weak_ptr.h revision 5821806d5e7f356e8fa4b058a389a808ea183019
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) 55821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Weak pointers help in cases where you have many objects referring back to a 65821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// shared object and you wish for the lifetime of the shared object to not be 75821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// bound to the lifetime of the referrers. In other words, this is useful when 85821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// reference counting is not a good fit. 95821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 105821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// A common alternative to weak pointers is to have the shared object hold a 115821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// list of all referrers, and then when the shared object is destroyed, it 125821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// calls a method on the referrers to tell them to drop their references. This 135821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// approach also requires the referrers to tell the shared object when they get 145821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// destroyed so that the shared object can remove the referrer from its list of 155821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// referrers. Such a solution works, but it is a bit complex. 165821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 175821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// EXAMPLE: 185821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 195821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// class Controller : public SupportsWeakPtr<Controller> { 205821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// public: 215821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// void SpawnWorker() { Worker::StartNew(AsWeakPtr()); } 225821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// void WorkComplete(const Result& result) { ... } 235821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// }; 245821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 255821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// class Worker { 265821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// public: 275821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// static void StartNew(const WeakPtr<Controller>& controller) { 285821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Worker* worker = new Worker(controller); 295821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// // Kick off asynchronous processing... 305821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// } 315821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// private: 325821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Worker(const WeakPtr<Controller>& controller) 335821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// : controller_(controller) {} 345821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// void DidCompleteAsynchronousProcessing(const Result& result) { 355821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// if (controller_) 365821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// controller_->WorkComplete(result); 375821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// } 385821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// WeakPtr<Controller> controller_; 395821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// }; 405821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 415821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Given the above classes, a consumer may allocate a Controller object, call 425821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// SpawnWorker several times, and then destroy the Controller object before all 435821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// of the workers have completed. Because the Worker class only holds a weak 445821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// pointer to the Controller, we don't have to worry about the Worker 455821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// dereferencing the Controller back pointer after the Controller has been 465821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// destroyed. 475821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 485821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// ------------------------ Thread-safety notes ------------------------ 495821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// When you get a WeakPtr (from a WeakPtrFactory or SupportsWeakPtr), if it's 505821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// the only one pointing to the object, the object become bound to the 515821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// current thread, as well as this WeakPtr and all later ones get created. 525821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 535821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// You may only dereference the WeakPtr on the thread it binds to. However, it 545821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// is safe to destroy the WeakPtr object on another thread. Because of this, 555821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// querying WeakPtrFactory's HasWeakPtrs() method can be racy. 565821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 575821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// On the other hand, the object that supports WeakPtr (extends SupportsWeakPtr) 585821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// can only be deleted from the thread it binds to, until all WeakPtrs are 595821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// deleted. 605821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 615821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Calling SupportsWeakPtr::DetachFromThread() can work around the limitations 625821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// above and cancel the thread binding of the object and all WeakPtrs pointing 635821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// to it, but it's not recommended and unsafe. 645821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 655821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// WeakPtrs may be copy-constructed or assigned on threads other than the thread 665821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// they are bound to. This does not change the thread binding. So these WeakPtrs 675821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// may only be dereferenced on the thread that the original WeakPtr was bound 685821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// to. 695821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 705821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#ifndef BASE_MEMORY_WEAK_PTR_H_ 715821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#define BASE_MEMORY_WEAK_PTR_H_ 725821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 735821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include "base/basictypes.h" 745821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include "base/base_export.h" 755821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include "base/logging.h" 765821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include "base/memory/ref_counted.h" 775821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include "base/template_util.h" 785821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include "base/threading/thread_checker.h" 795821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 805821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)namespace base { 815821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 825821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template <typename T> class SupportsWeakPtr; 835821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template <typename T> class WeakPtr; 845821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 855821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)namespace internal { 865821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// These classes are part of the WeakPtr implementation. 875821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// DO NOT USE THESE CLASSES DIRECTLY YOURSELF. 885821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 895821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)class BASE_EXPORT WeakReference { 905821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) public: 915821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // While Flag is bound to a specific thread, it may be deleted from another 925821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // via base::WeakPtr::~WeakPtr(). 935821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) class Flag : public RefCountedThreadSafe<Flag> { 945821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) public: 955821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) Flag(); 965821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 975821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) void Invalidate(); 985821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) bool IsValid() const; 995821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1005821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) void DetachFromThread() { thread_checker_.DetachFromThread(); } 1015821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1025821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) private: 1035821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) friend class base::RefCountedThreadSafe<Flag>; 1045821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1055821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) ~Flag(); 1065821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1075821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) ThreadChecker thread_checker_; 1085821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) bool is_valid_; 1095821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) }; 1105821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1115821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) WeakReference(); 1125821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) explicit WeakReference(const Flag* flag); 1135821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) ~WeakReference(); 1145821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1155821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) bool is_valid() const; 1165821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1175821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) private: 1185821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) scoped_refptr<const Flag> flag_; 1195821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 1205821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1215821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)class BASE_EXPORT WeakReferenceOwner { 1225821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) public: 1235821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) WeakReferenceOwner(); 1245821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) ~WeakReferenceOwner(); 1255821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1265821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) WeakReference GetRef() const; 1275821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1285821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) bool HasRefs() const { 1295821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) return flag_.get() && !flag_->HasOneRef(); 1305821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 1315821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1325821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) void Invalidate(); 1335821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1345821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Indicates that this object will be used on another thread from now on. 1355821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) void DetachFromThread() { 1365821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) if (flag_) flag_->DetachFromThread(); 1375821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 1385821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1395821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) private: 1405821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) mutable scoped_refptr<WeakReference::Flag> flag_; 1415821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 1425821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1435821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// This class simplifies the implementation of WeakPtr's type conversion 1445821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// constructor by avoiding the need for a public accessor for ref_. A 1455821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// WeakPtr<T> cannot access the private members of WeakPtr<U>, so this 1465821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// base class gives us a way to access ref_ in a protected fashion. 1475821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)class BASE_EXPORT WeakPtrBase { 1485821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) public: 1495821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) WeakPtrBase(); 1505821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) ~WeakPtrBase(); 1515821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1525821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) protected: 1535821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) explicit WeakPtrBase(const WeakReference& ref); 1545821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1555821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) WeakReference ref_; 1565821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 1575821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1585821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// This class provides a common implementation of common functions that would 1595821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// otherwise get instantiated separately for each distinct instantiation of 1605821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// SupportsWeakPtr<>. 1615821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)class SupportsWeakPtrBase { 1625821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) public: 1635821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // A safe static downcast of a WeakPtr<Base> to WeakPtr<Derived>. This 1645821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // conversion will only compile if there is exists a Base which inherits 1655821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // from SupportsWeakPtr<Base>. See base::AsWeakPtr() below for a helper 1665821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // function that makes calling this easier. 1675821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) template<typename Derived> 1685821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) static WeakPtr<Derived> StaticAsWeakPtr(Derived* t) { 1695821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) typedef 1705821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) is_convertible<Derived, internal::SupportsWeakPtrBase&> convertible; 1715821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) COMPILE_ASSERT(convertible::value, 1725821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) AsWeakPtr_argument_inherits_from_SupportsWeakPtr); 1735821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) return AsWeakPtrImpl<Derived>(t, *t); 1745821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 1755821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1765821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) private: 1775821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // This template function uses type inference to find a Base of Derived 1785821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // which is an instance of SupportsWeakPtr<Base>. We can then safely 1795821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // static_cast the Base* to a Derived*. 1805821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) template <typename Derived, typename Base> 1815821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) static WeakPtr<Derived> AsWeakPtrImpl( 1825821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) Derived* t, const SupportsWeakPtr<Base>&) { 1835821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) WeakPtr<Base> ptr = t->Base::AsWeakPtr(); 1845821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) return WeakPtr<Derived>(ptr.ref_, static_cast<Derived*>(ptr.ptr_)); 1855821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 1865821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 1875821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1885821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)} // namespace internal 1895821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1905821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template <typename T> class WeakPtrFactory; 1915821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1925821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// The WeakPtr class holds a weak reference to |T*|. 1935821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 1945821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// This class is designed to be used like a normal pointer. You should always 1955821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// null-test an object of this class before using it or invoking a method that 1965821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// may result in the underlying object being destroyed. 1975821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 1985821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// EXAMPLE: 1995821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 2005821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// class Foo { ... }; 2015821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// WeakPtr<Foo> foo; 2025821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// if (foo) 2035821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// foo->method(); 2045821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 2055821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template <typename T> 2065821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)class WeakPtr : public internal::WeakPtrBase { 2075821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) public: 2085821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) WeakPtr() : ptr_(NULL) { 2095821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 2105821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 2115821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Allow conversion from U to T provided U "is a" T. 2125821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) template <typename U> 2135821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) WeakPtr(const WeakPtr<U>& other) : WeakPtrBase(other), ptr_(other.get()) { 2145821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 2155821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 2165821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) T* get() const { return ref_.is_valid() ? ptr_ : NULL; } 2175821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) operator T*() const { return get(); } 2185821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 2195821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) T& operator*() const { 2205821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) DCHECK(get() != NULL); 2215821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) return *get(); 2225821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 2235821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) T* operator->() const { 2245821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) DCHECK(get() != NULL); 2255821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) return get(); 2265821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 2275821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 2285821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) void reset() { 2295821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) ref_ = internal::WeakReference(); 2305821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) ptr_ = NULL; 2315821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 2325821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 2335821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) private: 2345821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) friend class internal::SupportsWeakPtrBase; 2355821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) friend class SupportsWeakPtr<T>; 2365821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) friend class WeakPtrFactory<T>; 2375821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 2385821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) WeakPtr(const internal::WeakReference& ref, T* ptr) 2395821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) : WeakPtrBase(ref), 2405821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) ptr_(ptr) { 2415821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 2425821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 2435821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // This pointer is only valid when ref_.is_valid() is true. Otherwise, its 2445821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // value is undefined (as opposed to NULL). 2455821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) T* ptr_; 2465821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 2475821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 2485821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// A class may extend from SupportsWeakPtr to expose weak pointers to itself. 2495821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// This is useful in cases where you want others to be able to get a weak 2505821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// pointer to your class. It also has the property that you don't need to 2515821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// initialize it from your constructor. 2525821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template <class T> 2535821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)class SupportsWeakPtr : public internal::SupportsWeakPtrBase { 2545821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) public: 2555821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) SupportsWeakPtr() {} 2565821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 2575821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) WeakPtr<T> AsWeakPtr() { 2585821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) return WeakPtr<T>(weak_reference_owner_.GetRef(), static_cast<T*>(this)); 2595821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 2605821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 2615821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Indicates that this object will be used on another thread from now on. 2625821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) void DetachFromThread() { 2635821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) weak_reference_owner_.DetachFromThread(); 2645821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 2655821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 2665821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) protected: 2675821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) ~SupportsWeakPtr() {} 2685821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 2695821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) private: 2705821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) internal::WeakReferenceOwner weak_reference_owner_; 2715821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) DISALLOW_COPY_AND_ASSIGN(SupportsWeakPtr); 2725821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 2735821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 2745821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Helper function that uses type deduction to safely return a WeakPtr<Derived> 2755821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// when Derived doesn't directly extend SupportsWeakPtr<Derived>, instead it 2765821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// extends a Base that extends SupportsWeakPtr<Base>. 2775821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 2785821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// EXAMPLE: 2795821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// class Base : public base::SupportsWeakPtr<Producer> {}; 2805821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// class Derived : public Base {}; 2815821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 2825821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Derived derived; 2835821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// base::WeakPtr<Derived> ptr = base::AsWeakPtr(&derived); 2845821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 2855821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Note that the following doesn't work (invalid type conversion) since 2865821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Derived::AsWeakPtr() is WeakPtr<Base> SupportsWeakPtr<Base>::AsWeakPtr(), 2875821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// and there's no way to safely cast WeakPtr<Base> to WeakPtr<Derived> at 2885821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// the caller. 2895821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 2905821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// base::WeakPtr<Derived> ptr = derived.AsWeakPtr(); // Fails. 2915821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 2925821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template <typename Derived> 2935821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)WeakPtr<Derived> AsWeakPtr(Derived* t) { 2945821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) return internal::SupportsWeakPtrBase::StaticAsWeakPtr<Derived>(t); 2955821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)} 2965821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 2975821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// A class may alternatively be composed of a WeakPtrFactory and thereby 2985821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// control how it exposes weak pointers to itself. This is helpful if you only 2995821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// need weak pointers within the implementation of a class. This class is also 3005821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// useful when working with primitive types. For example, you could have a 3015821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// WeakPtrFactory<bool> that is used to pass around a weak reference to a bool. 3025821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template <class T> 3035821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)class WeakPtrFactory { 3045821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) public: 3055821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) explicit WeakPtrFactory(T* ptr) : ptr_(ptr) { 3065821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 3075821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 3085821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) ~WeakPtrFactory() { 3095821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) ptr_ = NULL; 3105821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 3115821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 3125821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) WeakPtr<T> GetWeakPtr() { 3135821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) DCHECK(ptr_); 3145821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) return WeakPtr<T>(weak_reference_owner_.GetRef(), ptr_); 3155821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 3165821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 3175821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Call this method to invalidate all existing weak pointers. 3185821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) void InvalidateWeakPtrs() { 3195821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) DCHECK(ptr_); 3205821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) weak_reference_owner_.Invalidate(); 3215821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 3225821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 3235821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Call this method to determine if any weak pointers exist. 3245821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) bool HasWeakPtrs() const { 3255821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) DCHECK(ptr_); 3265821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) return weak_reference_owner_.HasRefs(); 3275821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 3285821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 3295821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Indicates that this object will be used on another thread from now on. 3305821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) void DetachFromThread() { 3315821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) DCHECK(ptr_); 3325821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) weak_reference_owner_.DetachFromThread(); 3335821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 3345821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 3355821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) private: 3365821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) internal::WeakReferenceOwner weak_reference_owner_; 3375821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) T* ptr_; 3385821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) DISALLOW_IMPLICIT_CONSTRUCTORS(WeakPtrFactory); 3395821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 3405821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 3415821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)} // namespace base 3425821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 3435821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#endif // BASE_MEMORY_WEAK_PTR_H_ 344