pointer-policies.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_POINTER_POLICIES_H_
#define INCLUDE_CPPGC_INTERNAL_POINTER_POLICIES_H_
 
#include <cstdint>
#include <type_traits>
 
#include "cppgc/internal/member-storage.h"
#include "cppgc/internal/write-barrier.h"
#include "cppgc/sentinel-pointer.h"
#include "cppgc/source-location.h"
#include "cppgc/type-traits.h"
#include "v8config.h"  // NOLINT(build/include_directory)
 
namespace cppgc {
namespace internal {
 
class HeapBase;
class PersistentRegion;
class CrossThreadPersistentRegion;
 
// Tags to distinguish between strong and weak member types.
class StrongMemberTag;
class WeakMemberTag;
class UntracedMemberTag;
 
struct DijkstraWriteBarrierPolicy {
  V8_INLINE static void InitializingBarrier(const void*, const void*) {
    // Since in initializing writes the source object is always white, having no
    // barrier doesn't break the tri-color invariant.
  }
 
  template <WriteBarrierSlotType SlotType>
  V8_INLINE static void AssigningBarrier(const void* slot, const void* value) {
#ifdef CPPGC_SLIM_WRITE_BARRIER
    if (V8_UNLIKELY(WriteBarrier::IsEnabled()))
      WriteBarrier::CombinedWriteBarrierSlow<SlotType>(slot);
#else   // !CPPGC_SLIM_WRITE_BARRIER
    WriteBarrier::Params params;
    const WriteBarrier::Type type =
        WriteBarrier::GetWriteBarrierType(slot, value, params);
    WriteBarrier(type, params, slot, value);
#endif  // !CPPGC_SLIM_WRITE_BARRIER
  }
 
  template <WriteBarrierSlotType SlotType>
  V8_INLINE static void AssigningBarrier(const void* slot, RawPointer storage) {
    static_assert(
        SlotType == WriteBarrierSlotType::kUncompressed,
        "Assigning storages of Member and UncompressedMember is not supported");
#ifdef CPPGC_SLIM_WRITE_BARRIER
    if (V8_UNLIKELY(WriteBarrier::IsEnabled()))
      WriteBarrier::CombinedWriteBarrierSlow<SlotType>(slot);
#else   // !CPPGC_SLIM_WRITE_BARRIER
    WriteBarrier::Params params;
    const WriteBarrier::Type type =
        WriteBarrier::GetWriteBarrierType(slot, storage, params);
    WriteBarrier(type, params, slot, storage.Load());
#endif  // !CPPGC_SLIM_WRITE_BARRIER
  }
 
#if defined(CPPGC_POINTER_COMPRESSION)
  template <WriteBarrierSlotType SlotType>
  V8_INLINE static void AssigningBarrier(const void* slot,
                                         CompressedPointer storage) {
    static_assert(
        SlotType == WriteBarrierSlotType::kCompressed,
        "Assigning storages of Member and UncompressedMember is not supported");
#ifdef CPPGC_SLIM_WRITE_BARRIER
    if (V8_UNLIKELY(WriteBarrier::IsEnabled()))
      WriteBarrier::CombinedWriteBarrierSlow<SlotType>(slot);
#else   // !CPPGC_SLIM_WRITE_BARRIER
    WriteBarrier::Params params;
    const WriteBarrier::Type type =
        WriteBarrier::GetWriteBarrierType(slot, storage, params);
    WriteBarrier(type, params, slot, storage.Load());
#endif  // !CPPGC_SLIM_WRITE_BARRIER
  }
#endif  // defined(CPPGC_POINTER_COMPRESSION)
 
 private:
  V8_INLINE static void WriteBarrier(WriteBarrier::Type type,
                                     const WriteBarrier::Params& params,
                                     const void* slot, const void* value) {
    switch (type) {
      case WriteBarrier::Type::kGenerational:
        WriteBarrier::GenerationalBarrier<
            WriteBarrier::GenerationalBarrierType::kPreciseSlot>(params, slot);
        break;
      case WriteBarrier::Type::kMarking:
        WriteBarrier::DijkstraMarkingBarrier(params, value);
        break;
      case WriteBarrier::Type::kNone:
        break;
    }
  }
};
 
struct NoWriteBarrierPolicy {
  V8_INLINE static void InitializingBarrier(const void*, const void*) {}
  template <WriteBarrierSlotType>
  V8_INLINE static void AssigningBarrier(const void*, const void*) {}
  template <WriteBarrierSlotType, typename MemberStorage>
  V8_INLINE static void AssigningBarrier(const void*, MemberStorage) {}
};
 
class V8_EXPORT SameThreadEnabledCheckingPolicyBase {
 protected:
  void CheckPointerImpl(const void* ptr, bool points_to_payload,
                        bool check_off_heap_assignments);
 
  const HeapBase* heap_ = nullptr;
};
 
template <bool kCheckOffHeapAssignments>
class V8_EXPORT SameThreadEnabledCheckingPolicy
    : private SameThreadEnabledCheckingPolicyBase {
 protected:
  template <typename T>
  void CheckPointer(const T* ptr) {
    if (!ptr || (kSentinelPointer == ptr)) return;
 
    CheckPointersImplTrampoline<T>::Call(this, ptr);
  }
 
 private:
  template <typename T, bool = IsCompleteV<T>>
  struct CheckPointersImplTrampoline {
    static void Call(SameThreadEnabledCheckingPolicy* policy, const T* ptr) {
      policy->CheckPointerImpl(ptr, false, kCheckOffHeapAssignments);
    }
  };
 
  template <typename T>
  struct CheckPointersImplTrampoline<T, true> {
    static void Call(SameThreadEnabledCheckingPolicy* policy, const T* ptr) {
      policy->CheckPointerImpl(ptr, IsGarbageCollectedTypeV<T>,
                               kCheckOffHeapAssignments);
    }
  };
};
 
class DisabledCheckingPolicy {
 protected:
  V8_INLINE void CheckPointer(const void*) {}
};
 
#ifdef DEBUG
// Off heap members are not connected to object graph and thus cannot ressurect
// dead objects.
using DefaultMemberCheckingPolicy =
    SameThreadEnabledCheckingPolicy<false /* kCheckOffHeapAssignments*/>;
using DefaultPersistentCheckingPolicy =
    SameThreadEnabledCheckingPolicy<true /* kCheckOffHeapAssignments*/>;
#else   // !DEBUG
using DefaultMemberCheckingPolicy = DisabledCheckingPolicy;
using DefaultPersistentCheckingPolicy = DisabledCheckingPolicy;
#endif  // !DEBUG
// For CT(W)P neither marking information (for value), nor objectstart bitmap
// (for slot) are guaranteed to be present because there's no synchronization
// between heaps after marking.
using DefaultCrossThreadPersistentCheckingPolicy = DisabledCheckingPolicy;
 
class KeepLocationPolicy {
 public:
  constexpr const SourceLocation& Location() const { return location_; }
 
 protected:
  constexpr KeepLocationPolicy() = default;
  constexpr explicit KeepLocationPolicy(const SourceLocation& location)
      : location_(location) {}
 
  // KeepLocationPolicy must not copy underlying source locations.
  KeepLocationPolicy(const KeepLocationPolicy&) = delete;
  KeepLocationPolicy& operator=(const KeepLocationPolicy&) = delete;
 
  // Location of the original moved from object should be preserved.
  KeepLocationPolicy(KeepLocationPolicy&&) = default;
  KeepLocationPolicy& operator=(KeepLocationPolicy&&) = default;
 
 private:
  SourceLocation location_;
};
 
class IgnoreLocationPolicy {
 public:
  constexpr SourceLocation Location() const { return {}; }
 
 protected:
  constexpr IgnoreLocationPolicy() = default;
  constexpr explicit IgnoreLocationPolicy(const SourceLocation&) {}
};
 
#if CPPGC_SUPPORTS_OBJECT_NAMES
using DefaultLocationPolicy = KeepLocationPolicy;
#else
using DefaultLocationPolicy = IgnoreLocationPolicy;
#endif
 
struct StrongPersistentPolicy {
  using IsStrongPersistent = std::true_type;
  static V8_EXPORT PersistentRegion& GetPersistentRegion(const void* object);
};
 
struct WeakPersistentPolicy {
  using IsStrongPersistent = std::false_type;
  static V8_EXPORT PersistentRegion& GetPersistentRegion(const void* object);
};
 
struct StrongCrossThreadPersistentPolicy {
  using IsStrongPersistent = std::true_type;
  static V8_EXPORT CrossThreadPersistentRegion& GetPersistentRegion(
      const void* object);
};
 
struct WeakCrossThreadPersistentPolicy {
  using IsStrongPersistent = std::false_type;
  static V8_EXPORT CrossThreadPersistentRegion& GetPersistentRegion(
      const void* object);
};
 
// Forward declarations setting up the default policies.
template <typename T, typename WeaknessPolicy,
          typename LocationPolicy = DefaultLocationPolicy,
          typename CheckingPolicy = DefaultCrossThreadPersistentCheckingPolicy>
class BasicCrossThreadPersistent;
template <typename T, typename WeaknessPolicy,
          typename LocationPolicy = DefaultLocationPolicy,
          typename CheckingPolicy = DefaultPersistentCheckingPolicy>
class BasicPersistent;
template <typename T, typename WeaknessTag, typename WriteBarrierPolicy,
          typename CheckingPolicy = DefaultMemberCheckingPolicy,
          typename StorageType = DefaultMemberStorage>
class BasicMember;
 
}  // namespace internal
 
}  // namespace cppgc
 
#endif  // INCLUDE_CPPGC_INTERNAL_POINTER_POLICIES_H_