libstdc++-v3/include/debug/safe_base.h

   1 // Safe sequence/iterator base implementation  -*- C++ -*-
   2
   3 // Copyright (C) 2003-2024 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     _GLIBCXX20_CONSTEXPR
  79     _Safe_iterator_base()
  80     : _M_sequence(0), _M_version(0), _M_prior(0), _M_next(0)
  81     { }
  82
  83     /** Initialize the iterator to reference the sequence pointed to
  84      *  by @p __seq. @p __constant is true when we are initializing a
  85      *  constant iterator, and false if it is a mutable iterator. Note
  86      *  that @p __seq may be NULL, in which case the iterator will be
  87      *  singular. Otherwise, the iterator will reference @p __seq and
  88      *  be nonsingular.
  89      */
  90     _GLIBCXX20_CONSTEXPR
  91     _Safe_iterator_base(const _Safe_sequence_base* __seq, bool __constant)
  92     : _M_sequence(0), _M_version(0), _M_prior(0), _M_next(0)
  93     {
  94       if (!std::__is_constant_evaluated())
  95         this->_M_attach(const_cast<_Safe_sequence_base*>(__seq), __constant);
  96     }
  97
  98     /** Initializes the iterator to reference the same sequence that
  99         @p __x does. @p __constant is true if this is a constant
 100         iterator, and false if it is mutable. */
 101     _GLIBCXX20_CONSTEXPR
 102     _Safe_iterator_base(const _Safe_iterator_base& __x, bool __constant)
 103     : _M_sequence(0), _M_version(0), _M_prior(0), _M_next(0)
 104     {
 105       if (!std::__is_constant_evaluated())
 106         this->_M_attach(__x._M_sequence, __constant);
 107     }
 108
 109     _GLIBCXX20_CONSTEXPR
 110     ~_Safe_iterator_base()
 111     {
 112       if (!std::__is_constant_evaluated())
 113         this->_M_detach();
 114     }
 115
 116     /** For use in _Safe_iterator. */
 117     __gnu_cxx::__mutex&
 118     _M_get_mutex() throw ();
 119
 120     /** Attaches this iterator to the given sequence, detaching it
 121      *  from whatever sequence it was attached to originally. If the
 122      *  new sequence is the NULL pointer, the iterator is left
 123      *  unattached.
 124      */
 125     void
 126     _M_attach(_Safe_sequence_base* __seq, bool __constant);
 127
 128     /** Likewise, but not thread-safe. */
 129     void
 130     _M_attach_single(_Safe_sequence_base* __seq, bool __constant) throw ();
 131
 132     /** Detach the iterator for whatever sequence it is attached to,
 133      *  if any.
 134     */
 135     void
 136     _M_detach();
 137
 138   public:
 139     /** Likewise, but not thread-safe. */
 140     void
 141     _M_detach_single() throw ();
 142
 143     /** Determines if we are attached to the given sequence. */
 144     bool
 145     _M_attached_to(const _Safe_sequence_base* __seq) const
 146     { return _M_sequence == __seq; }
 147
 148     /** Is this iterator singular? */
 149     _GLIBCXX_PURE bool
 150     _M_singular() const throw ();
 151
 152     /** Can we compare this iterator to the given iterator @p __x?
 153         Returns true if both iterators are nonsingular and reference
 154         the same sequence. */
 155     _GLIBCXX_PURE bool
 156     _M_can_compare(const _Safe_iterator_base& __x) const throw ();
 157
 158     /** Invalidate the iterator, making it singular. */
 159     void
 160     _M_invalidate()
 161     { _M_version = 0; }
 162
 163     /** Reset all member variables */
 164     void
 165     _M_reset() throw ();
 166
 167     /** Unlink itself */
 168     void
 169     _M_unlink() throw ()
 170     {
 171       if (_M_prior)
 172         _M_prior->_M_next = _M_next;
 173       if (_M_next)
 174         _M_next->_M_prior = _M_prior;
 175     }
 176   };
 177
 178   /** Iterators that derive from _Safe_iterator_base can be determined singular
 179    *  or non-singular.
 180    **/
 181   inline bool
 182   __check_singular_aux(const _Safe_iterator_base* __x)
 183   { return __x->_M_singular(); }
 184
 185   /**
 186    * @brief Base class that supports tracking of iterators that
 187    * reference a sequence.
 188    *
 189    * The %_Safe_sequence_base class provides basic support for
 190    * tracking iterators into a sequence. Sequences that track
 191    * iterators must derived from %_Safe_sequence_base publicly, so
 192    * that safe iterators (which inherit _Safe_iterator_base) can
 193    * attach to them. This class contains two linked lists of
 194    * iterators, one for constant iterators and one for mutable
 195    * iterators, and a version number that allows very fast
 196    * invalidation of all iterators that reference the container.
 197    *
 198    * This class must ensure that no operation on it may throw an
 199    * exception, otherwise @a safe sequences may fail to provide the
 200    * exception-safety guarantees required by the C++ standard.
 201    */
 202   class _Safe_sequence_base
 203   {
 204     friend class _Safe_iterator_base;
 205
 206   public:
 207     /// The list of mutable iterators that reference this container
 208     _Safe_iterator_base* _M_iterators;
 209
 210     /// The list of constant iterators that reference this container
 211     _Safe_iterator_base* _M_const_iterators;
 212
 213     /// The container version number. This number may never be 0.
 214     mutable unsigned int _M_version;
 215
 216   protected:
 217     // Initialize with a version number of 1 and no iterators
 218     _GLIBCXX20_CONSTEXPR
 219     _Safe_sequence_base() _GLIBCXX_NOEXCEPT
 220     : _M_iterators(0), _M_const_iterators(0), _M_version(1)
 221     { }
 222
 223 #if __cplusplus >= 201103L
 224     _GLIBCXX20_CONSTEXPR
 225     _Safe_sequence_base(const _Safe_sequence_base&) noexcept
 226     : _Safe_sequence_base() { }
 227
 228     // Move constructor swap iterators.
 229     _GLIBCXX20_CONSTEXPR
 230     _Safe_sequence_base(_Safe_sequence_base&& __seq) noexcept
 231     : _Safe_sequence_base()
 232     {
 233       if (!std::__is_constant_evaluated())
 234         _M_swap(__seq);
 235     }
 236 #endif
 237
 238     /** Notify all iterators that reference this sequence that the
 239         sequence is being destroyed. */
 240     _GLIBCXX20_CONSTEXPR
 241     ~_Safe_sequence_base()
 242     {
 243       if (!std::__is_constant_evaluated())
 244         this->_M_detach_all();
 245     }
 246
 247     /** Detach all iterators, leaving them singular. */
 248     void
 249     _M_detach_all();
 250
 251     /** Detach all singular iterators.
 252      *  @post for all iterators i attached to this sequence,
 253      *   i->_M_version == _M_version.
 254      */
 255     void
 256     _M_detach_singular();
 257
 258     /** Revalidates all attached singular iterators.  This method may
 259      *  be used to validate iterators that were invalidated before
 260      *  (but for some reason, such as an exception, need to become
 261      *  valid again).
 262      */
 263     void
 264     _M_revalidate_singular();
 265
 266     /** Swap this sequence with the given sequence. This operation
 267      *  also swaps ownership of the iterators, so that when the
 268      *  operation is complete all iterators that originally referenced
 269      *  one container now reference the other container.
 270      */
 271     void
 272     _M_swap(_Safe_sequence_base& __x) _GLIBCXX_USE_NOEXCEPT;
 273
 274     /** For use in _Safe_sequence. */
 275     __gnu_cxx::__mutex&
 276     _M_get_mutex() throw ();
 277
 278     /** Invalidates all iterators. */
 279     void
 280     _M_invalidate_all() const
 281     { if (++_M_version == 0) _M_version = 1; }
 282
 283   private:
 284     /** Attach an iterator to this sequence. */
 285     void
 286     _M_attach(_Safe_iterator_base* __it, bool __constant);
 287
 288     /** Likewise but not thread safe. */
 289     void
 290     _M_attach_single(_Safe_iterator_base* __it, bool __constant) throw ();
 291
 292     /** Detach an iterator from this sequence */
 293     void
 294     _M_detach(_Safe_iterator_base* __it);
 295
 296     /** Likewise but not thread safe. */
 297     void
 298     _M_detach_single(_Safe_iterator_base* __it) throw ();
 299   };
 300 } // namespace __gnu_debug
 301
 302 #endif