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 GTEST_API_ GTEST_DECLARE_STATIC_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 void join(linked_ptr_internal const* ptr) 109 GTEST_LOCK_EXCLUDED_(g_linked_ptr_mutex) { 110 MutexLock lock(&g_linked_ptr_mutex); 111 112 linked_ptr_internal const* p = ptr; 113 while (p->next_ != ptr) { 114 assert(p->next_ != this && 115 "Trying to join() a linked ring we are already in. " 116 "Is GMock thread safety enabled?"); 117 p = p->next_; 118 } 119 p->next_ = this; 120 next_ = ptr; 121 } 122 123 // Leave whatever circle we're part of. Returns true if we were the 124 // last member of the circle. Once this is done, you can join() another. 125 bool depart() 126 GTEST_LOCK_EXCLUDED_(g_linked_ptr_mutex) { 127 MutexLock lock(&g_linked_ptr_mutex); 128 129 if (next_ == this) return true; 130 linked_ptr_internal const* p = next_; 131 while (p->next_ != this) { 132 assert(p->next_ != next_ && 133 "Trying to depart() a linked ring we are not in. " 134 "Is GMock thread safety enabled?"); 135 p = p->next_; 136 } 137 p->next_ = next_; 138 return false; 139 } 140 141 private: 142 mutable linked_ptr_internal const* next_; 143 }; 144 145 template <typename T> 146 class linked_ptr { 147 public: 148 typedef T element_type; 149 150 // Take over ownership of a raw pointer. This should happen as soon as 151 // possible after the object is created. 152 explicit linked_ptr(T* ptr = NULL) { capture(ptr); } 153 ~linked_ptr() { depart(); } 154 155 // Copy an existing linked_ptr<>, adding ourselves to the list of references. 156 template <typename U> linked_ptr(linked_ptr<U> const& ptr) { copy(&ptr); } 157 linked_ptr(linked_ptr const& ptr) { // NOLINT 158 assert(&ptr != this); 159 copy(&ptr); 160 } 161 162 // Assignment releases the old value and acquires the new. 163 template <typename U> linked_ptr& operator=(linked_ptr<U> const& ptr) { 164 depart(); 165 copy(&ptr); 166 return *this; 167 } 168 169 linked_ptr& operator=(linked_ptr const& ptr) { 170 if (&ptr != this) { 171 depart(); 172 copy(&ptr); 173 } 174 return *this; 175 } 176 177 // Smart pointer members. 178 void reset(T* ptr = NULL) { 179 depart(); 180 capture(ptr); 181 } 182 T* get() const { return value_; } 183 T* operator->() const { return value_; } 184 T& operator*() const { return *value_; } 185 186 bool operator==(T* p) const { return value_ == p; } 187 bool operator!=(T* p) const { return value_ != p; } 188 template <typename U> 189 bool operator==(linked_ptr<U> const& ptr) const { 190 return value_ == ptr.get(); 191 } 192 template <typename U> 193 bool operator!=(linked_ptr<U> const& ptr) const { 194 return value_ != ptr.get(); 195 } 196 197 private: 198 template <typename U> 199 friend class linked_ptr; 200 201 T* value_; 202 linked_ptr_internal link_; 203 204 void depart() { 205 if (link_.depart()) delete value_; 206 } 207 208 void capture(T* ptr) { 209 value_ = ptr; 210 link_.join_new(); 211 } 212 213 template <typename U> void copy(linked_ptr<U> const* ptr) { 214 value_ = ptr->get(); 215 if (value_) 216 link_.join(&ptr->link_); 217 else 218 link_.join_new(); 219 } 220 }; 221 222 template<typename T> inline 223 bool operator==(T* ptr, const linked_ptr<T>& x) { 224 return ptr == x.get(); 225 } 226 227 template<typename T> inline 228 bool operator!=(T* ptr, const linked_ptr<T>& x) { 229 return ptr != x.get(); 230 } 231 232 // A function to convert T* into linked_ptr<T> 233 // Doing e.g. make_linked_ptr(new FooBarBaz<type>(arg)) is a shorter notation 234 // for linked_ptr<FooBarBaz<type> >(new FooBarBaz<type>(arg)) 235 template <typename T> 236 linked_ptr<T> make_linked_ptr(T* ptr) { 237 return linked_ptr<T>(ptr); 238 } 239 240 } // namespace internal 241 } // namespace testing 242 243 #endif // GTEST_INCLUDE_GTEST_INTERNAL_GTEST_LINKED_PTR_H_ 244