libstdc++
safe_base.h
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00001 // Safe sequence/iterator base implementation  -*- C++ -*-
00002 
00003 // Copyright (C) 2003-2015 Free Software Foundation, Inc.
00004 //
00005 // This file is part of the GNU ISO C++ Library.  This library is free
00006 // software; you can redistribute it and/or modify it under the
00007 // terms of the GNU General Public License as published by the
00008 // Free Software Foundation; either version 3, or (at your option)
00009 // any later version.
00010 
00011 // This library is distributed in the hope that it will be useful,
00012 // but WITHOUT ANY WARRANTY; without even the implied warranty of
00013 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00014 // GNU General Public License for more details.
00015 
00016 // Under Section 7 of GPL version 3, you are granted additional
00017 // permissions described in the GCC Runtime Library Exception, version
00018 // 3.1, as published by the Free Software Foundation.
00019 
00020 // You should have received a copy of the GNU General Public License and
00021 // a copy of the GCC Runtime Library Exception along with this program;
00022 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
00023 // <http://www.gnu.org/licenses/>.
00024 
00025 /** @file debug/safe_base.h
00026  *  This file is a GNU debug extension to the Standard C++ Library.
00027  */
00028 
00029 #ifndef _GLIBCXX_DEBUG_SAFE_BASE_H
00030 #define _GLIBCXX_DEBUG_SAFE_BASE_H 1
00031 
00032 #include <ext/concurrence.h>
00033 
00034 namespace __gnu_debug
00035 {
00036   class _Safe_sequence_base;
00037 
00038   /** \brief Basic functionality for a @a safe iterator.
00039    *
00040    *  The %_Safe_iterator_base base class implements the functionality
00041    *  of a safe iterator that is not specific to a particular iterator
00042    *  type. It contains a pointer back to the sequence it references
00043    *  along with iterator version information and pointers to form a
00044    *  doubly-linked list of iterators referenced by the container.
00045    *
00046    *  This class must not perform any operations that can throw an
00047    *  exception, or the exception guarantees of derived iterators will
00048    *  be broken.
00049    */
00050   class _Safe_iterator_base
00051   {
00052   public:
00053     /** The sequence this iterator references; may be NULL to indicate
00054         a singular iterator. */
00055     _Safe_sequence_base*        _M_sequence;
00056 
00057     /** The version number of this iterator. The sentinel value 0 is
00058      *  used to indicate an invalidated iterator (i.e., one that is
00059      *  singular because of an operation on the container). This
00060      *  version number must equal the version number in the sequence
00061      *  referenced by _M_sequence for the iterator to be
00062      *  non-singular.
00063      */
00064     unsigned int                _M_version;
00065 
00066     /** Pointer to the previous iterator in the sequence's list of
00067         iterators. Only valid when _M_sequence != NULL. */
00068     _Safe_iterator_base*        _M_prior;
00069 
00070     /** Pointer to the next iterator in the sequence's list of
00071         iterators. Only valid when _M_sequence != NULL. */
00072     _Safe_iterator_base*        _M_next;
00073 
00074   protected:
00075     /** Initializes the iterator and makes it singular. */
00076     _Safe_iterator_base()
00077     : _M_sequence(0), _M_version(0), _M_prior(0), _M_next(0)
00078     { }
00079 
00080     /** Initialize the iterator to reference the sequence pointed to
00081      *  by @p __seq. @p __constant is true when we are initializing a
00082      *  constant iterator, and false if it is a mutable iterator. Note
00083      *  that @p __seq may be NULL, in which case the iterator will be
00084      *  singular. Otherwise, the iterator will reference @p __seq and
00085      *  be nonsingular.
00086      */
00087     _Safe_iterator_base(const _Safe_sequence_base* __seq, bool __constant)
00088     : _M_sequence(0), _M_version(0), _M_prior(0), _M_next(0)
00089     { this->_M_attach(const_cast<_Safe_sequence_base*>(__seq), __constant); }
00090 
00091     /** Initializes the iterator to reference the same sequence that
00092         @p __x does. @p __constant is true if this is a constant
00093         iterator, and false if it is mutable. */
00094     _Safe_iterator_base(const _Safe_iterator_base& __x, bool __constant)
00095     : _M_sequence(0), _M_version(0), _M_prior(0), _M_next(0)
00096     { this->_M_attach(__x._M_sequence, __constant); }
00097 
00098     ~_Safe_iterator_base() { this->_M_detach(); }
00099 
00100     /** For use in _Safe_iterator. */
00101     __gnu_cxx::__mutex&
00102     _M_get_mutex() throw ();
00103 
00104   public:
00105     /** Attaches this iterator to the given sequence, detaching it
00106      *  from whatever sequence it was attached to originally. If the
00107      *  new sequence is the NULL pointer, the iterator is left
00108      *  unattached.
00109      */
00110     void
00111     _M_attach(_Safe_sequence_base* __seq, bool __constant);
00112 
00113     /** Likewise, but not thread-safe. */
00114     void
00115     _M_attach_single(_Safe_sequence_base* __seq, bool __constant) throw ();
00116 
00117     /** Detach the iterator for whatever sequence it is attached to,
00118      *  if any.
00119     */
00120     void
00121     _M_detach();
00122 
00123     /** Likewise, but not thread-safe. */
00124     void
00125     _M_detach_single() throw ();
00126 
00127     /** Determines if we are attached to the given sequence. */
00128     bool
00129     _M_attached_to(const _Safe_sequence_base* __seq) const
00130     { return _M_sequence == __seq; }
00131 
00132     /** Is this iterator singular? */
00133     _GLIBCXX_PURE bool
00134     _M_singular() const throw ();
00135 
00136     /** Can we compare this iterator to the given iterator @p __x?
00137         Returns true if both iterators are nonsingular and reference
00138         the same sequence. */
00139     _GLIBCXX_PURE bool
00140     _M_can_compare(const _Safe_iterator_base& __x) const throw ();
00141 
00142     /** Invalidate the iterator, making it singular. */
00143     void
00144     _M_invalidate()
00145     { _M_version = 0; }
00146 
00147     /** Reset all member variables */
00148     void
00149     _M_reset() throw ();
00150 
00151     /** Unlink itself */
00152     void
00153     _M_unlink() throw ()
00154     {
00155       if (_M_prior)
00156         _M_prior->_M_next = _M_next;
00157       if (_M_next)
00158         _M_next->_M_prior = _M_prior;
00159     }
00160   };
00161 
00162   /**
00163    * @brief Base class that supports tracking of iterators that
00164    * reference a sequence.
00165    *
00166    * The %_Safe_sequence_base class provides basic support for
00167    * tracking iterators into a sequence. Sequences that track
00168    * iterators must derived from %_Safe_sequence_base publicly, so
00169    * that safe iterators (which inherit _Safe_iterator_base) can
00170    * attach to them. This class contains two linked lists of
00171    * iterators, one for constant iterators and one for mutable
00172    * iterators, and a version number that allows very fast
00173    * invalidation of all iterators that reference the container.
00174    *
00175    * This class must ensure that no operation on it may throw an
00176    * exception, otherwise @a safe sequences may fail to provide the
00177    * exception-safety guarantees required by the C++ standard.
00178    */
00179   class _Safe_sequence_base
00180   {
00181   public:
00182     /// The list of mutable iterators that reference this container
00183     _Safe_iterator_base* _M_iterators;
00184 
00185     /// The list of constant iterators that reference this container
00186     _Safe_iterator_base* _M_const_iterators;
00187 
00188     /// The container version number. This number may never be 0.
00189     mutable unsigned int _M_version;
00190 
00191   protected:
00192     // Initialize with a version number of 1 and no iterators
00193     _Safe_sequence_base() _GLIBCXX_NOEXCEPT
00194     : _M_iterators(0), _M_const_iterators(0), _M_version(1)
00195     { }
00196 
00197 #if __cplusplus >= 201103L
00198     _Safe_sequence_base(const _Safe_sequence_base&) noexcept
00199     : _Safe_sequence_base() { }
00200 #endif
00201 
00202     /** Notify all iterators that reference this sequence that the
00203         sequence is being destroyed. */
00204     ~_Safe_sequence_base()
00205     { this->_M_detach_all(); }
00206 
00207     /** Detach all iterators, leaving them singular. */
00208     void
00209     _M_detach_all();
00210 
00211     /** Detach all singular iterators.
00212      *  @post for all iterators i attached to this sequence,
00213      *   i->_M_version == _M_version.
00214      */
00215     void
00216     _M_detach_singular();
00217 
00218     /** Revalidates all attached singular iterators.  This method may
00219      *  be used to validate iterators that were invalidated before
00220      *  (but for some reason, such as an exception, need to become
00221      *  valid again).
00222      */
00223     void
00224     _M_revalidate_singular();
00225 
00226     /** Swap this sequence with the given sequence. This operation
00227      *  also swaps ownership of the iterators, so that when the
00228      *  operation is complete all iterators that originally referenced
00229      *  one container now reference the other container.
00230      */
00231     void
00232     _M_swap(_Safe_sequence_base& __x) _GLIBCXX_USE_NOEXCEPT;
00233 
00234     /** For use in _Safe_sequence. */
00235     __gnu_cxx::__mutex&
00236     _M_get_mutex() throw ();
00237 
00238   public:
00239     /** Invalidates all iterators. */
00240     void
00241     _M_invalidate_all() const
00242     { if (++_M_version == 0) _M_version = 1; }
00243 
00244     /** Attach an iterator to this sequence. */
00245     void
00246     _M_attach(_Safe_iterator_base* __it, bool __constant);
00247 
00248     /** Likewise but not thread safe. */
00249     void
00250     _M_attach_single(_Safe_iterator_base* __it, bool __constant) throw ();
00251 
00252     /** Detach an iterator from this sequence */
00253     void
00254     _M_detach(_Safe_iterator_base* __it);
00255 
00256     /** Likewise but not thread safe. */
00257     void
00258     _M_detach_single(_Safe_iterator_base* __it) throw ();
00259   };
00260 } // namespace __gnu_debug
00261 
00262 #endif