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@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@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 76namespace testing { 77namespace internal { 78 79// Protects copying of all linked_ptr objects. 80GTEST_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>. 89class 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 145template <typename T> 146class 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 222template<typename T> inline 223bool operator==(T* ptr, const linked_ptr<T>& x) { 224 return ptr == x.get(); 225} 226 227template<typename T> inline 228bool 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)) 235template <typename T> 236linked_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