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write-barrier.h
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write-barrier.h
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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`.
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.
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>
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>
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, MemberStorage value,
WriteBarrier::Params& params,
HeapHandleCallback callback) {
// `MemberStorage` will always be `RawPointer` for non-caged heap builds.
// Just convert to `void*` in this case.
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
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_