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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/details/allocator.h>
36 #include <cds/intrusive/details/iterable_list_base.h>
38 namespace cds { namespace intrusive {
40 /// Michael's hash set
41 /** @ingroup cds_intrusive_map
42 \anchor cds_intrusive_MichaelHashSet_hp
45 - [2002] Maged Michael "High performance dynamic lock-free hash tables and list-based sets"
47 Michael's hash table algorithm is based on lock-free ordered list and it is very simple.
48 The main structure is an array \p T of size \p M. Each element in \p T is basically a pointer
49 to a hash bucket, implemented as a singly linked list. The array of buckets cannot be dynamically expanded.
50 However, each bucket may contain unbounded number of items.
52 Template parameters are:
53 - \p GC - Garbage collector used. Note the \p GC must be the same as the GC used for \p OrderedList
54 - \p OrderedList - ordered list implementation used as bucket for hash set, for example, \p MichaelList, \p LazyList.
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 ordered_list bucket_type; ///< bucket type
253 typedef Traits traits; ///< Set traits
255 typedef typename ordered_list::value_type value_type ; ///< type of value to be stored in the set
256 typedef typename ordered_list::key_comparator key_comparator ; ///< key comparing functor
257 typedef typename ordered_list::disposer disposer ; ///< Node disposer functor
259 /// Hash functor for \p value_type and all its derivatives that you use
260 typedef typename cds::opt::v::hash_selector< typename traits::hash >::type hash;
261 typedef typename traits::item_counter item_counter; ///< Item counter type
263 typedef typename ordered_list::guarded_ptr guarded_ptr; ///< Guarded pointer
265 /// Bucket table allocator
266 typedef cds::details::Allocator< bucket_type, typename traits::allocator > bucket_table_allocator;
268 /// Count of hazard pointer required for the algorithm
269 static CDS_CONSTEXPR const size_t c_nHazardPtrCount = ordered_list::c_nHazardPtrCount;
272 item_counter m_ItemCounter; ///< Item counter
273 hash m_HashFunctor; ///< Hash functor
274 bucket_type * m_Buckets; ///< bucket table
278 const size_t m_nHashBitmask;
283 /// Calculates hash value of \p key
284 template <typename Q>
285 size_t hash_value( const Q& key ) const
287 return m_HashFunctor( key ) & m_nHashBitmask;
290 /// Returns the bucket (ordered list) for \p key
291 template <typename Q>
292 bucket_type& bucket( const Q& key )
294 return m_Buckets[ hash_value( key ) ];
299 ///@name Forward iterators
303 The forward iterator for Michael's set is based on \p OrderedList forward iterator and has some features:
304 - it has no post-increment operator
305 - it iterates items in unordered fashion
306 - The iterator cannot be moved across thread boundary because it may contain GC's guard that is thread-private GC data.
308 Iterator thread safety depends on type of \p OrderedList:
309 - for \p MichaelList and \p LazyList: iterator guarantees safety even if you delete the item that iterator points to
310 because that item is guarded by hazard pointer.
311 However, in case of concurrent deleting operations it is no guarantee that you iterate all item in the set.
312 Moreover, a crash is possible when you try to iterate the next element that has been deleted by concurrent thread.
313 Use this iterator on the concurrent container for debugging purpose only.
314 - for \p IterableList: iterator is thread-safe. You may use it freely in concurrent environment.
317 typedef michael_set::details::iterator< bucket_type, false > iterator;
319 /// Const forward iterator
321 For iterator's features and requirements see \ref iterator
323 typedef michael_set::details::iterator< bucket_type, true > const_iterator;
325 /// Returns a forward iterator addressing the first element in a set
327 For empty set \code begin() == end() \endcode
331 return iterator( m_Buckets[0].begin(), bucket_begin(), bucket_end() );
334 /// Returns an iterator that addresses the location succeeding the last element in a set
336 Do not use the value returned by <tt>end</tt> function to access any item.
337 The returned value can be used only to control reaching the end of the set.
338 For empty set \code begin() == end() \endcode
342 return iterator( m_Buckets[bucket_count() - 1].end(), bucket_end() + 1, bucket_end() );
345 /// Returns a forward const iterator addressing the first element in a set
346 const_iterator begin() const
348 return get_const_begin();
351 /// Returns a forward const iterator addressing the first element in a set
352 const_iterator cbegin() const
354 return get_const_begin();
357 /// Returns an const iterator that addresses the location succeeding the last element in a set
358 const_iterator end() const
360 return get_const_end();
363 /// Returns an const iterator that addresses the location succeeding the last element in a set
364 const_iterator cend() const
366 return get_const_end();
372 bucket_type * bucket_begin() const
377 bucket_type * bucket_end() const
379 return m_Buckets + bucket_count();
382 const_iterator get_const_begin() const
384 return const_iterator( m_Buckets[0].cbegin(), bucket_begin(), bucket_end() );
386 const_iterator get_const_end() const
388 return const_iterator( m_Buckets[bucket_count() - 1].cend(), bucket_end() - 1, bucket_end() );
393 /// Initializes hash set
394 /** @anchor cds_intrusive_MichaelHashSet_hp_ctor
395 The Michael's hash set is an unbounded container, but its hash table is non-expandable.
396 At construction time you should pass estimated maximum item count and a load factor.
397 The load factor is average size of one bucket - a small number between 1 and 10.
398 The bucket is an ordered single-linked list, searching in the bucket has linear complexity <tt>O(nLoadFactor)</tt>.
399 The constructor defines hash table size as rounding <tt>nMaxItemCount / nLoadFactor</tt> up to nearest power of two.
402 size_t nMaxItemCount, ///< estimation of max item count in the hash set
403 size_t nLoadFactor ///< load factor: estimation of max number of items in the bucket. Small integer up to 10.
404 ) : m_nHashBitmask( michael_set::details::init_hash_bitmask( nMaxItemCount, nLoadFactor ))
406 // GC and OrderedList::gc must be the same
407 static_assert( std::is_same<gc, typename bucket_type::gc>::value, "GC and OrderedList::gc must be the same");
409 // atomicity::empty_item_counter is not allowed as a item counter
410 static_assert( !std::is_same<item_counter, atomicity::empty_item_counter>::value,
411 "cds::atomicity::empty_item_counter is not allowed as a item counter");
413 m_Buckets = bucket_table_allocator().NewArray( bucket_count() );
416 /// Clears hash set object and destroys it
420 bucket_table_allocator().Delete( m_Buckets, bucket_count() );
425 The function inserts \p val in the set if it does not contain
426 an item with key equal to \p val.
428 Returns \p true if \p val is placed into the set, \p false otherwise.
430 bool insert( value_type& val )
432 bool bRet = bucket( val ).insert( val );
440 This function is intended for derived non-intrusive containers.
442 The function allows to split creating of new item into two part:
443 - create item with key only
444 - insert new item into the set
445 - if inserting is success, calls \p f functor to initialize value-field of \p val.
447 The functor signature is:
449 void func( value_type& val );
451 where \p val is the item inserted.
453 The user-defined functor is called only if the inserting is success.
455 @warning For \ref cds_intrusive_MichaelList_hp "MichaelList" as the bucket see \ref cds_intrusive_item_creating "insert item troubleshooting".
456 \ref cds_intrusive_LazyList_hp "LazyList" provides exclusive access to inserted item and does not require any node-level
459 template <typename Func>
460 bool insert( value_type& val, Func f )
462 bool bRet = bucket( val ).insert( val, f );
468 /// Updates the element
470 The operation performs inserting or changing data with lock-free manner.
472 If the item \p val not found in the set, then \p val is inserted iff \p bAllowInsert is \p true.
473 Otherwise, the functor \p func is called with item found.
475 The functor signature depends of the type of \p OrderedList:
477 <b>for \p MichaelList, \p LazyList</b>
480 void operator()( bool bNew, value_type& item, value_type& val );
484 - \p bNew - \p true if the item has been inserted, \p false otherwise
485 - \p item - item of the set
486 - \p val - argument \p val passed into the \p %update() function
487 If new item has been inserted (i.e. \p bNew is \p true) then \p item and \p val arguments
488 refers to the same thing.
490 The functor may change non-key fields of the \p item.
491 @warning For \ref cds_intrusive_MichaelList_hp "MichaelList" as the bucket see \ref cds_intrusive_item_creating "insert item troubleshooting".
492 \ref cds_intrusive_LazyList_hp "LazyList" provides exclusive access to inserted item and does not require any node-level
495 <b>for \p IterableList</b>
497 void func( value_type& val, value_type * old );
500 - \p val - argument \p val passed into the \p %update() function
501 - \p old - old value that will be retired. If new item has been inserted then \p old is \p nullptr.
503 Returns <tt> std::pair<bool, bool> </tt> where \p first is \p true if operation is successful,
504 \p second is \p true if new item has been added or \p false if the item with \p key
505 already is in the set.
507 template <typename Func>
508 std::pair<bool, bool> update( value_type& val, Func func, bool bAllowInsert = true )
510 std::pair<bool, bool> bRet = bucket( val ).update( val, func, bAllowInsert );
516 template <typename Func>
517 CDS_DEPRECATED("ensure() is deprecated, use update()")
518 std::pair<bool, bool> ensure( value_type& val, Func func )
520 return update( val, func, true );
524 /// Inserts or updates the node (only for \p IterableList)
526 The operation performs inserting or changing data with lock-free manner.
528 If the item \p val is not found in the set, then \p val is inserted iff \p bAllowInsert is \p true.
529 Otherwise, the current element is changed to \p val, the old element will be retired later
530 by call \p Traits::disposer.
532 Returns std::pair<bool, bool> where \p first is \p true if operation is successful,
533 \p second is \p true if \p val has been added or \p false if the item with that key
536 #ifdef CDS_DOXYGEN_INVOKED
537 std::pair<bool, bool> upsert( value_type& val, bool bAllowInsert = true )
539 template <typename Q>
540 typename std::enable_if<
541 std::is_same< Q, value_type>::value && is_iterable_list< ordered_list >::value,
542 std::pair<bool, bool>
544 upsert( Q& val, bool bAllowInsert = true )
547 std::pair<bool, bool> bRet = bucket( val ).upsert( val, bAllowInsert );
553 /// Unlinks the item \p val from the set
555 The function searches the item \p val in the set and unlink it
556 if it is found and is equal to \p val.
558 The function returns \p true if success and \p false otherwise.
560 bool unlink( value_type& val )
562 bool bRet = bucket( val ).unlink( val );
568 /// Deletes the item from the set
569 /** \anchor cds_intrusive_MichaelHashSet_hp_erase
570 The function searches an item with key equal to \p key in the set,
571 unlinks it, and returns \p true.
572 If the item with key equal to \p key is not found the function return \p false.
574 Note the hash functor should accept a parameter of type \p Q that can be not the same as \p value_type.
576 template <typename Q>
577 bool erase( Q const& key )
579 if ( bucket( key ).erase( key )) {
586 /// Deletes the item from the set using \p pred predicate for searching
588 The function is an analog of \ref cds_intrusive_MichaelHashSet_hp_erase "erase(Q const&)"
589 but \p pred is used for key comparing.
590 \p Less functor has the interface like \p std::less.
591 \p pred must imply the same element order as the comparator used for building the set.
593 template <typename Q, typename Less>
594 bool erase_with( Q const& key, Less pred )
596 if ( bucket( key ).erase_with( key, pred )) {
603 /// Deletes the item from the set
604 /** \anchor cds_intrusive_MichaelHashSet_hp_erase_func
605 The function searches an item with key equal to \p key in the set,
606 call \p f functor with item found, and unlinks it from the set.
607 The \ref disposer specified in \p OrderedList class template parameter is called
608 by garbage collector \p GC asynchronously.
610 The \p Func interface is
613 void operator()( value_type const& item );
617 If the item with key equal to \p key is not found the function return \p false.
619 Note the hash functor should accept a parameter of type \p Q that can be not the same as \p value_type.
621 template <typename Q, typename Func>
622 bool erase( Q const& key, Func f )
624 if ( bucket( key ).erase( key, f )) {
631 /// Deletes the item from the set using \p pred predicate for searching
633 The function is an analog of \ref cds_intrusive_MichaelHashSet_hp_erase_func "erase(Q const&, Func)"
634 but \p pred is used for key comparing.
635 \p Less functor has the interface like \p std::less.
636 \p pred must imply the same element order as the comparator used for building the set.
638 template <typename Q, typename Less, typename Func>
639 bool erase_with( Q const& key, Less pred, Func f )
641 if ( bucket( key ).erase_with( key, pred, f )) {
648 /// Extracts the item with specified \p key
649 /** \anchor cds_intrusive_MichaelHashSet_hp_extract
650 The function searches an item with key equal to \p key,
651 unlinks it from the set, and returns an guarded pointer to the item extracted.
652 If \p key is not found the function returns an empty guarded pointer.
654 Note the compare functor should accept a parameter of type \p Q that may be not the same as \p value_type.
656 The \p disposer specified in \p OrderedList class' template parameter is called automatically
657 by garbage collector \p GC when returned \ref guarded_ptr object will be destroyed or released.
658 @note Each \p guarded_ptr object uses the GC's guard that can be limited resource.
662 typedef cds::intrusive::MichaelHashSet< your_template_args > michael_set;
666 michael_set::guarded_ptr gp( theSet.extract( 5 ));
671 // Destructor of gp releases internal HP guard
675 template <typename Q>
676 guarded_ptr extract( Q const& key )
678 guarded_ptr gp = bucket( key ).extract( key );
684 /// Extracts the item using compare functor \p pred
686 The function is an analog of \ref cds_intrusive_MichaelHashSet_hp_extract "extract(Q const&)"
687 but \p pred predicate is used for key comparing.
689 \p Less functor has the semantics like \p std::less but should take arguments of type \ref value_type and \p Q
691 \p pred must imply the same element order as the comparator used for building the list.
693 template <typename Q, typename Less>
694 guarded_ptr extract_with( Q const& key, Less pred )
696 guarded_ptr gp = bucket( key ).extract_with( key, pred );
702 /// Finds the key \p key
703 /** \anchor cds_intrusive_MichaelHashSet_hp_find_func
704 The function searches the item with key equal to \p key and calls the functor \p f for item found.
705 The interface of \p Func functor is:
708 void operator()( value_type& item, Q& key );
711 where \p item is the item found, \p key is the <tt>find</tt> function argument.
713 The functor may change non-key fields of \p item. Note that the functor is only guarantee
714 that \p item cannot be disposed during functor is executing.
715 The functor does not serialize simultaneous access to the set \p item. If such access is
716 possible you must provide your own synchronization schema on item level to exclude unsafe item modifications.
718 The \p key argument is non-const since it can be used as \p f functor destination i.e., the functor
719 may modify both arguments.
721 Note the hash functor specified for class \p Traits template parameter
722 should accept a parameter of type \p Q that can be not the same as \p value_type.
724 The function returns \p true if \p key is found, \p false otherwise.
726 template <typename Q, typename Func>
727 bool find( Q& key, Func f )
729 return bucket( key ).find( key, f );
732 template <typename Q, typename Func>
733 bool find( Q const& key, Func f )
735 return bucket( key ).find( key, f );
739 /// Finds \p key and returns iterator pointed to the item found (only for \p IterableList)
741 If \p key is not found the function returns \p end().
743 @note This function is supported only for the set based on \p IterableList
745 template <typename Q>
746 #ifdef CDS_DOXYGEN_INVOKED
749 typename std::enable_if< std::is_same<Q,Q>::value && is_iterable_list< ordered_list >::value, iterator >::type
753 bucket_type& b = bucket( key );
754 typename ordered_list::iterator it = b.find( key );
757 return iterator( it, &b, bucket_end());
760 template <typename Q>
761 typename std::enable_if< std::is_same<Q, Q>::value && is_iterable_list< ordered_list >::value, iterator >::type
764 bucket_type& b = bucket( key );
765 typename ordered_list::iterator it = b.find( key );
768 return iterator( it, &b, bucket_end() );
773 /// Finds the key \p key using \p pred predicate for searching
775 The function is an analog of \ref cds_intrusive_MichaelHashSet_hp_find_func "find(Q&, Func)"
776 but \p pred is used for key comparing.
777 \p Less functor has the interface like \p std::less.
778 \p pred must imply the same element order as the comparator used for building the set.
780 template <typename Q, typename Less, typename Func>
781 bool find_with( Q& key, Less pred, Func f )
783 return bucket( key ).find_with( key, pred, f );
786 template <typename Q, typename Less, typename Func>
787 bool find_with( Q const& key, Less pred, Func f )
789 return bucket( key ).find_with( key, pred, f );
793 /// Finds \p key using \p pred predicate and returns iterator pointed to the item found (only for \p IterableList)
795 The function is an analog of \p find(Q&) but \p pred is used for key comparing.
796 \p Less functor has the interface like \p std::less.
797 \p pred must imply the same element order as the comparator used for building the set.
799 If \p key is not found the function returns \p end().
801 @note This function is supported only for the set based on \p IterableList
803 template <typename Q, typename Less>
804 #ifdef CDS_DOXYGEN_INVOKED
807 typename std::enable_if< std::is_same<Q, Q>::value && is_iterable_list< ordered_list >::value, iterator >::type
809 find_with( Q& key, Less pred )
811 bucket_type& b = bucket( key );
812 typename ordered_list::iterator it = b.find_with( key, pred );
815 return iterator( it, &b, bucket_end() );
818 template <typename Q, typename Less>
819 typename std::enable_if< std::is_same<Q, Q>::value && is_iterable_list< ordered_list >::value, iterator >::type
820 find_with( Q const& key, Less pred )
822 bucket_type& b = bucket( key );
823 typename ordered_list::iterator it = b.find_with( key, pred );
826 return iterator( it, &b, bucket_end() );
830 /// Checks whether the set contains \p key
833 The function searches the item with key equal to \p key
834 and returns \p true if the key is found, and \p false otherwise.
836 Note the hash functor specified for class \p Traits template parameter
837 should accept a parameter of type \p Q that can be not the same as \p value_type.
839 template <typename Q>
840 bool contains( Q const& key )
842 return bucket( key ).contains( key );
845 /// Checks whether the set contains \p key using \p pred predicate for searching
847 The function is an analog of <tt>contains( key )</tt> but \p pred is used for key comparing.
848 \p Less functor has the interface like \p std::less.
849 \p Less must imply the same element order as the comparator used for building the set.
851 template <typename Q, typename Less>
852 bool contains( Q const& key, Less pred )
854 return bucket( key ).contains( key, pred );
857 /// Finds the key \p key and return the item found
858 /** \anchor cds_intrusive_MichaelHashSet_hp_get
859 The function searches the item with key equal to \p key
860 and returns the guarded pointer to the item found.
861 If \p key is not found the function returns an empty \p guarded_ptr.
863 @note Each \p guarded_ptr object uses one GC's guard which can be limited resource.
867 typedef cds::intrusive::MichaelHashSet< your_template_params > michael_set;
871 michael_set::guarded_ptr gp( theSet.get( 5 ));
872 if ( theSet.get( 5 )) {
876 // Destructor of guarded_ptr releases internal HP guard
880 Note the compare functor specified for \p OrderedList template parameter
881 should accept a parameter of type \p Q that can be not the same as \p value_type.
883 template <typename Q>
884 guarded_ptr get( Q const& key )
886 return bucket( key ).get( key );
889 /// Finds the key \p key and return the item found
891 The function is an analog of \ref cds_intrusive_MichaelHashSet_hp_get "get( Q const&)"
892 but \p pred is used for comparing the keys.
894 \p Less functor has the semantics like \p std::less but should take arguments of type \ref value_type and \p Q
896 \p pred must imply the same element order as the comparator used for building the set.
898 template <typename Q, typename Less>
899 guarded_ptr get_with( Q const& key, Less pred )
901 return bucket( key ).get_with( key, pred );
904 /// Clears the set (non-atomic)
906 The function unlink all items from the set.
907 The function is not atomic. It cleans up each bucket and then resets the item counter to zero.
908 If there are a thread that performs insertion while \p %clear() is working the result is undefined in general case:
909 \p empty() may return \p true but the set may contain item(s).
910 Therefore, \p %clear() may be used only for debugging purposes.
912 For each item the \p disposer is called after unlinking.
916 for ( size_t i = 0; i < bucket_count(); ++i )
917 m_Buckets[i].clear();
918 m_ItemCounter.reset();
921 /// Checks if the set is empty
923 Emptiness is checked by item counting: if item count is zero then the set is empty.
924 Thus, the correct item counting feature is an important part of Michael's set implementation.
931 /// Returns item count in the set
934 return m_ItemCounter;
937 /// Returns the size of hash table
939 Since \p %MichaelHashSet cannot dynamically extend the hash table size,
940 the value returned is an constant depending on object initialization parameters,
941 see \p MichaelHashSet::MichaelHashSet.
943 size_t bucket_count() const
945 return m_nHashBitmask + 1;
949 }} // namespace cds::intrusive
951 #endif // ifndef CDSLIB_INTRUSIVE_MICHAEL_SET_H