weak_ptr.h revision f8ee788a64d60abd8f2d742a5fdedde054ecd910
15821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Copyright (c) 2012 The Chromium Authors. All rights reserved. 25821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Use of this source code is governed by a BSD-style license that can be 35821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// found in the LICENSE file. 45821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 5c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)// Weak pointers are pointers to an object that do not affect its lifetime, 6c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)// and which may be invalidated (i.e. reset to NULL) by the object, or its 7c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)// owner, at any time, most commonly when the object is about to be deleted. 8c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) 9c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)// Weak pointers are useful when an object needs to be accessed safely by one 10c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)// or more objects other than its owner, and those callers can cope with the 11c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)// object vanishing and e.g. tasks posted to it being silently dropped. 12c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)// Reference-counting such an object would complicate the ownership graph and 13c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)// make it harder to reason about the object's lifetime. 14c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) 155821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// EXAMPLE: 165821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 17c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)// class Controller { 185821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// public: 19c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)// void SpawnWorker() { Worker::StartNew(weak_factory_.GetWeakPtr()); } 205821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// void WorkComplete(const Result& result) { ... } 21c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)// private: 2290dce4d38c5ff5333bea97d859d4e484e27edf0cTorne (Richard Coles)// // Member variables should appear before the WeakPtrFactory, to ensure 2390dce4d38c5ff5333bea97d859d4e484e27edf0cTorne (Richard Coles)// // that any WeakPtrs to Controller are invalidated before its members 2490dce4d38c5ff5333bea97d859d4e484e27edf0cTorne (Richard Coles)// // variable's destructors are executed, rendering them invalid. 25c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)// WeakPtrFactory<Controller> weak_factory_; 265821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// }; 275821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 285821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// class Worker { 295821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// public: 305821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// static void StartNew(const WeakPtr<Controller>& controller) { 315821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Worker* worker = new Worker(controller); 325821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// // Kick off asynchronous processing... 335821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// } 345821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// private: 355821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Worker(const WeakPtr<Controller>& controller) 365821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// : controller_(controller) {} 375821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// void DidCompleteAsynchronousProcessing(const Result& result) { 385821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// if (controller_) 395821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// controller_->WorkComplete(result); 405821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// } 415821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// WeakPtr<Controller> controller_; 425821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// }; 435821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 44c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)// With this implementation a caller may use SpawnWorker() to dispatch multiple 45c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)// Workers and subsequently delete the Controller, without waiting for all 46c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)// Workers to have completed. 47c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) 48c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)// ------------------------- IMPORTANT: Thread-safety ------------------------- 49c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) 5090dce4d38c5ff5333bea97d859d4e484e27edf0cTorne (Richard Coles)// Weak pointers may be passed safely between threads, but must always be 5190dce4d38c5ff5333bea97d859d4e484e27edf0cTorne (Richard Coles)// dereferenced and invalidated on the same thread otherwise checking the 5290dce4d38c5ff5333bea97d859d4e484e27edf0cTorne (Richard Coles)// pointer would be racey. 5390dce4d38c5ff5333bea97d859d4e484e27edf0cTorne (Richard Coles)// 5490dce4d38c5ff5333bea97d859d4e484e27edf0cTorne (Richard Coles)// To ensure correct use, the first time a WeakPtr issued by a WeakPtrFactory 5590dce4d38c5ff5333bea97d859d4e484e27edf0cTorne (Richard Coles)// is dereferenced, the factory and its WeakPtrs become bound to the calling 5690dce4d38c5ff5333bea97d859d4e484e27edf0cTorne (Richard Coles)// thread, and cannot be dereferenced or invalidated on any other thread. Bound 5790dce4d38c5ff5333bea97d859d4e484e27edf0cTorne (Richard Coles)// WeakPtrs can still be handed off to other threads, e.g. to use to post tasks 5890dce4d38c5ff5333bea97d859d4e484e27edf0cTorne (Richard Coles)// back to object on the bound thread. 5990dce4d38c5ff5333bea97d859d4e484e27edf0cTorne (Richard Coles)// 6090dce4d38c5ff5333bea97d859d4e484e27edf0cTorne (Richard Coles)// Invalidating the factory's WeakPtrs un-binds it from the thread, allowing it 6190dce4d38c5ff5333bea97d859d4e484e27edf0cTorne (Richard Coles)// to be passed for a different thread to use or delete it. 625821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 635821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#ifndef BASE_MEMORY_WEAK_PTR_H_ 645821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#define BASE_MEMORY_WEAK_PTR_H_ 655821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 665821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include "base/basictypes.h" 675821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include "base/base_export.h" 685821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include "base/logging.h" 695821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include "base/memory/ref_counted.h" 70fb250657ef40d7500f20882d5c9909c1013367d3Ben Murdoch#include "base/sequence_checker.h" 715821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include "base/template_util.h" 725821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 735821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)namespace base { 745821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 755821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template <typename T> class SupportsWeakPtr; 765821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template <typename T> class WeakPtr; 775821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 785821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)namespace internal { 795821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// These classes are part of the WeakPtr implementation. 805821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// DO NOT USE THESE CLASSES DIRECTLY YOURSELF. 815821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 825821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)class BASE_EXPORT WeakReference { 835821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) public: 8490dce4d38c5ff5333bea97d859d4e484e27edf0cTorne (Richard Coles) // Although Flag is bound to a specific thread, it may be deleted from another 855821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // via base::WeakPtr::~WeakPtr(). 86f8ee788a64d60abd8f2d742a5fdedde054ecd910Torne (Richard Coles) class BASE_EXPORT Flag : public RefCountedThreadSafe<Flag> { 875821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) public: 885821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) Flag(); 895821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 905821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) void Invalidate(); 915821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) bool IsValid() const; 925821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 935821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) private: 945821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) friend class base::RefCountedThreadSafe<Flag>; 955821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 965821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) ~Flag(); 975821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 98fb250657ef40d7500f20882d5c9909c1013367d3Ben Murdoch SequenceChecker sequence_checker_; 995821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) bool is_valid_; 1005821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) }; 1015821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1025821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) WeakReference(); 1035821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) explicit WeakReference(const Flag* flag); 1045821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) ~WeakReference(); 1055821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1065821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) bool is_valid() const; 1075821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1085821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) private: 1095821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) scoped_refptr<const Flag> flag_; 1105821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 1115821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1125821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)class BASE_EXPORT WeakReferenceOwner { 1135821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) public: 1145821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) WeakReferenceOwner(); 1155821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) ~WeakReferenceOwner(); 1165821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1175821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) WeakReference GetRef() const; 1185821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1195821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) bool HasRefs() const { 1205821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) return flag_.get() && !flag_->HasOneRef(); 1215821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 1225821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1235821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) void Invalidate(); 1245821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1255821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) private: 1265821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) mutable scoped_refptr<WeakReference::Flag> flag_; 1275821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 1285821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1295821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// This class simplifies the implementation of WeakPtr's type conversion 1305821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// constructor by avoiding the need for a public accessor for ref_. A 1315821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// WeakPtr<T> cannot access the private members of WeakPtr<U>, so this 1325821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// base class gives us a way to access ref_ in a protected fashion. 1335821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)class BASE_EXPORT WeakPtrBase { 1345821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) public: 1355821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) WeakPtrBase(); 1365821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) ~WeakPtrBase(); 1375821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1385821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) protected: 1395821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) explicit WeakPtrBase(const WeakReference& ref); 1405821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1415821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) WeakReference ref_; 1425821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 1435821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1445821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// This class provides a common implementation of common functions that would 1455821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// otherwise get instantiated separately for each distinct instantiation of 1465821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// SupportsWeakPtr<>. 1475821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)class SupportsWeakPtrBase { 1485821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) public: 1495821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // A safe static downcast of a WeakPtr<Base> to WeakPtr<Derived>. This 1505821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // conversion will only compile if there is exists a Base which inherits 1515821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // from SupportsWeakPtr<Base>. See base::AsWeakPtr() below for a helper 1525821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // function that makes calling this easier. 1535821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) template<typename Derived> 1545821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) static WeakPtr<Derived> StaticAsWeakPtr(Derived* t) { 1555821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) typedef 1565821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) is_convertible<Derived, internal::SupportsWeakPtrBase&> convertible; 1575821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) COMPILE_ASSERT(convertible::value, 1585821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) AsWeakPtr_argument_inherits_from_SupportsWeakPtr); 1595821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) return AsWeakPtrImpl<Derived>(t, *t); 1605821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 1615821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1625821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) private: 1635821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // This template function uses type inference to find a Base of Derived 1645821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // which is an instance of SupportsWeakPtr<Base>. We can then safely 1655821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // static_cast the Base* to a Derived*. 1665821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) template <typename Derived, typename Base> 1675821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) static WeakPtr<Derived> AsWeakPtrImpl( 1685821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) Derived* t, const SupportsWeakPtr<Base>&) { 1695821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) WeakPtr<Base> ptr = t->Base::AsWeakPtr(); 1705821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) return WeakPtr<Derived>(ptr.ref_, static_cast<Derived*>(ptr.ptr_)); 1715821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 1725821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 1735821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1745821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)} // namespace internal 1755821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1765821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template <typename T> class WeakPtrFactory; 1775821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1785821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// The WeakPtr class holds a weak reference to |T*|. 1795821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 1805821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// This class is designed to be used like a normal pointer. You should always 1815821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// null-test an object of this class before using it or invoking a method that 1825821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// may result in the underlying object being destroyed. 1835821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 1845821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// EXAMPLE: 1855821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 1865821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// class Foo { ... }; 1875821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// WeakPtr<Foo> foo; 1885821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// if (foo) 1895821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// foo->method(); 1905821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 1915821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template <typename T> 1925821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)class WeakPtr : public internal::WeakPtrBase { 1935821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) public: 1945821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) WeakPtr() : ptr_(NULL) { 1955821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 1965821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1972a99a7e74a7f215066514fe81d2bfa6639d9edddTorne (Richard Coles) // Allow conversion from U to T provided U "is a" T. Note that this 1982a99a7e74a7f215066514fe81d2bfa6639d9edddTorne (Richard Coles) // is separate from the (implicit) copy constructor. 1995821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) template <typename U> 2002a99a7e74a7f215066514fe81d2bfa6639d9edddTorne (Richard Coles) WeakPtr(const WeakPtr<U>& other) : WeakPtrBase(other), ptr_(other.ptr_) { 2015821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 2025821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 2035821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) T* get() const { return ref_.is_valid() ? ptr_ : NULL; } 2045821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 2055821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) T& operator*() const { 2065821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) DCHECK(get() != NULL); 2075821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) return *get(); 2085821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 2095821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) T* operator->() const { 2105821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) DCHECK(get() != NULL); 2115821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) return get(); 2125821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 2135821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 214868fa2fe829687343ffae624259930155e16dbd8Torne (Richard Coles) // Allow WeakPtr<element_type> to be used in boolean expressions, but not 215868fa2fe829687343ffae624259930155e16dbd8Torne (Richard Coles) // implicitly convertible to a real bool (which is dangerous). 216868fa2fe829687343ffae624259930155e16dbd8Torne (Richard Coles) // 217868fa2fe829687343ffae624259930155e16dbd8Torne (Richard Coles) // Note that this trick is only safe when the == and != operators 218868fa2fe829687343ffae624259930155e16dbd8Torne (Richard Coles) // are declared explicitly, as otherwise "weak_ptr1 == weak_ptr2" 219868fa2fe829687343ffae624259930155e16dbd8Torne (Richard Coles) // will compile but do the wrong thing (i.e., convert to Testable 220868fa2fe829687343ffae624259930155e16dbd8Torne (Richard Coles) // and then do the comparison). 221868fa2fe829687343ffae624259930155e16dbd8Torne (Richard Coles) private: 222868fa2fe829687343ffae624259930155e16dbd8Torne (Richard Coles) typedef T* WeakPtr::*Testable; 223868fa2fe829687343ffae624259930155e16dbd8Torne (Richard Coles) 224868fa2fe829687343ffae624259930155e16dbd8Torne (Richard Coles) public: 225868fa2fe829687343ffae624259930155e16dbd8Torne (Richard Coles) operator Testable() const { return get() ? &WeakPtr::ptr_ : NULL; } 226868fa2fe829687343ffae624259930155e16dbd8Torne (Richard Coles) 2275821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) void reset() { 2285821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) ref_ = internal::WeakReference(); 2295821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) ptr_ = NULL; 2305821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 2315821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 2325821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) private: 233868fa2fe829687343ffae624259930155e16dbd8Torne (Richard Coles) // Explicitly declare comparison operators as required by the bool 234868fa2fe829687343ffae624259930155e16dbd8Torne (Richard Coles) // trick, but keep them private. 235868fa2fe829687343ffae624259930155e16dbd8Torne (Richard Coles) template <class U> bool operator==(WeakPtr<U> const&) const; 236868fa2fe829687343ffae624259930155e16dbd8Torne (Richard Coles) template <class U> bool operator!=(WeakPtr<U> const&) const; 237868fa2fe829687343ffae624259930155e16dbd8Torne (Richard Coles) 2385821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) friend class internal::SupportsWeakPtrBase; 2392a99a7e74a7f215066514fe81d2bfa6639d9edddTorne (Richard Coles) template <typename U> friend class WeakPtr; 2405821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) friend class SupportsWeakPtr<T>; 2415821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) friend class WeakPtrFactory<T>; 2425821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 2435821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) WeakPtr(const internal::WeakReference& ref, T* ptr) 2445821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) : WeakPtrBase(ref), 2455821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) ptr_(ptr) { 2465821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 2475821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 2485821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // This pointer is only valid when ref_.is_valid() is true. Otherwise, its 2495821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // value is undefined (as opposed to NULL). 2505821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) T* ptr_; 2515821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 2525821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 253c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)// A class may be composed of a WeakPtrFactory and thereby 254c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)// control how it exposes weak pointers to itself. This is helpful if you only 255c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)// need weak pointers within the implementation of a class. This class is also 256c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)// useful when working with primitive types. For example, you could have a 257c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)// WeakPtrFactory<bool> that is used to pass around a weak reference to a bool. 258c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)template <class T> 259c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)class WeakPtrFactory { 260c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) public: 261c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) explicit WeakPtrFactory(T* ptr) : ptr_(ptr) { 262c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) } 263c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) 264c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) ~WeakPtrFactory() { 265c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) ptr_ = NULL; 266c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) } 267c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) 268c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) WeakPtr<T> GetWeakPtr() { 269c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) DCHECK(ptr_); 270c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) return WeakPtr<T>(weak_reference_owner_.GetRef(), ptr_); 271c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) } 272c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) 273c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) // Call this method to invalidate all existing weak pointers. 274c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) void InvalidateWeakPtrs() { 275c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) DCHECK(ptr_); 276c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) weak_reference_owner_.Invalidate(); 277c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) } 278c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) 279c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) // Call this method to determine if any weak pointers exist. 280c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) bool HasWeakPtrs() const { 281c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) DCHECK(ptr_); 282c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) return weak_reference_owner_.HasRefs(); 283c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) } 284c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) 285c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) private: 286c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) internal::WeakReferenceOwner weak_reference_owner_; 287c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) T* ptr_; 288c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) DISALLOW_IMPLICIT_CONSTRUCTORS(WeakPtrFactory); 289c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)}; 290c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles) 291c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)// A class may extend from SupportsWeakPtr to let others take weak pointers to 292c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)// it. This avoids the class itself implementing boilerplate to dispense weak 293c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)// pointers. However, since SupportsWeakPtr's destructor won't invalidate 294c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)// weak pointers to the class until after the derived class' members have been 295c2e0dbddbe15c98d52c4786dac06cb8952a8ae6dTorne (Richard Coles)// destroyed, its use can lead to subtle use-after-destroy issues. 2965821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template <class T> 2975821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)class SupportsWeakPtr : public internal::SupportsWeakPtrBase { 2985821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) public: 2995821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) SupportsWeakPtr() {} 3005821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 3015821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) WeakPtr<T> AsWeakPtr() { 3025821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) return WeakPtr<T>(weak_reference_owner_.GetRef(), static_cast<T*>(this)); 3035821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 3045821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 3055821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) protected: 3065821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) ~SupportsWeakPtr() {} 3075821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 3085821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) private: 3095821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) internal::WeakReferenceOwner weak_reference_owner_; 3105821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) DISALLOW_COPY_AND_ASSIGN(SupportsWeakPtr); 3115821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 3125821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 3135821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Helper function that uses type deduction to safely return a WeakPtr<Derived> 3145821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// when Derived doesn't directly extend SupportsWeakPtr<Derived>, instead it 3155821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// extends a Base that extends SupportsWeakPtr<Base>. 3165821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 3175821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// EXAMPLE: 3185821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// class Base : public base::SupportsWeakPtr<Producer> {}; 3195821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// class Derived : public Base {}; 3205821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 3215821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Derived derived; 3225821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// base::WeakPtr<Derived> ptr = base::AsWeakPtr(&derived); 3235821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 3245821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Note that the following doesn't work (invalid type conversion) since 3255821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Derived::AsWeakPtr() is WeakPtr<Base> SupportsWeakPtr<Base>::AsWeakPtr(), 3265821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// and there's no way to safely cast WeakPtr<Base> to WeakPtr<Derived> at 3275821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// the caller. 3285821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 3295821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// base::WeakPtr<Derived> ptr = derived.AsWeakPtr(); // Fails. 3305821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 3315821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template <typename Derived> 3325821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)WeakPtr<Derived> AsWeakPtr(Derived* t) { 3335821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) return internal::SupportsWeakPtrBase::StaticAsWeakPtr<Derived>(t); 3345821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)} 3355821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 3365821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)} // namespace base 3375821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 3385821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#endif // BASE_MEMORY_WEAK_PTR_H_ 339