| /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ |
| /* vim:set ts=2 sw=2 sts=2 et cindent: */ |
| /* ***** BEGIN LICENSE BLOCK ***** |
| * Version: MPL 1.1/GPL 2.0/LGPL 2.1 |
| * |
| * The contents of this file are subject to the Mozilla Public License Version |
| * 1.1 (the "License"); you may not use this file except in compliance with |
| * the License. You may obtain a copy of the License at |
| * http://www.mozilla.org/MPL/ |
| * |
| * Software distributed under the License is distributed on an "AS IS" basis, |
| * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License |
| * for the specific language governing rights and limitations under the |
| * License. |
| * |
| * The Original Code is Mozilla code. |
| * |
| * The Initial Developer of the Original Code is Google Inc. |
| * Portions created by the Initial Developer are Copyright (C) 2006 |
| * the Initial Developer. All Rights Reserved. |
| * |
| * Contributor(s): |
| * Darin Fisher <darin@meer.net> |
| * |
| * Alternatively, the contents of this file may be used under the terms of |
| * either the GNU General Public License Version 2 or later (the "GPL"), or |
| * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"), |
| * in which case the provisions of the GPL or the LGPL are applicable instead |
| * of those above. If you wish to allow use of your version of this file only |
| * under the terms of either the GPL or the LGPL, and not to allow others to |
| * use your version of this file under the terms of the MPL, indicate your |
| * decision by deleting the provisions above and replace them with the notice |
| * and other provisions required by the GPL or the LGPL. If you do not delete |
| * the provisions above, a recipient may use your version of this file under |
| * the terms of any one of the MPL, the GPL or the LGPL. |
| * |
| * ***** END LICENSE BLOCK ***** */ |
| |
| #ifndef nsTWeakRef_h__ |
| #define nsTWeakRef_h__ |
| |
| #ifndef nsDebug_h___ |
| #include "nsDebug.h" |
| #endif |
| |
| /** |
| * A weak reference class for use with generic C++ objects. NOT THREADSAFE! |
| * |
| * Example usage: |
| * |
| * class A { |
| * public: |
| * A() : mWeakSelf(this) { |
| * } |
| * ~A() { |
| * mWeakSelf.forget(); |
| * } |
| * void Bar() { printf("Bar!\n"); } |
| * const nsTWeakRef<A> &AsWeakRef() const { return mWeakSelf; } |
| * private: |
| * nsTWeakRef<A> mWeakSelf; |
| * }; |
| * |
| * class B { |
| * public: |
| * void SetA(const nsTWeakRef<A> &a) { |
| * mA = a; |
| * } |
| * void Foo() { |
| * if (mA) |
| * mA->Bar(); |
| * } |
| * private: |
| * nsTWeakRef<A> mA; |
| * }; |
| * |
| * void Test() { |
| * B b; |
| * { |
| * A a; |
| * b.SetA(a.AsWeakRef()); |
| * b.Foo(); // prints "Bar!" |
| * } |
| * b.Foo(); // prints nothing because |a| has already been destroyed |
| * } |
| * |
| * One can imagine much more complex examples, especially when asynchronous |
| * event processing is involved. |
| * |
| * Keep in mind that you should only ever need a class like this when you have |
| * multiple instances of B, such that it is not possible for A and B to simply |
| * have pointers to one another. |
| */ |
| template <class Type> |
| class nsTWeakRef { |
| public: |
| ~nsTWeakRef() { |
| if (mRef) |
| mRef->Release(); |
| } |
| |
| /** |
| * Construct from an object pointer (may be null). |
| */ |
| explicit |
| nsTWeakRef(Type *obj = nsnull) { |
| if (obj) { |
| mRef = new Inner(obj); |
| } else { |
| mRef = nsnull; |
| } |
| } |
| |
| /** |
| * Construct from another weak reference object. |
| */ |
| explicit |
| nsTWeakRef(const nsTWeakRef<Type> &other) : mRef(other.mRef) { |
| if (mRef) |
| mRef->AddRef(); |
| } |
| |
| /** |
| * Assign from an object pointer. |
| */ |
| nsTWeakRef<Type> &operator=(Type *obj) { |
| if (mRef) |
| mRef->Release(); |
| if (obj) { |
| mRef = new Inner(obj); |
| } else { |
| mRef = nsnull; |
| } |
| return *this; |
| } |
| |
| /** |
| * Assign from another weak reference object. |
| */ |
| nsTWeakRef<Type> &operator=(const nsTWeakRef<Type> &other) { |
| if (mRef) |
| mRef->Release(); |
| mRef = other.mRef; |
| if (mRef) |
| mRef->AddRef(); |
| return *this; |
| } |
| |
| /** |
| * Get the referenced object. This method may return null if the reference |
| * has been cleared or if an out-of-memory error occured at assignment. |
| */ |
| Type *get() const { |
| return mRef ? mRef->mObj : nsnull; |
| } |
| |
| /** |
| * Called to "null out" the weak reference. Typically, the object referenced |
| * by this weak reference calls this method when it is being destroyed. |
| * @returns The former referenced object. |
| */ |
| Type *forget() { |
| Type *obj; |
| if (mRef) { |
| obj = mRef->mObj; |
| mRef->mObj = nsnull; |
| mRef->Release(); |
| mRef = nsnull; |
| } else { |
| obj = nsnull; |
| } |
| return obj; |
| } |
| |
| /** |
| * Allow |*this| to be treated as a |Type*| for convenience. |
| */ |
| operator Type *() const { |
| return get(); |
| } |
| |
| /** |
| * Allow |*this| to be treated as a |Type*| for convenience. Use with |
| * caution since this method will crash if the referenced object is null. |
| */ |
| Type *operator->() const { |
| NS_ASSERTION(mRef && mRef->mObj, |
| "You can't dereference a null weak reference with operator->()."); |
| return get(); |
| } |
| |
| private: |
| |
| struct Inner { |
| int mCnt; |
| Type *mObj; |
| |
| Inner(Type *obj) : mCnt(1), mObj(obj) {} |
| void AddRef() { ++mCnt; } |
| void Release() { if (--mCnt == 0) delete this; } |
| }; |
| |
| Inner *mRef; |
| }; |
| |
| #endif // nsTWeakRef_h__ |