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v8/include/cppgc/internal/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.
+  }
+
+  V8_INLINE static void AssigningBarrier(const void* slot, const void* value) {
+    WriteBarrier::Params params;
+    const WriteBarrier::Type type =
+        WriteBarrier::GetWriteBarrierType(slot, value, params);
+    WriteBarrier(type, params, slot, value);
+  }
+
+  V8_INLINE static void AssigningBarrier(const void* slot,
+                                         MemberStorage storage) {
+    WriteBarrier::Params params;
+    const WriteBarrier::Type type =
+        WriteBarrier::GetWriteBarrierType(slot, storage, params);
+    WriteBarrier(type, params, slot, storage.Load());
+  }
+
+ 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*) {}
+  V8_INLINE static void AssigningBarrier(const void*, const void*) {}
+  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>
+class BasicMember;
+
+}  // namespace internal
+
+}  // namespace cppgc
+
+#endif  // INCLUDE_CPPGC_INTERNAL_POINTER_POLICIES_H_