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/thirdparty/breakpad/processor/linked_ptr.h

http://github.com/tomahawk-player/tomahawk
C++ Header | 193 lines | 98 code | 24 blank | 71 comment | 16 complexity | bcf0909d50e6c769364865c63dc3fda1 MD5 | raw file
  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
 56namespace 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>.
 65class 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
 94template <typename T>
 95class 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    bool last = 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
173template<typename T> inline
174bool operator==(T* ptr, const linked_ptr<T>& x) {
175  return ptr == x.get();
176}
177
178template<typename T> inline
179bool 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))
186template <typename T>
187linked_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__