safe_local_iterator.h

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// Safe iterator implementation  -*- C++ -*-

// Copyright (C) 2011-2026 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.

/** @file debug/safe_local_iterator.h
 *  This file is a GNU debug extension to the Standard C++ Library.
 */

#ifndef _GLIBCXX_DEBUG_SAFE_LOCAL_ITERATOR_H
#define _GLIBCXX_DEBUG_SAFE_LOCAL_ITERATOR_H 1

#include <debug/safe_unordered_base.h>

#define _GLIBCXX_DEBUG_VERIFY_OPERANDS(_Lhs, _Rhs) \
  _GLIBCXX_DEBUG_VERIFY((!_Lhs._M_singular() && !_Rhs._M_singular())    \
                        || (_Lhs._M_value_initialized()                 \
                            && _Rhs._M_value_initialized()),            \
                        _M_message(__msg_iter_compare_bad)              \
                        ._M_iterator(_Lhs, "lhs")                       \
                        ._M_iterator(_Rhs, "rhs"));                     \
  _GLIBCXX_DEBUG_VERIFY(_Lhs._M_can_compare(_Rhs),                      \
                        _M_message(__msg_compare_different)             \
                        ._M_iterator(_Lhs, "lhs")                       \
                        ._M_iterator(_Rhs, "rhs"));                     \
  _GLIBCXX_DEBUG_VERIFY(_Lhs._M_in_same_bucket(_Rhs),                   \
                        _M_message(__msg_local_iter_compare_bad)        \
                        ._M_iterator(_Lhs, "lhs")                       \
                        ._M_iterator(_Rhs, "rhs"))

namespace __gnu_debug
{
  /** \brief Safe iterator wrapper.
   *
   *  The class template %_Safe_local_iterator is a wrapper around an
   *  iterator that tracks the iterator's movement among unordered containers
   *  and checks that operations performed on the "safe" iterator are
   *  legal. In additional to the basic iterator operations (which are
   *  validated, and then passed to the underlying iterator),
   *  %_Safe_local_iterator has member functions for iterator invalidation,
   *  attaching/detaching the iterator from unordered containers, and querying
   *  the iterator's state.
   */
  template<typename _Iterator, typename _UContainer>
    class _Safe_local_iterator
    : private _Iterator
    , public _Safe_local_iterator_base
    {
      typedef _Iterator _Iter_base;
      typedef _Safe_local_iterator_base _Safe_base;

      typedef typename _UContainer::size_type size_type;

      typedef std::iterator_traits<_Iterator> _Traits;

      using _IsConstant = std::__are_same<
        typename _UContainer::_Base::const_local_iterator, _Iterator>;

      using _OtherIterator = std::__conditional_t<
        _IsConstant::__value,
        typename _UContainer::_Base::local_iterator,
        typename _UContainer::_Base::const_local_iterator>;

      typedef _Safe_local_iterator _Self;
      typedef _Safe_local_iterator<_OtherIterator, _UContainer> _OtherSelf;

      struct _Unchecked { };

      _Safe_local_iterator(const _Safe_local_iterator& __x,
                           _Unchecked) noexcept
      : _Iter_base(__x.base())
      { _M_attach(__x._M_safe_container()); }

    public:
      typedef _Iterator                                 iterator_type;
      typedef typename _Traits::iterator_category       iterator_category;
      typedef typename _Traits::value_type              value_type;
      typedef typename _Traits::difference_type         difference_type;
      typedef typename _Traits::reference               reference;
      typedef typename _Traits::pointer                 pointer;

      /// @post the iterator is singular and unattached
      _Safe_local_iterator() noexcept : _Iter_base() { }

      /**
       * @brief Safe iterator construction from an unsafe iterator and
       * its unordered container.
       *
       * @pre @p cont is not NULL
       * @post this is not singular
       */
      _Safe_local_iterator(_Iterator __i,
                           const _Safe_unordered_container_base* __cont)
      : _Iter_base(__i), _Safe_base(__cont, _S_constant())
      { }

      /**
       * @brief Copy construction.
       */
      _Safe_local_iterator(const _Safe_local_iterator& __x) noexcept
      : _Iter_base(__x.base())
      {
        // _GLIBCXX_RESOLVE_LIB_DEFECTS
        // DR 408. Is vector<reverse_iterator<char*> > forbidden?
        _GLIBCXX_DEBUG_VERIFY(!__x._M_singular()
                              || __x._M_value_initialized(),
                              _M_message(__msg_init_copy_singular)
                              ._M_iterator(*this, "this")
                              ._M_iterator(__x, "other"));
        _M_attach(__x._M_safe_container());
      }

      /**
       * @brief Move construction.
       * @post __x is singular and unattached
       */
      _Safe_local_iterator(_Safe_local_iterator&& __x) noexcept
      : _Iter_base()
      {
        _GLIBCXX_DEBUG_VERIFY(!__x._M_singular()
                              || __x._M_value_initialized(),
                              _M_message(__msg_init_copy_singular)
                              ._M_iterator(*this, "this")
                              ._M_iterator(__x, "other"));
        auto __cont = __x._M_safe_container();
        __x._M_detach();
        std::swap(base(), __x.base());
        _M_attach(__cont);
      }

      /**
       *  @brief Converting constructor from a mutable iterator to a
       *  constant iterator.
      */
      template<typename _MutableIterator>
        _Safe_local_iterator(
          const _Safe_local_iterator<_MutableIterator,
          typename __gnu_cxx::__enable_if<_IsConstant::__value &&
            std::__are_same<_MutableIterator, _OtherIterator>::__value,
                                          _UContainer>::__type>& __x) noexcept
        : _Iter_base(__x.base())
        {
          // _GLIBCXX_RESOLVE_LIB_DEFECTS
          // DR 408. Is vector<reverse_iterator<char*> > forbidden?
          _GLIBCXX_DEBUG_VERIFY(!__x._M_singular()
                                || __x._M_value_initialized(),
                                _M_message(__msg_init_const_singular)
                                ._M_iterator(*this, "this")
                                ._M_iterator(__x, "other"));
          _M_attach(__x._M_safe_container());
        }

      /**
       * @brief Copy assignment.
       */
      _Safe_local_iterator&
      operator=(const _Safe_local_iterator& __x)
      {
        // _GLIBCXX_RESOLVE_LIB_DEFECTS
        // DR 408. Is vector<reverse_iterator<char*> > forbidden?
        _GLIBCXX_DEBUG_VERIFY(!__x._M_singular()
                              || __x._M_value_initialized(),
                              _M_message(__msg_copy_singular)
                              ._M_iterator(*this, "this")
                              ._M_iterator(__x, "other"));

        if (this->_M_sequence && this->_M_sequence == __x._M_sequence)
          {
            __gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
            base() = __x.base();
            _M_version = __x._M_sequence->_M_version;
          }
        else
          {
            _M_detach();
            base() = __x.base();
            _M_attach(__x._M_safe_container());
          }

        return *this;
      }

      /**
       * @brief Move assignment.
       * @post __x is singular and unattached
       */
      _Safe_local_iterator&
      operator=(_Safe_local_iterator&& __x) noexcept
      {
        _GLIBCXX_DEBUG_VERIFY(!__x._M_singular()
                              || __x._M_value_initialized(),
                              _M_message(__msg_copy_singular)
                              ._M_iterator(*this, "this")
                              ._M_iterator(__x, "other"));

        if (std::__addressof(__x) == this)
          return *this;

        if (this->_M_sequence && this->_M_sequence == __x._M_sequence)
          {
            __gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
            base() = __x.base();
            _M_version = __x._M_sequence->_M_version;
          }
        else
          {
            _M_detach();
            base() = __x.base();
            _M_attach(__x._M_safe_container());
          }

        __x._M_detach();
        __x.base() = _Iterator();
        return *this;
      }

      /**
       *  @brief Iterator dereference.
       *  @pre iterator is dereferenceable
       */
      reference
      operator*() const
      {
        _GLIBCXX_DEBUG_VERIFY(this->_M_dereferenceable(),
                              _M_message(__msg_bad_deref)
                              ._M_iterator(*this, "this"));
        return *base();
      }

      /**
       *  @brief Iterator dereference.
       *  @pre iterator is dereferenceable
       */
      pointer
      operator->() const
      {
        _GLIBCXX_DEBUG_VERIFY(this->_M_dereferenceable(),
                              _M_message(__msg_bad_deref)
                              ._M_iterator(*this, "this"));
        return base().operator->();
      }

      // ------ Input iterator requirements ------
      /**
       *  @brief Iterator preincrement
       *  @pre iterator is incrementable
       */
      _Safe_local_iterator&
      operator++()
      {
        _GLIBCXX_DEBUG_VERIFY(this->_M_incrementable(),
                              _M_message(__msg_bad_inc)
                              ._M_iterator(*this, "this"));
        __gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
        ++base();
        return *this;
      }

      /**
       *  @brief Iterator postincrement
       *  @pre iterator is incrementable
       */
      _Safe_local_iterator
      operator++(int)
      {
        _GLIBCXX_DEBUG_VERIFY(this->_M_incrementable(),
                              _M_message(__msg_bad_inc)
                              ._M_iterator(*this, "this"));
        _Safe_local_iterator __ret(*this, _Unchecked{});
        ++*this;
        return __ret;
      }

      // ------ Utilities ------

      /// Determine if this is a constant iterator.
      static constexpr bool
      _S_constant()
      { return _IsConstant::__value; }

      /**
       * @brief Return the underlying iterator
       */
      _Iterator&
      base() noexcept { return *this; }

      const _Iterator&
      base() const noexcept { return *this; }

      /**
       * @brief Return the bucket
       */
      size_type
      bucket() const { return base()._M_get_bucket(); }

      /**
       * @brief Conversion to underlying non-debug iterator to allow
       * better interaction with non-debug containers.
       */
      operator _Iterator() const { return *this; }

      /** Attach iterator to the given unordered container. */
      void
      _M_attach(const _Safe_unordered_container_base* __cont)
      { _Safe_base::_M_attach(__cont, _S_constant()); }

      /** Likewise, but not thread-safe. */
      void
      _M_attach_single(const _Safe_unordered_container_base* __cont)
      { _Safe_base::_M_attach_single(__cont, _S_constant()); }

      /// Is the iterator dereferenceable?
      bool
      _M_dereferenceable() const
      { return !this->_M_singular() && !_M_is_end(); }

      /// Is the iterator incrementable?
      bool
      _M_incrementable() const
      { return !this->_M_singular() && !_M_is_end(); }

      /// Is the iterator value-initialized?
      bool
      _M_value_initialized() const
      { return _M_version == 0 && base() == _Iter_base{}; }

      // Is the iterator range [*this, __rhs) valid?
      bool
      _M_valid_range(const _Safe_local_iterator& __rhs,
                     std::pair<difference_type,
                               _Distance_precision>& __dist_info) const;

      // Get distance to __rhs.
      typename _Distance_traits<_Iterator>::__type
      _M_get_distance_to(const _Safe_local_iterator& __rhs) const;

      // The unordered container this iterator references.
      std::__conditional_t<
        _IsConstant::__value, const _UContainer*, _UContainer*>
      _M_get_ucontainer() const
      {
        // Looks like not const-correct, but if _IsConstant the constness
        // is restored when returning the container pointer and if not
        // _IsConstant we are allowed to remove constness.
        return static_cast<_UContainer*>
          (const_cast<_Safe_unordered_container_base*>(_M_safe_container()));
      }

      /// Is this iterator equal to the container's begin(bucket) iterator?
      bool _M_is_begin() const
      { return base() == _M_get_ucontainer()->_M_base().begin(bucket()); }

      /// Is this iterator equal to the container's end(bucket) iterator?
      bool _M_is_end() const
      { return base() == _M_get_ucontainer()->_M_base().end(bucket()); }

      /// Is this iterator part of the same bucket as the other one?
      template<typename _Other>
        bool
        _M_in_same_bucket(const _Safe_local_iterator<_Other,
                                                     _UContainer>& __other) const
        { return bucket() == __other.bucket(); }

      friend inline bool
      operator==(const _Self& __lhs, const _OtherSelf& __rhs) noexcept
      {
        _GLIBCXX_DEBUG_VERIFY_OPERANDS(__lhs, __rhs);
        return __lhs.base() == __rhs.base();
      }

      friend inline bool
      operator==(const _Self& __lhs, const _Self& __rhs) noexcept
      {
        _GLIBCXX_DEBUG_VERIFY_OPERANDS(__lhs, __rhs);
        return __lhs.base() == __rhs.base();
      }

      friend inline bool
      operator!=(const _Self& __lhs, const _OtherSelf& __rhs) noexcept
      {
        _GLIBCXX_DEBUG_VERIFY_OPERANDS(__lhs, __rhs);
        return __lhs.base() != __rhs.base();
      }

      friend inline bool
      operator!=(const _Self& __lhs, const _Self& __rhs) noexcept
      {
        _GLIBCXX_DEBUG_VERIFY_OPERANDS(__lhs, __rhs);
        return __lhs.base() != __rhs.base();
      }
    };

  /** Safe local iterators know how to check if they form a valid range. */
  template<typename _Iterator, typename _UContainer>
    inline bool
    __valid_range(const _Safe_local_iterator<_Iterator, _UContainer>& __first,
                  const _Safe_local_iterator<_Iterator, _UContainer>& __last,
                  typename _Distance_traits<_Iterator>::__type& __dist_info)
    { return __first._M_valid_range(__last, __dist_info); }

  template<typename _Iterator, typename _UContainer>
    inline bool
    __valid_range(const _Safe_local_iterator<_Iterator, _UContainer>& __first,
                  const _Safe_local_iterator<_Iterator, _UContainer>& __last)
    {
      typename _Distance_traits<_Iterator>::__type __dist_info;
      return __first._M_valid_range(__last, __dist_info);
    }

#if __cplusplus < 201103L
  template<typename _Iterator, typename _UContainer>
    struct _Unsafe_type<_Safe_local_iterator<_Iterator, _UContainer> >
    { typedef _Iterator _Type; };
#endif

  template<typename _Iterator, typename _UContainer>
    inline _Iterator
    __unsafe(const _Safe_local_iterator<_Iterator, _UContainer>& __it)
    { return __it.base(); }

} // namespace __gnu_debug

#undef _GLIBCXX_DEBUG_VERIFY_OPERANDS

#include <debug/safe_local_iterator.tcc>

#endif