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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 ) ];
297 The forward iterator for Michael's set is based on \p OrderedList forward iterator and has some features:
298 - it has no post-increment operator
299 - it iterates items in unordered fashion
300 - The iterator cannot be moved across thread boundary since it may contain GC's guard that is thread-private GC data.
301 - Iterator ensures thread-safety even if you delete the item that iterator points to. However, in case of concurrent
302 deleting operations it is no guarantee that you iterate all item in the set.
304 Therefore, the use of iterators in concurrent environment is not good idea. Use the iterator for the concurrent container
305 for debug purpose only.
307 typedef michael_set::details::iterator< bucket_type, false > iterator;
309 /// Const forward iterator
311 For iterator's features and requirements see \ref iterator
313 typedef michael_set::details::iterator< bucket_type, true > const_iterator;
315 /// Returns a forward iterator addressing the first element in a set
317 For empty set \code begin() == end() \endcode
321 return iterator( m_Buckets[0].begin(), m_Buckets, m_Buckets + bucket_count() );
324 /// Returns an iterator that addresses the location succeeding the last element in a set
326 Do not use the value returned by <tt>end</tt> function to access any item.
327 The returned value can be used only to control reaching the end of the set.
328 For empty set \code begin() == end() \endcode
332 return iterator( m_Buckets[bucket_count() - 1].end(), m_Buckets + bucket_count() - 1, m_Buckets + bucket_count() );
335 /// Returns a forward const iterator addressing the first element in a set
337 const_iterator begin() const
339 return get_const_begin();
341 const_iterator cbegin() const
343 return get_const_begin();
347 /// Returns an const iterator that addresses the location succeeding the last element in a set
349 const_iterator end() const
351 return get_const_end();
353 const_iterator cend() const
355 return get_const_end();
361 const_iterator get_const_begin() const
363 return const_iterator( m_Buckets[0].cbegin(), m_Buckets, m_Buckets + bucket_count() );
365 const_iterator get_const_end() const
367 return const_iterator( m_Buckets[bucket_count() - 1].cend(), m_Buckets + bucket_count() - 1, m_Buckets + bucket_count() );
372 /// Initializes hash set
373 /** @anchor cds_intrusive_MichaelHashSet_hp_ctor
374 The Michael's hash set is an unbounded container, but its hash table is non-expandable.
375 At construction time you should pass estimated maximum item count and a load factor.
376 The load factor is average size of one bucket - a small number between 1 and 10.
377 The bucket is an ordered single-linked list, searching in the bucket has linear complexity <tt>O(nLoadFactor)</tt>.
378 The constructor defines hash table size as rounding <tt>nMaxItemCount / nLoadFactor</tt> up to nearest power of two.
381 size_t nMaxItemCount, ///< estimation of max item count in the hash set
382 size_t nLoadFactor ///< load factor: estimation of max number of items in the bucket. Small integer up to 10.
383 ) : m_nHashBitmask( michael_set::details::init_hash_bitmask( nMaxItemCount, nLoadFactor ))
385 // GC and OrderedList::gc must be the same
386 static_assert( std::is_same<gc, typename bucket_type::gc>::value, "GC and OrderedList::gc must be the same");
388 // atomicity::empty_item_counter is not allowed as a item counter
389 static_assert( !std::is_same<item_counter, atomicity::empty_item_counter>::value,
390 "cds::atomicity::empty_item_counter is not allowed as a item counter");
392 m_Buckets = bucket_table_allocator().NewArray( bucket_count() );
395 /// Clears hash set object and destroys it
399 bucket_table_allocator().Delete( m_Buckets, bucket_count() );
404 The function inserts \p val in the set if it does not contain
405 an item with key equal to \p val.
407 Returns \p true if \p val is placed into the set, \p false otherwise.
409 bool insert( value_type& val )
411 bool bRet = bucket( val ).insert( val );
419 This function is intended for derived non-intrusive containers.
421 The function allows to split creating of new item into two part:
422 - create item with key only
423 - insert new item into the set
424 - if inserting is success, calls \p f functor to initialize value-field of \p val.
426 The functor signature is:
428 void func( value_type& val );
430 where \p val is the item inserted.
432 The user-defined functor is called only if the inserting is success.
434 @warning For \ref cds_intrusive_MichaelList_hp "MichaelList" as the bucket see \ref cds_intrusive_item_creating "insert item troubleshooting".
435 \ref cds_intrusive_LazyList_hp "LazyList" provides exclusive access to inserted item and does not require any node-level
438 template <typename Func>
439 bool insert( value_type& val, Func f )
441 bool bRet = bucket( val ).insert( val, f );
447 /// Updates the element
449 The operation performs inserting or changing data with lock-free manner.
451 If the item \p val not found in the set, then \p val is inserted iff \p bAllowInsert is \p true.
452 Otherwise, the functor \p func is called with item found.
453 The functor signature is:
456 void operator()( bool bNew, value_type& item, value_type& val );
460 - \p bNew - \p true if the item has been inserted, \p false otherwise
461 - \p item - item of the set
462 - \p val - argument \p val passed into the \p %update() function
463 If new item has been inserted (i.e. \p bNew is \p true) then \p item and \p val arguments
464 refers to the same thing.
466 The functor may change non-key fields of the \p item.
468 Returns <tt> std::pair<bool, bool> </tt> where \p first is \p true if operation is successfull,
469 \p second is \p true if new item has been added or \p false if the item with \p key
470 already is in the set.
472 @warning For \ref cds_intrusive_MichaelList_hp "MichaelList" as the bucket see \ref cds_intrusive_item_creating "insert item troubleshooting".
473 \ref cds_intrusive_LazyList_hp "LazyList" provides exclusive access to inserted item and does not require any node-level
476 template <typename Func>
477 std::pair<bool, bool> update( value_type& val, Func func, bool bAllowInsert = true )
479 std::pair<bool, bool> bRet = bucket( val ).update( val, func, bAllowInsert );
485 template <typename Func>
486 CDS_DEPRECATED("ensure() is deprecated, use update()")
487 std::pair<bool, bool> ensure( value_type& val, Func func )
489 return update( val, func, true );
493 /// Unlinks the item \p val from the set
495 The function searches the item \p val in the set and unlink it
496 if it is found and is equal to \p val.
498 The function returns \p true if success and \p false otherwise.
500 bool unlink( value_type& val )
502 bool bRet = bucket( val ).unlink( val );
508 /// Deletes the item from the set
509 /** \anchor cds_intrusive_MichaelHashSet_hp_erase
510 The function searches an item with key equal to \p key in the set,
511 unlinks it, and returns \p true.
512 If the item with key equal to \p key is not found the function return \p false.
514 Note the hash functor should accept a parameter of type \p Q that can be not the same as \p value_type.
516 template <typename Q>
517 bool erase( Q const& key )
519 if ( bucket( key ).erase( key )) {
526 /// Deletes the item from the set using \p pred predicate for searching
528 The function is an analog of \ref cds_intrusive_MichaelHashSet_hp_erase "erase(Q const&)"
529 but \p pred is used for key comparing.
530 \p Less functor has the interface like \p std::less.
531 \p pred must imply the same element order as the comparator used for building the set.
533 template <typename Q, typename Less>
534 bool erase_with( Q const& key, Less pred )
536 if ( bucket( key ).erase_with( key, pred )) {
543 /// Deletes the item from the set
544 /** \anchor cds_intrusive_MichaelHashSet_hp_erase_func
545 The function searches an item with key equal to \p key in the set,
546 call \p f functor with item found, and unlinks it from the set.
547 The \ref disposer specified in \p OrderedList class template parameter is called
548 by garbage collector \p GC asynchronously.
550 The \p Func interface is
553 void operator()( value_type const& item );
557 If the item with key equal to \p key is not found the function return \p false.
559 Note the hash functor should accept a parameter of type \p Q that can be not the same as \p value_type.
561 template <typename Q, typename Func>
562 bool erase( const Q& key, Func f )
564 if ( bucket( key ).erase( key, f )) {
571 /// Deletes the item from the set using \p pred predicate for searching
573 The function is an analog of \ref cds_intrusive_MichaelHashSet_hp_erase_func "erase(Q const&, Func)"
574 but \p pred is used for key comparing.
575 \p Less functor has the interface like \p std::less.
576 \p pred must imply the same element order as the comparator used for building the set.
578 template <typename Q, typename Less, typename Func>
579 bool erase_with( const Q& key, Less pred, Func f )
581 if ( bucket( key ).erase_with( key, pred, f )) {
588 /// Extracts the item with specified \p key
589 /** \anchor cds_intrusive_MichaelHashSet_hp_extract
590 The function searches an item with key equal to \p key,
591 unlinks it from the set, and returns an guarded pointer to the item extracted.
592 If \p key is not found the function returns an empty guarded pointer.
594 Note the compare functor should accept a parameter of type \p Q that may be not the same as \p value_type.
596 The \p disposer specified in \p OrderedList class' template parameter is called automatically
597 by garbage collector \p GC when returned \ref guarded_ptr object will be destroyed or released.
598 @note Each \p guarded_ptr object uses the GC's guard that can be limited resource.
602 typedef cds::intrusive::MichaelHashSet< your_template_args > michael_set;
606 michael_set::guarded_ptr gp( theSet.extract( 5 ));
611 // Destructor of gp releases internal HP guard
615 template <typename Q>
616 guarded_ptr extract( Q const& key )
618 guarded_ptr gp = bucket( key ).extract( key );
624 /// Extracts the item using compare functor \p pred
626 The function is an analog of \ref cds_intrusive_MichaelHashSet_hp_extract "extract(Q const&)"
627 but \p pred predicate is used for key comparing.
629 \p Less functor has the semantics like \p std::less but should take arguments of type \ref value_type and \p Q
631 \p pred must imply the same element order as the comparator used for building the list.
633 template <typename Q, typename Less>
634 guarded_ptr extract_with( Q const& key, Less pred )
636 guarded_ptr gp = bucket( key ).extract_with( key, pred );
642 /// Finds the key \p key
643 /** \anchor cds_intrusive_MichaelHashSet_hp_find_func
644 The function searches the item with key equal to \p key and calls the functor \p f for item found.
645 The interface of \p Func functor is:
648 void operator()( value_type& item, Q& key );
651 where \p item is the item found, \p key is the <tt>find</tt> function argument.
653 The functor may change non-key fields of \p item. Note that the functor is only guarantee
654 that \p item cannot be disposed during functor is executing.
655 The functor does not serialize simultaneous access to the set \p item. If such access is
656 possible you must provide your own synchronization schema on item level to exclude unsafe item modifications.
658 The \p key argument is non-const since it can be used as \p f functor destination i.e., the functor
659 may modify both arguments.
661 Note the hash functor specified for class \p Traits template parameter
662 should accept a parameter of type \p Q that can be not the same as \p value_type.
664 The function returns \p true if \p key is found, \p false otherwise.
666 template <typename Q, typename Func>
667 bool find( Q& key, Func f )
669 return bucket( key ).find( key, f );
672 template <typename Q, typename Func>
673 bool find( Q const& key, Func f )
675 return bucket( key ).find( key, f );
679 /// Finds the key \p key using \p pred predicate for searching
681 The function is an analog of \ref cds_intrusive_MichaelHashSet_hp_find_func "find(Q&, Func)"
682 but \p pred is used for key comparing.
683 \p Less functor has the interface like \p std::less.
684 \p pred must imply the same element order as the comparator used for building the set.
686 template <typename Q, typename Less, typename Func>
687 bool find_with( Q& key, Less pred, Func f )
689 return bucket( key ).find_with( key, pred, f );
692 template <typename Q, typename Less, typename Func>
693 bool find_with( Q const& key, Less pred, Func f )
695 return bucket( key ).find_with( key, pred, f );
699 /// Checks whether the set contains \p key
702 The function searches the item with key equal to \p key
703 and returns \p true if the key is found, and \p false otherwise.
705 Note the hash functor specified for class \p Traits template parameter
706 should accept a parameter of type \p Q that can be not the same as \p value_type.
708 template <typename Q>
709 bool contains( Q const& key )
711 return bucket( key ).contains( key );
714 template <typename Q>
715 CDS_DEPRECATED("use contains()")
716 bool find( Q const& key )
718 return contains( key );
722 /// Checks whether the set contains \p key using \p pred predicate for searching
724 The function is an analog of <tt>contains( key )</tt> but \p pred is used for key comparing.
725 \p Less functor has the interface like \p std::less.
726 \p Less must imply the same element order as the comparator used for building the set.
728 template <typename Q, typename Less>
729 bool contains( Q const& key, Less pred )
731 return bucket( key ).contains( key, pred );
734 template <typename Q, typename Less>
735 CDS_DEPRECATED("use contains()")
736 bool find_with( Q const& key, Less pred )
738 return contains( key, pred );
742 /// Finds the key \p key and return the item found
743 /** \anchor cds_intrusive_MichaelHashSet_hp_get
744 The function searches the item with key equal to \p key
745 and returns the guarded pointer to the item found.
746 If \p key is not found the function returns an empty \p guarded_ptr.
748 @note Each \p guarded_ptr object uses one GC's guard which can be limited resource.
752 typedef cds::intrusive::MichaelHashSet< your_template_params > michael_set;
756 michael_set::guarded_ptr gp( theSet.get( 5 ));
757 if ( theSet.get( 5 )) {
761 // Destructor of guarded_ptr releases internal HP guard
765 Note the compare functor specified for \p OrderedList template parameter
766 should accept a parameter of type \p Q that can be not the same as \p value_type.
768 template <typename Q>
769 guarded_ptr get( Q const& key )
771 return bucket( key ).get( key );
774 /// Finds the key \p key and return the item found
776 The function is an analog of \ref cds_intrusive_MichaelHashSet_hp_get "get( Q const&)"
777 but \p pred is used for comparing the keys.
779 \p Less functor has the semantics like \p std::less but should take arguments of type \ref value_type and \p Q
781 \p pred must imply the same element order as the comparator used for building the set.
783 template <typename Q, typename Less>
784 guarded_ptr get_with( Q const& key, Less pred )
786 return bucket( key ).get_with( key, pred );
789 /// Clears the set (non-atomic)
791 The function unlink all items from the set.
792 The function is not atomic. It cleans up each bucket and then resets the item counter to zero.
793 If there are a thread that performs insertion while \p %clear() is working the result is undefined in general case:
794 \p empty() may return \p true but the set may contain item(s).
795 Therefore, \p %clear() may be used only for debugging purposes.
797 For each item the \p disposer is called after unlinking.
801 for ( size_t i = 0; i < bucket_count(); ++i )
802 m_Buckets[i].clear();
803 m_ItemCounter.reset();
806 /// Checks if the set is empty
808 Emptiness is checked by item counting: if item count is zero then the set is empty.
809 Thus, the correct item counting feature is an important part of Michael's set implementation.
816 /// Returns item count in the set
819 return m_ItemCounter;
822 /// Returns the size of hash table
824 Since \p %MichaelHashSet cannot dynamically extend the hash table size,
825 the value returned is an constant depending on object initialization parameters,
826 see \p MichaelHashSet::MichaelHashSet.
828 size_t bucket_count() const
830 return m_nHashBitmask + 1;
834 }} // namespace cds::intrusive
836 #endif // ifndef CDSLIB_INTRUSIVE_MICHAEL_SET_H