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4 (C) Copyright Maxim Khizhinsky (libcds.dev@gmail.com) 2006-2016
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31 #ifndef CDSLIB_INTRUSIVE_MICHAEL_SET_H
32 #define CDSLIB_INTRUSIVE_MICHAEL_SET_H
34 #include <cds/intrusive/details/michael_set_base.h>
35 #include <cds/intrusive/details/iterable_list_base.h>
37 namespace cds { namespace intrusive {
39 /// Michael's hash set
40 /** @ingroup cds_intrusive_map
41 \anchor cds_intrusive_MichaelHashSet_hp
44 - [2002] Maged Michael "High performance dynamic lock-free hash tables and list-based sets"
46 Michael's hash table algorithm is based on lock-free ordered list and it is very simple.
47 The main structure is an array \p T of size \p M. Each element in \p T is basically a pointer
48 to a hash bucket, implemented as a singly linked list. The array of buckets cannot be dynamically expanded.
49 However, each bucket may contain unbounded number of items.
51 Template parameters are:
52 - \p GC - Garbage collector used. Note the \p GC must be the same as the GC used for \p OrderedList
53 - \p OrderedList - ordered list implementation used as bucket for hash set, possible implementations:
54 \p MichaelList, \p LazyList, \p IterableList.
55 The intrusive ordered list implementation specifies the type \p T stored in the hash-set, the reclamation
56 schema \p GC used by hash-set, the comparison functor for the type \p T and other features specific for
58 - \p Traits - type traits. See \p michael_set::traits for explanation.
59 Instead of defining \p Traits struct you can use option-based syntax with \p michael_set::make_traits metafunction.
61 There are several specializations of \p %MichaelHashSet for each GC. You should include:
62 - <tt><cds/intrusive/michael_set_rcu.h></tt> for \ref cds_intrusive_MichaelHashSet_rcu "RCU type"
63 - <tt><cds/intrusive/michael_set_nogc.h></tt> for \ref cds_intrusive_MichaelHashSet_nogc for append-only set
64 - <tt><cds/intrusive/michael_set.h></tt> for \p gc::HP, \p gc::DHP
68 Some member functions of Michael's hash set accept the key parameter of type \p Q which differs from \p value_type.
69 It is expected that type \p Q contains full key of \p value_type, and for equal keys of type \p Q and \p value_type
70 the hash values of these keys must be equal.
71 The hash functor \p Traits::hash should accept parameters of both type:
75 std::string key_; // key field
81 size_t operator()( const std::string& s ) const
83 return std::hash( s );
86 size_t operator()( const Foo& f ) const
88 return (*this)( f.key_ );
95 First, you should define ordered list type to use in your hash set:
97 // For gc::HP-based MichaelList implementation
98 #include <cds/intrusive/michael_list_hp.h>
100 // cds::intrusive::MichaelHashSet declaration
101 #include <cds/intrusive/michael_set.h>
103 // Type of hash-set items
104 struct Foo: public cds::intrusive::michael_list::node< cds::gc::HP >
106 std::string key_ ; // key field
107 unsigned val_ ; // value field
108 // ... other value fields
111 // Declare comparator for the item
114 int operator()( const Foo& f1, const Foo& f2 ) const
116 return f1.key_.compare( f2.key_ );
120 // Declare bucket type for Michael's hash set
121 // The bucket type is any ordered list type like MichaelList, LazyList
122 typedef cds::intrusive::MichaelList< cds::gc::HP, Foo,
123 typename cds::intrusive::michael_list::make_traits<
125 cds::intrusive::opt::hook< cds::intrusive::michael_list::base_hook< cds::opt::gc< cds::gc::HP > > >
126 // item comparator option
127 ,cds::opt::compare< FooCmp >
132 Second, you should declare Michael's hash set container:
135 // Declare hash functor
136 // Note, the hash functor accepts parameter type Foo and std::string
138 size_t operator()( const Foo& f ) const
140 return cds::opt::v::hash<std::string>()( f.key_ );
142 size_t operator()( const std::string& f ) const
144 return cds::opt::v::hash<std::string>()( f );
148 // Michael's set typedef
149 typedef cds::intrusive::MichaelHashSet<
152 ,typename cds::intrusive::michael_set::make_traits<
153 cds::opt::hash< FooHash >
158 Now, you can use \p Foo_set in your application.
160 Like other intrusive containers, you may build several containers on single item structure:
162 #include <cds/intrusive/michael_list_hp.h>
163 #include <cds/intrusive/michael_list_dhp.h>
164 #include <cds/intrusive/michael_set.h>
170 // The first key is maintained by gc::HP, second key is maintained by gc::DHP garbage collectors
171 // (I don't know what is needed for, but it is correct)
173 : public cds::intrusive::michael_list::node< cds::gc::HP, tag_key1_idx >
174 , public cds::intrusive::michael_list::node< cds::gc::DHP, tag_key2_idx >
176 std::string key1_ ; // first key field
177 unsigned int key2_ ; // second key field
179 // ... value fields and fields for controlling item's lifetime
182 // Declare comparators for the item
185 int operator()( const Foo& f1, const Foo& f2 ) const { return f1.key1_.compare( f2.key1_ ) ; }
189 bool operator()( const Foo& f1, const Foo& f2 ) const { return f1.key2_ < f2.key1_ ; }
192 // Declare bucket type for Michael's hash set indexed by key1_ field and maintained by gc::HP
193 typedef cds::intrusive::MichaelList< cds::gc::HP, Foo,
194 typename cds::intrusive::michael_list::make_traits<
196 cds::intrusive::opt::hook< cds::intrusive::michael_list::base_hook< cds::opt::gc< cds::gc::HP >, tag_key1_idx > >
197 // item comparator option
198 ,cds::opt::compare< Key1Cmp >
202 // Declare bucket type for Michael's hash set indexed by key2_ field and maintained by gc::DHP
203 typedef cds::intrusive::MichaelList< cds::gc::DHP, Foo,
204 typename cds::intrusive::michael_list::make_traits<
206 cds::intrusive::opt::hook< cds::intrusive::michael_list::base_hook< cds::opt::gc< cds::gc::DHP >, tag_key2_idx > >
207 // item comparator option
208 ,cds::opt::less< Key2Less >
212 // Declare hash functor
214 size_t operator()( const Foo& f ) const { return cds::opt::v::hash<std::string>()( f.key1_ ) ; }
215 size_t operator()( const std::string& s ) const { return cds::opt::v::hash<std::string>()( s ) ; }
217 inline size_t Key2Hash( const Foo& f ) { return (size_t) f.key2_ ; }
219 // Michael's set indexed by key1_ field
220 typedef cds::intrusive::MichaelHashSet<
223 ,typename cds::intrusive::michael_set::make_traits<
224 cds::opt::hash< Key1Hash >
228 // Michael's set indexed by key2_ field
229 typedef cds::intrusive::MichaelHashSet<
232 ,typename cds::intrusive::michael_set::make_traits<
233 cds::opt::hash< Key2Hash >
241 #ifdef CDS_DOXYGEN_INVOKED
242 class Traits = michael_set::traits
250 typedef GC gc; ///< Garbage collector
251 typedef OrderedList ordered_list; ///< type of ordered list used as a bucket implementation
252 typedef Traits traits; ///< Set traits
254 typedef typename ordered_list::value_type value_type ; ///< type of value to be stored in the set
255 typedef typename ordered_list::key_comparator key_comparator ; ///< key comparing functor
256 typedef typename ordered_list::disposer disposer ; ///< Node disposer functor
257 #ifdef CDS_DOXYGEN_INVOKED
258 typedef typename ordered_list::stat stat ; ///< Internal statistics
261 /// Hash functor for \p value_type and all its derivatives that you use
262 typedef typename cds::opt::v::hash_selector< typename traits::hash >::type hash;
263 typedef typename traits::item_counter item_counter; ///< Item counter type
264 typedef typename traits::allocator allocator; ///< Bucket table allocator
266 typedef typename ordered_list::guarded_ptr guarded_ptr; ///< Guarded pointer
268 /// Count of hazard pointer required for the algorithm
269 static CDS_CONSTEXPR const size_t c_nHazardPtrCount = ordered_list::c_nHazardPtrCount;
271 // GC and OrderedList::gc must be the same
272 static_assert(std::is_same<gc, typename ordered_list::gc>::value, "GC and OrderedList::gc must be the same");
274 // atomicity::empty_item_counter is not allowed as a item counter
275 static_assert(!std::is_same<item_counter, atomicity::empty_item_counter>::value,
276 "cds::atomicity::empty_item_counter is not allowed as a item counter");
280 typedef typename ordered_list::template select_stat_wrapper< typename ordered_list::stat > bucket_stat;
282 typedef typename ordered_list::template rebind_traits<
283 cds::opt::item_counter< cds::atomicity::empty_item_counter >
284 , cds::opt::stat< typename bucket_stat::wrapped_stat >
285 >::type internal_bucket_type;
287 typedef typename allocator::template rebind< internal_bucket_type >::other bucket_table_allocator;
292 typedef typename bucket_stat::stat stat;
297 hash m_HashFunctor; ///< Hash functor
298 size_t const m_nHashBitmask;
299 internal_bucket_type* m_Buckets; ///< bucket table
300 item_counter m_ItemCounter; ///< Item counter
301 stat m_Stat; ///< Internal statistics
305 ///@name Forward iterators
309 The forward iterator for Michael's set is based on \p OrderedList forward iterator and has some features:
310 - it has no post-increment operator
311 - it iterates items in unordered fashion
312 - The iterator cannot be moved across thread boundary because it may contain GC's guard that is thread-private GC data.
314 Iterator thread safety depends on type of \p OrderedList:
315 - for \p MichaelList and \p LazyList: iterator guarantees safety even if you delete the item that iterator points to
316 because that item is guarded by hazard pointer.
317 However, in case of concurrent deleting operations it is no guarantee that you iterate all item in the set.
318 Moreover, a crash is possible when you try to iterate the next element that has been deleted by concurrent thread.
319 Use this iterator on the concurrent container for debugging purpose only.
320 - for \p IterableList: iterator is thread-safe. You may use it freely in concurrent environment.
323 typedef michael_set::details::iterator< internal_bucket_type, false > iterator;
325 /// Const forward iterator
327 For iterator's features and requirements see \ref iterator
329 typedef michael_set::details::iterator< internal_bucket_type, true > const_iterator;
331 /// Returns a forward iterator addressing the first element in a set
333 For empty set \code begin() == end() \endcode
337 return iterator( m_Buckets[0].begin(), bucket_begin(), bucket_end() );
340 /// Returns an iterator that addresses the location succeeding the last element in a set
342 Do not use the value returned by <tt>end</tt> function to access any item.
343 The returned value can be used only to control reaching the end of the set.
344 For empty set \code begin() == end() \endcode
348 return iterator( bucket_end()[-1].end(), bucket_end() - 1, bucket_end() );
351 /// Returns a forward const iterator addressing the first element in a set
352 const_iterator begin() const
354 return get_const_begin();
357 /// Returns a forward const iterator addressing the first element in a set
358 const_iterator cbegin() const
360 return get_const_begin();
363 /// Returns an const iterator that addresses the location succeeding the last element in a set
364 const_iterator end() const
366 return get_const_end();
369 /// Returns an const iterator that addresses the location succeeding the last element in a set
370 const_iterator cend() const
372 return get_const_end();
377 /// Initializes hash set
379 The Michael's hash set is an unbounded container, but its hash table is non-expandable.
380 At construction time you should pass estimated maximum item count and a load factor.
381 The load factor is average size of one bucket - a small number between 1 and 10.
382 The bucket is an ordered single-linked list, searching in the bucket has linear complexity <tt>O(nLoadFactor)</tt>.
383 The constructor defines hash table size as rounding <tt>nMaxItemCount / nLoadFactor</tt> up to nearest power of two.
386 size_t nMaxItemCount, ///< estimation of max item count in the hash set
387 size_t nLoadFactor ///< load factor: estimation of max number of items in the bucket. Small integer up to 10.
388 ) : m_nHashBitmask( michael_set::details::init_hash_bitmask( nMaxItemCount, nLoadFactor ))
389 , m_Buckets( bucket_table_allocator().allocate( bucket_count()))
391 for ( auto it = m_Buckets, itEnd = m_Buckets + bucket_count(); it != itEnd; ++it )
392 construct_bucket<bucket_stat>( it );
395 /// Clears hash set object and destroys it
400 for ( auto it = m_Buckets, itEnd = m_Buckets + bucket_count(); it != itEnd; ++it )
401 it->~internal_bucket_type();
402 bucket_table_allocator().deallocate( m_Buckets, bucket_count() );
407 The function inserts \p val in the set if it does not contain
408 an item with key equal to \p val.
410 Returns \p true if \p val is placed into the set, \p false otherwise.
412 bool insert( value_type& val )
414 bool bRet = bucket( val ).insert( val );
422 This function is intended for derived non-intrusive containers.
424 The function allows to split creating of new item into two part:
425 - create item with key only
426 - insert new item into the set
427 - if inserting is success, calls \p f functor to initialize value-field of \p val.
429 The functor signature is:
431 void func( value_type& val );
433 where \p val is the item inserted.
435 The user-defined functor is called only if the inserting is success.
437 @warning For \ref cds_intrusive_MichaelList_hp "MichaelList" as the bucket see \ref cds_intrusive_item_creating "insert item troubleshooting".
438 \ref cds_intrusive_LazyList_hp "LazyList" provides exclusive access to inserted item and does not require any node-level
441 template <typename Func>
442 bool insert( value_type& val, Func f )
444 bool bRet = bucket( val ).insert( val, f );
450 /// Updates the element
452 The operation performs inserting or changing data with lock-free manner.
454 If the item \p val not found in the set, then \p val is inserted iff \p bAllowInsert is \p true.
455 Otherwise, the functor \p func is called with item found.
457 The functor signature depends of the type of \p OrderedList:
459 <b>for \p MichaelList, \p LazyList</b>
462 void operator()( bool bNew, value_type& item, value_type& val );
466 - \p bNew - \p true if the item has been inserted, \p false otherwise
467 - \p item - item of the set
468 - \p val - argument \p val passed into the \p %update() function
469 If new item has been inserted (i.e. \p bNew is \p true) then \p item and \p val arguments
470 refers to the same thing.
472 The functor may change non-key fields of the \p item.
473 @warning For \ref cds_intrusive_MichaelList_hp "MichaelList" as the bucket see \ref cds_intrusive_item_creating "insert item troubleshooting".
474 \ref cds_intrusive_LazyList_hp "LazyList" provides exclusive access to inserted item and does not require any node-level
477 <b>for \p IterableList</b>
479 void func( value_type& val, value_type * old );
482 - \p val - argument \p val passed into the \p %update() function
483 - \p old - old value that will be retired. If new item has been inserted then \p old is \p nullptr.
485 Returns <tt> std::pair<bool, bool> </tt> where \p first is \p true if operation is successful,
486 \p second is \p true if new item has been added or \p false if the item with \p key
487 already is in the set.
489 template <typename Func>
490 std::pair<bool, bool> update( value_type& val, Func func, bool bAllowInsert = true )
492 std::pair<bool, bool> bRet = bucket( val ).update( val, func, bAllowInsert );
498 template <typename Func>
499 CDS_DEPRECATED("ensure() is deprecated, use update()")
500 std::pair<bool, bool> ensure( value_type& val, Func func )
502 return update( val, func, true );
506 /// Inserts or updates the node (only for \p IterableList)
508 The operation performs inserting or changing data with lock-free manner.
510 If the item \p val is not found in the set, then \p val is inserted iff \p bAllowInsert is \p true.
511 Otherwise, the current element is changed to \p val, the old element will be retired later
512 by call \p Traits::disposer.
514 Returns std::pair<bool, bool> where \p first is \p true if operation is successful,
515 \p second is \p true if \p val has been added or \p false if the item with that key
518 #ifdef CDS_DOXYGEN_INVOKED
519 std::pair<bool, bool> upsert( value_type& val, bool bAllowInsert = true )
521 template <typename Q>
522 typename std::enable_if<
523 std::is_same< Q, value_type>::value && is_iterable_list< ordered_list >::value,
524 std::pair<bool, bool>
526 upsert( Q& val, bool bAllowInsert = true )
529 std::pair<bool, bool> bRet = bucket( val ).upsert( val, bAllowInsert );
535 /// Unlinks the item \p val from the set
537 The function searches the item \p val in the set and unlink it
538 if it is found and is equal to \p val.
540 The function returns \p true if success and \p false otherwise.
542 bool unlink( value_type& val )
544 bool bRet = bucket( val ).unlink( val );
550 /// Deletes the item from the set
551 /** \anchor cds_intrusive_MichaelHashSet_hp_erase
552 The function searches an item with key equal to \p key in the set,
553 unlinks it, and returns \p true.
554 If the item with key equal to \p key is not found the function return \p false.
556 Note the hash functor should accept a parameter of type \p Q that can be not the same as \p value_type.
558 template <typename Q>
559 bool erase( Q const& key )
561 if ( bucket( key ).erase( key )) {
568 /// Deletes the item from the set using \p pred predicate for searching
570 The function is an analog of \ref cds_intrusive_MichaelHashSet_hp_erase "erase(Q const&)"
571 but \p pred is used for key comparing.
572 \p Less functor has the interface like \p std::less.
573 \p pred must imply the same element order as the comparator used for building the set.
575 template <typename Q, typename Less>
576 bool erase_with( Q const& key, Less pred )
578 if ( bucket( key ).erase_with( key, pred )) {
585 /// Deletes the item from the set
586 /** \anchor cds_intrusive_MichaelHashSet_hp_erase_func
587 The function searches an item with key equal to \p key in the set,
588 call \p f functor with item found, and unlinks it from the set.
589 The \ref disposer specified in \p OrderedList class template parameter is called
590 by garbage collector \p GC asynchronously.
592 The \p Func interface is
595 void operator()( value_type const& item );
599 If the item with key equal to \p key is not found the function return \p false.
601 Note the hash functor should accept a parameter of type \p Q that can be not the same as \p value_type.
603 template <typename Q, typename Func>
604 bool erase( Q const& key, Func f )
606 if ( bucket( key ).erase( key, f )) {
613 /// Deletes the item from the set using \p pred predicate for searching
615 The function is an analog of \ref cds_intrusive_MichaelHashSet_hp_erase_func "erase(Q const&, Func)"
616 but \p pred is used for key comparing.
617 \p Less functor has the interface like \p std::less.
618 \p pred must imply the same element order as the comparator used for building the set.
620 template <typename Q, typename Less, typename Func>
621 bool erase_with( Q const& key, Less pred, Func f )
623 if ( bucket( key ).erase_with( key, pred, f )) {
630 /// Extracts the item with specified \p key
631 /** \anchor cds_intrusive_MichaelHashSet_hp_extract
632 The function searches an item with key equal to \p key,
633 unlinks it from the set, and returns an guarded pointer to the item extracted.
634 If \p key is not found the function returns an empty guarded pointer.
636 Note the compare functor should accept a parameter of type \p Q that may be not the same as \p value_type.
638 The \p disposer specified in \p OrderedList class' template parameter is called automatically
639 by garbage collector \p GC when returned \ref guarded_ptr object will be destroyed or released.
640 @note Each \p guarded_ptr object uses the GC's guard that can be limited resource.
644 typedef cds::intrusive::MichaelHashSet< your_template_args > michael_set;
648 michael_set::guarded_ptr gp( theSet.extract( 5 ));
653 // Destructor of gp releases internal HP guard
657 template <typename Q>
658 guarded_ptr extract( Q const& key )
660 guarded_ptr gp = bucket( key ).extract( key );
666 /// Extracts the item using compare functor \p pred
668 The function is an analog of \ref cds_intrusive_MichaelHashSet_hp_extract "extract(Q const&)"
669 but \p pred predicate is used for key comparing.
671 \p Less functor has the semantics like \p std::less but should take arguments of type \ref value_type and \p Q
673 \p pred must imply the same element order as the comparator used for building the list.
675 template <typename Q, typename Less>
676 guarded_ptr extract_with( Q const& key, Less pred )
678 guarded_ptr gp = bucket( key ).extract_with( key, pred );
684 /// Finds the key \p key
685 /** \anchor cds_intrusive_MichaelHashSet_hp_find_func
686 The function searches the item with key equal to \p key and calls the functor \p f for item found.
687 The interface of \p Func functor is:
690 void operator()( value_type& item, Q& key );
693 where \p item is the item found, \p key is the <tt>find</tt> function argument.
695 The functor may change non-key fields of \p item. Note that the functor is only guarantee
696 that \p item cannot be disposed during functor is executing.
697 The functor does not serialize simultaneous access to the set \p item. If such access is
698 possible you must provide your own synchronization schema on item level to exclude unsafe item modifications.
700 The \p key argument is non-const since it can be used as \p f functor destination i.e., the functor
701 may modify both arguments.
703 Note the hash functor specified for class \p Traits template parameter
704 should accept a parameter of type \p Q that can be not the same as \p value_type.
706 The function returns \p true if \p key is found, \p false otherwise.
708 template <typename Q, typename Func>
709 bool find( Q& key, Func f )
711 return bucket( key ).find( key, f );
714 template <typename Q, typename Func>
715 bool find( Q const& key, Func f )
717 return bucket( key ).find( key, f );
721 /// Finds \p key and returns iterator pointed to the item found (only for \p IterableList)
723 If \p key is not found the function returns \p end().
725 @note This function is supported only for the set based on \p IterableList
727 template <typename Q>
728 #ifdef CDS_DOXYGEN_INVOKED
731 typename std::enable_if< std::is_same<Q,Q>::value && is_iterable_list< ordered_list >::value, iterator >::type
735 internal_bucket_type& b = bucket( key );
736 typename internal_bucket_type::iterator it = b.find( key );
739 return iterator( it, &b, bucket_end());
742 template <typename Q>
743 typename std::enable_if< std::is_same<Q, Q>::value && is_iterable_list< ordered_list >::value, iterator >::type
746 internal_bucket_type& b = bucket( key );
747 typename internal_bucket_type::iterator it = b.find( key );
750 return iterator( it, &b, bucket_end() );
755 /// Finds the key \p key using \p pred predicate for searching
757 The function is an analog of \ref cds_intrusive_MichaelHashSet_hp_find_func "find(Q&, Func)"
758 but \p pred is used for key comparing.
759 \p Less functor has the interface like \p std::less.
760 \p pred must imply the same element order as the comparator used for building the set.
762 template <typename Q, typename Less, typename Func>
763 bool find_with( Q& key, Less pred, Func f )
765 return bucket( key ).find_with( key, pred, f );
768 template <typename Q, typename Less, typename Func>
769 bool find_with( Q const& key, Less pred, Func f )
771 return bucket( key ).find_with( key, pred, f );
775 /// Finds \p key using \p pred predicate and returns iterator pointed to the item found (only for \p IterableList)
777 The function is an analog of \p find(Q&) but \p pred is used for key comparing.
778 \p Less functor has the interface like \p std::less.
779 \p pred must imply the same element order as the comparator used for building the set.
781 If \p key is not found the function returns \p end().
783 @note This function is supported only for the set based on \p IterableList
785 template <typename Q, typename Less>
786 #ifdef CDS_DOXYGEN_INVOKED
789 typename std::enable_if< std::is_same<Q, Q>::value && is_iterable_list< ordered_list >::value, iterator >::type
791 find_with( Q& key, Less pred )
793 internal_bucket_type& b = bucket( key );
794 typename internal_bucket_type::iterator it = b.find_with( key, pred );
797 return iterator( it, &b, bucket_end() );
800 template <typename Q, typename Less>
801 typename std::enable_if< std::is_same<Q, Q>::value && is_iterable_list< ordered_list >::value, iterator >::type
802 find_with( Q const& key, Less pred )
804 internal_bucket_type& b = bucket( key );
805 typename internal_bucket_type::iterator it = b.find_with( key, pred );
808 return iterator( it, &b, bucket_end() );
812 /// Checks whether the set contains \p key
815 The function searches the item with key equal to \p key
816 and returns \p true if the key is found, and \p false otherwise.
818 Note the hash functor specified for class \p Traits template parameter
819 should accept a parameter of type \p Q that can be not the same as \p value_type.
821 template <typename Q>
822 bool contains( Q const& key )
824 return bucket( key ).contains( key );
827 /// Checks whether the set contains \p key using \p pred predicate for searching
829 The function is an analog of <tt>contains( key )</tt> but \p pred is used for key comparing.
830 \p Less functor has the interface like \p std::less.
831 \p Less must imply the same element order as the comparator used for building the set.
833 template <typename Q, typename Less>
834 bool contains( Q const& key, Less pred )
836 return bucket( key ).contains( key, pred );
839 /// Finds the key \p key and return the item found
840 /** \anchor cds_intrusive_MichaelHashSet_hp_get
841 The function searches the item with key equal to \p key
842 and returns the guarded pointer to the item found.
843 If \p key is not found the function returns an empty \p guarded_ptr.
845 @note Each \p guarded_ptr object uses one GC's guard which can be limited resource.
849 typedef cds::intrusive::MichaelHashSet< your_template_params > michael_set;
853 michael_set::guarded_ptr gp( theSet.get( 5 ));
854 if ( theSet.get( 5 )) {
858 // Destructor of guarded_ptr releases internal HP guard
862 Note the compare functor specified for \p OrderedList template parameter
863 should accept a parameter of type \p Q that can be not the same as \p value_type.
865 template <typename Q>
866 guarded_ptr get( Q const& key )
868 return bucket( key ).get( key );
871 /// Finds the key \p key and return the item found
873 The function is an analog of \ref cds_intrusive_MichaelHashSet_hp_get "get( Q const&)"
874 but \p pred is used for comparing the keys.
876 \p Less functor has the semantics like \p std::less but should take arguments of type \ref value_type and \p Q
878 \p pred must imply the same element order as the comparator used for building the set.
880 template <typename Q, typename Less>
881 guarded_ptr get_with( Q const& key, Less pred )
883 return bucket( key ).get_with( key, pred );
886 /// Clears the set (non-atomic)
888 The function unlink all items from the set.
889 The function is not atomic. It cleans up each bucket and then resets the item counter to zero.
890 If there are a thread that performs insertion while \p %clear() is working the result is undefined in general case:
891 \p empty() may return \p true but the set may contain item(s).
892 Therefore, \p %clear() may be used only for debugging purposes.
894 For each item the \p disposer is called after unlinking.
898 for ( size_t i = 0; i < bucket_count(); ++i )
899 m_Buckets[i].clear();
900 m_ItemCounter.reset();
903 /// Checks if the set is empty
905 Emptiness is checked by item counting: if item count is zero then the set is empty.
906 Thus, the correct item counting feature is an important part of Michael's set implementation.
913 /// Returns item count in the set
916 return m_ItemCounter;
919 /// Returns const reference to internal statistics
920 stat const& statistics() const
925 /// Returns the size of hash table
927 Since \p %MichaelHashSet cannot dynamically extend the hash table size,
928 the value returned is an constant depending on object initialization parameters,
929 see \p MichaelHashSet::MichaelHashSet.
931 size_t bucket_count() const
933 return m_nHashBitmask + 1;
938 internal_bucket_type * bucket_begin() const
943 internal_bucket_type * bucket_end() const
945 return m_Buckets + bucket_count();
948 const_iterator get_const_begin() const
950 return const_iterator( m_Buckets[0].cbegin(), bucket_begin(), bucket_end() );
952 const_iterator get_const_end() const
954 return const_iterator( bucket_end()[-1].cend(), bucket_end() - 1, bucket_end() );
957 template <typename Stat>
958 typename std::enable_if< Stat::empty >::type construct_bucket( internal_bucket_type * bucket )
960 new (bucket) internal_bucket_type;
963 template <typename Stat>
964 typename std::enable_if< !Stat::empty >::type construct_bucket( internal_bucket_type * bucket )
966 new (bucket) internal_bucket_type( m_Stat );
969 /// Calculates hash value of \p key
970 template <typename Q>
971 size_t hash_value( const Q& key ) const
973 return m_HashFunctor( key ) & m_nHashBitmask;
976 /// Returns the bucket (ordered list) for \p key
977 template <typename Q>
978 internal_bucket_type& bucket( const Q& key )
980 return m_Buckets[hash_value( key )];
985 }} // namespace cds::intrusive
987 #endif // ifndef CDSLIB_INTRUSIVE_MICHAEL_SET_H