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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>
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, for example, \p MichaelList, \p LazyList.
54 The intrusive ordered list implementation specifies the type \p T stored in the hash-set, the reclamation
55 schema \p GC used by hash-set, the comparison functor for the type \p T and other features specific for
57 - \p Traits - type traits. See \p michael_set::traits for explanation.
58 Instead of defining \p Traits struct you can use option-based syntax with \p michael_set::make_traits metafunction.
60 There are several specializations of \p %MichaelHashSet for each GC. You should include:
61 - <tt><cds/intrusive/michael_set_rcu.h></tt> for \ref cds_intrusive_MichaelHashSet_rcu "RCU type"
62 - <tt><cds/intrusive/michael_set_nogc.h></tt> for \ref cds_intrusive_MichaelHashSet_nogc for append-only set
63 - <tt><cds/intrusive/michael_set.h></tt> for \p gc::HP, \p gc::DHP
67 Some member functions of Michael's hash set accept the key parameter of type \p Q which differs from \p value_type.
68 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
69 the hash values of these keys must be equal.
70 The hash functor \p Traits::hash should accept parameters of both type:
74 std::string key_; // key field
80 size_t operator()( const std::string& s ) const
82 return std::hash( s );
85 size_t operator()( const Foo& f ) const
87 return (*this)( f.key_ );
94 First, you should define ordered list type to use in your hash set:
96 // For gc::HP-based MichaelList implementation
97 #include <cds/intrusive/michael_list_hp.h>
99 // cds::intrusive::MichaelHashSet declaration
100 #include <cds/intrusive/michael_set.h>
102 // Type of hash-set items
103 struct Foo: public cds::intrusive::michael_list::node< cds::gc::HP >
105 std::string key_ ; // key field
106 unsigned val_ ; // value field
107 // ... other value fields
110 // Declare comparator for the item
113 int operator()( const Foo& f1, const Foo& f2 ) const
115 return f1.key_.compare( f2.key_ );
119 // Declare bucket type for Michael's hash set
120 // The bucket type is any ordered list type like MichaelList, LazyList
121 typedef cds::intrusive::MichaelList< cds::gc::HP, Foo,
122 typename cds::intrusive::michael_list::make_traits<
124 cds::intrusive::opt::hook< cds::intrusive::michael_list::base_hook< cds::opt::gc< cds::gc::HP > > >
125 // item comparator option
126 ,cds::opt::compare< FooCmp >
131 Second, you should declare Michael's hash set container:
134 // Declare hash functor
135 // Note, the hash functor accepts parameter type Foo and std::string
137 size_t operator()( const Foo& f ) const
139 return cds::opt::v::hash<std::string>()( f.key_ );
141 size_t operator()( const std::string& f ) const
143 return cds::opt::v::hash<std::string>()( f );
147 // Michael's set typedef
148 typedef cds::intrusive::MichaelHashSet<
151 ,typename cds::intrusive::michael_set::make_traits<
152 cds::opt::hash< FooHash >
157 Now, you can use \p Foo_set in your application.
159 Like other intrusive containers, you may build several containers on single item structure:
161 #include <cds/intrusive/michael_list_hp.h>
162 #include <cds/intrusive/michael_list_dhp.h>
163 #include <cds/intrusive/michael_set.h>
169 // The first key is maintained by gc::HP, second key is maintained by gc::DHP garbage collectors
170 // (I don't know what is needed for, but it is correct)
172 : public cds::intrusive::michael_list::node< cds::gc::HP, tag_key1_idx >
173 , public cds::intrusive::michael_list::node< cds::gc::DHP, tag_key2_idx >
175 std::string key1_ ; // first key field
176 unsigned int key2_ ; // second key field
178 // ... value fields and fields for controlling item's lifetime
181 // Declare comparators for the item
184 int operator()( const Foo& f1, const Foo& f2 ) const { return f1.key1_.compare( f2.key1_ ) ; }
188 bool operator()( const Foo& f1, const Foo& f2 ) const { return f1.key2_ < f2.key1_ ; }
191 // Declare bucket type for Michael's hash set indexed by key1_ field and maintained by gc::HP
192 typedef cds::intrusive::MichaelList< cds::gc::HP, Foo,
193 typename cds::intrusive::michael_list::make_traits<
195 cds::intrusive::opt::hook< cds::intrusive::michael_list::base_hook< cds::opt::gc< cds::gc::HP >, tag_key1_idx > >
196 // item comparator option
197 ,cds::opt::compare< Key1Cmp >
201 // Declare bucket type for Michael's hash set indexed by key2_ field and maintained by gc::DHP
202 typedef cds::intrusive::MichaelList< cds::gc::DHP, Foo,
203 typename cds::intrusive::michael_list::make_traits<
205 cds::intrusive::opt::hook< cds::intrusive::michael_list::base_hook< cds::opt::gc< cds::gc::DHP >, tag_key2_idx > >
206 // item comparator option
207 ,cds::opt::less< Key2Less >
211 // Declare hash functor
213 size_t operator()( const Foo& f ) const { return cds::opt::v::hash<std::string>()( f.key1_ ) ; }
214 size_t operator()( const std::string& s ) const { return cds::opt::v::hash<std::string>()( s ) ; }
216 inline size_t Key2Hash( const Foo& f ) { return (size_t) f.key2_ ; }
218 // Michael's set indexed by key1_ field
219 typedef cds::intrusive::MichaelHashSet<
222 ,typename cds::intrusive::michael_set::make_traits<
223 cds::opt::hash< Key1Hash >
227 // Michael's set indexed by key2_ field
228 typedef cds::intrusive::MichaelHashSet<
231 ,typename cds::intrusive::michael_set::make_traits<
232 cds::opt::hash< Key2Hash >
240 #ifdef CDS_DOXYGEN_INVOKED
241 class Traits = michael_set::traits
249 typedef GC gc; ///< Garbage collector
250 typedef OrderedList ordered_list; ///< type of ordered list used as a bucket implementation
251 typedef ordered_list bucket_type; ///< bucket type
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
258 /// Hash functor for \p value_type and all its derivatives that you use
259 typedef typename cds::opt::v::hash_selector< typename traits::hash >::type hash;
260 typedef typename traits::item_counter item_counter; ///< Item counter type
262 typedef typename ordered_list::guarded_ptr guarded_ptr; ///< Guarded pointer
264 /// Bucket table allocator
265 typedef cds::details::Allocator< bucket_type, typename traits::allocator > bucket_table_allocator;
268 item_counter m_ItemCounter; ///< Item counter
269 hash m_HashFunctor; ///< Hash functor
270 bucket_type * m_Buckets; ///< bucket table
274 const size_t m_nHashBitmask;
279 /// Calculates hash value of \p key
280 template <typename Q>
281 size_t hash_value( const Q& key ) const
283 return m_HashFunctor( key ) & m_nHashBitmask;
286 /// Returns the bucket (ordered list) for \p key
287 template <typename Q>
288 bucket_type& bucket( const Q& key )
290 return m_Buckets[ hash_value( key ) ];
295 ///@name Forward iterators (only for debugging purpose)
299 The forward iterator for Michael's set is based on \p OrderedList forward iterator and has some features:
300 - it has no post-increment operator
301 - it iterates items in unordered fashion
302 - The iterator cannot be moved across thread boundary since it may contain GC's guard that is thread-private GC data.
303 - Iterator ensures thread-safety even if you delete the item that iterator points to. However, in case of concurrent
304 deleting operations it is no guarantee that you iterate all item in the set.
305 Moreover, a crash is possible when you try to iterate the next element that has been deleted by concurrent thread.
307 @warning Use this iterator on the concurrent container for debugging purpose only.
309 typedef michael_set::details::iterator< bucket_type, false > iterator;
311 /// Const forward iterator
313 For iterator's features and requirements see \ref iterator
315 typedef michael_set::details::iterator< bucket_type, true > const_iterator;
317 /// Returns a forward iterator addressing the first element in a set
319 For empty set \code begin() == end() \endcode
323 return iterator( m_Buckets[0].begin(), m_Buckets, m_Buckets + bucket_count() );
326 /// Returns an iterator that addresses the location succeeding the last element in a set
328 Do not use the value returned by <tt>end</tt> function to access any item.
329 The returned value can be used only to control reaching the end of the set.
330 For empty set \code begin() == end() \endcode
334 return iterator( m_Buckets[bucket_count() - 1].end(), m_Buckets + bucket_count() - 1, m_Buckets + bucket_count() );
337 /// Returns a forward const iterator addressing the first element in a set
338 const_iterator begin() const
340 return get_const_begin();
343 /// Returns a forward const iterator addressing the first element in a set
344 const_iterator cbegin() const
346 return get_const_begin();
349 /// Returns an const iterator that addresses the location succeeding the last element in a set
350 const_iterator end() const
352 return get_const_end();
355 /// Returns an const iterator that addresses the location succeeding the last element in a set
356 const_iterator cend() const
358 return get_const_end();
364 const_iterator get_const_begin() const
366 return const_iterator( m_Buckets[0].cbegin(), m_Buckets, m_Buckets + bucket_count() );
368 const_iterator get_const_end() const
370 return const_iterator( m_Buckets[bucket_count() - 1].cend(), m_Buckets + bucket_count() - 1, m_Buckets + bucket_count() );
375 /// Initializes hash set
376 /** @anchor cds_intrusive_MichaelHashSet_hp_ctor
377 The Michael's hash set is an unbounded container, but its hash table is non-expandable.
378 At construction time you should pass estimated maximum item count and a load factor.
379 The load factor is average size of one bucket - a small number between 1 and 10.
380 The bucket is an ordered single-linked list, searching in the bucket has linear complexity <tt>O(nLoadFactor)</tt>.
381 The constructor defines hash table size as rounding <tt>nMaxItemCount / nLoadFactor</tt> up to nearest power of two.
384 size_t nMaxItemCount, ///< estimation of max item count in the hash set
385 size_t nLoadFactor ///< load factor: estimation of max number of items in the bucket. Small integer up to 10.
386 ) : m_nHashBitmask( michael_set::details::init_hash_bitmask( nMaxItemCount, nLoadFactor ))
388 // GC and OrderedList::gc must be the same
389 static_assert( std::is_same<gc, typename bucket_type::gc>::value, "GC and OrderedList::gc must be the same");
391 // atomicity::empty_item_counter is not allowed as a item counter
392 static_assert( !std::is_same<item_counter, atomicity::empty_item_counter>::value,
393 "cds::atomicity::empty_item_counter is not allowed as a item counter");
395 m_Buckets = bucket_table_allocator().NewArray( bucket_count() );
398 /// Clears hash set object and destroys it
402 bucket_table_allocator().Delete( 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.
456 The functor signature is:
459 void operator()( bool bNew, value_type& item, value_type& val );
463 - \p bNew - \p true if the item has been inserted, \p false otherwise
464 - \p item - item of the set
465 - \p val - argument \p val passed into the \p %update() function
466 If new item has been inserted (i.e. \p bNew is \p true) then \p item and \p val arguments
467 refers to the same thing.
469 The functor may change non-key fields of the \p item.
471 Returns <tt> std::pair<bool, bool> </tt> where \p first is \p true if operation is successfull,
472 \p second is \p true if new item has been added or \p false if the item with \p key
473 already is in the set.
475 @warning For \ref cds_intrusive_MichaelList_hp "MichaelList" as the bucket see \ref cds_intrusive_item_creating "insert item troubleshooting".
476 \ref cds_intrusive_LazyList_hp "LazyList" provides exclusive access to inserted item and does not require any node-level
479 template <typename Func>
480 std::pair<bool, bool> update( value_type& val, Func func, bool bAllowInsert = true )
482 std::pair<bool, bool> bRet = bucket( val ).update( val, func, bAllowInsert );
488 template <typename Func>
489 CDS_DEPRECATED("ensure() is deprecated, use update()")
490 std::pair<bool, bool> ensure( value_type& val, Func func )
492 return update( val, func, true );
496 /// Unlinks the item \p val from the set
498 The function searches the item \p val in the set and unlink it
499 if it is found and is equal to \p val.
501 The function returns \p true if success and \p false otherwise.
503 bool unlink( value_type& val )
505 bool bRet = bucket( val ).unlink( val );
511 /// Deletes the item from the set
512 /** \anchor cds_intrusive_MichaelHashSet_hp_erase
513 The function searches an item with key equal to \p key in the set,
514 unlinks it, and returns \p true.
515 If the item with key equal to \p key is not found the function return \p false.
517 Note the hash functor should accept a parameter of type \p Q that can be not the same as \p value_type.
519 template <typename Q>
520 bool erase( Q const& key )
522 if ( bucket( key ).erase( key )) {
529 /// Deletes the item from the set using \p pred predicate for searching
531 The function is an analog of \ref cds_intrusive_MichaelHashSet_hp_erase "erase(Q const&)"
532 but \p pred is used for key comparing.
533 \p Less functor has the interface like \p std::less.
534 \p pred must imply the same element order as the comparator used for building the set.
536 template <typename Q, typename Less>
537 bool erase_with( Q const& key, Less pred )
539 if ( bucket( key ).erase_with( key, pred )) {
546 /// Deletes the item from the set
547 /** \anchor cds_intrusive_MichaelHashSet_hp_erase_func
548 The function searches an item with key equal to \p key in the set,
549 call \p f functor with item found, and unlinks it from the set.
550 The \ref disposer specified in \p OrderedList class template parameter is called
551 by garbage collector \p GC asynchronously.
553 The \p Func interface is
556 void operator()( value_type const& item );
560 If the item with key equal to \p key is not found the function return \p false.
562 Note the hash functor should accept a parameter of type \p Q that can be not the same as \p value_type.
564 template <typename Q, typename Func>
565 bool erase( Q const& key, Func f )
567 if ( bucket( key ).erase( key, f )) {
574 /// Deletes the item from the set using \p pred predicate for searching
576 The function is an analog of \ref cds_intrusive_MichaelHashSet_hp_erase_func "erase(Q const&, Func)"
577 but \p pred is used for key comparing.
578 \p Less functor has the interface like \p std::less.
579 \p pred must imply the same element order as the comparator used for building the set.
581 template <typename Q, typename Less, typename Func>
582 bool erase_with( Q const& key, Less pred, Func f )
584 if ( bucket( key ).erase_with( key, pred, f )) {
591 /// Extracts the item with specified \p key
592 /** \anchor cds_intrusive_MichaelHashSet_hp_extract
593 The function searches an item with key equal to \p key,
594 unlinks it from the set, and returns an guarded pointer to the item extracted.
595 If \p key is not found the function returns an empty guarded pointer.
597 Note the compare functor should accept a parameter of type \p Q that may be not the same as \p value_type.
599 The \p disposer specified in \p OrderedList class' template parameter is called automatically
600 by garbage collector \p GC when returned \ref guarded_ptr object will be destroyed or released.
601 @note Each \p guarded_ptr object uses the GC's guard that can be limited resource.
605 typedef cds::intrusive::MichaelHashSet< your_template_args > michael_set;
609 michael_set::guarded_ptr gp( theSet.extract( 5 ));
614 // Destructor of gp releases internal HP guard
618 template <typename Q>
619 guarded_ptr extract( Q const& key )
621 guarded_ptr gp = bucket( key ).extract( key );
627 /// Extracts the item using compare functor \p pred
629 The function is an analog of \ref cds_intrusive_MichaelHashSet_hp_extract "extract(Q const&)"
630 but \p pred predicate is used for key comparing.
632 \p Less functor has the semantics like \p std::less but should take arguments of type \ref value_type and \p Q
634 \p pred must imply the same element order as the comparator used for building the list.
636 template <typename Q, typename Less>
637 guarded_ptr extract_with( Q const& key, Less pred )
639 guarded_ptr gp = bucket( key ).extract_with( key, pred );
645 /// Finds the key \p key
646 /** \anchor cds_intrusive_MichaelHashSet_hp_find_func
647 The function searches the item with key equal to \p key and calls the functor \p f for item found.
648 The interface of \p Func functor is:
651 void operator()( value_type& item, Q& key );
654 where \p item is the item found, \p key is the <tt>find</tt> function argument.
656 The functor may change non-key fields of \p item. Note that the functor is only guarantee
657 that \p item cannot be disposed during functor is executing.
658 The functor does not serialize simultaneous access to the set \p item. If such access is
659 possible you must provide your own synchronization schema on item level to exclude unsafe item modifications.
661 The \p key argument is non-const since it can be used as \p f functor destination i.e., the functor
662 may modify both arguments.
664 Note the hash functor specified for class \p Traits template parameter
665 should accept a parameter of type \p Q that can be not the same as \p value_type.
667 The function returns \p true if \p key is found, \p false otherwise.
669 template <typename Q, typename Func>
670 bool find( Q& key, Func f )
672 return bucket( key ).find( key, f );
675 template <typename Q, typename Func>
676 bool find( Q const& key, Func f )
678 return bucket( key ).find( key, f );
682 /// Finds the key \p key using \p pred predicate for searching
684 The function is an analog of \ref cds_intrusive_MichaelHashSet_hp_find_func "find(Q&, Func)"
685 but \p pred is used for key comparing.
686 \p Less functor has the interface like \p std::less.
687 \p pred must imply the same element order as the comparator used for building the set.
689 template <typename Q, typename Less, typename Func>
690 bool find_with( Q& key, Less pred, Func f )
692 return bucket( key ).find_with( key, pred, f );
695 template <typename Q, typename Less, typename Func>
696 bool find_with( Q const& key, Less pred, Func f )
698 return bucket( key ).find_with( key, pred, f );
702 /// Checks whether the set contains \p key
705 The function searches the item with key equal to \p key
706 and returns \p true if the key is found, and \p false otherwise.
708 Note the hash functor specified for class \p Traits template parameter
709 should accept a parameter of type \p Q that can be not the same as \p value_type.
711 template <typename Q>
712 bool contains( Q const& key )
714 return bucket( key ).contains( key );
717 template <typename Q>
718 CDS_DEPRECATED("use contains()")
719 bool find( Q const& key )
721 return contains( key );
725 /// Checks whether the set contains \p key using \p pred predicate for searching
727 The function is an analog of <tt>contains( key )</tt> but \p pred is used for key comparing.
728 \p Less functor has the interface like \p std::less.
729 \p Less must imply the same element order as the comparator used for building the set.
731 template <typename Q, typename Less>
732 bool contains( Q const& key, Less pred )
734 return bucket( key ).contains( key, pred );
737 template <typename Q, typename Less>
738 CDS_DEPRECATED("use contains()")
739 bool find_with( Q const& key, Less pred )
741 return contains( key, pred );
745 /// Finds the key \p key and return the item found
746 /** \anchor cds_intrusive_MichaelHashSet_hp_get
747 The function searches the item with key equal to \p key
748 and returns the guarded pointer to the item found.
749 If \p key is not found the function returns an empty \p guarded_ptr.
751 @note Each \p guarded_ptr object uses one GC's guard which can be limited resource.
755 typedef cds::intrusive::MichaelHashSet< your_template_params > michael_set;
759 michael_set::guarded_ptr gp( theSet.get( 5 ));
760 if ( theSet.get( 5 )) {
764 // Destructor of guarded_ptr releases internal HP guard
768 Note the compare functor specified for \p OrderedList template parameter
769 should accept a parameter of type \p Q that can be not the same as \p value_type.
771 template <typename Q>
772 guarded_ptr get( Q const& key )
774 return bucket( key ).get( key );
777 /// Finds the key \p key and return the item found
779 The function is an analog of \ref cds_intrusive_MichaelHashSet_hp_get "get( Q const&)"
780 but \p pred is used for comparing the keys.
782 \p Less functor has the semantics like \p std::less but should take arguments of type \ref value_type and \p Q
784 \p pred must imply the same element order as the comparator used for building the set.
786 template <typename Q, typename Less>
787 guarded_ptr get_with( Q const& key, Less pred )
789 return bucket( key ).get_with( key, pred );
792 /// Clears the set (non-atomic)
794 The function unlink all items from the set.
795 The function is not atomic. It cleans up each bucket and then resets the item counter to zero.
796 If there are a thread that performs insertion while \p %clear() is working the result is undefined in general case:
797 \p empty() may return \p true but the set may contain item(s).
798 Therefore, \p %clear() may be used only for debugging purposes.
800 For each item the \p disposer is called after unlinking.
804 for ( size_t i = 0; i < bucket_count(); ++i )
805 m_Buckets[i].clear();
806 m_ItemCounter.reset();
809 /// Checks if the set is empty
811 Emptiness is checked by item counting: if item count is zero then the set is empty.
812 Thus, the correct item counting feature is an important part of Michael's set implementation.
819 /// Returns item count in the set
822 return m_ItemCounter;
825 /// Returns the size of hash table
827 Since \p %MichaelHashSet cannot dynamically extend the hash table size,
828 the value returned is an constant depending on object initialization parameters,
829 see \p MichaelHashSet::MichaelHashSet.
831 size_t bucket_count() const
833 return m_nHashBitmask + 1;
837 }} // namespace cds::intrusive
839 #endif // ifndef CDSLIB_INTRUSIVE_MICHAEL_SET_H