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444 lines
11 KiB
C++
444 lines
11 KiB
C++
/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
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* vim: set ts=8 sw=4 et tw=99 ft=cpp:
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*
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* ***** BEGIN LICENSE BLOCK *****
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* Version: MPL 1.1/GPL 2.0/LGPL 2.1
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*
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* The contents of this file are subject to the Mozilla Public License Version
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* 1.1 (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at:
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* http://www.mozilla.org/MPL/
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*
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* Software distributed under the License is distributed on an "AS IS" basis,
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* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
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* for the specific language governing rights and limitations under the
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* License.
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*
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* The Original Code is Mozilla Code.
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*
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* The Initial Developer of the Original Code is
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* The Mozilla Foundation
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* Portions created by the Initial Developer are Copyright (C) 2011
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* the Initial Developer. All Rights Reserved.
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*
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* Contributor(s):
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* Chris Jones <jones.chris.g@gmail.com>
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*
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* Alternatively, the contents of this file may be used under the terms of
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* either the GNU General Public License Version 2 or later (the "GPL"), or
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* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
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* in which case the provisions of the GPL or the LGPL are applicable instead
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* of those above. If you wish to allow use of your version of this file only
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* under the terms of either the GPL or the LGPL, and not to allow others to
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* use your version of this file under the terms of the MPL, indicate your
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* decision by deleting the provisions above and replace them with the notice
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* and other provisions required by the GPL or the LGPL. If you do not delete
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* the provisions above, a recipient may use your version of this file under
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* the terms of any one of the MPL, the GPL or the LGPL.
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*
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* ***** END LICENSE BLOCK ***** */
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/* Helpers for defining and using refcounted objects. */
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#ifndef mozilla_RefPtr_h_
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#define mozilla_RefPtr_h_
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#include "mozilla/Assertions.h"
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#include "mozilla/Attributes.h"
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namespace mozilla {
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template<typename T> class RefCounted;
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template<typename T> class RefPtr;
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template<typename T> class TemporaryRef;
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template<typename T> class OutParamRef;
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template<typename T> OutParamRef<T> byRef(RefPtr<T>&);
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/**
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* RefCounted<T> is a sort of a "mixin" for a class T. RefCounted
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* manages, well, refcounting for T, and because RefCounted is
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* parameterized on T, RefCounted<T> can call T's destructor directly.
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* This means T doesn't need to have a virtual dtor and so doesn't
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* need a vtable.
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*
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* RefCounted<T> is created with refcount == 0. Newly-allocated
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* RefCounted<T> must immediately be assigned to a RefPtr to make the
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* refcount > 0. It's an error to allocate and free a bare
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* RefCounted<T>, i.e. outside of the RefPtr machinery. Attempts to
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* do so will abort DEBUG builds.
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*
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* Live RefCounted<T> have refcount > 0. The lifetime (refcounts) of
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* live RefCounted<T> are controlled by RefPtr<T> and
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* RefPtr<super/subclass of T>. Upon a transition from refcounted==1
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* to 0, the RefCounted<T> "dies" and is destroyed. The "destroyed"
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* state is represented in DEBUG builds by refcount==-0xdead. This
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* state distinguishes use-before-ref (refcount==0) from
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* use-after-destroy (refcount==-0xdead).
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*/
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template<typename T>
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class RefCounted
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{
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friend class RefPtr<T>;
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public:
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RefCounted() : refCnt(0) { }
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~RefCounted() { MOZ_ASSERT(refCnt == -0xdead); }
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// Compatibility with nsRefPtr.
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void AddRef() {
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MOZ_ASSERT(refCnt >= 0);
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++refCnt;
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}
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void Release() {
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MOZ_ASSERT(refCnt > 0);
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if (0 == --refCnt) {
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#ifdef DEBUG
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refCnt = -0xdead;
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#endif
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delete static_cast<T*>(this);
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}
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}
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// Compatibility with wtf::RefPtr.
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void ref() { AddRef(); }
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void deref() { Release(); }
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int refCount() const { return refCnt; }
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bool hasOneRef() const {
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MOZ_ASSERT(refCnt > 0);
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return refCnt == 1;
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}
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private:
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int refCnt;
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};
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/**
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* RefPtr points to a refcounted thing that has AddRef and Release
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* methods to increase/decrease the refcount, respectively. After a
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* RefPtr<T> is assigned a T*, the T* can be used through the RefPtr
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* as if it were a T*.
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*
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* A RefPtr can forget its underlying T*, which results in the T*
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* being wrapped in a temporary object until the T* is either
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* re-adopted from or released by the temporary.
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*/
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template<typename T>
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class RefPtr
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{
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// To allow them to use unref()
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friend class TemporaryRef<T>;
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friend class OutParamRef<T>;
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struct dontRef {};
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public:
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RefPtr() : ptr(0) { }
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RefPtr(const RefPtr& o) : ptr(ref(o.ptr)) {}
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RefPtr(const TemporaryRef<T>& o) : ptr(o.drop()) {}
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RefPtr(T* t) : ptr(ref(t)) {}
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template<typename U>
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RefPtr(const RefPtr<U>& o) : ptr(ref(o.get())) {}
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~RefPtr() { unref(ptr); }
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RefPtr& operator=(const RefPtr& o) {
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assign(ref(o.ptr));
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return *this;
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}
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RefPtr& operator=(const TemporaryRef<T>& o) {
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assign(o.drop());
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return *this;
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}
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RefPtr& operator=(T* t) {
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assign(ref(t));
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return *this;
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}
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template<typename U>
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RefPtr& operator=(const RefPtr<U>& o) {
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assign(ref(o.get()));
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return *this;
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}
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TemporaryRef<T> forget() {
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T* tmp = ptr;
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ptr = 0;
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return TemporaryRef<T>(tmp, dontRef());
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}
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T* get() const { return ptr; }
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operator T*() const { return ptr; }
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T* operator->() const { return ptr; }
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T& operator*() const { return *ptr; }
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template<typename U>
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operator TemporaryRef<U>() { return TemporaryRef<U>(ptr); }
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private:
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void assign(T* t) {
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unref(ptr);
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ptr = t;
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}
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T* ptr;
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static MOZ_ALWAYS_INLINE T* ref(T* t) {
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if (t) {
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t->AddRef();
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}
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return t;
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}
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static MOZ_ALWAYS_INLINE void unref(T* t) {
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if (t) {
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t->Release();
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}
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}
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};
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/**
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* TemporaryRef<T> represents an object that holds a temporary
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* reference to a T. TemporaryRef objects can't be manually ref'd or
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* unref'd (being temporaries, not lvalues), so can only relinquish
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* references to other objects, or unref on destruction.
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*/
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template<typename T>
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class TemporaryRef
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{
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// To allow it to construct TemporaryRef from a bare T*
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friend class RefPtr<T>;
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typedef typename RefPtr<T>::dontRef dontRef;
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public:
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TemporaryRef(T* t) : ptr(RefPtr<T>::ref(t)) {}
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TemporaryRef(const TemporaryRef& o) : ptr(o.drop()) {}
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template<typename U>
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TemporaryRef(const TemporaryRef<U>& o) : ptr(o.drop()) {}
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~TemporaryRef() { RefPtr<T>::unref(ptr); }
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T* drop() const {
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T* tmp = ptr;
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ptr = 0;
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return tmp;
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}
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private:
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TemporaryRef(T* t, const dontRef&) : ptr(t) {}
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mutable T* ptr;
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TemporaryRef();
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TemporaryRef& operator=(const TemporaryRef&);
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};
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/**
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* OutParamRef is a wrapper that tracks a refcounted pointer passed as
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* an outparam argument to a function. OutParamRef implements COM T**
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* outparam semantics: this requires the callee to AddRef() the T*
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* returned through the T** outparam on behalf of the caller. This
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* means the caller (through OutParamRef) must Release() the old
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* object contained in the tracked RefPtr. It's OK if the callee
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* returns the same T* passed to it through the T** outparam, as long
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* as the callee obeys the COM discipline.
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*
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* Prefer returning TemporaryRef<T> from functions over creating T**
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* outparams and passing OutParamRef<T> to T**. Prefer RefPtr<T>*
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* outparams over T** outparams.
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*/
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template<typename T>
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class OutParamRef
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{
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friend OutParamRef byRef<T>(RefPtr<T>&);
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public:
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~OutParamRef() {
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RefPtr<T>::unref(refPtr.ptr);
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refPtr.ptr = tmp;
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}
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operator T**() { return &tmp; }
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private:
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OutParamRef(RefPtr<T>& p) : refPtr(p), tmp(p.get()) {}
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RefPtr<T>& refPtr;
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T* tmp;
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OutParamRef() MOZ_DELETE;
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OutParamRef& operator=(const OutParamRef&) MOZ_DELETE;
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};
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/**
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* byRef cooperates with OutParamRef to implement COM outparam semantics.
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*/
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template<typename T>
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OutParamRef<T>
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byRef(RefPtr<T>& ptr)
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{
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return OutParamRef<T>(ptr);
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}
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} // namespace mozilla
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#endif // mozilla_RefPtr_h_
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#if 0
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// Command line that builds these tests
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//
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// cp RefPtr.h test.cc && g++ -g -Wall -pedantic -DDEBUG -o test test.cc && ./test
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using namespace mozilla;
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struct Foo : public RefCounted<Foo>
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{
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Foo() : dead(false) { }
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~Foo() {
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MOZ_ASSERT(!dead);
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dead = true;
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numDestroyed++;
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}
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bool dead;
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static int numDestroyed;
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};
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int Foo::numDestroyed;
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struct Bar : public Foo { };
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TemporaryRef<Foo>
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NewFoo()
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{
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return RefPtr<Foo>(new Foo());
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}
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TemporaryRef<Foo>
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NewBar()
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{
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return new Bar();
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}
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void
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GetNewFoo(Foo** f)
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{
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*f = new Bar();
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// Kids, don't try this at home
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(*f)->AddRef();
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}
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void
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GetPassedFoo(Foo** f)
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{
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// Kids, don't try this at home
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(*f)->AddRef();
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}
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void
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GetNewFoo(RefPtr<Foo>* f)
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{
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*f = new Bar();
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}
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void
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GetPassedFoo(RefPtr<Foo>* f)
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{}
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TemporaryRef<Foo>
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GetNullFoo()
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{
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return 0;
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}
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int
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main(int argc, char** argv)
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{
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// This should blow up
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// Foo* f = new Foo(); delete f;
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MOZ_ASSERT(0 == Foo::numDestroyed);
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{
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RefPtr<Foo> f = new Foo();
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MOZ_ASSERT(f->refCount() == 1);
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}
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MOZ_ASSERT(1 == Foo::numDestroyed);
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{
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RefPtr<Foo> f1 = NewFoo();
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RefPtr<Foo> f2(NewFoo());
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MOZ_ASSERT(1 == Foo::numDestroyed);
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}
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MOZ_ASSERT(3 == Foo::numDestroyed);
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{
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RefPtr<Foo> b = NewBar();
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MOZ_ASSERT(3 == Foo::numDestroyed);
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}
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MOZ_ASSERT(4 == Foo::numDestroyed);
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{
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RefPtr<Foo> f1;
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{
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f1 = new Foo();
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RefPtr<Foo> f2(f1);
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RefPtr<Foo> f3 = f2;
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MOZ_ASSERT(4 == Foo::numDestroyed);
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}
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MOZ_ASSERT(4 == Foo::numDestroyed);
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}
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MOZ_ASSERT(5 == Foo::numDestroyed);
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{
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RefPtr<Foo> f = new Foo();
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f.forget();
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MOZ_ASSERT(6 == Foo::numDestroyed);
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}
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{
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RefPtr<Foo> f = new Foo();
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GetNewFoo(byRef(f));
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MOZ_ASSERT(7 == Foo::numDestroyed);
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}
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MOZ_ASSERT(8 == Foo::numDestroyed);
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{
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RefPtr<Foo> f = new Foo();
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GetPassedFoo(byRef(f));
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MOZ_ASSERT(8 == Foo::numDestroyed);
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}
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MOZ_ASSERT(9 == Foo::numDestroyed);
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{
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RefPtr<Foo> f = new Foo();
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GetNewFoo(&f);
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MOZ_ASSERT(10 == Foo::numDestroyed);
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}
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MOZ_ASSERT(11 == Foo::numDestroyed);
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{
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RefPtr<Foo> f = new Foo();
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GetPassedFoo(&f);
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MOZ_ASSERT(11 == Foo::numDestroyed);
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}
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MOZ_ASSERT(12 == Foo::numDestroyed);
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{
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RefPtr<Foo> f1 = new Bar();
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}
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MOZ_ASSERT(13 == Foo::numDestroyed);
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{
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RefPtr<Foo> f = GetNullFoo();
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MOZ_ASSERT(13 == Foo::numDestroyed);
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}
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MOZ_ASSERT(13 == Foo::numDestroyed);
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return 0;
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}
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#endif
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