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/firmware/tests/gtest-1.4.0/include/gtest/internal/gtest-linked_ptr.h

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  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.
 80extern 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  // 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
135template <typename T>
136class 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
221template<typename T> inline
222bool operator==(T* ptr, const linked_ptr<T>& x) {
223  return ptr == x.get();
224}
225
226template<typename T> inline
227bool 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))
234template <typename T>
235linked_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_