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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/pointer-policies.h"
#include "cppgc/type-traits.h"
#include "v8config.h" // NOLINT(build/include_directory)
namespace cppgc {
class Visitor;
namespace internal {
class MemberBase {
protected:
MemberBase() = default;
explicit MemberBase(void* value) : raw_(value) {}
void* const* GetRawSlot() const { return &raw_; }
void* GetRaw() const { return raw_; }
void SetRaw(void* value) { raw_ = value; }
void* GetRawAtomic() const {
return reinterpret_cast<const std::atomic<void*>*>(&raw_)->load(
std::memory_order_relaxed);
}
void SetRawAtomic(void* value) {
reinterpret_cast<std::atomic<void*>*>(&raw_)->store(
value, std::memory_order_relaxed);
}
void ClearFromGC() const { raw_ = nullptr; }
private:
mutable void* raw_ = nullptr;
};
// The basic class from which all Member classes are 'generated'.
template <typename T, typename WeaknessTag, typename WriteBarrierPolicy,
typename CheckingPolicy>
class BasicMember final : private MemberBase, private CheckingPolicy {
public:
using PointeeType = T;
constexpr BasicMember() = default;
constexpr BasicMember(std::nullptr_t) {} // NOLINT
BasicMember(SentinelPointer s) : MemberBase(s) {} // NOLINT
BasicMember(T* raw) : MemberBase(raw) { // NOLINT
InitializingWriteBarrier();
this->CheckPointer(Get());
}
BasicMember(T& raw) : BasicMember(&raw) {} // NOLINT
BasicMember(const BasicMember& other) : BasicMember(other.Get()) {}
// Allow heterogeneous construction.
template <typename U, typename OtherBarrierPolicy, typename OtherWeaknessTag,
typename OtherCheckingPolicy,
typename = std::enable_if_t<std::is_base_of<T, U>::value>>
BasicMember( // NOLINT
const BasicMember<U, OtherWeaknessTag, OtherBarrierPolicy,
OtherCheckingPolicy>& other)
: BasicMember(other.Get()) {}
// Construction from Persistent.
template <typename U, typename PersistentWeaknessPolicy,
typename PersistentLocationPolicy,
typename PersistentCheckingPolicy,
typename = std::enable_if_t<std::is_base_of<T, U>::value>>
BasicMember( // NOLINT
const BasicPersistent<U, PersistentWeaknessPolicy,
PersistentLocationPolicy, PersistentCheckingPolicy>&
p)
: BasicMember(p.Get()) {}
BasicMember& operator=(const BasicMember& other) {
return operator=(other.Get());
}
// Allow heterogeneous assignment.
template <typename U, typename OtherWeaknessTag, typename OtherBarrierPolicy,
typename OtherCheckingPolicy,
typename = std::enable_if_t<std::is_base_of<T, U>::value>>
BasicMember& operator=(
const BasicMember<U, OtherWeaknessTag, OtherBarrierPolicy,
OtherCheckingPolicy>& other) {
return operator=(other.Get());
}
// Assignment from Persistent.
template <typename U, typename PersistentWeaknessPolicy,
typename PersistentLocationPolicy,
typename PersistentCheckingPolicy,
typename = std::enable_if_t<std::is_base_of<T, U>::value>>
BasicMember& operator=(
const BasicPersistent<U, PersistentWeaknessPolicy,
PersistentLocationPolicy, PersistentCheckingPolicy>&
other) {
return operator=(other.Get());
}
BasicMember& operator=(T* other) {
SetRawAtomic(other);
AssigningWriteBarrier();
this->CheckPointer(Get());
return *this;
}
BasicMember& operator=(std::nullptr_t) {
Clear();
return *this;
}
BasicMember& operator=(SentinelPointer s) {
SetRawAtomic(s);
return *this;
}
template <typename OtherWeaknessTag, typename OtherBarrierPolicy,
typename OtherCheckingPolicy>
void Swap(BasicMember<T, OtherWeaknessTag, OtherBarrierPolicy,
OtherCheckingPolicy>& other) {
T* tmp = Get();
*this = other;
other = tmp;
}
explicit operator bool() const { return Get(); }
operator T*() const { return Get(); } // NOLINT
T* operator->() const { return Get(); }
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_CLANG_NO_SANITIZE("cfi-unrelated-cast") T* Get() const {
// Executed by the mutator, hence non atomic load.
return static_cast<T*>(MemberBase::GetRaw());
}
void Clear() { SetRawAtomic(nullptr); }
T* Release() {
T* result = Get();
Clear();
return result;
}
private:
T* GetRawAtomic() const {
return static_cast<T*>(MemberBase::GetRawAtomic());
}
void InitializingWriteBarrier() const {
WriteBarrierPolicy::InitializingBarrier(GetRawSlot(), GetRaw());
}
void AssigningWriteBarrier() const {
WriteBarrierPolicy::AssigningBarrier(GetRawSlot(), GetRaw());
}
void ClearFromGC() const { MemberBase::ClearFromGC(); }
friend class cppgc::Visitor;
};
template <typename T1, typename WeaknessTag1, typename WriteBarrierPolicy1,
typename CheckingPolicy1, typename T2, typename WeaknessTag2,
typename WriteBarrierPolicy2, typename CheckingPolicy2>
bool operator==(
BasicMember<T1, WeaknessTag1, WriteBarrierPolicy1, CheckingPolicy1> member1,
BasicMember<T2, WeaknessTag2, WriteBarrierPolicy2, CheckingPolicy2>
member2) {
return member1.Get() == member2.Get();
}
template <typename T1, typename WeaknessTag1, typename WriteBarrierPolicy1,
typename CheckingPolicy1, typename T2, typename WeaknessTag2,
typename WriteBarrierPolicy2, typename CheckingPolicy2>
bool operator!=(
BasicMember<T1, WeaknessTag1, WriteBarrierPolicy1, CheckingPolicy1> member1,
BasicMember<T2, WeaknessTag2, WriteBarrierPolicy2, CheckingPolicy2>
member2) {
return !(member1 == member2);
}
template <typename T, typename WriteBarrierPolicy, typename CheckingPolicy>
struct IsWeak<
internal::BasicMember<T, WeakMemberTag, WriteBarrierPolicy, CheckingPolicy>>
: 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>;
/**
* 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>;
/**
* 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>;
} // namespace cppgc
#endif // INCLUDE_CPPGC_MEMBER_H_
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