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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-state.h"
#include "cppgc/internal/api-constants.h"
#include "cppgc/internal/atomic-entry-flag.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"
#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,
};
struct Params {
HeapHandle* heap = nullptr;
#if V8_ENABLE_CHECKS
Type type = Type::kNone;
#endif // !V8_ENABLE_CHECKS
#if defined(CPPGC_CAGED_HEAP)
uintptr_t start = 0;
CagedHeapLocalData& caged_heap() const {
return *reinterpret_cast<CagedHeapLocalData*>(start);
}
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`.
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);
template <typename HeapHandleCallback>
static V8_INLINE Type GetWriteBarrierTypeForExternallyReferencedObject(
const void* value, Params& params, HeapHandleCallback callback);
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)
static V8_INLINE void GenerationalBarrier(const Params& params,
const void* slot);
#else // !CPPGC_YOUNG_GENERATION
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 IncrementalOrConcurrentUpdater class allows cppgc internal to update
// |incremental_or_concurrent_marking_flag_|.
class IncrementalOrConcurrentMarkingFlagUpdater;
static bool IsAnyIncrementalOrConcurrentMarking() {
return incremental_or_concurrent_marking_flag_.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& ageTable,
const void* slot, uintptr_t value_offset);
#endif // CPPGC_YOUNG_GENERATION
static AtomicEntryFlag incremental_or_concurrent_marking_flag_;
};
template <WriteBarrier::Type type>
V8_INLINE WriteBarrier::Type SetAndReturnType(WriteBarrier::Params& params) {
if (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>
static V8_INLINE WriteBarrier::Type Get(const void* value,
WriteBarrier::Params& params,
HeapHandleCallback callback) {
return GetNoSlot(value, params, callback);
}
template <typename HeapHandleCallback>
static V8_INLINE WriteBarrier::Type GetForExternallyReferenced(
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) {
if (!TryGetCagedHeap(value, value, params)) {
return WriteBarrier::Type::kNone;
}
if (V8_UNLIKELY(params.caged_heap().is_incremental_marking_in_progress)) {
return SetAndReturnType<WriteBarrier::Type::kMarking>(params);
}
return SetAndReturnType<WriteBarrier::Type::kNone>(params);
}
template <WriteBarrier::ValueMode value_mode>
struct ValueModeDispatch;
static V8_INLINE bool TryGetCagedHeap(const void* slot, const void* value,
WriteBarrier::Params& params) {
// TODO(chromium:1056170): Check if the null check can be folded in with
// the rest of the write barrier.
if (!value) return false;
params.start = reinterpret_cast<uintptr_t>(value) &
~(api_constants::kCagedHeapReservationAlignment - 1);
const uintptr_t slot_offset =
reinterpret_cast<uintptr_t>(slot) - params.start;
if (slot_offset > api_constants::kCagedHeapReservationSize) {
// Check if slot is on stack or value is sentinel or nullptr. This relies
// on the fact that kSentinelPointer is encoded as 0x1.
return false;
}
return true;
}
// Returns whether marking is in progress. If marking is not in progress
// sets the start of the cage accordingly.
//
// TODO(chromium:1056170): Create fast path on API.
static bool IsMarking(const HeapHandle&, WriteBarrier::Params&);
};
template <>
struct WriteBarrierTypeForCagedHeapPolicy::ValueModeDispatch<
WriteBarrier::ValueMode::kValuePresent> {
template <typename HeapHandleCallback>
static V8_INLINE WriteBarrier::Type Get(const void* slot, const void* value,
WriteBarrier::Params& params,
HeapHandleCallback) {
bool within_cage = TryGetCagedHeap(slot, value, params);
if (!within_cage) {
return WriteBarrier::Type::kNone;
}
if (V8_LIKELY(!params.caged_heap().is_incremental_marking_in_progress)) {
#if defined(CPPGC_YOUNG_GENERATION)
params.heap = reinterpret_cast<HeapHandle*>(params.start);
params.slot_offset = reinterpret_cast<uintptr_t>(slot) - params.start;
params.value_offset = reinterpret_cast<uintptr_t>(value) - params.start;
return SetAndReturnType<WriteBarrier::Type::kGenerational>(params);
#else // !CPPGC_YOUNG_GENERATION
return SetAndReturnType<WriteBarrier::Type::kNone>(params);
#endif // !CPPGC_YOUNG_GENERATION
}
params.heap = reinterpret_cast<HeapHandle*>(params.start);
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 defined(CPPGC_YOUNG_GENERATION)
HeapHandle& handle = callback();
if (V8_LIKELY(!IsMarking(handle, params))) {
// params.start is populated by IsMarking().
params.heap = &handle;
params.slot_offset = reinterpret_cast<uintptr_t>(slot) - params.start;
// params.value_offset stays 0.
if (params.slot_offset > api_constants::kCagedHeapReservationSize) {
// Check if slot is on stack.
return SetAndReturnType<WriteBarrier::Type::kNone>(params);
}
return SetAndReturnType<WriteBarrier::Type::kGenerational>(params);
}
#else // !CPPGC_YOUNG_GENERATION
if (V8_LIKELY(!WriteBarrier::IsAnyIncrementalOrConcurrentMarking())) {
return SetAndReturnType<WriteBarrier::Type::kNone>(params);
}
HeapHandle& handle = callback();
if (V8_UNLIKELY(!subtle::HeapState::IsMarking(handle))) {
return SetAndReturnType<WriteBarrier::Type::kNone>(params);
}
#endif // !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* value,
WriteBarrier::Params& params,
HeapHandleCallback callback) {
// The slot will never be used in `Get()` below.
return Get<WriteBarrier::ValueMode::kValuePresent>(nullptr, value, params,
callback);
}
template <typename HeapHandleCallback>
static V8_INLINE WriteBarrier::Type GetForExternallyReferenced(
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;
// TODO(chromium:1056170): Create fast path on API.
static bool IsMarking(const void*, HeapHandle**);
// TODO(chromium:1056170): Create fast path on API.
static bool IsMarking(HeapHandle&);
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 WriteBarrier::Type::kNone;
}
if (IsMarking(object, ¶ms.heap)) {
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::IsAnyIncrementalOrConcurrentMarking())) {
HeapHandle& handle = callback();
if (IsMarking(handle)) {
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 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
template <typename HeapHandleCallback>
WriteBarrier::Type
WriteBarrier::GetWriteBarrierTypeForExternallyReferencedObject(
const void* value, Params& params, HeapHandleCallback callback) {
return WriteBarrierTypePolicy::GetForExternallyReferenced(value, params,
callback);
}
// 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
void WriteBarrier::GenerationalBarrier(const Params& params, const void* slot) {
CheckParams(Type::kGenerational, params);
const CagedHeapLocalData& local_data = params.caged_heap();
const AgeTable& age_table = local_data.age_table;
// Bail out if the slot is in young generation.
if (V8_LIKELY(age_table[params.slot_offset] == AgeTable::Age::kYoung)) return;
GenerationalBarrierSlow(local_data, age_table, slot, params.value_offset);
}
#endif // !CPPGC_YOUNG_GENERATION
} // namespace internal
} // namespace cppgc
#endif // INCLUDE_CPPGC_INTERNAL_WRITE_BARRIER_H_
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