Init

2025-02-10 00:44:11 +08:00
parent ece733c0e5
commit 1e0c4b8d8c
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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, &params.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_