File: IpReferenced.hpp

package info (click to toggle)
coinor-ipopt 3.11.9-2.1
  • links: PTS, VCS
  • area: main
  • in suites: stretch
  • size: 24,616 kB
  • sloc: cpp: 75,373; sh: 11,170; ansic: 2,798; makefile: 2,247; java: 632; fortran: 342
file content (258 lines) | stat: -rw-r--r-- 9,172 bytes parent folder | download | duplicates (4)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
// Copyright (C) 2004, 2006 International Business Machines and others.
// All Rights Reserved.
// This code is published under the Eclipse Public License.
//
// $Id: IpReferenced.hpp 2182 2013-03-30 20:02:18Z stefan $
//
// Authors:  Carl Laird, Andreas Waechter     IBM    2004-08-13

#ifndef __IPREFERENCED_HPP__
#define __IPREFERENCED_HPP__

#include "IpTypes.hpp"
#include "IpDebug.hpp"

#include <list>

#if COIN_IPOPT_CHECKLEVEL > 3
  #define IP_DEBUG_REFERENCED
#endif

namespace Ipopt
{

  /** Psydo-class, from which everything has to inherit that wants to
   *  use be registered as a Referencer for a ReferencedObject.
   */
  class Referencer
    {}
  ;

  /** ReferencedObject class.
   * This is part of the implementation of an intrusive smart pointer 
   * design. This class stores the reference count of all the smart
   * pointers that currently reference it. See the documentation for
   * the SmartPtr class for more details.
   * 
   * A SmartPtr behaves much like a raw pointer, but manages the lifetime 
   * of an object, deleting the object automatically. This class implements
   * a reference-counting, intrusive smart pointer design, where all
   * objects pointed to must inherit off of ReferencedObject, which
   * stores the reference count. Although this is intrusive (native types
   * and externally authored classes require wrappers to be referenced
   * by smart pointers), it is a safer design. A more detailed discussion of
   * these issues follows after the usage information.
   * 
   * Usage Example:
   * Note: to use the SmartPtr, all objects to which you point MUST
   * inherit off of ReferencedObject.
   * 
   * \verbatim
   * 
   * In MyClass.hpp...
   * 
   * #include "IpReferenced.hpp"

   * namespace Ipopt {
   * 
   *  class MyClass : public ReferencedObject // must derive from ReferencedObject
   *    {
   *      ...
   *    }
   * } // namespace Ipopt
   * 
   * 
   * In my_usage.cpp...
   * 
   * #include "IpSmartPtr.hpp"
   * #include "MyClass.hpp"
   * 
   * void func(AnyObject& obj)
   *  {
   *    SmartPtr<MyClass> ptr_to_myclass = new MyClass(...);
   *    // ptr_to_myclass now points to a new MyClass,
   *    // and the reference count is 1
   *  
   *    ...
   * 
   *    obj.SetMyClass(ptr_to_myclass);
   *    // Here, let's assume that AnyObject uses a
   *    // SmartPtr<MyClass> internally here.
   *    // Now, both ptr_to_myclass and the internal
   *    // SmartPtr in obj point to the same MyClass object
   *    // and its reference count is 2.
   * 
   *    ...
   * 
   *    // No need to delete ptr_to_myclass, this
   *    // will be done automatically when the
   *    // reference count drops to zero.
   * 
   *  }  
   *  
   * \endverbatim
   * 
   * Other Notes:
   *  The SmartPtr implements both dereference operators -> & *.
   *  The SmartPtr does NOT implement a conversion operator to
   *    the raw pointer. Use the GetRawPtr() method when this
   *    is necessary. Make sure that the raw pointer is NOT
   *    deleted. 
   *  The SmartPtr implements the comparison operators == & !=
   *    for a variety of types. Use these instead of
   *    \verbatim
   *    if (GetRawPtr(smrt_ptr) == ptr) // Don't use this
   *    \endverbatim
   *  SmartPtr's, as currently implemented, do NOT handle circular references.
   *    For example: consider a higher level object using SmartPtrs to point to 
   *    A and B, but A and B also point to each other (i.e. A has a SmartPtr 
   *    to B and B has a SmartPtr to A). In this scenario, when the higher
   *    level object is finished with A and B, their reference counts will 
   *    never drop to zero (since they reference each other) and they
   *    will not be deleted. This can be detected by memory leak tools like
   *    valgrind. If the circular reference is necessary, the problem can be
   *    overcome by a number of techniques:
   *  
   *    1) A and B can have a method that "releases" each other, that is
   *        they set their internal SmartPtrs to NULL.
   *        \verbatim
   *        void AClass::ReleaseCircularReferences()
   *          {
   *          smart_ptr_to_B = NULL;
   *          }
   *        \endverbatim
   *        Then, the higher level class can call these methods before
   *        it is done using A & B.
   * 
   *    2) Raw pointers can be used in A and B to reference each other.
   *        Here, an implicit assumption is made that the lifetime is
   *        controlled by the higher level object and that A and B will
   *        both exist in a controlled manner. Although this seems 
   *        dangerous, in many situations, this type of referencing
   *        is very controlled and this is reasonably safe.
   * 
   *    3) This SmartPtr class could be redesigned with the Weak/Strong
   *        design concept. Here, the SmartPtr is identified as being
   *        Strong (controls lifetime of the object) or Weak (merely
   *        referencing the object). The Strong SmartPtr increments 
   *        (and decrements) the reference count in ReferencedObject
   *        but the Weak SmartPtr does not. In the example above,
   *        the higher level object would have Strong SmartPtrs to
   *        A and B, but A and B would have Weak SmartPtrs to each
   *        other. Then, when the higher level object was done with
   *        A and B, they would be deleted. The Weak SmartPtrs in A
   *        and B would not decrement the reference count and would,
   *        of course, not delete the object. This idea is very similar
   *        to item (2), where it is implied that the sequence of events 
   *        is controlled such that A and B will not call anything using
   *        their pointers following the higher level delete (i.e. in
   *        their destructors!). This is somehow safer, however, because
   *        code can be written (however expensive) to perform run-time 
   *        detection of this situation. For example, the ReferencedObject
   *        could store pointers to all Weak SmartPtrs that are referencing
   *        it and, in its destructor, tell these pointers that it is
   *        dying. They could then set themselves to NULL, or set an
   *        internal flag to detect usage past this point.
   *
   *   For every most derived object only one ReferencedObject may exist,
   *   that is multiple inheritance requires virtual inheritance, see also
   *   the 2nd point in ticket #162.
   * 
   * Comments on Non-Intrusive Design:
   * In a non-intrusive design, the reference count is stored somewhere other
   * than the object being referenced. This means, unless the reference
   * counting pointer is the first referencer, it must get a pointer to the 
   * referenced object from another smart pointer (so it has access to the 
   * reference count location). In this non-intrusive design, if we are 
   * pointing to an object with a smart pointer (or a number of smart
   * pointers), and we then give another smart pointer the address through
   * a RAW pointer, we will have two independent, AND INCORRECT, reference
   * counts. To avoid this pitfall, we use an intrusive reference counting
   * technique where the reference count is stored in the object being
   * referenced. 
   */
  class ReferencedObject
  {
  public:
    ReferencedObject()
        :
        reference_count_(0)
    {}

    virtual ~ReferencedObject()
    {
      DBG_ASSERT(reference_count_ == 0);
    }

    inline
    Index ReferenceCount() const;

    inline
    void AddRef(const Referencer* referencer) const;

    inline
    void ReleaseRef(const Referencer* referencer) const;

  private:
    mutable Index reference_count_;

#   ifdef IP_DEBUG_REFERENCED
    mutable std::list<const Referencer*> referencers_;
#   endif

  };

  /* inline methods */
  inline
  Index ReferencedObject::ReferenceCount() const
  {
    //    DBG_START_METH("ReferencedObject::ReferenceCount()", 0);
    //    DBG_PRINT((1,"Returning reference_count_ = %d\n", reference_count_));
    return reference_count_;
  }

  inline
  void ReferencedObject::AddRef(const Referencer* referencer) const
  {
    //    DBG_START_METH("ReferencedObject::AddRef(const Referencer* referencer)", 0);
    reference_count_++;
    //    DBG_PRINT((1, "New reference_count_ = %d\n", reference_count_));
#   ifdef IP_DEBUG_REFERENCED
    referencers_.push_back(referencer);
#   endif

  }

  inline
  void ReferencedObject::ReleaseRef(const Referencer* referencer) const
  {
    //    DBG_START_METH("ReferencedObject::ReleaseRef(const Referencer* referencer)",
    //                   0);
    reference_count_--;
    //    DBG_PRINT((1, "New reference_count_ = %d\n", reference_count_));

#   ifdef IP_DEBUG_REFERENCED

    bool found = false;
    std::list<const Referencer*>::iterator iter;
    for (iter = referencers_.begin(); iter != referencers_.end(); iter++) {
      if ((*iter) == referencer) {
        found = true;
        break;
      }
    }

    // cannot call release on a reference that was never added...
    DBG_ASSERT(found);

    if (found) {
      referencers_.erase(iter);
    }
#   endif

  }


} // namespace Ipopt

#endif