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v8/include/cppgc/persistent.h
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366
v8/include/cppgc/persistent.h
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// Copyright 2020 the V8 project authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef INCLUDE_CPPGC_PERSISTENT_H_
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#define INCLUDE_CPPGC_PERSISTENT_H_
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#include <type_traits>
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#include "cppgc/internal/persistent-node.h"
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#include "cppgc/internal/pointer-policies.h"
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#include "cppgc/sentinel-pointer.h"
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#include "cppgc/source-location.h"
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#include "cppgc/type-traits.h"
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#include "cppgc/visitor.h"
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#include "v8config.h" // NOLINT(build/include_directory)
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namespace cppgc {
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namespace internal {
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// PersistentBase always refers to the object as const object and defers to
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// BasicPersistent on casting to the right type as needed.
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class PersistentBase {
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protected:
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PersistentBase() = default;
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explicit PersistentBase(const void* raw) : raw_(raw) {}
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const void* GetValue() const { return raw_; }
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void SetValue(const void* value) { raw_ = value; }
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PersistentNode* GetNode() const { return node_; }
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void SetNode(PersistentNode* node) { node_ = node; }
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// Performs a shallow clear which assumes that internal persistent nodes are
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// destroyed elsewhere.
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void ClearFromGC() const {
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raw_ = nullptr;
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node_ = nullptr;
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}
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protected:
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mutable const void* raw_ = nullptr;
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mutable PersistentNode* node_ = nullptr;
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friend class PersistentRegionBase;
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};
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// The basic class from which all Persistent classes are generated.
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template <typename T, typename WeaknessPolicy, typename LocationPolicy,
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typename CheckingPolicy>
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class BasicPersistent final : public PersistentBase,
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public LocationPolicy,
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private WeaknessPolicy,
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private CheckingPolicy {
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public:
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using typename WeaknessPolicy::IsStrongPersistent;
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using PointeeType = T;
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// Null-state/sentinel constructors.
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BasicPersistent( // NOLINT
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const SourceLocation& loc = SourceLocation::Current())
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: LocationPolicy(loc) {}
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BasicPersistent(std::nullptr_t, // NOLINT
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const SourceLocation& loc = SourceLocation::Current())
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: LocationPolicy(loc) {}
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BasicPersistent( // NOLINT
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SentinelPointer s, const SourceLocation& loc = SourceLocation::Current())
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: PersistentBase(s), LocationPolicy(loc) {}
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// Raw value constructors.
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BasicPersistent(T* raw, // NOLINT
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const SourceLocation& loc = SourceLocation::Current())
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: PersistentBase(raw), LocationPolicy(loc) {
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if (!IsValid()) return;
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SetNode(WeaknessPolicy::GetPersistentRegion(GetValue())
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.AllocateNode(this, &TraceAsRoot));
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this->CheckPointer(Get());
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}
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BasicPersistent(T& raw, // NOLINT
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const SourceLocation& loc = SourceLocation::Current())
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: BasicPersistent(&raw, loc) {}
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// Copy ctor.
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BasicPersistent(const BasicPersistent& other,
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const SourceLocation& loc = SourceLocation::Current())
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: BasicPersistent(other.Get(), loc) {}
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// Heterogeneous ctor.
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template <typename U, typename OtherWeaknessPolicy,
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typename OtherLocationPolicy, typename OtherCheckingPolicy,
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typename = std::enable_if_t<std::is_base_of<T, U>::value>>
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BasicPersistent(
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const BasicPersistent<U, OtherWeaknessPolicy, OtherLocationPolicy,
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OtherCheckingPolicy>& other,
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const SourceLocation& loc = SourceLocation::Current())
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: BasicPersistent(other.Get(), loc) {}
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// Move ctor. The heterogeneous move ctor is not supported since e.g.
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// persistent can't reuse persistent node from weak persistent.
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BasicPersistent(
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BasicPersistent&& other,
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const SourceLocation& loc = SourceLocation::Current()) noexcept
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: PersistentBase(std::move(other)), LocationPolicy(std::move(other)) {
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if (!IsValid()) return;
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GetNode()->UpdateOwner(this);
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other.SetValue(nullptr);
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other.SetNode(nullptr);
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this->CheckPointer(Get());
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}
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// Constructor from member.
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template <typename U, typename MemberBarrierPolicy,
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typename MemberWeaknessTag, typename MemberCheckingPolicy,
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typename = std::enable_if_t<std::is_base_of<T, U>::value>>
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BasicPersistent(
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const internal::BasicMember<U, MemberBarrierPolicy, MemberWeaknessTag,
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MemberCheckingPolicy>& member,
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const SourceLocation& loc = SourceLocation::Current())
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: BasicPersistent(member.Get(), loc) {}
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~BasicPersistent() { Clear(); }
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// Copy assignment.
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BasicPersistent& operator=(const BasicPersistent& other) {
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return operator=(other.Get());
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}
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template <typename U, typename OtherWeaknessPolicy,
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typename OtherLocationPolicy, typename OtherCheckingPolicy,
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typename = std::enable_if_t<std::is_base_of<T, U>::value>>
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BasicPersistent& operator=(
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const BasicPersistent<U, OtherWeaknessPolicy, OtherLocationPolicy,
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OtherCheckingPolicy>& other) {
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return operator=(other.Get());
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}
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// Move assignment.
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BasicPersistent& operator=(BasicPersistent&& other) noexcept {
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if (this == &other) return *this;
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Clear();
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PersistentBase::operator=(std::move(other));
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LocationPolicy::operator=(std::move(other));
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if (!IsValid()) return *this;
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GetNode()->UpdateOwner(this);
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other.SetValue(nullptr);
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other.SetNode(nullptr);
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this->CheckPointer(Get());
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return *this;
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}
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// Assignment from member.
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template <typename U, typename MemberBarrierPolicy,
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typename MemberWeaknessTag, typename MemberCheckingPolicy,
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typename = std::enable_if_t<std::is_base_of<T, U>::value>>
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BasicPersistent& operator=(
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const internal::BasicMember<U, MemberBarrierPolicy, MemberWeaknessTag,
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MemberCheckingPolicy>& member) {
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return operator=(member.Get());
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}
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BasicPersistent& operator=(T* other) {
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Assign(other);
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return *this;
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}
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BasicPersistent& operator=(std::nullptr_t) {
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Clear();
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return *this;
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}
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BasicPersistent& operator=(SentinelPointer s) {
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Assign(s);
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return *this;
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}
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explicit operator bool() const { return Get(); }
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operator T*() const { return Get(); }
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T* operator->() const { return Get(); }
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T& operator*() const { return *Get(); }
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// CFI cast exemption to allow passing SentinelPointer through T* and support
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// heterogeneous assignments between different Member and Persistent handles
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// based on their actual types.
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V8_CLANG_NO_SANITIZE("cfi-unrelated-cast") T* Get() const {
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// The const_cast below removes the constness from PersistentBase storage.
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// The following static_cast re-adds any constness if specified through the
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// user-visible template parameter T.
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return static_cast<T*>(const_cast<void*>(GetValue()));
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}
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void Clear() {
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// Simplified version of `Assign()` to allow calling without a complete type
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// `T`.
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if (IsValid()) {
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WeaknessPolicy::GetPersistentRegion(GetValue()).FreeNode(GetNode());
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SetNode(nullptr);
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}
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SetValue(nullptr);
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}
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T* Release() {
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T* result = Get();
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Clear();
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return result;
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}
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template <typename U, typename OtherWeaknessPolicy = WeaknessPolicy,
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typename OtherLocationPolicy = LocationPolicy,
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typename OtherCheckingPolicy = CheckingPolicy>
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BasicPersistent<U, OtherWeaknessPolicy, OtherLocationPolicy,
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OtherCheckingPolicy>
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To() const {
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return BasicPersistent<U, OtherWeaknessPolicy, OtherLocationPolicy,
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OtherCheckingPolicy>(static_cast<U*>(Get()));
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}
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private:
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static void TraceAsRoot(RootVisitor& root_visitor, const void* ptr) {
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root_visitor.Trace(*static_cast<const BasicPersistent*>(ptr));
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}
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bool IsValid() const {
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// Ideally, handling kSentinelPointer would be done by the embedder. On the
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// other hand, having Persistent aware of it is beneficial since no node
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// gets wasted.
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return GetValue() != nullptr && GetValue() != kSentinelPointer;
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}
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void Assign(T* ptr) {
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if (IsValid()) {
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if (ptr && ptr != kSentinelPointer) {
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// Simply assign the pointer reusing the existing node.
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SetValue(ptr);
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this->CheckPointer(ptr);
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return;
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}
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WeaknessPolicy::GetPersistentRegion(GetValue()).FreeNode(GetNode());
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SetNode(nullptr);
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}
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SetValue(ptr);
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if (!IsValid()) return;
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SetNode(WeaknessPolicy::GetPersistentRegion(GetValue())
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.AllocateNode(this, &TraceAsRoot));
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this->CheckPointer(Get());
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}
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void ClearFromGC() const {
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if (IsValid()) {
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WeaknessPolicy::GetPersistentRegion(GetValue()).FreeNode(GetNode());
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PersistentBase::ClearFromGC();
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}
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}
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// Set Get() for details.
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V8_CLANG_NO_SANITIZE("cfi-unrelated-cast")
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T* GetFromGC() const {
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return static_cast<T*>(const_cast<void*>(GetValue()));
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}
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friend class internal::RootVisitor;
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};
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template <typename T1, typename WeaknessPolicy1, typename LocationPolicy1,
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typename CheckingPolicy1, typename T2, typename WeaknessPolicy2,
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typename LocationPolicy2, typename CheckingPolicy2>
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bool operator==(const BasicPersistent<T1, WeaknessPolicy1, LocationPolicy1,
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CheckingPolicy1>& p1,
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const BasicPersistent<T2, WeaknessPolicy2, LocationPolicy2,
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CheckingPolicy2>& p2) {
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return p1.Get() == p2.Get();
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}
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template <typename T1, typename WeaknessPolicy1, typename LocationPolicy1,
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typename CheckingPolicy1, typename T2, typename WeaknessPolicy2,
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typename LocationPolicy2, typename CheckingPolicy2>
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bool operator!=(const BasicPersistent<T1, WeaknessPolicy1, LocationPolicy1,
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CheckingPolicy1>& p1,
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const BasicPersistent<T2, WeaknessPolicy2, LocationPolicy2,
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CheckingPolicy2>& p2) {
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return !(p1 == p2);
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}
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template <typename T1, typename PersistentWeaknessPolicy,
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typename PersistentLocationPolicy, typename PersistentCheckingPolicy,
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typename T2, typename MemberWriteBarrierPolicy,
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typename MemberWeaknessTag, typename MemberCheckingPolicy>
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bool operator==(
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const BasicPersistent<T1, PersistentWeaknessPolicy,
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PersistentLocationPolicy, PersistentCheckingPolicy>&
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p,
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const BasicMember<T2, MemberWeaknessTag, MemberWriteBarrierPolicy,
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MemberCheckingPolicy>& m) {
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return p.Get() == m.Get();
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}
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template <typename T1, typename PersistentWeaknessPolicy,
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typename PersistentLocationPolicy, typename PersistentCheckingPolicy,
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typename T2, typename MemberWriteBarrierPolicy,
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typename MemberWeaknessTag, typename MemberCheckingPolicy>
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bool operator!=(
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const BasicPersistent<T1, PersistentWeaknessPolicy,
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PersistentLocationPolicy, PersistentCheckingPolicy>&
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p,
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const BasicMember<T2, MemberWeaknessTag, MemberWriteBarrierPolicy,
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MemberCheckingPolicy>& m) {
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return !(p == m);
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}
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template <typename T1, typename MemberWriteBarrierPolicy,
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typename MemberWeaknessTag, typename MemberCheckingPolicy,
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typename T2, typename PersistentWeaknessPolicy,
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typename PersistentLocationPolicy, typename PersistentCheckingPolicy>
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bool operator==(
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const BasicMember<T2, MemberWeaknessTag, MemberWriteBarrierPolicy,
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MemberCheckingPolicy>& m,
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const BasicPersistent<T1, PersistentWeaknessPolicy,
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PersistentLocationPolicy, PersistentCheckingPolicy>&
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p) {
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return m.Get() == p.Get();
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}
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template <typename T1, typename MemberWriteBarrierPolicy,
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typename MemberWeaknessTag, typename MemberCheckingPolicy,
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typename T2, typename PersistentWeaknessPolicy,
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typename PersistentLocationPolicy, typename PersistentCheckingPolicy>
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bool operator!=(
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const BasicMember<T2, MemberWeaknessTag, MemberWriteBarrierPolicy,
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MemberCheckingPolicy>& m,
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const BasicPersistent<T1, PersistentWeaknessPolicy,
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PersistentLocationPolicy, PersistentCheckingPolicy>&
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p) {
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return !(m == p);
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}
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template <typename T, typename LocationPolicy, typename CheckingPolicy>
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struct IsWeak<BasicPersistent<T, internal::WeakPersistentPolicy, LocationPolicy,
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CheckingPolicy>> : std::true_type {};
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} // namespace internal
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/**
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* Persistent is a way to create a strong pointer from an off-heap object to
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* another on-heap object. As long as the Persistent handle is alive the GC will
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* keep the object pointed to alive. The Persistent handle is always a GC root
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* from the point of view of the GC. Persistent must be constructed and
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* destructed in the same thread.
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*/
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template <typename T>
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using Persistent =
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internal::BasicPersistent<T, internal::StrongPersistentPolicy>;
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/**
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* WeakPersistent is a way to create a weak pointer from an off-heap object to
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* an on-heap object. The pointer is automatically cleared when the pointee gets
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* collected. WeakPersistent must be constructed and destructed in the same
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* thread.
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*/
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template <typename T>
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using WeakPersistent =
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internal::BasicPersistent<T, internal::WeakPersistentPolicy>;
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} // namespace cppgc
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#endif // INCLUDE_CPPGC_PERSISTENT_H_
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