chromium/v8/include/cppgc/persistent.h

// 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_PERSISTENT_H_
#define INCLUDE_CPPGC_PERSISTENT_H_

#include <type_traits>

#include "cppgc/internal/persistent-node.h"
#include "cppgc/internal/pointer-policies.h"
#include "cppgc/sentinel-pointer.h"
#include "cppgc/source-location.h"
#include "cppgc/type-traits.h"
#include "cppgc/visitor.h"
#include "v8config.h"  // NOLINT(build/include_directory)

namespace cppgc {
namespace internal {

// PersistentBase always refers to the object as const object and defers to
// BasicPersistent on casting to the right type as needed.
class PersistentBase { … };

// The basic class from which all Persistent classes are generated.
template <typename T, typename WeaknessPolicy, typename LocationPolicy,
          typename CheckingPolicy>
class BasicPersistent final : public PersistentBase,
                              public LocationPolicy,
                              private WeaknessPolicy,
                              private CheckingPolicy { … };

template <typename T1, typename WeaknessPolicy1, typename LocationPolicy1,
          typename CheckingPolicy1, typename T2, typename WeaknessPolicy2,
          typename LocationPolicy2, typename CheckingPolicy2>
bool operator==(const BasicPersistent<T1, WeaknessPolicy1, LocationPolicy1,
                                      CheckingPolicy1>& p1,
                const BasicPersistent<T2, WeaknessPolicy2, LocationPolicy2,
                                      CheckingPolicy2>& p2) { … }

template <typename T1, typename WeaknessPolicy1, typename LocationPolicy1,
          typename CheckingPolicy1, typename T2, typename WeaknessPolicy2,
          typename LocationPolicy2, typename CheckingPolicy2>
bool operator!=(const BasicPersistent<T1, WeaknessPolicy1, LocationPolicy1,
                                      CheckingPolicy1>& p1,
                const BasicPersistent<T2, WeaknessPolicy2, LocationPolicy2,
                                      CheckingPolicy2>& p2) { … }

template <typename T1, typename PersistentWeaknessPolicy,
          typename PersistentLocationPolicy, typename PersistentCheckingPolicy,
          typename T2, typename MemberWriteBarrierPolicy,
          typename MemberWeaknessTag, typename MemberCheckingPolicy,
          typename MemberStorageType>
bool operator==(
    const BasicPersistent<T1, PersistentWeaknessPolicy,
                          PersistentLocationPolicy, PersistentCheckingPolicy>&
        p,
    const BasicMember<T2, MemberWeaknessTag, MemberWriteBarrierPolicy,
                      MemberCheckingPolicy, MemberStorageType>& m) { … }

template <typename T1, typename PersistentWeaknessPolicy,
          typename PersistentLocationPolicy, typename PersistentCheckingPolicy,
          typename T2, typename MemberWriteBarrierPolicy,
          typename MemberWeaknessTag, typename MemberCheckingPolicy,
          typename MemberStorageType>
bool operator!=(
    const BasicPersistent<T1, PersistentWeaknessPolicy,
                          PersistentLocationPolicy, PersistentCheckingPolicy>&
        p,
    const BasicMember<T2, MemberWeaknessTag, MemberWriteBarrierPolicy,
                      MemberCheckingPolicy, MemberStorageType>& m) { … }

template <typename T1, typename MemberWriteBarrierPolicy,
          typename MemberWeaknessTag, typename MemberCheckingPolicy,
          typename MemberStorageType, typename T2,
          typename PersistentWeaknessPolicy, typename PersistentLocationPolicy,
          typename PersistentCheckingPolicy>
bool operator==(
    const BasicMember<T2, MemberWeaknessTag, MemberWriteBarrierPolicy,
                      MemberCheckingPolicy, MemberStorageType>& m,
    const BasicPersistent<T1, PersistentWeaknessPolicy,
                          PersistentLocationPolicy, PersistentCheckingPolicy>&
        p) { … }

template <typename T1, typename MemberWriteBarrierPolicy,
          typename MemberWeaknessTag, typename MemberCheckingPolicy,
          typename MemberStorageType, typename T2,
          typename PersistentWeaknessPolicy, typename PersistentLocationPolicy,
          typename PersistentCheckingPolicy>
bool operator!=(
    const BasicMember<T2, MemberWeaknessTag, MemberWriteBarrierPolicy,
                      MemberCheckingPolicy, MemberStorageType>& m,
    const BasicPersistent<T1, PersistentWeaknessPolicy,
                          PersistentLocationPolicy, PersistentCheckingPolicy>&
        p) { … }

IsWeak<BasicPersistent<T, internal::WeakPersistentPolicy, LocationPolicy, CheckingPolicy>>;
}  // namespace internal

/**
 * Persistent is a way to create a strong pointer from an off-heap object to
 * another on-heap object. As long as the Persistent handle is alive the GC will
 * keep the object pointed to alive. The Persistent handle is always a GC root
 * from the point of view of the GC. Persistent must be constructed and
 * destructed in the same thread.
 */
Persistent;

/**
 * WeakPersistent is a way to create a weak pointer from an off-heap object to
 * an on-heap object. The pointer is automatically cleared when the pointee gets
 * collected. WeakPersistent must be constructed and destructed in the same
 * thread.
 */
WeakPersistent;

}  // namespace cppgc

#endif  // INCLUDE_CPPGC_PERSISTENT_H_