1 // Copyright 2003 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 // Authors: Dan Egnor (egnor (at) google.com) 31 // 32 // A "smart" pointer type with reference tracking. Every pointer to a 33 // particular object is kept on a circular linked list. When the last pointer 34 // to an object is destroyed or reassigned, the object is deleted. 35 // 36 // Used properly, this deletes the object when the last reference goes away. 37 // There are several caveats: 38 // - Like all reference counting schemes, cycles lead to leaks. 39 // - Each smart pointer is actually two pointers (8 bytes instead of 4). 40 // - Every time a pointer is assigned, the entire list of pointers to that 41 // object is traversed. This class is therefore NOT SUITABLE when there 42 // will often be more than two or three pointers to a particular object. 43 // - References are only tracked as long as linked_ptr<> objects are copied. 44 // If a linked_ptr<> is converted to a raw pointer and back, BAD THINGS 45 // will happen (double deletion). 46 // 47 // A good use of this class is storing object references in STL containers. 48 // You can safely put linked_ptr<> in a vector<>. 49 // Other uses may not be as good. 50 // 51 // Note: If you use an incomplete type with linked_ptr<>, the class 52 // *containing* linked_ptr<> must have a constructor and destructor (even 53 // if they do nothing!). 54 // 55 // Bill Gibbons suggested we use something like this. 56 // 57 // Thread Safety: 58 // Unlike other linked_ptr implementations, in this implementation 59 // a linked_ptr object is thread-safe in the sense that: 60 // - it's safe to copy linked_ptr objects concurrently, 61 // - it's safe to copy *from* a linked_ptr and read its underlying 62 // raw pointer (e.g. via get()) concurrently, and 63 // - it's safe to write to two linked_ptrs that point to the same 64 // shared object concurrently. 65 // TODO(wan (at) google.com): rename this to safe_linked_ptr to avoid 66 // confusion with normal linked_ptr. 67 68 #ifndef GTEST_INCLUDE_GTEST_INTERNAL_GTEST_LINKED_PTR_H_ 69 #define GTEST_INCLUDE_GTEST_INTERNAL_GTEST_LINKED_PTR_H_ 70 71 #include <stdlib.h> 72 #include <assert.h> 73 74 #include <gtest/internal/gtest-port.h> 75 76 namespace testing { 77 namespace internal { 78 79 // Protects copying of all linked_ptr objects. 80 extern Mutex g_linked_ptr_mutex; 81 82 // This is used internally by all instances of linked_ptr<>. It needs to be 83 // a non-template class because different types of linked_ptr<> can refer to 84 // the same object (linked_ptr<Superclass>(obj) vs linked_ptr<Subclass>(obj)). 85 // So, it needs to be possible for different types of linked_ptr to participate 86 // in the same circular linked list, so we need a single class type here. 87 // 88 // DO NOT USE THIS CLASS DIRECTLY YOURSELF. Use linked_ptr<T>. 89 class linked_ptr_internal { 90 public: 91 // Create a new circle that includes only this instance. 92 void join_new() { 93 next_ = this; 94 } 95 96 // Many linked_ptr operations may change p.link_ for some linked_ptr 97 // variable p in the same circle as this object. Therefore we need 98 // to prevent two such operations from occurring concurrently. 99 // 100 // Note that different types of linked_ptr objects can coexist in a 101 // circle (e.g. linked_ptr<Base>, linked_ptr<Derived1>, and 102 // linked_ptr<Derived2>). Therefore we must use a single mutex to 103 // protect all linked_ptr objects. This can create serious 104 // contention in production code, but is acceptable in a testing 105 // framework. 106 107 // Join an existing circle. 108 // L < g_linked_ptr_mutex 109 void join(linked_ptr_internal const* ptr) { 110 MutexLock lock(&g_linked_ptr_mutex); 111 112 linked_ptr_internal const* p = ptr; 113 while (p->next_ != ptr) p = p->next_; 114 p->next_ = this; 115 next_ = ptr; 116 } 117 118 // Leave whatever circle we're part of. Returns true if we were the 119 // last member of the circle. Once this is done, you can join() another. 120 // L < g_linked_ptr_mutex 121 bool depart() { 122 MutexLock lock(&g_linked_ptr_mutex); 123 124 if (next_ == this) return true; 125 linked_ptr_internal const* p = next_; 126 while (p->next_ != this) p = p->next_; 127 p->next_ = next_; 128 return false; 129 } 130 131 private: 132 mutable linked_ptr_internal const* next_; 133 }; 134 135 template <typename T> 136 class linked_ptr { 137 public: 138 typedef T element_type; 139 140 // Take over ownership of a raw pointer. This should happen as soon as 141 // possible after the object is created. 142 explicit linked_ptr(T* ptr = NULL) { capture(ptr); } 143 ~linked_ptr() { depart(); } 144 145 // Copy an existing linked_ptr<>, adding ourselves to the list of references. 146 template <typename U> linked_ptr(linked_ptr<U> const& ptr) { copy(&ptr); } 147 linked_ptr(linked_ptr const& ptr) { // NOLINT 148 assert(&ptr != this); 149 copy(&ptr); 150 } 151 152 // Assignment releases the old value and acquires the new. 153 template <typename U> linked_ptr& operator=(linked_ptr<U> const& ptr) { 154 depart(); 155 copy(&ptr); 156 return *this; 157 } 158 159 linked_ptr& operator=(linked_ptr const& ptr) { 160 if (&ptr != this) { 161 depart(); 162 copy(&ptr); 163 } 164 return *this; 165 } 166 167 // Smart pointer members. 168 void reset(T* ptr = NULL) { 169 depart(); 170 capture(ptr); 171 } 172 T* get() const { return value_; } 173 T* operator->() const { return value_; } 174 T& operator*() const { return *value_; } 175 // Release ownership of the pointed object and returns it. 176 // Sole ownership by this linked_ptr object is required. 177 T* release() { 178 bool last = link_.depart(); 179 assert(last); 180 T* v = value_; 181 value_ = NULL; 182 return v; 183 } 184 185 bool operator==(T* p) const { return value_ == p; } 186 bool operator!=(T* p) const { return value_ != p; } 187 template <typename U> 188 bool operator==(linked_ptr<U> const& ptr) const { 189 return value_ == ptr.get(); 190 } 191 template <typename U> 192 bool operator!=(linked_ptr<U> const& ptr) const { 193 return value_ != ptr.get(); 194 } 195 196 private: 197 template <typename U> 198 friend class linked_ptr; 199 200 T* value_; 201 linked_ptr_internal link_; 202 203 void depart() { 204 if (link_.depart()) delete value_; 205 } 206 207 void capture(T* ptr) { 208 value_ = ptr; 209 link_.join_new(); 210 } 211 212 template <typename U> void copy(linked_ptr<U> const* ptr) { 213 value_ = ptr->get(); 214 if (value_) 215 link_.join(&ptr->link_); 216 else 217 link_.join_new(); 218 } 219 }; 220 221 template<typename T> inline 222 bool operator==(T* ptr, const linked_ptr<T>& x) { 223 return ptr == x.get(); 224 } 225 226 template<typename T> inline 227 bool operator!=(T* ptr, const linked_ptr<T>& x) { 228 return ptr != x.get(); 229 } 230 231 // A function to convert T* into linked_ptr<T> 232 // Doing e.g. make_linked_ptr(new FooBarBaz<type>(arg)) is a shorter notation 233 // for linked_ptr<FooBarBaz<type> >(new FooBarBaz<type>(arg)) 234 template <typename T> 235 linked_ptr<T> make_linked_ptr(T* ptr) { 236 return linked_ptr<T>(ptr); 237 } 238 239 } // namespace internal 240 } // namespace testing 241 242 #endif // GTEST_INCLUDE_GTEST_INTERNAL_GTEST_LINKED_PTR_H_ 243
