1 // Copyright (c) 2006, Google Inc. 2 // All rights reserved. 3 // 4 // Redistribution and use in source and binary forms, with or without 5 // modification, are permitted provided that the following conditions are 6 // met: 7 // 8 // * Redistributions of source code must retain the above copyright 9 // notice, this list of conditions and the following disclaimer. 10 // * Redistributions in binary form must reproduce the above 11 // copyright notice, this list of conditions and the following disclaimer 12 // in the documentation and/or other materials provided with the 13 // distribution. 14 // * Neither the name of Google Inc. nor the names of its 15 // contributors may be used to endorse or promote products derived from 16 // this software without specific prior written permission. 17 // 18 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 19 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 20 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 21 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 22 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 23 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 24 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 25 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 26 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 27 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 28 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 29 30 // A "smart" pointer type with reference tracking. Every pointer to a 31 // particular object is kept on a circular linked list. When the last pointer 32 // to an object is destroyed or reassigned, the object is deleted. 33 // 34 // Used properly, this deletes the object when the last reference goes away. 35 // There are several caveats: 36 // - Like all reference counting schemes, cycles lead to leaks. 37 // - Each smart pointer is actually two pointers (8 bytes instead of 4). 38 // - Every time a pointer is assigned, the entire list of pointers to that 39 // object is traversed. This class is therefore NOT SUITABLE when there 40 // will often be more than two or three pointers to a particular object. 41 // - References are only tracked as long as linked_ptr<> objects are copied. 42 // If a linked_ptr<> is converted to a raw pointer and back, BAD THINGS 43 // will happen (double deletion). 44 // 45 // A good use of this class is storing object references in STL containers. 46 // You can safely put linked_ptr<> in a vector<>. 47 // Other uses may not be as good. 48 // 49 // Note: If you use an incomplete type with linked_ptr<>, the class 50 // *containing* linked_ptr<> must have a constructor and destructor (even 51 // if they do nothing!). 52 53 #ifndef PROCESSOR_LINKED_PTR_H__ 54 #define PROCESSOR_LINKED_PTR_H__ 55 56 namespace google_breakpad { 57 58 // This is used internally by all instances of linked_ptr<>. It needs to be 59 // a non-template class because different types of linked_ptr<> can refer to 60 // the same object (linked_ptr<Superclass>(obj) vs linked_ptr<Subclass>(obj)). 61 // So, it needs to be possible for different types of linked_ptr to participate 62 // in the same circular linked list, so we need a single class type here. 63 // 64 // DO NOT USE THIS CLASS DIRECTLY YOURSELF. Use linked_ptr<T>. 65 class linked_ptr_internal { 66 public: 67 // Create a new circle that includes only this instance. 68 void join_new() { 69 next_ = this; 70 } 71 72 // Join an existing circle. 73 void join(linked_ptr_internal const* ptr) { 74 linked_ptr_internal const* p = ptr; 75 while (p->next_ != ptr) p = p->next_; 76 p->next_ = this; 77 next_ = ptr; 78 } 79 80 // Leave whatever circle we're part of. Returns true iff we were the 81 // last member of the circle. Once this is done, you can join() another. 82 bool depart() { 83 if (next_ == this) return true; 84 linked_ptr_internal const* p = next_; 85 while (p->next_ != this) p = p->next_; 86 p->next_ = next_; 87 return false; 88 } 89 90 private: 91 mutable linked_ptr_internal const* next_; 92 }; 93 94 template <typename T> 95 class linked_ptr { 96 public: 97 typedef T element_type; 98 99 // Take over ownership of a raw pointer. This should happen as soon as 100 // possible after the object is created. 101 explicit linked_ptr(T* ptr = NULL) { capture(ptr); } 102 ~linked_ptr() { depart(); } 103 104 // Copy an existing linked_ptr<>, adding ourselves to the list of references. 105 template <typename U> linked_ptr(linked_ptr<U> const& ptr) { copy(&ptr); } 106 linked_ptr(linked_ptr const& ptr) { copy(&ptr); } 107 108 // Assignment releases the old value and acquires the new. 109 template <typename U> linked_ptr& operator=(linked_ptr<U> const& ptr) { 110 depart(); 111 copy(&ptr); 112 return *this; 113 } 114 115 linked_ptr& operator=(linked_ptr const& ptr) { 116 if (&ptr != this) { 117 depart(); 118 copy(&ptr); 119 } 120 return *this; 121 } 122 123 // Smart pointer members. 124 void reset(T* ptr = NULL) { depart(); capture(ptr); } 125 T* get() const { return value_; } 126 T* operator->() const { return value_; } 127 T& operator*() const { return *value_; } 128 // Release ownership of the pointed object and returns it. 129 // Sole ownership by this linked_ptr object is required. 130 T* release() { 131 link_.depart(); 132 T* v = value_; 133 value_ = NULL; 134 return v; 135 } 136 137 bool operator==(T* p) const { return value_ == p; } 138 bool operator!=(T* p) const { return value_ != p; } 139 template <typename U> 140 bool operator==(linked_ptr<U> const& ptr) const { 141 return value_ == ptr.get(); 142 } 143 template <typename U> 144 bool operator!=(linked_ptr<U> const& ptr) const { 145 return value_ != ptr.get(); 146 } 147 148 private: 149 template <typename U> 150 friend class linked_ptr; 151 152 T* value_; 153 linked_ptr_internal link_; 154 155 void depart() { 156 if (link_.depart()) delete value_; 157 } 158 159 void capture(T* ptr) { 160 value_ = ptr; 161 link_.join_new(); 162 } 163 164 template <typename U> void copy(linked_ptr<U> const* ptr) { 165 value_ = ptr->get(); 166 if (value_) 167 link_.join(&ptr->link_); 168 else 169 link_.join_new(); 170 } 171 }; 172 173 template<typename T> inline 174 bool operator==(T* ptr, const linked_ptr<T>& x) { 175 return ptr == x.get(); 176 } 177 178 template<typename T> inline 179 bool operator!=(T* ptr, const linked_ptr<T>& x) { 180 return ptr != x.get(); 181 } 182 183 // A function to convert T* into linked_ptr<T> 184 // Doing e.g. make_linked_ptr(new FooBarBaz<type>(arg)) is a shorter notation 185 // for linked_ptr<FooBarBaz<type> >(new FooBarBaz<type>(arg)) 186 template <typename T> 187 linked_ptr<T> make_linked_ptr(T* ptr) { 188 return linked_ptr<T>(ptr); 189 } 190 191 } // namespace google_breakpad 192 193 #endif // PROCESSOR_LINKED_PTR_H__ 194
