1// Safe sequence/iterator base implementation -*- C++ -*-
2
3// Copyright (C) 2003-2026 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
34namespace __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. Stored as pointer-to-const because sequence
57 * could be declared as const.
58 */
59 const _Safe_sequence_base* _M_sequence;
60
61 /** The version number of this iterator. The sentinel value 0 is
62 * used to indicate an invalidated iterator (i.e., one that is
63 * singular because of an operation on the container). This
64 * version number must equal the version number in the sequence
65 * referenced by _M_sequence for the iterator to be
66 * non-singular.
67 */
68 unsigned int _M_version;
69
70 /** Pointer to the previous iterator in the sequence's list of
71 iterators. Only valid when _M_sequence != NULL. */
72 _Safe_iterator_base* _M_prior;
73
74 /** Pointer to the next iterator in the sequence's list of
75 iterators. Only valid when _M_sequence != NULL. */
76 _Safe_iterator_base* _M_next;
77
78 protected:
79 /** Initializes the iterator and makes it singular. */
80 _GLIBCXX20_CONSTEXPR
81 _Safe_iterator_base()
82 : _M_sequence(0), _M_version(0), _M_prior(0), _M_next(0)
83 { }
84
85 /** Initialize the iterator to reference the sequence pointed to
86 * by @p __seq. @p __constant is true when we are initializing a
87 * constant iterator, and false if it is a mutable iterator. Note
88 * that @p __seq may be NULL, in which case the iterator will be
89 * singular. Otherwise, the iterator will reference @p __seq and
90 * be nonsingular.
91 */
92 _GLIBCXX20_CONSTEXPR
93 _Safe_iterator_base(const _Safe_sequence_base* __seq, bool __constant)
94 : _M_sequence(0), _M_version(0), _M_prior(0), _M_next(0)
95 {
96 if (!std::__is_constant_evaluated())
97 this->_M_attach(__seq, __constant);
98 }
99
100 /** Initializes the iterator to reference the same sequence that
101 @p __x does. @p __constant is true if this is a constant
102 iterator, and false if it is mutable. */
103 _GLIBCXX20_CONSTEXPR
104 _Safe_iterator_base(const _Safe_iterator_base& __x, bool __constant)
105 : _M_sequence(0), _M_version(0), _M_prior(0), _M_next(0)
106 {
107 if (!std::__is_constant_evaluated())
108 this->_M_attach(seq: __x._M_sequence, __constant);
109 }
110
111 _GLIBCXX20_CONSTEXPR
112 ~_Safe_iterator_base()
113 {
114 if (!std::__is_constant_evaluated())
115 this->_M_detach();
116 }
117
118 /** For use in _Safe_iterator. */
119 __gnu_cxx::__mutex&
120 _M_get_mutex() _GLIBCXX_USE_NOEXCEPT;
121
122 /** Attaches this iterator to the given sequence, detaching it
123 * from whatever sequence it was attached to originally. If the
124 * new sequence is the NULL pointer, the iterator is left
125 * unattached.
126 */
127 void
128 _M_attach(const _Safe_sequence_base* __seq, bool __constant);
129
130 /** Likewise, but not thread-safe. */
131 void
132 _M_attach_single(const _Safe_sequence_base* __seq,
133 bool __constant) _GLIBCXX_USE_NOEXCEPT;
134
135 /** Detach the iterator for whatever sequence it is attached to,
136 * if any.
137 */
138 void
139 _M_detach();
140
141#if !_GLIBCXX_INLINE_VERSION
142 private:
143 /***************************************************************/
144 /** Not-const method preserved for abi backward compatibility. */
145 void
146 _M_attach(_Safe_sequence_base* __seq, bool __constant);
147
148 void
149 _M_attach_single(_Safe_sequence_base* __seq,
150 bool __constant) _GLIBCXX_USE_NOEXCEPT;
151 /***************************************************************/
152#endif
153
154 public:
155 /** Likewise, but not thread-safe. */
156 void
157 _M_detach_single() _GLIBCXX_USE_NOEXCEPT;
158
159 /** Determines if we are attached to the given sequence. */
160 bool
161 _M_attached_to(const _Safe_sequence_base* __seq) const
162 { return _M_sequence == __seq; }
163
164 /** Is this iterator singular? */
165 _GLIBCXX_PURE bool
166 _M_singular() const _GLIBCXX_USE_NOEXCEPT;
167
168 /** Can we compare this iterator to the given iterator @p __x?
169 Returns true if both iterators are nonsingular and reference
170 the same sequence. */
171 _GLIBCXX_PURE bool
172 _M_can_compare(const _Safe_iterator_base& __x) const _GLIBCXX_USE_NOEXCEPT;
173
174 /** Invalidate the iterator, making it singular. */
175 void
176 _M_invalidate()
177 { _M_version = 0; }
178
179 /** Reset all member variables */
180 void
181 _M_reset() _GLIBCXX_USE_NOEXCEPT;
182
183 /** Unlink itself */
184 void
185 _M_unlink() _GLIBCXX_USE_NOEXCEPT
186 {
187 if (_M_prior)
188 _M_prior->_M_next = _M_next;
189 if (_M_next)
190 _M_next->_M_prior = _M_prior;
191 }
192 };
193
194 /** Iterators that derive from _Safe_iterator_base can be determined singular
195 * or non-singular.
196 **/
197 inline bool
198 __check_singular_aux(const _Safe_iterator_base* __x)
199 { return __x->_M_singular(); }
200
201 /**
202 * @brief Base class that supports tracking of iterators that
203 * reference a sequence.
204 *
205 * The %_Safe_sequence_base class provides basic support for
206 * tracking iterators into a sequence. Sequences that track
207 * iterators must derived from %_Safe_sequence_base publicly, so
208 * that safe iterators (which inherit _Safe_iterator_base) can
209 * attach to them. This class contains two linked lists of
210 * iterators, one for constant iterators and one for mutable
211 * iterators, and a version number that allows very fast
212 * invalidation of all iterators that reference the container.
213 *
214 * This class must ensure that no operation on it may throw an
215 * exception, otherwise @a safe sequences may fail to provide the
216 * exception-safety guarantees required by the C++ standard.
217 */
218 class _Safe_sequence_base
219 {
220 friend class _Safe_iterator_base;
221
222 public:
223 /// The list of mutable iterators that reference this container
224 mutable _Safe_iterator_base* _M_iterators;
225
226 /// The list of constant iterators that reference this container
227 mutable _Safe_iterator_base* _M_const_iterators;
228
229 /// The container version number. This number may never be 0.
230 mutable unsigned int _M_version;
231
232 protected:
233 // Initialize with a version number of 1 and no iterators
234 _GLIBCXX20_CONSTEXPR
235 _Safe_sequence_base() _GLIBCXX_NOEXCEPT
236 : _M_iterators(0), _M_const_iterators(0), _M_version(1)
237 { }
238
239#if __cplusplus >= 201103L
240 _GLIBCXX20_CONSTEXPR
241 _Safe_sequence_base(const _Safe_sequence_base&) noexcept
242 : _Safe_sequence_base() { }
243
244 // Move constructor swap iterators.
245 _GLIBCXX20_CONSTEXPR
246 _Safe_sequence_base(_Safe_sequence_base&& __seq) noexcept
247 : _Safe_sequence_base()
248 {
249 if (!std::__is_constant_evaluated())
250 _M_swap(x&: __seq);
251 }
252#endif
253
254 /** Notify all iterators that reference this sequence that the
255 sequence is being destroyed. */
256 _GLIBCXX20_CONSTEXPR
257 ~_Safe_sequence_base() _GLIBCXX_NOEXCEPT
258 {
259 if (!std::__is_constant_evaluated())
260 this->_M_detach_all();
261 }
262
263 // Copy assignment invalidate all iterators.
264 _GLIBCXX20_CONSTEXPR _Safe_sequence_base&
265 operator=(const _Safe_sequence_base&) _GLIBCXX_NOEXCEPT
266 {
267 _M_invalidate_all();
268 return *this;
269 }
270
271#if __cplusplus >= 201103L
272 _GLIBCXX20_CONSTEXPR _Safe_sequence_base&
273 operator=(_Safe_sequence_base&& __x) noexcept
274 {
275 _M_invalidate_all();
276 __x._M_invalidate_all();
277 return *this;
278 }
279#endif
280
281 /** Detach all iterators, leaving them singular. */
282 void
283 _M_detach_all() const;
284
285 /** Detach all singular iterators.
286 * @post for all iterators i attached to this sequence,
287 * i->_M_version == _M_version.
288 */
289 void
290 _M_detach_singular() const;
291
292 /** Revalidates all attached singular iterators. This method may
293 * be used to validate iterators that were invalidated before
294 * (but for some reason, such as an exception, need to become
295 * valid again).
296 */
297 void
298 _M_revalidate_singular() const;
299
300 /** Swap this sequence with the given sequence. This operation
301 * also swaps ownership of the iterators, so that when the
302 * operation is complete all iterators that originally referenced
303 * one container now reference the other container.
304 */
305 void
306 _M_swap(const _Safe_sequence_base& __x) const _GLIBCXX_USE_NOEXCEPT;
307
308 /** For use in _Safe_sequence. */
309 __gnu_cxx::__mutex&
310 _M_get_mutex() const _GLIBCXX_USE_NOEXCEPT;
311
312 /** Invalidates all iterators. */
313 _GLIBCXX20_CONSTEXPR void
314 _M_invalidate_all() const
315 { if (++_M_version == 0) _M_version = 1; }
316
317 private:
318#if !_GLIBCXX_INLINE_VERSION
319 /***************************************************************/
320 /** Not-const method preserved for abi backward compatibility. */
321 void
322 _M_detach_all();
323
324 void
325 _M_detach_singular();
326
327 void
328 _M_revalidate_singular();
329
330 void
331 _M_swap(_Safe_sequence_base& __x) _GLIBCXX_USE_NOEXCEPT;
332
333 __gnu_cxx::__mutex&
334 _M_get_mutex() _GLIBCXX_USE_NOEXCEPT;
335 /***************************************************************/
336#endif
337
338 /** Attach an iterator to this sequence. */
339 void
340 _M_attach(_Safe_iterator_base* __it, bool __constant) const;
341
342 /** Likewise but not thread safe. */
343 void
344 _M_attach_single(_Safe_iterator_base* __it,
345 bool __constant) const _GLIBCXX_USE_NOEXCEPT;
346
347 /** Detach an iterator from this sequence */
348 void
349 _M_detach(_Safe_iterator_base* __it) const;
350
351 /** Likewise but not thread safe. */
352 void
353 _M_detach_single(_Safe_iterator_base* __it) const _GLIBCXX_USE_NOEXCEPT;
354 };
355} // namespace __gnu_debug
356
357#endif
358