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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_MEMBER_H_
#define INCLUDE_CPPGC_MEMBER_H_
#include <atomic>
#include <cstddef>
#include <type_traits>
#include "cppgc/internal/api-constants.h"
#include "cppgc/internal/member-storage.h"
#include "cppgc/internal/pointer-policies.h"
#include "cppgc/sentinel-pointer.h"
#include "cppgc/type-traits.h"
#include "v8config.h" // NOLINT(build/include_directory)
namespace cppgc {
namespace subtle {
class HeapConsistency;
} // namespace subtle
class Visitor;
namespace internal {
// MemberBase always refers to the object as const object and defers to
// BasicMember on casting to the right type as needed.
template <typename StorageType>
class V8_TRIVIAL_ABI MemberBase {
public:
using RawStorage = StorageType;
protected:
struct AtomicInitializerTag {};
V8_INLINE MemberBase() = default;
V8_INLINE explicit MemberBase(const void* value) : raw_(value) {}
V8_INLINE MemberBase(const void* value, AtomicInitializerTag) {
SetRawAtomic(value);
}
V8_INLINE explicit MemberBase(RawStorage raw) : raw_(raw) {}
V8_INLINE explicit MemberBase(std::nullptr_t) : raw_(nullptr) {}
V8_INLINE explicit MemberBase(SentinelPointer s) : raw_(s) {}
V8_INLINE const void** GetRawSlot() const {
return reinterpret_cast<const void**>(const_cast<MemberBase*>(this));
}
V8_INLINE const void* GetRaw() const { return raw_.Load(); }
V8_INLINE void SetRaw(void* value) { raw_.Store(value); }
V8_INLINE const void* GetRawAtomic() const { return raw_.LoadAtomic(); }
V8_INLINE void SetRawAtomic(const void* value) { raw_.StoreAtomic(value); }
V8_INLINE RawStorage GetRawStorage() const { return raw_; }
V8_INLINE void SetRawStorageAtomic(RawStorage other) {
reinterpret_cast<std::atomic<RawStorage>&>(raw_).store(
other, std::memory_order_relaxed);
}
V8_INLINE bool IsCleared() const { return raw_.IsCleared(); }
V8_INLINE void ClearFromGC() const { raw_.Clear(); }
private:
friend class MemberDebugHelper;
mutable RawStorage raw_;
};
// The basic class from which all Member classes are 'generated'.
template <typename T, typename WeaknessTag, typename WriteBarrierPolicy,
typename CheckingPolicy, typename StorageType>
class V8_TRIVIAL_ABI BasicMember final : private MemberBase<StorageType>,
private CheckingPolicy {
using Base = MemberBase<StorageType>;
public:
using PointeeType = T;
using RawStorage = typename Base::RawStorage;
V8_INLINE constexpr BasicMember() = default;
V8_INLINE constexpr BasicMember(std::nullptr_t) {} // NOLINT
V8_INLINE BasicMember(SentinelPointer s) : Base(s) {} // NOLINT
V8_INLINE BasicMember(T* raw) : Base(raw) { // NOLINT
InitializingWriteBarrier(raw);
this->CheckPointer(Get());
}
V8_INLINE BasicMember(T& raw) // NOLINT
: BasicMember(&raw) {}
// Atomic ctor. Using the AtomicInitializerTag forces BasicMember to
// initialize using atomic assignments. This is required for preventing
// data races with concurrent marking.
using AtomicInitializerTag = typename Base::AtomicInitializerTag;
V8_INLINE BasicMember(std::nullptr_t, AtomicInitializerTag atomic)
: Base(nullptr, atomic) {}
V8_INLINE BasicMember(SentinelPointer s, AtomicInitializerTag atomic)
: Base(s, atomic) {}
V8_INLINE BasicMember(T* raw, AtomicInitializerTag atomic)
: Base(raw, atomic) {
InitializingWriteBarrier(raw);
this->CheckPointer(Get());
}
V8_INLINE BasicMember(T& raw, AtomicInitializerTag atomic)
: BasicMember(&raw, atomic) {}
// Copy ctor.
V8_INLINE BasicMember(const BasicMember& other)
: BasicMember(other.GetRawStorage()) {}
// Heterogeneous copy constructors. When the source pointer have a different
// type, perform a compress-decompress round, because the source pointer may
// need to be adjusted.
template <typename U, typename OtherBarrierPolicy, typename OtherWeaknessTag,
typename OtherCheckingPolicy,
std::enable_if_t<internal::IsDecayedSameV<T, U>>* = nullptr>
V8_INLINE BasicMember( // NOLINT
const BasicMember<U, OtherWeaknessTag, OtherBarrierPolicy,
OtherCheckingPolicy, StorageType>& other)
: BasicMember(other.GetRawStorage()) {}
template <typename U, typename OtherBarrierPolicy, typename OtherWeaknessTag,
typename OtherCheckingPolicy,
std::enable_if_t<internal::IsStrictlyBaseOfV<T, U>>* = nullptr>
V8_INLINE BasicMember( // NOLINT
const BasicMember<U, OtherWeaknessTag, OtherBarrierPolicy,
OtherCheckingPolicy, StorageType>& other)
: BasicMember(other.Get()) {}
// Move ctor.
V8_INLINE BasicMember(BasicMember&& other) noexcept
: BasicMember(other.GetRawStorage()) {
other.Clear();
}
// Heterogeneous move constructors. When the source pointer have a different
// type, perform a compress-decompress round, because the source pointer may
// need to be adjusted.
template <typename U, typename OtherBarrierPolicy, typename OtherWeaknessTag,
typename OtherCheckingPolicy,
std::enable_if_t<internal::IsDecayedSameV<T, U>>* = nullptr>
V8_INLINE BasicMember(
BasicMember<U, OtherWeaknessTag, OtherBarrierPolicy, OtherCheckingPolicy,
StorageType>&& other) noexcept
: BasicMember(other.GetRawStorage()) {
other.Clear();
}
template <typename U, typename OtherBarrierPolicy, typename OtherWeaknessTag,
typename OtherCheckingPolicy,
std::enable_if_t<internal::IsStrictlyBaseOfV<T, U>>* = nullptr>
V8_INLINE BasicMember(
BasicMember<U, OtherWeaknessTag, OtherBarrierPolicy, OtherCheckingPolicy,
StorageType>&& other) noexcept
: BasicMember(other.Get()) {
other.Clear();
}
// Construction from Persistent.
template <typename U, typename PersistentWeaknessPolicy,
typename PersistentLocationPolicy,
typename PersistentCheckingPolicy,
typename = std::enable_if_t<std::is_base_of<T, U>::value>>
V8_INLINE BasicMember(const BasicPersistent<U, PersistentWeaknessPolicy,
PersistentLocationPolicy,
PersistentCheckingPolicy>& p)
: BasicMember(p.Get()) {}
// Copy assignment.
V8_INLINE BasicMember& operator=(const BasicMember& other) {
return operator=(other.GetRawStorage());
}
// Heterogeneous copy assignment. When the source pointer have a different
// type, perform a compress-decompress round, because the source pointer may
// need to be adjusted.
template <typename U, typename OtherWeaknessTag, typename OtherBarrierPolicy,
typename OtherCheckingPolicy>
V8_INLINE BasicMember& operator=(
const BasicMember<U, OtherWeaknessTag, OtherBarrierPolicy,
OtherCheckingPolicy, StorageType>& other) {
if constexpr (internal::IsDecayedSameV<T, U>) {
return operator=(other.GetRawStorage());
} else {
static_assert(internal::IsStrictlyBaseOfV<T, U>);
return operator=(other.Get());
}
}
// Move assignment.
V8_INLINE BasicMember& operator=(BasicMember&& other) noexcept {
operator=(other.GetRawStorage());
other.Clear();
return *this;
}
// Heterogeneous move assignment. When the source pointer have a different
// type, perform a compress-decompress round, because the source pointer may
// need to be adjusted.
template <typename U, typename OtherWeaknessTag, typename OtherBarrierPolicy,
typename OtherCheckingPolicy>
V8_INLINE BasicMember& operator=(
BasicMember<U, OtherWeaknessTag, OtherBarrierPolicy, OtherCheckingPolicy,
StorageType>&& other) noexcept {
if constexpr (internal::IsDecayedSameV<T, U>) {
operator=(other.GetRawStorage());
} else {
static_assert(internal::IsStrictlyBaseOfV<T, U>);
operator=(other.Get());
}
other.Clear();
return *this;
}
// Assignment from Persistent.
template <typename U, typename PersistentWeaknessPolicy,
typename PersistentLocationPolicy,
typename PersistentCheckingPolicy,
typename = std::enable_if_t<std::is_base_of<T, U>::value>>
V8_INLINE BasicMember& operator=(
const BasicPersistent<U, PersistentWeaknessPolicy,
PersistentLocationPolicy, PersistentCheckingPolicy>&
other) {
return operator=(other.Get());
}
V8_INLINE BasicMember& operator=(T* other) {
Base::SetRawAtomic(other);
AssigningWriteBarrier(other);
this->CheckPointer(Get());
return *this;
}
V8_INLINE BasicMember& operator=(std::nullptr_t) {
Clear();
return *this;
}
V8_INLINE BasicMember& operator=(SentinelPointer s) {
Base::SetRawAtomic(s);
return *this;
}
template <typename OtherWeaknessTag, typename OtherBarrierPolicy,
typename OtherCheckingPolicy>
V8_INLINE void Swap(BasicMember<T, OtherWeaknessTag, OtherBarrierPolicy,
OtherCheckingPolicy, StorageType>& other) {
auto tmp = GetRawStorage();
*this = other;
other = tmp;
}
V8_INLINE explicit operator bool() const { return !Base::IsCleared(); }
V8_INLINE operator T*() const { return Get(); }
V8_INLINE T* operator->() const { return Get(); }
V8_INLINE T& operator*() const { return *Get(); }
// CFI cast exemption to allow passing SentinelPointer through T* and support
// heterogeneous assignments between different Member and Persistent handles
// based on their actual types.
V8_INLINE V8_CLANG_NO_SANITIZE("cfi-unrelated-cast") T* Get() const {
// Executed by the mutator, hence non atomic load.
//
// The const_cast below removes the constness from MemberBase storage. The
// following static_cast re-adds any constness if specified through the
// user-visible template parameter T.
return static_cast<T*>(const_cast<void*>(Base::GetRaw()));
}
V8_INLINE void Clear() {
Base::SetRawStorageAtomic(RawStorage{});
}
V8_INLINE T* Release() {
T* result = Get();
Clear();
return result;
}
V8_INLINE const T** GetSlotForTesting() const {
return reinterpret_cast<const T**>(Base::GetRawSlot());
}
V8_INLINE RawStorage GetRawStorage() const {
return Base::GetRawStorage();
}
private:
V8_INLINE explicit BasicMember(RawStorage raw) : Base(raw) {
InitializingWriteBarrier(Get());
this->CheckPointer(Get());
}
V8_INLINE BasicMember& operator=(RawStorage other) {
Base::SetRawStorageAtomic(other);
AssigningWriteBarrier();
this->CheckPointer(Get());
return *this;
}
V8_INLINE const T* GetRawAtomic() const {
return static_cast<const T*>(Base::GetRawAtomic());
}
V8_INLINE void InitializingWriteBarrier(T* value) const {
WriteBarrierPolicy::InitializingBarrier(Base::GetRawSlot(), value);
}
V8_INLINE void AssigningWriteBarrier(T* value) const {
WriteBarrierPolicy::template AssigningBarrier<
StorageType::kWriteBarrierSlotType>(Base::GetRawSlot(), value);
}
V8_INLINE void AssigningWriteBarrier() const {
WriteBarrierPolicy::template AssigningBarrier<
StorageType::kWriteBarrierSlotType>(Base::GetRawSlot(),
Base::GetRawStorage());
}
V8_INLINE void ClearFromGC() const { Base::ClearFromGC(); }
V8_INLINE T* GetFromGC() const { return Get(); }
friend class cppgc::subtle::HeapConsistency;
friend class cppgc::Visitor;
template <typename U>
friend struct cppgc::TraceTrait;
template <typename T1, typename WeaknessTag1, typename WriteBarrierPolicy1,
typename CheckingPolicy1, typename StorageType1>
friend class BasicMember;
};
// Member equality operators.
template <typename T1, typename WeaknessTag1, typename WriteBarrierPolicy1,
typename CheckingPolicy1, typename T2, typename WeaknessTag2,
typename WriteBarrierPolicy2, typename CheckingPolicy2,
typename StorageType>
V8_INLINE bool operator==(
const BasicMember<T1, WeaknessTag1, WriteBarrierPolicy1, CheckingPolicy1,
StorageType>& member1,
const BasicMember<T2, WeaknessTag2, WriteBarrierPolicy2, CheckingPolicy2,
StorageType>& member2) {
if constexpr (internal::IsDecayedSameV<T1, T2>) {
// Check compressed pointers if types are the same.
return member1.GetRawStorage() == member2.GetRawStorage();
} else {
static_assert(internal::IsStrictlyBaseOfV<T1, T2> ||
internal::IsStrictlyBaseOfV<T2, T1>);
// Otherwise, check decompressed pointers.
return member1.Get() == member2.Get();
}
}
template <typename T1, typename WeaknessTag1, typename WriteBarrierPolicy1,
typename CheckingPolicy1, typename T2, typename WeaknessTag2,
typename WriteBarrierPolicy2, typename CheckingPolicy2,
typename StorageType>
V8_INLINE bool operator!=(
const BasicMember<T1, WeaknessTag1, WriteBarrierPolicy1, CheckingPolicy1,
StorageType>& member1,
const BasicMember<T2, WeaknessTag2, WriteBarrierPolicy2, CheckingPolicy2,
StorageType>& member2) {
return !(member1 == member2);
}
// Equality with raw pointers.
template <typename T, typename WeaknessTag, typename WriteBarrierPolicy,
typename CheckingPolicy, typename StorageType, typename U>
V8_INLINE bool operator==(
const BasicMember<T, WeaknessTag, WriteBarrierPolicy, CheckingPolicy,
StorageType>& member,
U* raw) {
// Never allow comparison with erased pointers.
static_assert(!internal::IsDecayedSameV<void, U>);
if constexpr (internal::IsDecayedSameV<T, U>) {
// Check compressed pointers if types are the same.
return member.GetRawStorage() == StorageType(raw);
} else if constexpr (internal::IsStrictlyBaseOfV<T, U>) {
// Cast the raw pointer to T, which may adjust the pointer.
return member.GetRawStorage() == StorageType(static_cast<T*>(raw));
} else {
// Otherwise, decompressed the member.
return member.Get() == raw;
}
}
template <typename T, typename WeaknessTag, typename WriteBarrierPolicy,
typename CheckingPolicy, typename StorageType, typename U>
V8_INLINE bool operator!=(
const BasicMember<T, WeaknessTag, WriteBarrierPolicy, CheckingPolicy,
StorageType>& member,
U* raw) {
return !(member == raw);
}
template <typename T, typename U, typename WeaknessTag,
typename WriteBarrierPolicy, typename CheckingPolicy,
typename StorageType>
V8_INLINE bool operator==(
T* raw, const BasicMember<U, WeaknessTag, WriteBarrierPolicy,
CheckingPolicy, StorageType>& member) {
return member == raw;
}
template <typename T, typename U, typename WeaknessTag,
typename WriteBarrierPolicy, typename CheckingPolicy,
typename StorageType>
V8_INLINE bool operator!=(
T* raw, const BasicMember<U, WeaknessTag, WriteBarrierPolicy,
CheckingPolicy, StorageType>& member) {
return !(raw == member);
}
// Equality with sentinel.
template <typename T, typename WeaknessTag, typename WriteBarrierPolicy,
typename CheckingPolicy, typename StorageType>
V8_INLINE bool operator==(
const BasicMember<T, WeaknessTag, WriteBarrierPolicy, CheckingPolicy,
StorageType>& member,
SentinelPointer) {
return member.GetRawStorage().IsSentinel();
}
template <typename T, typename WeaknessTag, typename WriteBarrierPolicy,
typename CheckingPolicy, typename StorageType>
V8_INLINE bool operator!=(
const BasicMember<T, WeaknessTag, WriteBarrierPolicy, CheckingPolicy,
StorageType>& member,
SentinelPointer s) {
return !(member == s);
}
template <typename T, typename WeaknessTag, typename WriteBarrierPolicy,
typename CheckingPolicy, typename StorageType>
V8_INLINE bool operator==(
SentinelPointer s, const BasicMember<T, WeaknessTag, WriteBarrierPolicy,
CheckingPolicy, StorageType>& member) {
return member == s;
}
template <typename T, typename WeaknessTag, typename WriteBarrierPolicy,
typename CheckingPolicy, typename StorageType>
V8_INLINE bool operator!=(
SentinelPointer s, const BasicMember<T, WeaknessTag, WriteBarrierPolicy,
CheckingPolicy, StorageType>& member) {
return !(s == member);
}
// Equality with nullptr.
template <typename T, typename WeaknessTag, typename WriteBarrierPolicy,
typename CheckingPolicy, typename StorageType>
V8_INLINE bool operator==(
const BasicMember<T, WeaknessTag, WriteBarrierPolicy, CheckingPolicy,
StorageType>& member,
std::nullptr_t) {
return !static_cast<bool>(member);
}
template <typename T, typename WeaknessTag, typename WriteBarrierPolicy,
typename CheckingPolicy, typename StorageType>
V8_INLINE bool operator!=(
const BasicMember<T, WeaknessTag, WriteBarrierPolicy, CheckingPolicy,
StorageType>& member,
std::nullptr_t n) {
return !(member == n);
}
template <typename T, typename WeaknessTag, typename WriteBarrierPolicy,
typename CheckingPolicy, typename StorageType>
V8_INLINE bool operator==(
std::nullptr_t n, const BasicMember<T, WeaknessTag, WriteBarrierPolicy,
CheckingPolicy, StorageType>& member) {
return member == n;
}
template <typename T, typename WeaknessTag, typename WriteBarrierPolicy,
typename CheckingPolicy, typename StorageType>
V8_INLINE bool operator!=(
std::nullptr_t n, const BasicMember<T, WeaknessTag, WriteBarrierPolicy,
CheckingPolicy, StorageType>& member) {
return !(n == member);
}
// Relational operators.
template <typename T1, typename WeaknessTag1, typename WriteBarrierPolicy1,
typename CheckingPolicy1, typename T2, typename WeaknessTag2,
typename WriteBarrierPolicy2, typename CheckingPolicy2,
typename StorageType>
V8_INLINE bool operator<(
const BasicMember<T1, WeaknessTag1, WriteBarrierPolicy1, CheckingPolicy1,
StorageType>& member1,
const BasicMember<T2, WeaknessTag2, WriteBarrierPolicy2, CheckingPolicy2,
StorageType>& member2) {
static_assert(
internal::IsDecayedSameV<T1, T2>,
"Comparison works only for same pointer type modulo cv-qualifiers");
return member1.GetRawStorage() < member2.GetRawStorage();
}
template <typename T1, typename WeaknessTag1, typename WriteBarrierPolicy1,
typename CheckingPolicy1, typename T2, typename WeaknessTag2,
typename WriteBarrierPolicy2, typename CheckingPolicy2,
typename StorageType>
V8_INLINE bool operator<=(
const BasicMember<T1, WeaknessTag1, WriteBarrierPolicy1, CheckingPolicy1,
StorageType>& member1,
const BasicMember<T2, WeaknessTag2, WriteBarrierPolicy2, CheckingPolicy2,
StorageType>& member2) {
static_assert(
internal::IsDecayedSameV<T1, T2>,
"Comparison works only for same pointer type modulo cv-qualifiers");
return member1.GetRawStorage() <= member2.GetRawStorage();
}
template <typename T1, typename WeaknessTag1, typename WriteBarrierPolicy1,
typename CheckingPolicy1, typename T2, typename WeaknessTag2,
typename WriteBarrierPolicy2, typename CheckingPolicy2,
typename StorageType>
V8_INLINE bool operator>(
const BasicMember<T1, WeaknessTag1, WriteBarrierPolicy1, CheckingPolicy1,
StorageType>& member1,
const BasicMember<T2, WeaknessTag2, WriteBarrierPolicy2, CheckingPolicy2,
StorageType>& member2) {
static_assert(
internal::IsDecayedSameV<T1, T2>,
"Comparison works only for same pointer type modulo cv-qualifiers");
return member1.GetRawStorage() > member2.GetRawStorage();
}
template <typename T1, typename WeaknessTag1, typename WriteBarrierPolicy1,
typename CheckingPolicy1, typename T2, typename WeaknessTag2,
typename WriteBarrierPolicy2, typename CheckingPolicy2,
typename StorageType>
V8_INLINE bool operator>=(
const BasicMember<T1, WeaknessTag1, WriteBarrierPolicy1, CheckingPolicy1,
StorageType>& member1,
const BasicMember<T2, WeaknessTag2, WriteBarrierPolicy2, CheckingPolicy2,
StorageType>& member2) {
static_assert(
internal::IsDecayedSameV<T1, T2>,
"Comparison works only for same pointer type modulo cv-qualifiers");
return member1.GetRawStorage() >= member2.GetRawStorage();
}
template <typename T, typename WriteBarrierPolicy, typename CheckingPolicy,
typename StorageType>
struct IsWeak<internal::BasicMember<T, WeakMemberTag, WriteBarrierPolicy,
CheckingPolicy, StorageType>>
: std::true_type {};
} // namespace internal
/**
* Members are used in classes to contain strong pointers to other garbage
* collected objects. All Member fields of a class must be traced in the class'
* trace method.
*/
template <typename T>
using Member = internal::BasicMember<
T, internal::StrongMemberTag, internal::DijkstraWriteBarrierPolicy,
internal::DefaultMemberCheckingPolicy, internal::DefaultMemberStorage>;
/**
* WeakMember is similar to Member in that it is used to point to other garbage
* collected objects. However instead of creating a strong pointer to the
* object, the WeakMember creates a weak pointer, which does not keep the
* pointee alive. Hence if all pointers to to a heap allocated object are weak
* the object will be garbage collected. At the time of GC the weak pointers
* will automatically be set to null.
*/
template <typename T>
using WeakMember = internal::BasicMember<
T, internal::WeakMemberTag, internal::DijkstraWriteBarrierPolicy,
internal::DefaultMemberCheckingPolicy, internal::DefaultMemberStorage>;
/**
* UntracedMember is a pointer to an on-heap object that is not traced for some
* reason. Do not use this unless you know what you are doing. Keeping raw
* pointers to on-heap objects is prohibited unless used from stack. Pointee
* must be kept alive through other means.
*/
template <typename T>
using UntracedMember = internal::BasicMember<
T, internal::UntracedMemberTag, internal::NoWriteBarrierPolicy,
internal::DefaultMemberCheckingPolicy, internal::DefaultMemberStorage>;
namespace subtle {
/**
* UncompressedMember. Use with care in hot paths that would otherwise cause
* many decompression cycles.
*/
template <typename T>
using UncompressedMember = internal::BasicMember<
T, internal::StrongMemberTag, internal::DijkstraWriteBarrierPolicy,
internal::DefaultMemberCheckingPolicy, internal::RawPointer>;
#if defined(CPPGC_POINTER_COMPRESSION)
/**
* CompressedMember. Default implementation of cppgc::Member on builds with
* pointer compression.
*/
template <typename T>
using CompressedMember = internal::BasicMember<
T, internal::StrongMemberTag, internal::DijkstraWriteBarrierPolicy,
internal::DefaultMemberCheckingPolicy, internal::CompressedPointer>;
#endif // defined(CPPGC_POINTER_COMPRESSION)
} // namespace subtle
namespace internal {
struct Dummy;
static constexpr size_t kSizeOfMember = sizeof(Member<Dummy>);
static constexpr size_t kSizeOfUncompressedMember =
sizeof(subtle::UncompressedMember<Dummy>);
#if defined(CPPGC_POINTER_COMPRESSION)
static constexpr size_t kSizeofCompressedMember =
sizeof(subtle::CompressedMember<Dummy>);
#endif // defined(CPPGC_POINTER_COMPRESSION)
} // namespace internal
} // namespace cppgc
#endif // INCLUDE_CPPGC_MEMBER_H_