droger | c676265 | 2014-12-12 17:39:02 | [diff] [blame] | 1 | // Copyright 2013 The Chromium Authors. All rights reserved. |
| 2 | // Use of this source code is governed by a BSD-style license that can be |
| 3 | // found in the LICENSE file. |
| 4 | |
| 5 | #ifndef BASE_IOS_WEAK_NSOBJECT_H_ |
| 6 | #define BASE_IOS_WEAK_NSOBJECT_H_ |
| 7 | |
| 8 | #import <Foundation/Foundation.h> |
| 9 | #import <objc/runtime.h> |
| 10 | |
| 11 | #include "base/basictypes.h" |
| 12 | #include "base/compiler_specific.h" |
| 13 | #include "base/logging.h" |
| 14 | #include "base/memory/ref_counted.h" |
| 15 | #include "base/threading/non_thread_safe.h" |
| 16 | #include "base/threading/thread_checker.h" |
| 17 | |
| 18 | // WeakNSObject<> is patterned after scoped_nsobject<>, but instead of |
| 19 | // maintaining ownership of an NSObject subclass object, it will nil itself out |
| 20 | // when the object is deallocated. |
| 21 | // |
| 22 | // WeakNSProtocol<> has the same behavior as WeakNSObject, but can be used |
| 23 | // with protocols. |
| 24 | // |
| 25 | // Example usage (base::WeakNSObject<T>): |
| 26 | // scoped_nsobject<Foo> foo([[Foo alloc] init]); |
| 27 | // WeakNSObject<Foo> weak_foo; // No pointer |
| 28 | // weak_foo.reset(foo) // Now a weak reference is kept. |
| 29 | // [weak_foo description]; // Returns [foo description]. |
| 30 | // foo.reset(); // The reference is released. |
| 31 | // [weak_foo description]; // Returns nil, as weak_foo is pointing to nil. |
| 32 | // |
| 33 | // |
| 34 | // Implementation wise a WeakNSObject keeps a reference to a refcounted |
| 35 | // WeakContainer. There is one unique instance of a WeakContainer per watched |
| 36 | // NSObject, this relationship is maintained via the ObjectiveC associated |
| 37 | // object API, indirectly via an ObjectiveC CRBWeakNSProtocolSentinel class. |
| 38 | // |
droger | 4f05f5a8 | 2015-01-16 11:33:52 | [diff] [blame] | 39 | // Threading restrictions: |
| 40 | // - Several WeakNSObject pointing to the same underlying object must all be |
| 41 | // created and dereferenced on the same thread; |
| 42 | // - thread safety is enforced by the implementation, except in two cases: |
| 43 | // (1) it is allowed to copy a WeakNSObject on a different thread. However, |
| 44 | // that copy must return to the original thread before being dereferenced, |
| 45 | // (2) it is allowed to destroy a WeakNSObject on any thread; |
| 46 | // - the implementation assumes that the tracked object will be released on the |
| 47 | // same thread that the WeakNSObject is created on. |
droger | c676265 | 2014-12-12 17:39:02 | [diff] [blame] | 48 | namespace base { |
| 49 | |
| 50 | // WeakContainer keeps a weak pointer to an object and clears it when it |
| 51 | // receives nullify() from the object's sentinel. |
| 52 | class WeakContainer : public base::RefCountedThreadSafe<WeakContainer> { |
| 53 | public: |
droger | 4f05f5a8 | 2015-01-16 11:33:52 | [diff] [blame] | 54 | explicit WeakContainer(id object) : object_(object) {} |
| 55 | |
| 56 | id object() { |
| 57 | DCHECK(checker_.CalledOnValidThread()); |
| 58 | return object_; |
| 59 | } |
| 60 | |
droger | c676265 | 2014-12-12 17:39:02 | [diff] [blame] | 61 | void nullify() { |
| 62 | DCHECK(checker_.CalledOnValidThread()); |
| 63 | object_ = nil; |
| 64 | } |
| 65 | |
| 66 | private: |
| 67 | friend base::RefCountedThreadSafe<WeakContainer>; |
| 68 | ~WeakContainer() {} |
| 69 | base::ThreadChecker checker_; |
| 70 | id object_; |
| 71 | }; |
| 72 | |
| 73 | } // namespace base |
| 74 | |
| 75 | // Sentinel for observing the object contained in the weak pointer. The object |
| 76 | // will be deleted when the weak object is deleted and will notify its |
| 77 | // container. |
| 78 | @interface CRBWeakNSProtocolSentinel : NSObject |
| 79 | // Return the only associated container for this object. There can be only one. |
| 80 | // Will return null if object is nil . |
| 81 | + (scoped_refptr<base::WeakContainer>)containerForObject:(id)object; |
| 82 | @end |
| 83 | |
| 84 | namespace base { |
| 85 | |
| 86 | // Base class for all WeakNSObject derivatives. |
| 87 | template <typename NST> |
droger | 4f05f5a8 | 2015-01-16 11:33:52 | [diff] [blame] | 88 | class WeakNSProtocol { |
droger | c676265 | 2014-12-12 17:39:02 | [diff] [blame] | 89 | public: |
| 90 | explicit WeakNSProtocol(NST object = nil) { |
| 91 | container_ = [CRBWeakNSProtocolSentinel containerForObject:object]; |
| 92 | } |
| 93 | |
| 94 | WeakNSProtocol(const WeakNSProtocol<NST>& that) { |
droger | 4f05f5a8 | 2015-01-16 11:33:52 | [diff] [blame] | 95 | // A WeakNSProtocol object can be copied on one thread and used on |
| 96 | // another. |
| 97 | checker_.DetachFromThread(); |
droger | c676265 | 2014-12-12 17:39:02 | [diff] [blame] | 98 | container_ = that.container_; |
| 99 | } |
| 100 | |
| 101 | ~WeakNSProtocol() { |
droger | 4f05f5a8 | 2015-01-16 11:33:52 | [diff] [blame] | 102 | // A WeakNSProtocol object can be used on one thread and released on |
droger | c676265 | 2014-12-12 17:39:02 | [diff] [blame] | 103 | // another. This is not the case for the contained object. |
droger | 4f05f5a8 | 2015-01-16 11:33:52 | [diff] [blame] | 104 | checker_.DetachFromThread(); |
droger | c676265 | 2014-12-12 17:39:02 | [diff] [blame] | 105 | } |
| 106 | |
| 107 | void reset(NST object = nil) { |
droger | 4f05f5a8 | 2015-01-16 11:33:52 | [diff] [blame] | 108 | DCHECK(checker_.CalledOnValidThread()); |
droger | c676265 | 2014-12-12 17:39:02 | [diff] [blame] | 109 | container_ = [CRBWeakNSProtocolSentinel containerForObject:object]; |
| 110 | } |
| 111 | |
| 112 | NST get() const { |
droger | 4f05f5a8 | 2015-01-16 11:33:52 | [diff] [blame] | 113 | DCHECK(checker_.CalledOnValidThread()); |
droger | c676265 | 2014-12-12 17:39:02 | [diff] [blame] | 114 | if (!container_.get()) |
| 115 | return nil; |
| 116 | return container_->object(); |
| 117 | } |
| 118 | |
| 119 | WeakNSProtocol& operator=(const WeakNSProtocol<NST>& that) { |
droger | 1fd547a | 2015-03-17 15:13:08 | [diff] [blame] | 120 | // A WeakNSProtocol object can be copied on one thread and used on |
| 121 | // another. |
| 122 | checker_.DetachFromThread(); |
droger | c676265 | 2014-12-12 17:39:02 | [diff] [blame] | 123 | container_ = that.container_; |
| 124 | return *this; |
| 125 | } |
| 126 | |
| 127 | bool operator==(NST that) const { |
droger | 4f05f5a8 | 2015-01-16 11:33:52 | [diff] [blame] | 128 | DCHECK(checker_.CalledOnValidThread()); |
droger | c676265 | 2014-12-12 17:39:02 | [diff] [blame] | 129 | return get() == that; |
| 130 | } |
| 131 | |
droger | 4f05f5a8 | 2015-01-16 11:33:52 | [diff] [blame] | 132 | bool operator!=(NST that) const { |
| 133 | DCHECK(checker_.CalledOnValidThread()); |
| 134 | return get() != that; |
| 135 | } |
droger | c676265 | 2014-12-12 17:39:02 | [diff] [blame] | 136 | |
droger | 4f05f5a8 | 2015-01-16 11:33:52 | [diff] [blame] | 137 | operator NST() const { |
| 138 | DCHECK(checker_.CalledOnValidThread()); |
| 139 | return get(); |
| 140 | } |
droger | c676265 | 2014-12-12 17:39:02 | [diff] [blame] | 141 | |
| 142 | private: |
| 143 | // Refecounted reference to the container tracking the ObjectiveC object this |
| 144 | // class encapsulates. |
| 145 | scoped_refptr<base::WeakContainer> container_; |
droger | 4f05f5a8 | 2015-01-16 11:33:52 | [diff] [blame] | 146 | base::ThreadChecker checker_; |
droger | c676265 | 2014-12-12 17:39:02 | [diff] [blame] | 147 | }; |
| 148 | |
| 149 | // Free functions |
| 150 | template <class NST> |
| 151 | bool operator==(NST p1, const WeakNSProtocol<NST>& p2) { |
| 152 | return p1 == p2.get(); |
| 153 | } |
| 154 | |
| 155 | template <class NST> |
| 156 | bool operator!=(NST p1, const WeakNSProtocol<NST>& p2) { |
| 157 | return p1 != p2.get(); |
| 158 | } |
| 159 | |
| 160 | template <typename NST> |
| 161 | class WeakNSObject : public WeakNSProtocol<NST*> { |
| 162 | public: |
| 163 | explicit WeakNSObject(NST* object = nil) : WeakNSProtocol<NST*>(object) {} |
| 164 | |
| 165 | WeakNSObject(const WeakNSObject<NST>& that) : WeakNSProtocol<NST*>(that) {} |
| 166 | |
| 167 | WeakNSObject& operator=(const WeakNSObject<NST>& that) { |
| 168 | WeakNSProtocol<NST*>::operator=(that); |
| 169 | return *this; |
| 170 | } |
| 171 | }; |
| 172 | |
| 173 | // Specialization to make WeakNSObject<id> work. |
| 174 | template <> |
| 175 | class WeakNSObject<id> : public WeakNSProtocol<id> { |
| 176 | public: |
| 177 | explicit WeakNSObject(id object = nil) : WeakNSProtocol<id>(object) {} |
| 178 | |
| 179 | WeakNSObject(const WeakNSObject<id>& that) : WeakNSProtocol<id>(that) {} |
| 180 | |
| 181 | WeakNSObject& operator=(const WeakNSObject<id>& that) { |
| 182 | WeakNSProtocol<id>::operator=(that); |
| 183 | return *this; |
| 184 | } |
| 185 | }; |
| 186 | |
| 187 | } // namespace base |
| 188 | |
| 189 | #endif // BASE_IOS_WEAK_NSOBJECT_H_ |