.

	#ifndef INCLUDE_CPPGC_INTERNAL_WRITE_BARRIER_H_
	#define INCLUDE_CPPGC_INTERNAL_WRITE_BARRIER_H_

	#include <cstddef>
	#include <cstdint>

	#include "cppgc/heap-handle.h"
	#include "cppgc/heap-state.h"
	#include "cppgc/internal/api-constants.h"
	#include "cppgc/internal/atomic-entry-flag.h"
	#include "cppgc/internal/base-page-handle.h"
	#include "cppgc/internal/member-storage.h"
	#include "cppgc/platform.h"
	#include "cppgc/sentinel-pointer.h"
	#include "cppgc/trace-trait.h"
	#include "v8config.h" // NOLINT(build/include_directory)

	#if defined(CPPGC_CAGED_HEAP)
	#include "cppgc/internal/caged-heap-local-data.h"
	#include "cppgc/internal/caged-heap.h"
	#endif

	namespace cppgc {

	class HeapHandle;

	namespace internal {

	#if defined(CPPGC_CAGED_HEAP)
	class WriteBarrierTypeForCagedHeapPolicy;
	#else // !CPPGC_CAGED_HEAP
	class WriteBarrierTypeForNonCagedHeapPolicy;
	#endif // !CPPGC_CAGED_HEAP

	class V8_EXPORT WriteBarrier final {
	public:
	enum class Type : uint8_t {
	kNone,
	kMarking,
	kGenerational,
	};

	enum class GenerationalBarrierType : uint8_t {
	kPreciseSlot,
	kPreciseUncompressedSlot,
	kImpreciseSlot,
	};

	struct Params {
	HeapHandle* heap = nullptr;
	#if V8_ENABLE_CHECKS
	Type type = Type::kNone;
	#endif // !V8_ENABLE_CHECKS
	#if defined(CPPGC_CAGED_HEAP)
	uintptr_t slot_offset = 0;
	uintptr_t value_offset = 0;
	#endif // CPPGC_CAGED_HEAP
	};

	enum class ValueMode {
	kValuePresent,
	kNoValuePresent,
	};

	// Returns the required write barrier for a given `slot` and `value`.
	static V8_INLINE Type GetWriteBarrierType(const void* slot, const void* value,
	Params& params);
	// Returns the required write barrier for a given `slot` and `value`.
	template <typename MemberStorage>
	static V8_INLINE Type GetWriteBarrierType(const void* slot, MemberStorage,
	Params& params);
	// Returns the required write barrier for a given `slot`.
	template <typename HeapHandleCallback>
	static V8_INLINE Type GetWriteBarrierType(const void* slot, Params& params,
	HeapHandleCallback callback);
	// Returns the required write barrier for a given `value`.
	static V8_INLINE Type GetWriteBarrierType(const void* value, Params& params);

	#ifdef CPPGC_SLIM_WRITE_BARRIER
	// A write barrier that combines `GenerationalBarrier()` and
	// `DijkstraMarkingBarrier()`. We only pass a single parameter here to clobber
	// as few registers as possible.
	template <WriteBarrierSlotType>
	static V8_NOINLINE void V8_PRESERVE_MOST
	CombinedWriteBarrierSlow(const void* slot);
	#endif // CPPGC_SLIM_WRITE_BARRIER

	static V8_INLINE void DijkstraMarkingBarrier(const Params& params,
	const void* object);
	static V8_INLINE void DijkstraMarkingBarrierRange(
	const Params& params, const void* first_element, size_t element_size,
	size_t number_of_elements, TraceCallback trace_callback);
	static V8_INLINE void SteeleMarkingBarrier(const Params& params,
	const void* object);
	#if defined(CPPGC_YOUNG_GENERATION)
	template <GenerationalBarrierType>
	static V8_INLINE void GenerationalBarrier(const Params& params,
	const void* slot);
	#else // !CPPGC_YOUNG_GENERATION
	template <GenerationalBarrierType>
	static V8_INLINE void GenerationalBarrier(const Params& params,
	const void* slot){}
	#endif // CPPGC_YOUNG_GENERATION

	#if V8_ENABLE_CHECKS
	static void CheckParams(Type expected_type, const Params& params);
	#else // !V8_ENABLE_CHECKS
	static void CheckParams(Type expected_type, const Params& params) {}
	#endif // !V8_ENABLE_CHECKS

	// The FlagUpdater class allows cppgc internal to update
	// \|write_barrier_enabled_\|.
	class FlagUpdater;
	static bool IsEnabled() { return write_barrier_enabled_.MightBeEntered(); }

	private:
	WriteBarrier() = delete;

	#if defined(CPPGC_CAGED_HEAP)
	using WriteBarrierTypePolicy = WriteBarrierTypeForCagedHeapPolicy;
	#else // !CPPGC_CAGED_HEAP
	using WriteBarrierTypePolicy = WriteBarrierTypeForNonCagedHeapPolicy;
	#endif // !CPPGC_CAGED_HEAP

	static void DijkstraMarkingBarrierSlow(const void* value);
	static void DijkstraMarkingBarrierSlowWithSentinelCheck(const void* value);
	static void DijkstraMarkingBarrierRangeSlow(HeapHandle& heap_handle,
	const void* first_element,
	size_t element_size,
	size_t number_of_elements,
	TraceCallback trace_callback);
	static void SteeleMarkingBarrierSlow(const void* value);
	static void SteeleMarkingBarrierSlowWithSentinelCheck(const void* value);

	#if defined(CPPGC_YOUNG_GENERATION)
	static CagedHeapLocalData& GetLocalData(HeapHandle&);
	static void GenerationalBarrierSlow(const CagedHeapLocalData& local_data,
	const AgeTable& age_table,
	const void* slot, uintptr_t value_offset,
	HeapHandle* heap_handle);
	static void GenerationalBarrierForUncompressedSlotSlow(
	const CagedHeapLocalData& local_data, const AgeTable& age_table,
	const void* slot, uintptr_t value_offset, HeapHandle* heap_handle);
	static void GenerationalBarrierForSourceObjectSlow(
	const CagedHeapLocalData& local_data, const void* object,
	HeapHandle* heap_handle);
	#endif // CPPGC_YOUNG_GENERATION

	static AtomicEntryFlag write_barrier_enabled_;
	};

	template <WriteBarrier::Type type>
	V8_INLINE WriteBarrier::Type SetAndReturnType(WriteBarrier::Params& params) {
	if constexpr (type == WriteBarrier::Type::kNone)
	return WriteBarrier::Type::kNone;
	#if V8_ENABLE_CHECKS
	params.type = type;
	#endif // !V8_ENABLE_CHECKS
	return type;
	}

	#if defined(CPPGC_CAGED_HEAP)
	class V8_EXPORT WriteBarrierTypeForCagedHeapPolicy final {
	public:
	template <WriteBarrier::ValueMode value_mode, typename HeapHandleCallback>
	static V8_INLINE WriteBarrier::Type Get(const void* slot, const void* value,
	WriteBarrier::Params& params,
	HeapHandleCallback callback) {
	return ValueModeDispatch<value_mode>::Get(slot, value, params, callback);
	}

	template <WriteBarrier::ValueMode value_mode, typename HeapHandleCallback,
	typename MemberStorage>
	static V8_INLINE WriteBarrier::Type Get(const void* slot, MemberStorage value,
	WriteBarrier::Params& params,
	HeapHandleCallback callback) {
	return ValueModeDispatch<value_mode>::Get(slot, value, params, callback);
	}

	template <WriteBarrier::ValueMode value_mode, typename HeapHandleCallback>
	static V8_INLINE WriteBarrier::Type Get(const void* value,
	WriteBarrier::Params& params,
	HeapHandleCallback callback) {
	return GetNoSlot(value, params, callback);
	}

	private:
	WriteBarrierTypeForCagedHeapPolicy() = delete;

	template <typename HeapHandleCallback>
	static V8_INLINE WriteBarrier::Type GetNoSlot(const void* value,
	WriteBarrier::Params& params,
	HeapHandleCallback) {
	const bool within_cage = CagedHeapBase::IsWithinCage(value);
	if (!within_cage) return WriteBarrier::Type::kNone;

	// We know that \|value\| points either within the normal page or to the
	// beginning of large-page, so extract the page header by bitmasking.
	BasePageHandle* page =
	BasePageHandle::FromPayload(const_cast<void*>(value));

	HeapHandle& heap_handle = page->heap_handle();
	if (V8_UNLIKELY(heap_handle.is_incremental_marking_in_progress())) {
	return SetAndReturnType<WriteBarrier::Type::kMarking>(params);
	}

	return SetAndReturnType<WriteBarrier::Type::kNone>(params);
	}

	template <WriteBarrier::ValueMode value_mode>
	struct ValueModeDispatch;
	};

	template <>
	struct WriteBarrierTypeForCagedHeapPolicy::ValueModeDispatch<
	WriteBarrier::ValueMode::kValuePresent> {
	template <typename HeapHandleCallback, typename MemberStorage>
	static V8_INLINE WriteBarrier::Type Get(const void* slot,
	MemberStorage storage,
	WriteBarrier::Params& params,
	HeapHandleCallback) {
	if (V8_LIKELY(!WriteBarrier::IsEnabled()))
	return SetAndReturnType<WriteBarrier::Type::kNone>(params);

	return BarrierEnabledGet(slot, storage.Load(), params);
	}

	template <typename HeapHandleCallback>
	static V8_INLINE WriteBarrier::Type Get(const void* slot, const void* value,
	WriteBarrier::Params& params,
	HeapHandleCallback) {
	if (V8_LIKELY(!WriteBarrier::IsEnabled()))
	return SetAndReturnType<WriteBarrier::Type::kNone>(params);

	return BarrierEnabledGet(slot, value, params);
	}

	private:
	static V8_INLINE WriteBarrier::Type BarrierEnabledGet(
	const void* slot, const void* value, WriteBarrier::Params& params) {
	const bool within_cage = CagedHeapBase::AreWithinCage(slot, value);
	if (!within_cage) return WriteBarrier::Type::kNone;

	// We know that \|value\| points either within the normal page or to the
	// beginning of large-page, so extract the page header by bitmasking.
	BasePageHandle* page =
	BasePageHandle::FromPayload(const_cast<void*>(value));

	HeapHandle& heap_handle = page->heap_handle();
	if (V8_LIKELY(!heap_handle.is_incremental_marking_in_progress())) {
	#if defined(CPPGC_YOUNG_GENERATION)
	if (!heap_handle.is_young_generation_enabled())
	return WriteBarrier::Type::kNone;
	params.heap = &heap_handle;
	params.slot_offset = CagedHeapBase::OffsetFromAddress(slot);
	params.value_offset = CagedHeapBase::OffsetFromAddress(value);
	return SetAndReturnType<WriteBarrier::Type::kGenerational>(params);
	#else // !CPPGC_YOUNG_GENERATION
	return SetAndReturnType<WriteBarrier::Type::kNone>(params);
	#endif // !CPPGC_YOUNG_GENERATION
	}

	// Use marking barrier.
	params.heap = &heap_handle;
	return SetAndReturnType<WriteBarrier::Type::kMarking>(params);
	}
	};

	template <>
	struct WriteBarrierTypeForCagedHeapPolicy::ValueModeDispatch<
	WriteBarrier::ValueMode::kNoValuePresent> {
	template <typename HeapHandleCallback>
	static V8_INLINE WriteBarrier::Type Get(const void* slot, const void*,
	WriteBarrier::Params& params,
	HeapHandleCallback callback) {
	if (V8_LIKELY(!WriteBarrier::IsEnabled()))
	return SetAndReturnType<WriteBarrier::Type::kNone>(params);

	HeapHandle& handle = callback();
	#if defined(CPPGC_YOUNG_GENERATION)
	if (V8_LIKELY(!handle.is_incremental_marking_in_progress())) {
	if (!handle.is_young_generation_enabled()) {
	return WriteBarrier::Type::kNone;
	}
	params.heap = &handle;
	// Check if slot is on stack.
	if (V8_UNLIKELY(!CagedHeapBase::IsWithinCage(slot))) {
	return SetAndReturnType<WriteBarrier::Type::kNone>(params);
	}
	params.slot_offset = CagedHeapBase::OffsetFromAddress(slot);
	return SetAndReturnType<WriteBarrier::Type::kGenerational>(params);
	}
	#else // !defined(CPPGC_YOUNG_GENERATION)
	if (V8_UNLIKELY(!handle.is_incremental_marking_in_progress())) {
	return SetAndReturnType<WriteBarrier::Type::kNone>(params);
	}
	#endif // !defined(CPPGC_YOUNG_GENERATION)
	params.heap = &handle;
	return SetAndReturnType<WriteBarrier::Type::kMarking>(params);
	}
	};

	#endif // CPPGC_CAGED_HEAP

	class V8_EXPORT WriteBarrierTypeForNonCagedHeapPolicy final {
	public:
	template <WriteBarrier::ValueMode value_mode, typename HeapHandleCallback>
	static V8_INLINE WriteBarrier::Type Get(const void* slot, const void* value,
	WriteBarrier::Params& params,
	HeapHandleCallback callback) {
	return ValueModeDispatch<value_mode>::Get(slot, value, params, callback);
	}

	template <WriteBarrier::ValueMode value_mode, typename HeapHandleCallback>
	static V8_INLINE WriteBarrier::Type Get(const void* slot, RawPointer value,
	WriteBarrier::Params& params,
	HeapHandleCallback callback) {
	return ValueModeDispatch<value_mode>::Get(slot, value.Load(), params,
	callback);
	}

	template <WriteBarrier::ValueMode value_mode, typename HeapHandleCallback>
	static V8_INLINE WriteBarrier::Type Get(const void* value,
	WriteBarrier::Params& params,
	HeapHandleCallback callback) {
	// The slot will never be used in `Get()` below.
	return Get<WriteBarrier::ValueMode::kValuePresent>(nullptr, value, params,
	callback);
	}

	private:
	template <WriteBarrier::ValueMode value_mode>
	struct ValueModeDispatch;

	WriteBarrierTypeForNonCagedHeapPolicy() = delete;
	};

	template <>
	struct WriteBarrierTypeForNonCagedHeapPolicy::ValueModeDispatch<
	WriteBarrier::ValueMode::kValuePresent> {
	template <typename HeapHandleCallback>
	static V8_INLINE WriteBarrier::Type Get(const void, const void object,
	WriteBarrier::Params& params,
	HeapHandleCallback callback) {
	// The following check covers nullptr as well as sentinel pointer.
	if (object <= static_cast<void*>(kSentinelPointer)) {
	return SetAndReturnType<WriteBarrier::Type::kNone>(params);
	}
	if (V8_LIKELY(!WriteBarrier::IsEnabled())) {
	return SetAndReturnType<WriteBarrier::Type::kNone>(params);
	}
	// We know that \|object\| is within the normal page or in the beginning of a
	// large page, so extract the page header by bitmasking.
	BasePageHandle* page =
	BasePageHandle::FromPayload(const_cast<void*>(object));

	HeapHandle& heap_handle = page->heap_handle();
	if (V8_LIKELY(heap_handle.is_incremental_marking_in_progress())) {
	return SetAndReturnType<WriteBarrier::Type::kMarking>(params);
	}
	return SetAndReturnType<WriteBarrier::Type::kNone>(params);
	}
	};

	template <>
	struct WriteBarrierTypeForNonCagedHeapPolicy::ValueModeDispatch<
	WriteBarrier::ValueMode::kNoValuePresent> {
	template <typename HeapHandleCallback>
	static V8_INLINE WriteBarrier::Type Get(const void, const void,
	WriteBarrier::Params& params,
	HeapHandleCallback callback) {
	if (V8_UNLIKELY(WriteBarrier::IsEnabled())) {
	HeapHandle& handle = callback();
	if (V8_LIKELY(handle.is_incremental_marking_in_progress())) {
	params.heap = &handle;
	return SetAndReturnType<WriteBarrier::Type::kMarking>(params);
	}
	}
	return WriteBarrier::Type::kNone;
	}
	};

	// static
	WriteBarrier::Type WriteBarrier::GetWriteBarrierType(
	const void* slot, const void* value, WriteBarrier::Params& params) {
	return WriteBarrierTypePolicy::Get<ValueMode::kValuePresent>(slot, value,
	params, []() {});
	}

	// static
	template <typename MemberStorage>
	WriteBarrier::Type WriteBarrier::GetWriteBarrierType(
	const void* slot, MemberStorage value, WriteBarrier::Params& params) {
	return WriteBarrierTypePolicy::Get<ValueMode::kValuePresent>(slot, value,
	params, []() {});
	}

	// static
	template <typename HeapHandleCallback>
	WriteBarrier::Type WriteBarrier::GetWriteBarrierType(
	const void* slot, WriteBarrier::Params& params,
	HeapHandleCallback callback) {
	return WriteBarrierTypePolicy::Get<ValueMode::kNoValuePresent>(
	slot, nullptr, params, callback);
	}

	// static
	WriteBarrier::Type WriteBarrier::GetWriteBarrierType(
	const void* value, WriteBarrier::Params& params) {
	return WriteBarrierTypePolicy::Get<ValueMode::kValuePresent>(value, params,
	[]() {});
	}

	// static
	void WriteBarrier::DijkstraMarkingBarrier(const Params& params,
	const void* object) {
	CheckParams(Type::kMarking, params);
	#if defined(CPPGC_CAGED_HEAP)
	// Caged heap already filters out sentinels.
	DijkstraMarkingBarrierSlow(object);
	#else // !CPPGC_CAGED_HEAP
	DijkstraMarkingBarrierSlowWithSentinelCheck(object);
	#endif // !CPPGC_CAGED_HEAP
	}

	// static
	void WriteBarrier::DijkstraMarkingBarrierRange(const Params& params,
	const void* first_element,
	size_t element_size,
	size_t number_of_elements,
	TraceCallback trace_callback) {
	CheckParams(Type::kMarking, params);
	DijkstraMarkingBarrierRangeSlow(*params.heap, first_element, element_size,
	number_of_elements, trace_callback);
	}

	// static
	void WriteBarrier::SteeleMarkingBarrier(const Params& params,
	const void* object) {
	CheckParams(Type::kMarking, params);
	#if defined(CPPGC_CAGED_HEAP)
	// Caged heap already filters out sentinels.
	SteeleMarkingBarrierSlow(object);
	#else // !CPPGC_CAGED_HEAP
	SteeleMarkingBarrierSlowWithSentinelCheck(object);
	#endif // !CPPGC_CAGED_HEAP
	}

	#if defined(CPPGC_YOUNG_GENERATION)

	// static
	template <WriteBarrier::GenerationalBarrierType type>
	void WriteBarrier::GenerationalBarrier(const Params& params, const void* slot) {
	CheckParams(Type::kGenerational, params);

	const CagedHeapLocalData& local_data = CagedHeapLocalData::Get();
	const AgeTable& age_table = local_data.age_table;

	// Bail out if the slot (precise or imprecise) is in young generation.
	if (V8_LIKELY(age_table.GetAge(params.slot_offset) == AgeTable::Age::kYoung))
	return;

	// Dispatch between different types of barriers.
	// TODO(chromium:1029379): Consider reload local_data in the slow path to
	// reduce register pressure.
	if constexpr (type == GenerationalBarrierType::kPreciseSlot) {
	GenerationalBarrierSlow(local_data, age_table, slot, params.value_offset,
	params.heap);
	} else if constexpr (type ==
	GenerationalBarrierType::kPreciseUncompressedSlot) {
	GenerationalBarrierForUncompressedSlotSlow(
	local_data, age_table, slot, params.value_offset, params.heap);
	} else {
	GenerationalBarrierForSourceObjectSlow(local_data, slot, params.heap);
	}
	}

	#endif // !CPPGC_YOUNG_GENERATION

	} // namespace internal
	} // namespace cppgc

	#endif // INCLUDE_CPPGC_INTERNAL_WRITE_BARRIER_H_