1 // Safe sequence/iterator base implementation -*- C++ -*-
2
3 // Copyright (C) 2003-2023 Free Software Foundation, Inc.
4 //
5 // This file is part of the GNU ISO C++ Library. This library is free
6 // software; you can redistribute it and/or modify it under the
7 // terms of the GNU General Public License as published by the
8 // Free Software Foundation; either version 3, or (at your option)
9 // any later version.
10
11 // This library is distributed in the hope that it will be useful,
12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 // GNU General Public License for more details.
15
16 // Under Section 7 of GPL version 3, you are granted additional
17 // permissions described in the GCC Runtime Library Exception, version
18 // 3.1, as published by the Free Software Foundation.
19
20 // You should have received a copy of the GNU General Public License and
21 // a copy of the GCC Runtime Library Exception along with this program;
22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23 // <http://www.gnu.org/licenses/>.
24
25 /** @file debug/safe_base.h
26 * This file is a GNU debug extension to the Standard C++ Library.
27 */
28
29 #ifndef _GLIBCXX_DEBUG_SAFE_BASE_H
30 #define _GLIBCXX_DEBUG_SAFE_BASE_H 1
31
32 #include <ext/concurrence.h>
33
34 namespace __gnu_debug
35 {
36 class _Safe_sequence_base;
37
38 /** \brief Basic functionality for a @a safe iterator.
39 *
40 * The %_Safe_iterator_base base class implements the functionality
41 * of a safe iterator that is not specific to a particular iterator
42 * type. It contains a pointer back to the sequence it references
43 * along with iterator version information and pointers to form a
44 * doubly-linked list of iterators referenced by the container.
45 *
46 * This class must not perform any operations that can throw an
47 * exception, or the exception guarantees of derived iterators will
48 * be broken.
49 */
50 class _Safe_iterator_base
51 {
52 friend class _Safe_sequence_base;
53
54 public:
55 /** The sequence this iterator references; may be NULL to indicate
56 a singular iterator. */
57 _Safe_sequence_base* _M_sequence;
58
59 /** The version number of this iterator. The sentinel value 0 is
60 * used to indicate an invalidated iterator (i.e., one that is
61 * singular because of an operation on the container). This
62 * version number must equal the version number in the sequence
63 * referenced by _M_sequence for the iterator to be
64 * non-singular.
65 */
66 unsigned int _M_version;
67
68 /** Pointer to the previous iterator in the sequence's list of
69 iterators. Only valid when _M_sequence != NULL. */
70 _Safe_iterator_base* _M_prior;
71
72 /** Pointer to the next iterator in the sequence's list of
73 iterators. Only valid when _M_sequence != NULL. */
74 _Safe_iterator_base* _M_next;
75
76 protected:
77 /** Initializes the iterator and makes it singular. */
78 _Safe_iterator_base()
79 : _M_sequence(0), _M_version(0), _M_prior(0), _M_next(0)
80 { }
81
82 /** Initialize the iterator to reference the sequence pointed to
83 * by @p __seq. @p __constant is true when we are initializing a
84 * constant iterator, and false if it is a mutable iterator. Note
85 * that @p __seq may be NULL, in which case the iterator will be
86 * singular. Otherwise, the iterator will reference @p __seq and
87 * be nonsingular.
88 */
89 _Safe_iterator_base(const _Safe_sequence_base* __seq, bool __constant)
90 : _M_sequence(0), _M_version(0), _M_prior(0), _M_next(0)
91 { this->_M_attach(const_cast<_Safe_sequence_base*>(__seq), __constant); }
92
93 /** Initializes the iterator to reference the same sequence that
94 @p __x does. @p __constant is true if this is a constant
95 iterator, and false if it is mutable. */
96 _Safe_iterator_base(const _Safe_iterator_base& __x, bool __constant)
97 : _M_sequence(0), _M_version(0), _M_prior(0), _M_next(0)
98 { this->_M_attach(__x._M_sequence, __constant); }
99
100 ~_Safe_iterator_base() { this->_M_detach(); }
101
102 /** For use in _Safe_iterator. */
103 __gnu_cxx::__mutex&
104 _M_get_mutex() throw ();
105
106 /** Attaches this iterator to the given sequence, detaching it
107 * from whatever sequence it was attached to originally. If the
108 * new sequence is the NULL pointer, the iterator is left
109 * unattached.
110 */
111 void
112 _M_attach(_Safe_sequence_base* __seq, bool __constant);
113
114 /** Likewise, but not thread-safe. */
115 void
116 _M_attach_single(_Safe_sequence_base* __seq, bool __constant) throw ();
117
118 /** Detach the iterator for whatever sequence it is attached to,
119 * if any.
120 */
121 void
122 _M_detach();
123
124 public:
125 /** Likewise, but not thread-safe. */
126 void
127 _M_detach_single() throw ();
128
129 /** Determines if we are attached to the given sequence. */
130 bool
131 _M_attached_to(const _Safe_sequence_base* __seq) const
132 { return _M_sequence == __seq; }
133
134 /** Is this iterator singular? */
135 _GLIBCXX_PURE bool
136 _M_singular() const throw ();
137
138 /** Can we compare this iterator to the given iterator @p __x?
139 Returns true if both iterators are nonsingular and reference
140 the same sequence. */
141 _GLIBCXX_PURE bool
142 _M_can_compare(const _Safe_iterator_base& __x) const throw ();
143
144 /** Invalidate the iterator, making it singular. */
145 void
146 _M_invalidate()
147 { _M_version = 0; }
148
149 /** Reset all member variables */
150 void
151 _M_reset() throw ();
152
153 /** Unlink itself */
154 void
155 _M_unlink() throw ()
156 {
157 if (_M_prior)
158 _M_prior->_M_next = _M_next;
159 if (_M_next)
160 _M_next->_M_prior = _M_prior;
161 }
162 };
163
164 /** Iterators that derive from _Safe_iterator_base can be determined singular
165 * or non-singular.
166 **/
167 inline bool
168 __check_singular_aux(const _Safe_iterator_base* __x)
169 { return __x->_M_singular(); }
170
171 /**
172 * @brief Base class that supports tracking of iterators that
173 * reference a sequence.
174 *
175 * The %_Safe_sequence_base class provides basic support for
176 * tracking iterators into a sequence. Sequences that track
177 * iterators must derived from %_Safe_sequence_base publicly, so
178 * that safe iterators (which inherit _Safe_iterator_base) can
179 * attach to them. This class contains two linked lists of
180 * iterators, one for constant iterators and one for mutable
181 * iterators, and a version number that allows very fast
182 * invalidation of all iterators that reference the container.
183 *
184 * This class must ensure that no operation on it may throw an
185 * exception, otherwise @a safe sequences may fail to provide the
186 * exception-safety guarantees required by the C++ standard.
187 */
188 class _Safe_sequence_base
189 {
190 friend class _Safe_iterator_base;
191
192 public:
193 /// The list of mutable iterators that reference this container
194 _Safe_iterator_base* _M_iterators;
195
196 /// The list of constant iterators that reference this container
197 _Safe_iterator_base* _M_const_iterators;
198
199 /// The container version number. This number may never be 0.
200 mutable unsigned int _M_version;
201
202 protected:
203 // Initialize with a version number of 1 and no iterators
204 _Safe_sequence_base() _GLIBCXX_NOEXCEPT
205 : _M_iterators(0), _M_const_iterators(0), _M_version(1)
206 { }
207
208 #if __cplusplus >= 201103L
209 _Safe_sequence_base(const _Safe_sequence_base&) noexcept
210 : _Safe_sequence_base() { }
211
212 // Move constructor swap iterators.
213 _Safe_sequence_base(_Safe_sequence_base&& __seq) noexcept
214 : _Safe_sequence_base()
215 { _M_swap(__seq); }
216 #endif
217
218 /** Notify all iterators that reference this sequence that the
219 sequence is being destroyed. */
220 ~_Safe_sequence_base()
221 { this->_M_detach_all(); }
222
223 /** Detach all iterators, leaving them singular. */
224 void
225 _M_detach_all();
226
227 /** Detach all singular iterators.
228 * @post for all iterators i attached to this sequence,
229 * i->_M_version == _M_version.
230 */
231 void
232 _M_detach_singular();
233
234 /** Revalidates all attached singular iterators. This method may
235 * be used to validate iterators that were invalidated before
236 * (but for some reason, such as an exception, need to become
237 * valid again).
238 */
239 void
240 _M_revalidate_singular();
241
242 /** Swap this sequence with the given sequence. This operation
243 * also swaps ownership of the iterators, so that when the
244 * operation is complete all iterators that originally referenced
245 * one container now reference the other container.
246 */
247 void
248 _M_swap(_Safe_sequence_base& __x) _GLIBCXX_USE_NOEXCEPT;
249
250 /** For use in _Safe_sequence. */
251 __gnu_cxx::__mutex&
252 _M_get_mutex() throw ();
253
254 /** Invalidates all iterators. */
255 void
256 _M_invalidate_all() const
257 { if (++_M_version == 0) _M_version = 1; }
258
259 private:
260 /** Attach an iterator to this sequence. */
261 void
262 _M_attach(_Safe_iterator_base* __it, bool __constant);
263
264 /** Likewise but not thread safe. */
265 void
266 _M_attach_single(_Safe_iterator_base* __it, bool __constant) throw ();
267
268 /** Detach an iterator from this sequence */
269 void
270 _M_detach(_Safe_iterator_base* __it);
271
272 /** Likewise but not thread safe. */
273 void
274 _M_detach_single(_Safe_iterator_base* __it) throw ();
275 };
276 } // namespace __gnu_debug
277
278 #endif