зеркало из https://github.com/mozilla/gecko-dev.git
147 строки
3.9 KiB
C++
147 строки
3.9 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*/
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/* smart pointer for strong references to nsPresArena-allocated objects
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that might be held onto until the arena's destruction */
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#include "mozilla/Assertions.h"
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#include "mozilla/RefPtr.h"
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#ifndef mozilla_ArenaRefPtr_h
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#define mozilla_ArenaRefPtr_h
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class nsPresArena;
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namespace mozilla {
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/**
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* A class for holding strong references to nsPresArena-allocated
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* objects.
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*
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* Since the arena's lifetime is not related to the refcounts
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* of the objects allocated within it, it is possible to have a strong
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* reference to an arena-allocated object that lives until the
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* destruction of the arena. An ArenaRefPtr acts like a weak reference
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* in that it will clear its referent if the arena is about to go away.
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*
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* T must be a class that has these two methods:
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*
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* static mozilla::ArenaObjectID ArenaObjectID();
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* U* Arena();
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*
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* where U is a class that has these two methods:
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*
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* void RegisterArenaRefPtr(ArenaRefPtr<T>*);
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* void DeregisterArenaRefPtr(ArenaRefPtr<T>*);
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*
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* Currently, both nsPresArena and nsIPresShell can be used as U.
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*
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* The ArenaObjectID method must return the mozilla::ArenaObjectID that
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* uniquely identifies T, and the Arena method must return the nsPresArena
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* (or a proxy for it) in which the object was allocated.
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*/
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template <typename T>
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class ArenaRefPtr {
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friend class ::nsPresArena;
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public:
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ArenaRefPtr() { AssertValidType(); }
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template <typename I>
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MOZ_IMPLICIT ArenaRefPtr(already_AddRefed<I>& aRhs) {
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AssertValidType();
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assign(aRhs);
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}
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template <typename I>
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MOZ_IMPLICIT ArenaRefPtr(already_AddRefed<I>&& aRhs) {
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AssertValidType();
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assign(aRhs);
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}
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MOZ_IMPLICIT ArenaRefPtr(T* aRhs) {
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AssertValidType();
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assign(aRhs);
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}
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template <typename I>
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ArenaRefPtr<T>& operator=(already_AddRefed<I>& aRhs) {
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assign(aRhs);
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return *this;
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}
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template <typename I>
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ArenaRefPtr<T>& operator=(already_AddRefed<I>&& aRhs) {
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assign(aRhs);
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return *this;
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}
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ArenaRefPtr<T>& operator=(T* aRhs) {
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assign(aRhs);
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return *this;
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}
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~ArenaRefPtr() { assign(nullptr); }
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operator T*() const& { return get(); }
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operator T*() const&& = delete;
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explicit operator bool() const { return !!mPtr; }
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bool operator!() const { return !mPtr; }
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T* operator->() const { return mPtr.operator->(); }
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T& operator*() const { return *get(); }
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T* get() const { return mPtr; }
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private:
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void AssertValidType();
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/**
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* Clears the pointer to the arena-allocated object but skips the usual
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* step of deregistering the ArenaRefPtr from the nsPresArena. This
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* method is called by nsPresArena when clearing all registered ArenaRefPtrs
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* so that it can deregister them all at once, avoiding hash table churn.
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*/
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void ClearWithoutDeregistering() { mPtr = nullptr; }
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template <typename I>
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void assign(already_AddRefed<I>& aSmartPtr) {
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RefPtr<T> newPtr(aSmartPtr);
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assignFrom(newPtr);
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}
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template <typename I>
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void assign(already_AddRefed<I>&& aSmartPtr) {
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RefPtr<T> newPtr(aSmartPtr);
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assignFrom(newPtr);
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}
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void assign(T* aPtr) { assignFrom(aPtr); }
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template <typename I>
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void assignFrom(I& aPtr) {
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if (aPtr == mPtr) {
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return;
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}
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bool sameArena = mPtr && aPtr && mPtr->Arena() == aPtr->Arena();
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if (mPtr && !sameArena) {
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MOZ_ASSERT(mPtr->Arena());
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mPtr->Arena()->DeregisterArenaRefPtr(this);
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}
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mPtr = std::move(aPtr);
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if (mPtr && !sameArena) {
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MOZ_ASSERT(mPtr->Arena());
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mPtr->Arena()->RegisterArenaRefPtr(this);
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}
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}
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RefPtr<T> mPtr;
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};
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} // namespace mozilla
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#endif // mozilla_ArenaRefPtr_h
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