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/source-location.h"
#include "v8config.h"  // NOLINT(build/include_directory)
 
namespace cppgc {
namespace internal {
 
class PersistentRegion;
 
// Tags to distinguish between strong and weak member types.
class StrongMemberTag;
class WeakMemberTag;
class UntracedMemberTag;
 
struct DijkstraWriteBarrierPolicy {
  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.
  }
  static void AssigningBarrier(const void*, const void*) {
    // TODO(chromium:1056170): Add actual implementation.
  }
};
 
struct NoWriteBarrierPolicy {
  static void InitializingBarrier(const void*, const void*) {}
  static void AssigningBarrier(const void*, const void*) {}
};
 
class V8_EXPORT EnabledCheckingPolicy {
 protected:
  EnabledCheckingPolicy();
  void CheckPointer(const void* ptr);
 
 private:
  void* impl_;
};
 
class DisabledCheckingPolicy {
 protected:
  void CheckPointer(const void* raw) {}
};
 
#if V8_ENABLE_CHECKS
using DefaultCheckingPolicy = EnabledCheckingPolicy;
#else
using DefaultCheckingPolicy = DisabledCheckingPolicy;
#endif
 
class KeepLocationPolicy {
 public:
  constexpr const SourceLocation& Location() const { return location_; }
 
 protected:
  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 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(void* object);
};
 
struct WeakPersistentPolicy {
  using IsStrongPersistent = std::false_type;
 
  static V8_EXPORT PersistentRegion& GetPersistentRegion(void* object);
};
 
// Persistent/Member forward declarations.
template <typename T, typename WeaknessPolicy,
          typename LocationPolicy = DefaultLocationPolicy,
          typename CheckingPolicy = DefaultCheckingPolicy>
class BasicPersistent;
template <typename T, typename WeaknessTag, typename WriteBarrierPolicy,
          typename CheckingPolicy = DefaultCheckingPolicy>
class BasicMember;
 
// Special tag type used to denote some sentinel member. The semantics of the
// sentinel is defined by the embedder.
struct SentinelPointer {
  template <typename T>
  operator T*() const {  // NOLINT
    static constexpr intptr_t kSentinelValue = -1;
    return reinterpret_cast<T*>(kSentinelValue);
  }
  // Hidden friends.
  friend bool operator==(SentinelPointer, SentinelPointer) { return true; }
  friend bool operator!=(SentinelPointer, SentinelPointer) { return false; }
};
 
}  // namespace internal
 
constexpr internal::SentinelPointer kSentinelPointer;
 
}  // namespace cppgc
 
#endif  // INCLUDE_CPPGC_INTERNAL_POINTER_POLICIES_H_