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[c11concurrency-benchmarks.git] / gdax-orderbook-hpp / demo / dependencies / libcds-2.3.2 / cds / intrusive / impl / iterable_list.h
diff --git a/gdax-orderbook-hpp/demo/dependencies/libcds-2.3.2/cds/intrusive/impl/iterable_list.h b/gdax-orderbook-hpp/demo/dependencies/libcds-2.3.2/cds/intrusive/impl/iterable_list.h
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+/*
+    This file is a part of libcds - Concurrent Data Structures library
+
+    (C) Copyright Maxim Khizhinsky (libcds.dev@gmail.com) 2006-2017
+
+    Source code repo: http://github.com/khizmax/libcds/
+    Download: http://sourceforge.net/projects/libcds/files/
+
+    Redistribution and use in source and binary forms, with or without
+    modification, are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright notice, this
+      list of conditions and the following disclaimer.
+
+    * Redistributions in binary form must reproduce the above copyright notice,
+      this list of conditions and the following disclaimer in the documentation
+      and/or other materials provided with the distribution.
+
+    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+    AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+    DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+    FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+    DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+    SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+    OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+    OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+
+#ifndef CDSLIB_INTRUSIVE_IMPL_ITERABLE_LIST_H
+#define CDSLIB_INTRUSIVE_IMPL_ITERABLE_LIST_H
+
+#include <cds/intrusive/details/iterable_list_base.h>
+#include <cds/details/make_const_type.h>
+
+namespace cds { namespace intrusive {
+
+    /// Iterable lock-free ordered single-linked list
+    /** @ingroup cds_intrusive_list
+        \anchor cds_intrusive_IterableList_hp
+
+        This non-blocking list implementation supports thread-safe iterators;
+        searching and removing are lock-free, inserting is non-blocking because it
+        uses a light-weight synchronization based on marked pointers.
+
+        Unlike \p cds::intrusive::MichaelList the iterable list does not require
+        any hook in \p T to be stored in the list.
+
+        Usually, ordered single-linked list is used as a building block for the hash table implementation.
+        Iterable list is suitable for almost append-only hash table because the list doesn't delete
+        its internal node when erasing a key but it is marked them as empty to be reused in the future.
+        However, plenty of empty nodes degrades performance.
+        Separation of internal nodes and user data implies the need for an allocator for internal node
+        so the iterable list is not fully intrusive. Nevertheless, if you need thread-safe iterator,
+        the iterable list is good choice.
+
+        The complexity of searching is <tt>O(N)</tt>.
+
+        Template arguments:
+        - \p GC - Garbage collector used.
+        - \p T - type to be stored in the list.
+        - \p Traits - type traits, default is \p iterable_list::traits. It is possible to declare option-based
+             list with \p cds::intrusive::iterable_list::make_traits metafunction:
+            For example, the following traits-based declaration of \p gc::HP iterable list
+            \code
+            #include <cds/intrusive/iterable_list_hp.h>
+            // Declare item stored in your list
+            struct foo
+            {
+                int nKey;
+                // .... other data
+            };
+
+            // Declare comparator for the item
+            struct my_compare {
+                int operator()( foo const& i1, foo const& i2 ) const
+                {
+                    return i1.nKey - i2.nKey;
+                }
+            };
+
+            // Declare traits
+            struct my_traits: public cds::intrusive::iterable_list::traits
+            {
+                typedef my_compare compare;
+            };
+
+            // Declare list
+            typedef cds::intrusive::IterableList< cds::gc::HP, foo, my_traits > list_type;
+            \endcode
+            is equivalent for the following option-based list
+            \code
+            #include <cds/intrusive/iterable_list_hp.h>
+
+            // foo struct and my_compare are the same
+
+            // Declare option-based list
+            typedef cds::intrusive::IterableList< cds::gc::HP, foo,
+                typename cds::intrusive::iterable_list::make_traits<
+                    cds::intrusive::opt::compare< my_compare >     // item comparator option
+                >::type
+            > option_list_type;
+            \endcode
+
+        \par Usage
+        There are different specializations of this template for each garbage collecting schema.
+        You should select GC you want and include appropriate .h-file:
+        - for \p gc::HP: <tt> <cds/intrusive/iterable_list_hp.h> </tt>
+        - for \p gc::DHP: <tt> <cds/intrusive/iterable_list_dhp.h> </tt>
+    */
+    template <
+        class GC
+        ,typename T
+#ifdef CDS_DOXYGEN_INVOKED
+        ,class Traits = iterable_list::traits
+#else
+        ,class Traits
+#endif
+    >
+    class IterableList
+#ifndef CDS_DOXYGEN_INVOKED
+        : public iterable_list_tag
+#endif
+    {
+    public:
+        typedef T       value_type; ///< type of value stored in the list
+        typedef Traits  traits;     ///< Traits template parameter
+
+        typedef iterable_list::node< value_type > node_type; ///< node type
+
+#   ifdef CDS_DOXYGEN_INVOKED
+        typedef implementation_defined key_comparator  ;    ///< key comparison functor based on opt::compare and opt::less option setter.
+#   else
+        typedef typename opt::details::make_comparator< value_type, traits >::type key_comparator;
+#   endif
+
+        typedef typename traits::disposer  disposer; ///< disposer for \p value_type
+
+        typedef GC  gc;   ///< Garbage collector
+        typedef typename traits::back_off       back_off;       ///< back-off strategy
+        typedef typename traits::item_counter   item_counter;   ///< Item counting policy used
+        typedef typename traits::memory_model   memory_model;   ///< Memory ordering. See \p cds::opt::memory_model option
+        typedef typename traits::node_allocator node_allocator; ///< Node allocator
+        typedef typename traits::stat           stat;           ///< Internal statistics
+
+        typedef typename gc::template guarded_ptr< value_type > guarded_ptr; ///< Guarded pointer
+
+        static constexpr const size_t c_nHazardPtrCount = 4; ///< Count of hazard pointer required for the algorithm
+
+        //@cond
+        // Rebind traits (split-list support)
+        template <typename... Options>
+        struct rebind_traits {
+            typedef IterableList<
+                gc
+                , value_type
+                , typename cds::opt::make_options< traits, Options...>::type
+            > type;
+        };
+
+        // Stat selector
+        template <typename Stat>
+        using select_stat_wrapper = iterable_list::select_stat_wrapper< Stat >;
+        //@endcond
+
+    protected:
+        //@cond
+        typedef atomics::atomic< node_type* > atomic_node_ptr;  ///< Atomic node pointer
+        typedef atomic_node_ptr               auxiliary_head;   ///< Auxiliary head type (for split-list support)
+        typedef typename node_type::marked_data_ptr marked_data_ptr;
+
+        node_type       m_Head;
+        node_type       m_Tail;
+
+        item_counter    m_ItemCounter;  ///< Item counter
+        mutable stat    m_Stat;         ///< Internal statistics
+
+        typedef cds::details::Allocator< node_type, node_allocator > cxx_node_allocator;
+
+        /// Position pointer for item search
+        struct position {
+            node_type const*  pHead;
+            node_type *       pPrev;  ///< Previous node
+            node_type *       pCur;   ///< Current node
+
+            value_type *      pFound;       ///< Value of \p pCur->data, valid only if data found
+
+            typename gc::Guard guard;       ///< guard for \p pFound
+        };
+
+        struct insert_position: public position
+        {
+            value_type *        pPrevVal;     ///< Value of \p pPrev->data, can be \p nullptr
+            typename gc::Guard  prevGuard;   ///< guard for \p pPrevVal
+        };
+        //@endcond
+
+    protected:
+        //@cond
+        template <bool IsConst>
+        class iterator_type
+        {
+            friend class IterableList;
+
+        protected:
+            node_type*    m_pNode;
+            typename gc::Guard  m_Guard; // data guard
+
+            void next()
+            {
+                for ( node_type* p = m_pNode->next.load( memory_model::memory_order_relaxed ); p != m_pNode; p = p->next.load( memory_model::memory_order_relaxed ))
+                {
+                    m_pNode = p;
+                    if ( m_Guard.protect( p->data, []( marked_data_ptr ptr ) { return ptr.ptr(); }).ptr())
+                        return;
+                }
+                m_Guard.clear();
+            }
+
+            explicit iterator_type( node_type* pNode )
+                : m_pNode( pNode )
+            {
+                if ( !m_Guard.protect( pNode->data, []( marked_data_ptr p ) { return p.ptr(); }).ptr())
+                    next();
+            }
+
+            iterator_type( node_type* pNode, value_type* pVal )
+                : m_pNode( pNode )
+            {
+                if ( m_pNode ) {
+                    assert( pVal != nullptr );
+                    m_Guard.assign( pVal );
+                }
+            }
+
+            value_type* data() const
+            {
+                return m_Guard.template get<value_type>();
+            }
+
+        public:
+            typedef typename cds::details::make_const_type<value_type, IsConst>::pointer   value_ptr;
+            typedef typename cds::details::make_const_type<value_type, IsConst>::reference value_ref;
+
+            iterator_type()
+                : m_pNode( nullptr )
+            {}
+
+            iterator_type( iterator_type const& src )
+                : m_pNode( src.m_pNode )
+            {
+                m_Guard.copy( src.m_Guard );
+            }
+
+            value_ptr operator ->() const
+            {
+                return data();
+                //return m_Guard.template get<value_type>();
+            }
+
+            value_ref operator *() const
+            {
+                assert( m_Guard.get_native() != nullptr );
+                return *data();
+                //return *m_Guard.template get<value_type>();
+            }
+
+            /// Pre-increment
+            iterator_type& operator ++()
+            {
+                next();
+                return *this;
+            }
+
+            iterator_type& operator = (iterator_type const& src)
+            {
+                m_pNode = src.m_pNode;
+                m_Guard.copy( src.m_Guard );
+                return *this;
+            }
+
+            template <bool C>
+            bool operator ==(iterator_type<C> const& i ) const
+            {
+                return m_pNode == i.m_pNode;
+            }
+            template <bool C>
+            bool operator !=(iterator_type<C> const& i ) const
+            {
+                return !( *this == i );
+            }
+        };
+        //@endcond
+
+    public:
+    ///@name Thread-safe forward iterators
+    //@{
+        /// Forward iterator
+        /**
+            The forward iterator for iterable list has some features:
+            - it has no post-increment operator
+            - to protect the value, the iterator contains a GC-specific guard.
+              For some GC (like as \p gc::HP), a guard is a limited resource per thread, so an exception (or assertion) "no free guard"
+              may be thrown if the limit of guard count per thread is exceeded.
+            - The iterator cannot be moved across thread boundary since it contains thread-private GC's guard.
+            - Iterator is thread-safe: even if the element the iterator points to is removed, the iterator stays valid because
+              it contains the guard keeping the value from to be recycled.
+
+            The iterator interface:
+            \code
+            class iterator {
+            public:
+                // Default constructor
+                iterator();
+
+                // Copy construtor
+                iterator( iterator const& src );
+
+                // Dereference operator
+                value_type * operator ->() const;
+
+                // Dereference operator
+                value_type& operator *() const;
+
+                // Preincrement operator
+                iterator& operator ++();
+
+                // Assignment operator
+                iterator& operator = (iterator const& src);
+
+                // Equality operators
+                bool operator ==(iterator const& i ) const;
+                bool operator !=(iterator const& i ) const;
+            };
+            \endcode
+
+            @note For two iterators pointed to the same element the value can be different;
+            this code
+            \code
+                if ( it1 == it2 )
+                    assert( &(*it1) == &(*it2));
+            \endcode
+            can throw assertion. The point is that the iterator stores the value of element which can be modified later by other thread.
+            The guard inside the iterator prevents recycling that value so the iterator's value remains valid even after changing.
+            Other iterator may observe modified value of the element.
+        */
+        typedef iterator_type<false>    iterator;
+        /// Const forward iterator
+        /**
+            For iterator's features and requirements see \ref iterator
+        */
+        typedef iterator_type<true>     const_iterator;
+
+        /// Returns a forward iterator addressing the first element in a list
+        /**
+            For empty list \code begin() == end() \endcode
+        */
+        iterator begin()
+        {
+            return iterator( &m_Head );
+        }
+
+        /// Returns an iterator that addresses the location succeeding the last element in a list
+        /**
+            Do not use the value returned by <tt>end</tt> function to access any item.
+            Internally, <tt>end</tt> returning value equals to \p nullptr.
+
+            The returned value can be used only to control reaching the end of the list.
+            For empty list <tt>begin() == end()</tt>
+        */
+        iterator end()
+        {
+            return iterator( &m_Tail );
+        }
+
+        /// Returns a forward const iterator addressing the first element in a list
+        const_iterator cbegin() const
+        {
+            return const_iterator( const_cast<node_type*>( &m_Head ));
+        }
+
+        /// Returns a forward const iterator addressing the first element in a list
+        const_iterator begin() const
+        {
+            return const_iterator( const_cast<node_type*>( &m_Head ));
+        }
+
+        /// Returns an const iterator that addresses the location succeeding the last element in a list
+        const_iterator end() const
+        {
+            return const_iterator( const_cast<node_type*>( &m_Tail ));
+        }
+
+        /// Returns an const iterator that addresses the location succeeding the last element in a list
+        const_iterator cend() const
+        {
+            return const_iterator( const_cast<node_type*>( &m_Tail ));
+        }
+    //@}
+
+    public:
+        /// Default constructor initializes empty list
+        IterableList()
+        {
+            init_list();
+        }
+
+        //@cond
+        template <typename Stat, typename = std::enable_if<std::is_same<stat, iterable_list::wrapped_stat<Stat>>::value >>
+        explicit IterableList( Stat& st )
+            : m_Stat( st )
+        {
+            init_list();
+        }
+        //@endcond
+
+        /// Destroys the list object
+        ~IterableList()
+        {
+            destroy();
+        }
+
+        /// Inserts new node
+        /**
+            The function inserts \p val into the list if the list does not contain
+            an item with key equal to \p val.
+
+            Returns \p true if \p val has been linked to the list, \p false otherwise.
+        */
+        bool insert( value_type& val )
+        {
+            return insert_at( &m_Head, val );
+        }
+
+        /// Inserts new node
+        /**
+            This function is intended for derived non-intrusive containers.
+
+            The function allows to split new item creating into two part:
+            - create item with key only
+            - insert new item into the list
+            - if inserting is success, calls  \p f functor to initialize value-field of \p val.
+
+            The functor signature is:
+            \code
+                void func( value_type& val );
+            \endcode
+            where \p val is the item inserted. User-defined functor \p f should guarantee that during changing
+            \p val no any other changes could be made on this list's item by concurrent threads.
+            The user-defined functor is called only if the inserting is success.
+
+            @warning See \ref cds_intrusive_item_creating "insert item troubleshooting"
+        */
+        template <typename Func>
+        bool insert( value_type& val, Func f )
+        {
+            return insert_at( &m_Head, val, f );
+        }
+
+        /// Updates the node
+        /**
+            The operation performs inserting or changing data with lock-free manner.
+
+            If the item \p val is not found in the list, then \p val is inserted
+            iff \p bInsert is \p true.
+            Otherwise, the current element is changed to \p val, the element will be retired later
+            by call \p Traits::disposer.
+            The functor \p func is called after inserting or replacing, it signature is:
+            \code
+                void func( value_type& val, value_type * old );
+            \endcode
+            where
+            - \p val - argument \p val passed into the \p %update() function
+            - \p old - old value that will be retired. If new item has been inserted then \p old is \p nullptr.
+
+            Returns std::pair<bool, bool> where \p first is \p true if operation is successful,
+            \p second is \p true if \p val has been added or \p false if the item with that key
+            already in the list.
+        */
+        template <typename Func>
+        std::pair<bool, bool> update( value_type& val, Func func, bool bInsert = true )
+        {
+            return update_at( &m_Head, val, func, bInsert );
+        }
+
+        /// Insert or update
+        /**
+            The operation performs inserting or updating data with lock-free manner.
+
+            If the item \p val is not found in the list, then \p val is inserted
+            iff \p bInsert is \p true.
+            Otherwise, the current element is changed to \p val, the old element will be retired later
+            by call \p Traits::disposer.
+
+            Returns std::pair<bool, bool> where \p first is \p true if operation is successful,
+            \p second is \p true if \p val has been added or \p false if the item with that key
+            already in the list.
+        */
+        std::pair<bool, bool> upsert( value_type& val, bool bInsert = true )
+        {
+            return upsert_at( &m_Head, val, bInsert );
+        }
+
+        /// Unlinks the item \p val from the list
+        /**
+            The function searches the item \p val in the list and unlinks it from the list
+            if it is found and it is equal to \p val.
+
+            Difference between \p erase() and \p %unlink(): \p %erase() finds <i>a key</i>
+            and deletes the item found. \p %unlink() finds an item by key and deletes it
+            only if \p val is an item of the list, i.e. the pointer to item found
+            is equal to <tt> &val </tt>.
+
+            \p disposer specified in \p Traits is called for deleted item.
+
+            The function returns \p true if success and \p false otherwise.
+        */
+        bool unlink( value_type& val )
+        {
+            return unlink_at( &m_Head, val );
+        }
+
+        /// Deletes the item from the list
+        /** \anchor cds_intrusive_IterableList_hp_erase_val
+            The function searches an item with key equal to \p key in the list,
+            unlinks it from the list, and returns \p true.
+            If \p key is not found the function return \p false.
+
+            \p disposer specified in \p Traits is called for deleted item.
+        */
+        template <typename Q>
+        bool erase( Q const& key )
+        {
+            return erase_at( &m_Head, key, key_comparator());
+        }
+
+        /// Deletes the item from the list using \p pred predicate for searching
+        /**
+            The function is an analog of \ref cds_intrusive_IterableList_hp_erase_val "erase(Q const&)"
+            but \p pred is used for key comparing.
+            \p Less functor has the interface like \p std::less.
+            \p pred must imply the same element order as the comparator used for building the list.
+
+            \p disposer specified in \p Traits is called for deleted item.
+        */
+        template <typename Q, typename Less>
+        bool erase_with( Q const& key, Less pred )
+        {
+            CDS_UNUSED( pred );
+            return erase_at( &m_Head, key, cds::opt::details::make_comparator_from_less<Less>());
+        }
+
+        /// Deletes the item from the list
+        /** \anchor cds_intrusive_IterableList_hp_erase_func
+            The function searches an item with key equal to \p key in the list,
+            call \p func functor with item found, unlinks it from the list, and returns \p true.
+            The \p Func interface is
+            \code
+            struct functor {
+                void operator()( value_type const& item );
+            };
+            \endcode
+            If \p key is not found the function return \p false, \p func is not called.
+
+            \p disposer specified in \p Traits is called for deleted item.
+        */
+        template <typename Q, typename Func>
+        bool erase( Q const& key, Func func )
+        {
+            return erase_at( &m_Head, key, key_comparator(), func );
+        }
+
+        /// Deletes the item from the list using \p pred predicate for searching
+        /**
+            The function is an analog of \ref cds_intrusive_IterableList_hp_erase_func "erase(Q const&, Func)"
+            but \p pred is used for key comparing.
+            \p Less functor has the interface like \p std::less.
+            \p pred must imply the same element order as the comparator used for building the list.
+
+            \p disposer specified in \p Traits is called for deleted item.
+        */
+        template <typename Q, typename Less, typename Func>
+        bool erase_with( Q const& key, Less pred, Func f )
+        {
+            CDS_UNUSED( pred );
+            return erase_at( &m_Head, key, cds::opt::details::make_comparator_from_less<Less>(), f );
+        }
+
+        /// Deletes the item pointed by iterator \p iter
+        /**
+            Returns \p true if the operation is successful, \p false otherwise.
+            The function can return \p false if the node the iterator points to has already been deleted
+            by other thread.
+
+            The function does not invalidate the iterator, it remains valid and can be used for further traversing.
+        */
+        bool erase_at( iterator const& iter )
+        {
+            assert( iter != end());
+
+            marked_data_ptr val( iter.data());
+            if ( iter.m_pNode->data.compare_exchange_strong( val, marked_data_ptr(), memory_model::memory_order_acquire, atomics::memory_order_relaxed )) {
+                --m_ItemCounter;
+                retire_data( val.ptr());
+                m_Stat.onEraseSuccess();
+                return true;
+            }
+            return false;
+        }
+
+        /// Extracts the item from the list with specified \p key
+        /** \anchor cds_intrusive_IterableList_hp_extract
+            The function searches an item with key equal to \p key,
+            unlinks it from the list, and returns it as \p guarded_ptr.
+            If \p key is not found returns an empty guarded pointer.
+
+            Note the compare functor should accept a parameter of type \p Q that can be not the same as \p value_type.
+
+            The \ref disposer specified in \p Traits class template parameter is called automatically
+            by garbage collector \p GC when returned \ref guarded_ptr object will be destroyed or released.
+            @note Each \p guarded_ptr object uses the GC's guard that can be limited resource.
+
+            Usage:
+            \code
+            typedef cds::intrusive::IterableList< cds::gc::HP, foo, my_traits >  ord_list;
+            ord_list theList;
+            // ...
+            {
+                ord_list::guarded_ptr gp( theList.extract( 5 ));
+                if ( gp ) {
+                    // Deal with gp
+                    // ...
+                }
+                // Destructor of gp releases internal HP guard
+            }
+            \endcode
+        */
+        template <typename Q>
+        guarded_ptr extract( Q const& key )
+        {
+            return extract_at( &m_Head, key, key_comparator());
+        }
+
+        /// Extracts the item using compare functor \p pred
+        /**
+            The function is an analog of \ref cds_intrusive_IterableList_hp_extract "extract(Q const&)"
+            but \p pred predicate is used for key comparing.
+
+            \p Less functor has the semantics like \p std::less but should take arguments of type \ref value_type and \p Q
+            in any order.
+            \p pred must imply the same element order as the comparator used for building the list.
+        */
+        template <typename Q, typename Less>
+        guarded_ptr extract_with( Q const& key, Less pred )
+        {
+            CDS_UNUSED( pred );
+            return extract_at( &m_Head, key, cds::opt::details::make_comparator_from_less<Less>());
+        }
+
+        /// Finds \p key in the list
+        /** \anchor cds_intrusive_IterableList_hp_find_func
+            The function searches the item with key equal to \p key and calls the functor \p f for item found.
+            The interface of \p Func functor is:
+            \code
+            struct functor {
+                void operator()( value_type& item, Q& key );
+            };
+            \endcode
+            where \p item is the item found, \p key is the \p %find() function argument.
+
+            The functor may change non-key fields of \p item. Note that the function is only guarantee
+            that \p item cannot be disposed during functor is executing.
+            The function does not serialize simultaneous access to the \p item. If such access is
+            possible you must provide your own synchronization schema to keep out unsafe item modifications.
+
+            The function returns \p true if \p val is found, \p false otherwise.
+        */
+        template <typename Q, typename Func>
+        bool find( Q& key, Func f ) const
+        {
+            return find_at( &m_Head, key, key_comparator(), f );
+        }
+        //@cond
+        template <typename Q, typename Func>
+        bool find( Q const& key, Func f ) const
+        {
+            return find_at( &m_Head, key, key_comparator(), f );
+        }
+        //@endcond
+
+        /// Finds \p key in the list and returns iterator pointed to the item found
+        /**
+            If \p key is not found the function returns \p end().
+        */
+        template <typename Q>
+        iterator find( Q const& key ) const
+        {
+            return find_iterator_at( &m_Head, key, key_comparator());
+        }
+
+        /// Finds the \p key using \p pred predicate for searching
+        /**
+            The function is an analog of \ref cds_intrusive_IterableList_hp_find_func "find(Q&, Func)"
+            but \p pred is used for key comparing.
+            \p Less functor has the interface like \p std::less.
+            \p pred must imply the same element order as the comparator used for building the list.
+        */
+        template <typename Q, typename Less, typename Func>
+        bool find_with( Q& key, Less pred, Func f ) const
+        {
+            CDS_UNUSED( pred );
+            return find_at( &m_Head, key, cds::opt::details::make_comparator_from_less<Less>(), f );
+        }
+        //@cond
+        template <typename Q, typename Less, typename Func>
+        bool find_with( Q const& key, Less pred, Func f ) const
+        {
+            CDS_UNUSED( pred );
+            return find_at( &m_Head, key, cds::opt::details::make_comparator_from_less<Less>(), f );
+        }
+        //@endcond
+
+        /// Finds \p key in the list using \p pred predicate for searching and returns iterator pointed to the item found
+        /**
+            The function is an analog of \p find(Q&) but \p pred is used for key comparing.
+            \p Less functor has the interface like \p std::less.
+            \p pred must imply the same element order as the comparator used for building the list.
+
+            If \p key is not found the function returns \p end().
+        */
+        template <typename Q, typename Less>
+        iterator find_with( Q const& key, Less pred ) const
+        {
+            CDS_UNUSED( pred );
+            return find_iterator_at( &m_Head, key, cds::opt::details::make_comparator_from_less<Less>());
+        }
+
+        /// Checks whether the list contains \p key
+        /**
+            The function searches the item with key equal to \p key
+            and returns \p true if it is found, and \p false otherwise.
+        */
+        template <typename Q>
+        bool contains( Q const& key ) const
+        {
+            return find_at( &m_Head, key, key_comparator());
+        }
+
+        /// Checks whether the list contains \p key using \p pred predicate for searching
+        /**
+            The function is an analog of <tt>contains( key )</tt> but \p pred is used for key comparing.
+            \p Less functor has the interface like \p std::less.
+            \p Less must imply the same element order as the comparator used for building the list.
+        */
+        template <typename Q, typename Less>
+        bool contains( Q const& key, Less pred ) const
+        {
+            CDS_UNUSED( pred );
+            return find_at( &m_Head, key, cds::opt::details::make_comparator_from_less<Less>());
+        }
+
+        /// Finds the \p key and return the item found
+        /** \anchor cds_intrusive_IterableList_hp_get
+            The function searches the item with key equal to \p key
+            and returns it as \p guarded_ptr.
+            If \p key is not found the function returns an empty guarded pointer.
+
+            The \ref disposer specified in \p Traits class template parameter is called
+            by garbage collector \p GC automatically when returned \ref guarded_ptr object
+            will be destroyed or released.
+            @note Each \p guarded_ptr object uses one GC's guard which can be limited resource.
+
+            Usage:
+            \code
+            typedef cds::intrusive::IterableList< cds::gc::HP, foo, my_traits >  ord_list;
+            ord_list theList;
+            // ...
+            {
+                ord_list::guarded_ptr gp(theList.get( 5 ));
+                if ( gp ) {
+                    // Deal with gp
+                    //...
+                }
+                // Destructor of guarded_ptr releases internal HP guard
+            }
+            \endcode
+
+            Note the compare functor specified for \p Traits template parameter
+            should accept a parameter of type \p Q that can be not the same as \p value_type.
+        */
+        template <typename Q>
+        guarded_ptr get( Q const& key ) const
+        {
+            return get_at( &m_Head, key, key_comparator());
+        }
+
+        /// Finds the \p key and return the item found
+        /**
+            The function is an analog of \ref cds_intrusive_IterableList_hp_get "get( Q const&)"
+            but \p pred is used for comparing the keys.
+
+            \p Less functor has the semantics like \p std::less but should take arguments of type \ref value_type and \p Q
+            in any order.
+            \p pred must imply the same element order as the comparator used for building the list.
+        */
+        template <typename Q, typename Less>
+        guarded_ptr get_with( Q const& key, Less pred ) const
+        {
+            CDS_UNUSED( pred );
+            return get_at( &m_Head, key, cds::opt::details::make_comparator_from_less<Less>());
+        }
+
+        /// Clears the list (thread safe, not atomic)
+        void clear()
+        {
+            position pos;
+            pos.pPrev = nullptr;
+            for ( pos.pCur = m_Head.next.load( memory_model::memory_order_relaxed ); pos.pCur != pos.pPrev; pos.pCur = pos.pCur->next.load( memory_model::memory_order_relaxed )) {
+                while ( true ) {
+                    pos.pFound = pos.guard.protect( pos.pCur->data, []( marked_data_ptr p ) { return p.ptr(); }).ptr();
+                    if ( !pos.pFound )
+                        break;
+                    if ( cds_likely( unlink_data( pos ))) {
+                        --m_ItemCounter;
+                        break;
+                    }
+                }
+                pos.pPrev = pos.pCur;
+            }
+        }
+
+        /// Checks if the list is empty
+        /**
+            Emptiness is checked by item counting: if item count is zero then the set is empty.
+            Thus, if you need to use \p %empty() you should provide appropriate (non-empty) \p iterable_list::traits::item_counter
+            feature.
+        */
+        bool empty() const
+        {
+            return size() == 0;
+        }
+
+        /// Returns list's item count
+        /**
+            The value returned depends on item counter provided by \p iterable_list::traits::item_counter. For \p atomicity::empty_item_counter,
+            this function always returns 0.
+        */
+        size_t size() const
+        {
+            return m_ItemCounter.value();
+        }
+
+        /// Returns const reference to internal statistics
+        stat const& statistics() const
+        {
+            return m_Stat;
+        }
+
+    protected:
+        //@cond
+
+        // split-list support
+        bool insert_aux_node( node_type * pNode )
+        {
+            return insert_aux_node( &m_Head, pNode );
+        }
+
+        // split-list support
+        bool insert_aux_node( node_type* pHead, node_type * pNode )
+        {
+            assert( pNode != nullptr );
+            assert( pNode->data.load( memory_model::memory_order_relaxed ) != nullptr );
+
+            insert_position pos;
+
+            while ( true ) {
+                if ( inserting_search( pHead, *pNode->data.load(memory_model::memory_order_relaxed).ptr(), pos, key_comparator())) {
+                    m_Stat.onInsertFailed();
+                    return false;
+                }
+
+                if ( link_aux_node( pNode, pos, pHead )) {
+                    ++m_ItemCounter;
+                    m_Stat.onInsertSuccess();
+                    return true;
+                }
+
+                m_Stat.onInsertRetry();
+            }
+        }
+
+        bool insert_at( node_type* pHead, value_type& val )
+        {
+            insert_position pos;
+
+            while ( true ) {
+                if ( inserting_search( pHead, val, pos, key_comparator())) {
+                    m_Stat.onInsertFailed();
+                    return false;
+                }
+
+                if ( link_data( &val, pos, pHead )) {
+                    ++m_ItemCounter;
+                    m_Stat.onInsertSuccess();
+                    return true;
+                }
+
+                m_Stat.onInsertRetry();
+            }
+        }
+
+        template <typename Func>
+        bool insert_at( node_type* pHead, value_type& val, Func f )
+        {
+            insert_position pos;
+
+            typename gc::Guard guard;
+            guard.assign( &val );
+
+            while ( true ) {
+                if ( inserting_search( pHead, val, pos, key_comparator())) {
+                    m_Stat.onInsertFailed();
+                    return false;
+                }
+
+                if ( link_data( &val, pos, pHead )) {
+                    f( val );
+                    ++m_ItemCounter;
+                    m_Stat.onInsertSuccess();
+                    return true;
+                }
+
+                m_Stat.onInsertRetry();
+            }
+        }
+
+        template <typename Func>
+        std::pair<bool, bool> update_at( node_type* pHead, value_type& val, Func func, bool bInsert )
+        {
+            insert_position pos;
+
+            typename gc::Guard guard;
+            guard.assign( &val );
+
+            while ( true ) {
+                if ( inserting_search( pHead, val, pos, key_comparator())) {
+                    // try to replace pCur->data with val
+                    assert( pos.pFound != nullptr );
+                    assert( key_comparator()(*pos.pFound, val) == 0 );
+
+                    marked_data_ptr pFound( pos.pFound );
+                    if ( cds_likely( pos.pCur->data.compare_exchange_strong( pFound, marked_data_ptr( &val ),
+                            memory_model::memory_order_release, atomics::memory_order_relaxed )))
+                    {
+                        if ( pos.pFound != &val ) {
+                            retire_data( pos.pFound );
+                            func( val, pos.pFound );
+                        }
+                        m_Stat.onUpdateExisting();
+                        return std::make_pair( true, false );
+                    }
+                }
+                else {
+                    if ( !bInsert ) {
+                        m_Stat.onUpdateFailed();
+                        return std::make_pair( false, false );
+                    }
+
+                    if ( link_data( &val, pos, pHead )) {
+                        func( val, static_cast<value_type*>( nullptr ));
+                        ++m_ItemCounter;
+                        m_Stat.onUpdateNew();
+                        return std::make_pair( true, true );
+                    }
+                }
+
+                m_Stat.onUpdateRetry();
+            }
+        }
+
+        std::pair<bool, bool> upsert_at( node_type* pHead, value_type& val, bool bInsert )
+        {
+            return update_at( pHead, val, []( value_type&, value_type* ) {}, bInsert );
+        }
+
+        bool unlink_at( node_type* pHead, value_type& val )
+        {
+            position pos;
+
+            back_off bkoff;
+            while ( search( pHead, val, pos, key_comparator())) {
+                if ( pos.pFound == &val ) {
+                    if ( unlink_data( pos )) {
+                        --m_ItemCounter;
+                        m_Stat.onEraseSuccess();
+                        return true;
+                    }
+                    else
+                        bkoff();
+                }
+                else
+                    break;
+
+                m_Stat.onEraseRetry();
+            }
+
+            m_Stat.onEraseFailed();
+            return false;
+        }
+
+        template <typename Q, typename Compare, typename Func>
+        bool erase_at( node_type* pHead, Q const& val, Compare cmp, Func f, position& pos )
+        {
+            back_off bkoff;
+            while ( search( pHead, val, pos, cmp )) {
+                if ( unlink_data( pos )) {
+                    f( *pos.pFound );
+                    --m_ItemCounter;
+                    m_Stat.onEraseSuccess();
+                    return true;
+                }
+                else
+                    bkoff();
+
+                m_Stat.onEraseRetry();
+            }
+
+            m_Stat.onEraseFailed();
+            return false;
+        }
+
+        template <typename Q, typename Compare, typename Func>
+        bool erase_at( node_type* pHead, Q const& val, Compare cmp, Func f )
+        {
+            position pos;
+            return erase_at( pHead, val, cmp, f, pos );
+        }
+
+        template <typename Q, typename Compare>
+        bool erase_at( node_type* pHead, Q const& val, Compare cmp )
+        {
+            position pos;
+            return erase_at( pHead, val, cmp, [](value_type const&){}, pos );
+        }
+
+        template <typename Q, typename Compare>
+        guarded_ptr extract_at( node_type* pHead, Q const& val, Compare cmp )
+        {
+            position pos;
+            back_off bkoff;
+            while ( search( pHead, val, pos, cmp )) {
+                if ( unlink_data( pos )) {
+                    --m_ItemCounter;
+                    m_Stat.onEraseSuccess();
+                    assert( pos.pFound != nullptr );
+                    return guarded_ptr( std::move( pos.guard ));
+                }
+                else
+                    bkoff();
+
+                m_Stat.onEraseRetry();
+            }
+
+            m_Stat.onEraseFailed();
+            return guarded_ptr();
+        }
+
+        template <typename Q, typename Compare>
+        bool find_at( node_type const* pHead, Q const& val, Compare cmp ) const
+        {
+            position pos;
+            if ( search( pHead, val, pos, cmp )) {
+                m_Stat.onFindSuccess();
+                return true;
+            }
+
+            m_Stat.onFindFailed();
+            return false;
+        }
+
+        template <typename Q, typename Compare, typename Func>
+        bool find_at( node_type const* pHead, Q& val, Compare cmp, Func f ) const
+        {
+            position pos;
+            if ( search( pHead, val, pos, cmp )) {
+                assert( pos.pFound != nullptr );
+                f( *pos.pFound, val );
+                m_Stat.onFindSuccess();
+                return true;
+            }
+
+            m_Stat.onFindFailed();
+            return false;
+        }
+
+        template <typename Q, typename Compare>
+        iterator find_iterator_at( node_type const* pHead, Q const& val, Compare cmp ) const
+        {
+            position pos;
+            if ( search( pHead, val, pos, cmp )) {
+                assert( pos.pCur != nullptr );
+                assert( pos.pFound != nullptr );
+                m_Stat.onFindSuccess();
+                return iterator( pos.pCur, pos.pFound );
+            }
+
+            m_Stat.onFindFailed();
+            return iterator( const_cast<node_type*>( &m_Tail ));
+        }
+
+        template <typename Q, typename Compare>
+        guarded_ptr get_at( node_type const* pHead, Q const& val, Compare cmp ) const
+        {
+            position pos;
+            if ( search( pHead, val, pos, cmp )) {
+                m_Stat.onFindSuccess();
+                return guarded_ptr( std::move( pos.guard ));
+            }
+
+            m_Stat.onFindFailed();
+            return guarded_ptr();
+        }
+
+        node_type* head()
+        {
+            return &m_Head;
+        }
+
+        node_type const* head() const
+        {
+            return &m_Head;
+        }
+        //@endcond
+
+    protected:
+        //@cond
+        template <typename Q, typename Compare >
+        bool search( node_type const* pHead, Q const& val, position& pos, Compare cmp ) const
+        {
+            pos.pHead = pHead;
+            node_type*  pPrev = const_cast<node_type*>( pHead );
+
+            while ( true ) {
+                node_type * pCur = pPrev->next.load( memory_model::memory_order_relaxed );
+
+                if ( pCur == pCur->next.load( memory_model::memory_order_acquire )) {
+                    // end-of-list
+                    pos.pPrev = pPrev;
+                    pos.pCur = pCur;
+                    pos.pFound = nullptr;
+                    return false;
+                }
+
+                value_type * pVal = pos.guard.protect( pCur->data,
+                    []( marked_data_ptr p ) -> value_type*
+                    {
+                        return p.ptr();
+                    }).ptr();
+
+                if ( pVal ) {
+                    int const nCmp = cmp( *pVal, val );
+                    if ( nCmp >= 0 ) {
+                        pos.pPrev = pPrev;
+                        pos.pCur = pCur;
+                        pos.pFound = pVal;
+                        return nCmp == 0;
+                    }
+                }
+
+                pPrev = pCur;
+            }
+        }
+
+        template <typename Q, typename Compare >
+        bool inserting_search( node_type const* pHead, Q const& val, insert_position& pos, Compare cmp ) const
+        {
+            pos.pHead = pHead;
+            node_type*  pPrev = const_cast<node_type*>(pHead);
+            value_type* pPrevVal = pPrev->data.load( memory_model::memory_order_relaxed ).ptr();
+
+            while ( true ) {
+                node_type * pCur = pPrev->next.load( memory_model::memory_order_relaxed );
+
+                if ( pCur == pCur->next.load( memory_model::memory_order_acquire )) {
+                    // end-of-list
+                    pos.pPrev = pPrev;
+                    pos.pCur = pCur;
+                    pos.pFound = nullptr;
+                    pos.pPrevVal = pPrevVal;
+                    return false;
+                }
+
+                value_type * pVal = pos.guard.protect( pCur->data,
+                    []( marked_data_ptr p ) -> value_type*
+                {
+                    return p.ptr();
+                } ).ptr();
+
+                if ( pVal ) {
+                    int const nCmp = cmp( *pVal, val );
+                    if ( nCmp >= 0 ) {
+                        pos.pPrev = pPrev;
+                        pos.pCur = pCur;
+                        pos.pFound = pVal;
+                        pos.pPrevVal = pPrevVal;
+                        return nCmp == 0;
+                    }
+                }
+
+                pPrev = pCur;
+                pPrevVal = pVal;
+                pos.prevGuard.copy( pos.guard );
+            }
+        }
+
+        // split-list support
+        template <typename Predicate>
+        void destroy( Predicate pred )
+        {
+            node_type * pNode = m_Head.next.load( memory_model::memory_order_relaxed );
+            while ( pNode != pNode->next.load( memory_model::memory_order_relaxed )) {
+                value_type * pVal = pNode->data.load( memory_model::memory_order_relaxed ).ptr();
+                node_type * pNext = pNode->next.load( memory_model::memory_order_relaxed );
+                bool const is_regular_node = !pVal || pred( pVal );
+                if ( is_regular_node ) {
+                    if ( pVal )
+                        retire_data( pVal );
+                    delete_node( pNode );
+                }
+                pNode = pNext;
+            }
+
+            m_Head.next.store( &m_Tail, memory_model::memory_order_relaxed );
+        }
+        //@endcond
+
+    private:
+        //@cond
+        void init_list()
+        {
+            m_Head.next.store( &m_Tail, memory_model::memory_order_relaxed );
+            // end-of-list mark: node.next == node
+            m_Tail.next.store( &m_Tail, memory_model::memory_order_release );
+        }
+
+        node_type * alloc_node( value_type * pVal )
+        {
+            m_Stat.onNodeCreated();
+            return cxx_node_allocator().New( pVal );
+        }
+
+        void delete_node( node_type * pNode )
+        {
+            m_Stat.onNodeRemoved();
+            cxx_node_allocator().Delete( pNode );
+        }
+
+        static void retire_data( value_type * pVal )
+        {
+            assert( pVal != nullptr );
+            gc::template retire<disposer>( pVal );
+        }
+
+        void destroy()
+        {
+            node_type * pNode = m_Head.next.load( memory_model::memory_order_relaxed );
+            while ( pNode != pNode->next.load( memory_model::memory_order_relaxed )) {
+                value_type * pVal = pNode->data.load( memory_model::memory_order_relaxed ).ptr();
+                if ( pVal )
+                    retire_data( pVal );
+                node_type * pNext = pNode->next.load( memory_model::memory_order_relaxed );
+                delete_node( pNode );
+                pNode = pNext;
+            }
+        }
+
+        bool link_data( value_type* pVal, insert_position& pos, node_type* pHead )
+        {
+            assert( pos.pPrev != nullptr );
+            assert( pos.pCur != nullptr );
+
+            // We need pos.pCur data should be unchanged, otherwise ordering violation can be possible
+            // if current thread will be preempted and another thread will delete pos.pCur data
+            // and then set it to another.
+            // To prevent this we mark pos.pCur data as undeletable by setting LSB
+            marked_data_ptr valCur( pos.pFound );
+            if ( !pos.pCur->data.compare_exchange_strong( valCur, valCur | 1, memory_model::memory_order_acquire, atomics::memory_order_relaxed )) {
+                // oops, pos.pCur data has been changed or another thread is setting pos.pPrev data
+                m_Stat.onNodeMarkFailed();
+                return false;
+            }
+
+            marked_data_ptr valPrev( pos.pPrevVal );
+            if ( !pos.pPrev->data.compare_exchange_strong( valPrev, valPrev | 1, memory_model::memory_order_acquire, atomics::memory_order_relaxed )) {
+                pos.pCur->data.store( valCur, memory_model::memory_order_relaxed );
+
+                m_Stat.onNodeMarkFailed();
+                return false;
+            }
+
+            // checks if link pPrev -> pCur is broken
+            if ( pos.pPrev->next.load( memory_model::memory_order_acquire ) != pos.pCur ) {
+                // sequence pPrev - pCur is broken
+                pos.pPrev->data.store( valPrev, memory_model::memory_order_relaxed );
+                pos.pCur->data.store( valCur, memory_model::memory_order_relaxed );
+
+                m_Stat.onNodeSeqBreak();
+                return false;
+            }
+
+            if ( pos.pPrevVal == nullptr ) {
+                // Check ABA-problem for prev
+                // There is a possibility that the current thread was preempted
+                // on entry of this function. Other threads can link data to prev
+                // and then remove it. As a result, the order of items may be changed
+                if ( find_prev( pHead, *pVal ) != pos.pPrev ) {
+                    pos.pPrev->data.store( valPrev, memory_model::memory_order_relaxed );
+                    pos.pCur->data.store( valCur, memory_model::memory_order_relaxed );
+
+                    m_Stat.onNullPrevABA();
+                    return false;
+                }
+            }
+
+            if ( pos.pPrev != pos.pHead && pos.pPrevVal == nullptr ) {
+                // reuse pPrev
+
+                // Set pos.pPrev data if it is null
+                valPrev |= 1;
+                bool result = pos.pPrev->data.compare_exchange_strong( valPrev, marked_data_ptr( pVal ),
+                    memory_model::memory_order_release, atomics::memory_order_relaxed );
+
+                // Clears data marks
+                pos.pCur->data.store( valCur, memory_model::memory_order_relaxed );
+
+                if ( result ) {
+                    m_Stat.onReuseNode();
+                    return result;
+                }
+            }
+            else {
+                // insert new node between pos.pPrev and pos.pCur
+                node_type * pNode = alloc_node( pVal );
+                pNode->next.store( pos.pCur, memory_model::memory_order_relaxed );
+
+                bool result = pos.pPrev->next.compare_exchange_strong( pos.pCur, pNode, memory_model::memory_order_release, atomics::memory_order_relaxed );
+
+                // Clears data marks
+                pos.pPrev->data.store( valPrev, memory_model::memory_order_relaxed );
+                pos.pCur->data.store( valCur, memory_model::memory_order_relaxed );
+
+                if ( result ) {
+                    m_Stat.onNewNodeCreated();
+                    return result;
+                }
+
+                delete_node( pNode );
+            }
+
+            return false;
+        }
+
+        // split-list support
+        bool link_aux_node( node_type * pNode, insert_position& pos, node_type* pHead )
+        {
+            assert( pos.pPrev != nullptr );
+            assert( pos.pCur != nullptr );
+
+            // We need pos.pCur data should be unchanged, otherwise ordering violation can be possible
+            // if current thread will be preempted and another thread will delete pos.pCur data
+            // and then set it to another.
+            // To prevent this we mark pos.pCur data as undeletable by setting LSB
+            marked_data_ptr valCur( pos.pFound );
+            if ( !pos.pCur->data.compare_exchange_strong( valCur, valCur | 1, memory_model::memory_order_acquire, atomics::memory_order_relaxed )) {
+                // oops, pos.pCur data has been changed or another thread is setting pos.pPrev data
+                m_Stat.onNodeMarkFailed();
+                return false;
+            }
+
+            marked_data_ptr valPrev( pos.pPrevVal );
+            if ( !pos.pPrev->data.compare_exchange_strong( valPrev, valPrev | 1, memory_model::memory_order_acquire, atomics::memory_order_relaxed )) {
+                pos.pCur->data.store( valCur, memory_model::memory_order_relaxed );
+                m_Stat.onNodeMarkFailed();
+                return false;
+            }
+
+            // checks if link pPrev -> pCur is broken
+            if ( pos.pPrev->next.load( memory_model::memory_order_acquire ) != pos.pCur ) {
+                // sequence pPrev - pCur is broken
+                pos.pPrev->data.store( valPrev, memory_model::memory_order_relaxed );
+                pos.pCur->data.store( valCur, memory_model::memory_order_relaxed );
+                m_Stat.onNodeSeqBreak();
+                return false;
+            }
+
+            if ( pos.pPrevVal == nullptr ) {
+                // Check ABA-problem for prev
+                // There is a possibility that the current thread was preempted
+                // on entry of this function. Other threads can insert (link) an item to prev
+                // and then remove it. As a result, the order of items may be changed
+                if ( find_prev( pHead, *pNode->data.load( memory_model::memory_order_relaxed ).ptr()) != pos.pPrev ) {
+                    pos.pPrev->data.store( valPrev, memory_model::memory_order_relaxed );
+                    pos.pCur->data.store( valCur, memory_model::memory_order_relaxed );
+
+                    m_Stat.onNullPrevABA();
+                    return false;
+                }
+            }
+
+            // insert new node between pos.pPrev and pos.pCur
+            pNode->next.store( pos.pCur, memory_model::memory_order_relaxed );
+
+            bool result = pos.pPrev->next.compare_exchange_strong( pos.pCur, pNode, memory_model::memory_order_release, atomics::memory_order_relaxed );
+
+            // Clears data marks
+            pos.pPrev->data.store( valPrev, memory_model::memory_order_relaxed );
+            pos.pCur->data.store( valCur, memory_model::memory_order_relaxed );
+
+            return result;
+        }
+
+        static bool unlink_data( position& pos )
+        {
+            assert( pos.pCur != nullptr );
+            assert( pos.pFound != nullptr );
+
+            marked_data_ptr val( pos.pFound );
+            if ( pos.pCur->data.compare_exchange_strong( val, marked_data_ptr(), memory_model::memory_order_acquire, atomics::memory_order_relaxed )) {
+                retire_data( pos.pFound );
+                return true;
+            }
+            return false;
+        }
+
+        template <typename Q>
+        node_type* find_prev( node_type const* pHead, Q const& val ) const
+        {
+            node_type*  pPrev = const_cast<node_type*>(pHead);
+            typename gc::Guard guard;
+            key_comparator cmp;
+
+            while ( true ) {
+                node_type * pCur = pPrev->next.load( memory_model::memory_order_relaxed );
+
+                if ( pCur == pCur->next.load( memory_model::memory_order_acquire )) {
+                    // end-of-list
+                    return pPrev;
+                }
+
+                value_type * pVal = guard.protect( pCur->data,
+                    []( marked_data_ptr p ) -> value_type*
+                {
+                    return p.ptr();
+                } ).ptr();
+
+                if ( pVal && cmp( *pVal, val ) >= 0 )
+                    return pPrev;
+
+                pPrev = pCur;
+            }
+        }
+        //@endcond
+    };
+}} // namespace cds::intrusive
+
+#endif // #ifndef CDSLIB_INTRUSIVE_IMPL_ITERABLE_LIST_H