2 This file is a part of libcds - Concurrent Data Structures library
4 (C) Copyright Maxim Khizhinsky (libcds.dev@gmail.com) 2006-2016
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31 #ifndef CDSLIB_CONTAINER_MICHAEL_SET_RCU_H
32 #define CDSLIB_CONTAINER_MICHAEL_SET_RCU_H
34 #include <cds/container/details/michael_set_base.h>
35 #include <cds/details/allocator.h>
37 namespace cds { namespace container {
39 /// Michael's hash set (template specialization for \ref cds_urcu_desc "RCU")
40 /** @ingroup cds_nonintrusive_set
41 \anchor cds_nonintrusive_MichaelHashSet_rcu
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 RCU - one of \ref cds_urcu_gc "RCU type"
53 - \p OrderedList - ordered list implementation used as the bucket for hash set, for example,
54 \ref cds_nonintrusive_MichaelList_rcu "MichaelList".
55 The ordered list implementation specifies the type \p T stored in the hash-set,
56 the comparison functor for the type \p T and other features specific for
58 - \p Traits - set traits, default is michael_set::traits.
59 Instead of defining \p Traits struct you may use option-based syntax with michael_set::make_traits metafunction.
61 About hash functor see \ref cds_nonintrusive_MichaelHashSet_hash_functor "MichaelSet hash functor".
65 Suppose, we have the following type \p Foo that we want to store in your \p %MichaelHashSet:
68 int nKey ; // key field
69 int nVal ; // value field
73 To use \p %MichaelHashSet for \p Foo values, you should first choose suitable ordered list class
74 that will be used as a bucket for the set. We will cds::urcu::general_buffered<> RCU type and
75 MichaelList as a bucket type.
76 You should include RCU-related header file (<tt>cds/urcu/general_buffered.h</tt> in this example)
77 before including <tt>cds/container/michael_set_rcu.h</tt>.
78 Also, for ordered list we should develop a comparator for our \p Foo struct.
80 #include <cds/urcu/general_buffered.h>
81 #include <cds/container/michael_list_rcu.h>
82 #include <cds/container/michael_set_rcu.h>
84 namespace cc = cds::container;
88 int operator ()(Foo const& v1, Foo const& v2 ) const
90 if ( std::less( v1.nKey, v2.nKey ))
92 return std::less(v2.nKey, v1.nKey) ? 1 : 0;
97 typedef cc::MichaelList< cds::urcu::gc< cds::urcu::general_buffered<> >, Foo,
98 typename cc::michael_list::make_traits<
99 cc::opt::compare< Foo_cmp > // item comparator option
103 // Hash functor for Foo
105 size_t operator ()( int i ) const
107 return std::hash( i );
109 size_t operator()( Foo const& i ) const
111 return std::hash( i.nKey );
116 // Note that \p RCU template parameter of ordered list must be equal \p RCU for the set.
117 typedef cc::MichaelHashSet< cds::urcu::gc< cds::urcu::general_buffered<> >, bucket_list,
118 cc::michael_set::make_traits<
119 cc::opt::hash< foo_hash >
129 #ifdef CDS_DOXYGEN_INVOKED
130 class Traits = michael_set::traits
135 class MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >
138 typedef cds::urcu::gc< RCU > gc; ///< RCU used as garbage collector
139 typedef OrderedList bucket_type; ///< type of ordered list to be used as a bucket implementation
140 typedef Traits traits; ///< Set traits
142 typedef typename bucket_type::value_type value_type; ///< type of value to be stored in the list
143 typedef typename bucket_type::key_comparator key_comparator; ///< key comparing functor
145 /// Hash functor for \ref value_type and all its derivatives that you use
146 typedef typename cds::opt::v::hash_selector< typename traits::hash >::type hash;
147 typedef typename traits::item_counter item_counter; ///< Item counter type
149 typedef typename bucket_type::rcu_lock rcu_lock; ///< RCU scoped lock
150 typedef typename bucket_type::exempt_ptr exempt_ptr; ///< pointer to extracted node
151 typedef typename bucket_type::raw_ptr raw_ptr; ///< Return type of \p get() member function and its derivatives
152 /// Group of \p extract_xxx functions require external locking if underlying ordered list requires that
153 static CDS_CONSTEXPR const bool c_bExtractLockExternal = bucket_type::c_bExtractLockExternal;
157 class internal_bucket_type: public bucket_type
159 typedef bucket_type base_class;
161 using base_class::node_type;
162 using base_class::alloc_node;
163 using base_class::insert_node;
164 using base_class::node_to_value;
167 /// Bucket table allocator
168 typedef cds::details::Allocator< internal_bucket_type, typename traits::allocator > bucket_table_allocator;
173 item_counter m_ItemCounter; ///< Item counter
174 hash m_HashFunctor; ///< Hash functor
175 internal_bucket_type * m_Buckets; ///< bucket table
179 const size_t m_nHashBitmask;
184 /// Calculates hash value of \p key
185 template <typename Q>
186 size_t hash_value( Q const& key ) const
188 return m_HashFunctor( key ) & m_nHashBitmask;
191 /// Returns the bucket (ordered list) for \p key
192 template <typename Q>
193 internal_bucket_type& bucket( Q const& key )
195 return m_Buckets[ hash_value( key ) ];
197 template <typename Q>
198 internal_bucket_type const& bucket( Q const& key ) const
200 return m_Buckets[ hash_value( key ) ];
204 ///@name Forward iterators (thread-safe under RCU lock)
208 The forward iterator for Michael's set is based on \p OrderedList forward iterator and has some features:
209 - it has no post-increment operator
210 - it iterates items in unordered fashion
212 You may safely use iterators in multi-threaded environment only under RCU lock.
213 Otherwise, a crash is possible if another thread deletes the element the iterator points to.
215 The iterator interface:
219 // Default constructor
223 iterator( iterator const& src );
225 // Dereference operator
226 value_type * operator ->() const;
228 // Dereference operator
229 value_type& operator *() const;
231 // Preincrement operator
232 iterator& operator ++();
234 // Assignment operator
235 iterator& operator = (iterator const& src);
237 // Equality operators
238 bool operator ==(iterator const& i ) const;
239 bool operator !=(iterator const& i ) const;
243 typedef michael_set::details::iterator< bucket_type, false > iterator;
245 /// Const forward iterator
246 typedef michael_set::details::iterator< bucket_type, true > const_iterator;
248 /// Returns a forward iterator addressing the first element in a set
250 For empty set \code begin() == end() \endcode
254 return iterator( m_Buckets[0].begin(), m_Buckets, m_Buckets + bucket_count() );
257 /// Returns an iterator that addresses the location succeeding the last element in a set
259 Do not use the value returned by <tt>end</tt> function to access any item.
260 The returned value can be used only to control reaching the end of the set.
261 For empty set \code begin() == end() \endcode
265 return iterator( m_Buckets[bucket_count() - 1].end(), m_Buckets + bucket_count() - 1, m_Buckets + bucket_count() );
268 /// Returns a forward const iterator addressing the first element in a set
269 const_iterator begin() const
271 return get_const_begin();
274 /// Returns a forward const iterator addressing the first element in a set
275 const_iterator cbegin() const
277 return get_const_begin();
280 /// Returns an const iterator that addresses the location succeeding the last element in a set
281 const_iterator end() const
283 return get_const_end();
286 /// Returns an const iterator that addresses the location succeeding the last element in a set
287 const_iterator cend() const
289 return get_const_end();
295 const_iterator get_const_begin() const
297 return const_iterator( const_cast<internal_bucket_type const&>(m_Buckets[0]).begin(), m_Buckets, m_Buckets + bucket_count() );
299 const_iterator get_const_end() const
301 return const_iterator( const_cast<internal_bucket_type const&>(m_Buckets[bucket_count() - 1]).end(), m_Buckets + bucket_count() - 1, m_Buckets + bucket_count() );
306 /// Initialize hash set
308 The Michael's hash set is non-expandable container. You should point the average count of items \p nMaxItemCount
309 when you create an object.
310 \p nLoadFactor parameter defines average count of items per bucket and it should be small number between 1 and 10.
311 Remember, since the bucket implementation is an ordered list, searching in the bucket is linear [<tt>O(nLoadFactor)</tt>].
313 The ctor defines hash table size as rounding <tt>nMaxItemCount / nLoadFactor</tt> up to nearest power of two.
316 size_t nMaxItemCount, ///< estimation of max item count in the hash set
317 size_t nLoadFactor ///< load factor: estimation of max number of items in the bucket
318 ) : m_nHashBitmask( michael_set::details::init_hash_bitmask( nMaxItemCount, nLoadFactor ))
320 // GC and OrderedList::gc must be the same
321 static_assert( std::is_same<gc, typename bucket_type::gc>::value, "GC and OrderedList::gc must be the same");
323 static_assert( !std::is_same<item_counter, atomicity::empty_item_counter>::value,
324 "atomicity::empty_item_counter is not allowed as a item counter");
326 m_Buckets = bucket_table_allocator().NewArray( bucket_count() );
329 /// Clears hash set and destroys it
333 bucket_table_allocator().Delete( m_Buckets, bucket_count() );
338 The function creates a node with copy of \p val value
339 and then inserts the node created into the set.
341 The type \p Q should contain as minimum the complete key for the node.
342 The object of \ref value_type should be constructible from a value of type \p Q.
343 In trivial case, \p Q is equal to \ref value_type.
345 The function applies RCU lock internally.
347 Returns \p true if \p val is inserted into the set, \p false otherwise.
349 template <typename Q>
350 bool insert( Q const& val )
352 const bool bRet = bucket( val ).insert( val );
360 The function allows to split creating of new item into two part:
361 - create item with key only
362 - insert new item into the set
363 - if inserting is success, calls \p f functor to initialize value-fields of \p val.
365 The functor signature is:
367 void func( value_type& val );
369 where \p val is the item inserted.
370 The user-defined functor is called only if the inserting is success.
372 The function applies RCU lock internally.
374 @warning For \ref cds_nonintrusive_MichaelList_rcu "MichaelList" as the bucket see \ref cds_intrusive_item_creating "insert item troubleshooting".
375 \ref cds_nonintrusive_LazyList_rcu "LazyList" provides exclusive access to inserted item and does not require any node-level
378 template <typename Q, typename Func>
379 bool insert( Q const& val, Func f )
381 const bool bRet = bucket( val ).insert( val, f );
388 /// Updates the element
390 The operation performs inserting or changing data with lock-free manner.
392 If the item \p val not found in the set, then \p val is inserted iff \p bAllowInsert is \p true.
393 Otherwise, the functor \p func is called with item found.
394 The functor signature is:
397 void operator()( bool bNew, value_type& item, Q const& val );
401 - \p bNew - \p true if the item has been inserted, \p false otherwise
402 - \p item - item of the set
403 - \p val - argument \p val passed into the \p %update() function
405 The functor may change non-key fields of the \p item.
407 The function applies RCU lock internally.
409 Returns <tt> std::pair<bool, bool> </tt> where \p first is \p true if operation is successful,
410 \p second is \p true if new item has been added or \p false if the item with \p key
411 already is in the set.
413 @warning For \ref cds_intrusive_MichaelList_hp "MichaelList" as the bucket see \ref cds_intrusive_item_creating "insert item troubleshooting".
414 \ref cds_intrusive_LazyList_hp "LazyList" provides exclusive access to inserted item and does not require any node-level
417 template <typename Q, typename Func>
418 std::pair<bool, bool> update( const Q& val, Func func, bool bAllowInsert = true )
420 std::pair<bool, bool> bRet = bucket( val ).update( val, func, bAllowInsert );
425 template <typename Q, typename Func>
426 CDS_DEPRECATED("ensure() is deprecated, use update()")
427 std::pair<bool, bool> ensure( const Q& val, Func func )
429 return update( val, func, true );
433 /// Inserts data of type \p value_type created from \p args
435 Returns \p true if inserting successful, \p false otherwise.
437 The function applies RCU lock internally.
439 template <typename... Args>
440 bool emplace( Args&&... args )
442 typename internal_bucket_type::node_type * pNode = internal_bucket_type::alloc_node( std::forward<Args>( args )... );
443 bool bRet = bucket( internal_bucket_type::node_to_value( *pNode ) ).insert_node( pNode );
449 /// Deletes \p key from the set
450 /** \anchor cds_nonintrusive_MichealSet_rcu_erase_val
452 Since the key of MichaelHashSet's item type \p value_type is not explicitly specified,
453 template parameter \p Q defines the key type searching in the list.
454 The set item comparator should be able to compare the type \p value_type
457 RCU \p synchronize method can be called. RCU should not be locked.
459 Return \p true if key is found and deleted, \p false otherwise
461 template <typename Q>
462 bool erase( Q const& key )
464 const bool bRet = bucket( key ).erase( key );
470 /// Deletes the item from the set using \p pred predicate for searching
472 The function is an analog of \ref cds_nonintrusive_MichealSet_rcu_erase_val "erase(Q const&)"
473 but \p pred is used for key comparing.
474 \p Less functor has the interface like \p std::less.
475 \p Less must imply the same element order as the comparator used for building the set.
477 template <typename Q, typename Less>
478 bool erase_with( Q const& key, Less pred )
480 const bool bRet = bucket( key ).erase_with( key, pred );
486 /// Deletes \p key from the set
487 /** \anchor cds_nonintrusive_MichealSet_rcu_erase_func
489 The function searches an item with key \p key, calls \p f functor
490 and deletes the item. If \p key is not found, the functor is not called.
492 The functor \p Func interface:
495 void operator()(value_type const& val);
499 Since the key of %MichaelHashSet's \p value_type is not explicitly specified,
500 template parameter \p Q defines the key type searching in the list.
501 The list item comparator should be able to compare the type \p T of list item
504 RCU \p synchronize method can be called. RCU should not be locked.
506 Return \p true if key is found and deleted, \p false otherwise
508 template <typename Q, typename Func>
509 bool erase( Q const& key, Func f )
511 const bool bRet = bucket( key ).erase( key, f );
517 /// Deletes the item from the set using \p pred predicate for searching
519 The function is an analog of \ref cds_nonintrusive_MichealSet_rcu_erase_func "erase(Q const&, Func)"
520 but \p pred is used for key comparing.
521 \p Less functor has the interface like \p std::less.
522 \p Less must imply the same element order as the comparator used for building the set.
524 template <typename Q, typename Less, typename Func>
525 bool erase_with( Q const& key, Less pred, Func f )
527 const bool bRet = bucket( key ).erase_with( key, pred, f );
533 /// Extracts an item from the set
534 /** \anchor cds_nonintrusive_MichaelHashSet_rcu_extract
535 The function searches an item with key equal to \p key in the set,
536 unlinks it from the set, and returns \ref cds::urcu::exempt_ptr "exempt_ptr" pointer to the item found.
537 If the item with the key equal to \p key is not found the function return an empty \p exempt_ptr.
539 The function just excludes the item from the set and returns a pointer to item found.
540 Depends on \p bucket_type you should or should not lock RCU before calling of this function:
541 - for the set based on \ref cds_nonintrusive_MichaelList_rcu "MichaelList" RCU should not be locked
542 - for the set based on \ref cds_nonintrusive_LazyList_rcu "LazyList" RCU should be locked
543 See ordered list implementation for details.
546 #include <cds/urcu/general_buffered.h>
547 #include <cds/container/michael_list_rcu.h>
548 #include <cds/container/michael_set_rcu.h>
550 typedef cds::urcu::gc< general_buffered<> > rcu;
551 typedef cds::container::MichaelList< rcu, Foo > rcu_michael_list;
552 typedef cds::container::MichaelHashSet< rcu, rcu_michael_list, foo_traits > rcu_michael_set;
554 rcu_michael_set theSet;
557 typename rcu_michael_set::exempt_ptr p;
559 // For MichaelList we should not lock RCU
561 // Note that you must not delete the item found inside the RCU lock
562 p = theSet.extract( 10 );
564 // do something with p
568 // We may safely release p here
569 // release() passes the pointer to RCU reclamation cycle
573 template <typename Q>
574 exempt_ptr extract( Q const& key )
576 exempt_ptr p = bucket( key ).extract( key );
582 /// Extracts an item from the set using \p pred predicate for searching
584 The function is an analog of \p extract(Q const&) but \p pred is used for key comparing.
585 \p Less functor has the interface like \p std::less.
586 \p pred must imply the same element order as the comparator used for building the set.
588 template <typename Q, typename Less>
589 exempt_ptr extract_with( Q const& key, Less pred )
591 exempt_ptr p = bucket( key ).extract_with( key, pred );
597 /// Finds the key \p key
598 /** \anchor cds_nonintrusive_MichealSet_rcu_find_func
600 The function searches the item with key equal to \p key and calls the functor \p f for item found.
601 The interface of \p Func functor is:
604 void operator()( value_type& item, Q& key );
607 where \p item is the item found, \p key is the <tt>find</tt> function argument.
609 The functor may change non-key fields of \p item. Note that the functor is only guarantee
610 that \p item cannot be disposed during functor is executing.
611 The functor does not serialize simultaneous access to the set's \p item. If such access is
612 possible you must provide your own synchronization schema on item level to exclude unsafe item modifications.
614 The \p key argument is non-const since it can be used as \p f functor destination i.e., the functor
615 can modify both arguments.
617 Note the hash functor specified for class \p Traits template parameter
618 should accept a parameter of type \p Q that may be not the same as \p value_type.
620 The function applies RCU lock internally.
622 The function returns \p true if \p key is found, \p false otherwise.
624 template <typename Q, typename Func>
625 bool find( Q& key, Func f )
627 return bucket( key ).find( key, f );
630 template <typename Q, typename Func>
631 bool find( Q const& key, Func f )
633 return bucket( key ).find( key, f );
637 /// Finds the key \p key using \p pred predicate for searching
639 The function is an analog of \ref cds_nonintrusive_MichealSet_rcu_find_func "find(Q&, Func)"
640 but \p pred is used for key comparing.
641 \p Less functor has the interface like \p std::less.
642 \p Less must imply the same element order as the comparator used for building the set.
644 template <typename Q, typename Less, typename Func>
645 bool find_with( Q& key, Less pred, Func f )
647 return bucket( key ).find_with( key, pred, f );
650 template <typename Q, typename Less, typename Func>
651 bool find_with( Q const& key, Less pred, Func f )
653 return bucket( key ).find_with( key, pred, f );
657 /// Checks whether the set contains \p key
660 The function searches the item with key equal to \p key
661 and returns \p true if the key is found, and \p false otherwise.
663 Note the hash functor specified for class \p Traits template parameter
664 should accept a parameter of type \p Q that can be not the same as \p value_type.
666 template <typename Q>
667 bool contains( Q const& key )
669 return bucket( key ).contains( key );
672 template <typename Q>
673 CDS_DEPRECATED("use contains()")
674 bool find( Q const& key )
676 return contains( key );
680 /// Checks whether the set contains \p key using \p pred predicate for searching
682 The function is an analog of <tt>contains( key )</tt> but \p pred is used for key comparing.
683 \p Less functor has the interface like \p std::less.
684 \p Less must imply the same element order as the comparator used for building the set.
686 template <typename Q, typename Less>
687 bool contains( Q const& key, Less pred )
689 return bucket( key ).contains( key, pred );
692 template <typename Q, typename Less>
693 CDS_DEPRECATED("use contains()")
694 bool find_with( Q const& key, Less pred )
696 return contains( key, pred );
700 /// Finds the key \p key and return the item found
701 /** \anchor cds_nonintrusive_MichaelHashSet_rcu_get
702 The function searches the item with key equal to \p key and returns the pointer to item found.
703 If \p key is not found it returns \p nullptr.
704 Note the type of returned value depends on underlying \p bucket_type.
705 For details, see documentation of ordered list you use.
707 Note the compare functor should accept a parameter of type \p Q that can be not the same as \p value_type.
709 RCU should be locked before call of this function.
710 Returned item is valid only while RCU is locked:
712 typedef cds::container::MichaelHashSet< your_template_parameters > hash_set;
714 typename hash_set::raw_ptr gp;
718 hash_set::rcu_lock lock;
720 gp = theSet.get( 5 );
725 // Unlock RCU by rcu_lock destructor
726 // gp can be reclaimed at any time after RCU has been unlocked
730 template <typename Q>
731 raw_ptr get( Q const& key )
733 return bucket( key ).get( key );
736 /// Finds the key \p key and return the item found
738 The function is an analog of \ref cds_nonintrusive_MichaelHashSet_rcu_get "get(Q const&)"
739 but \p pred is used for comparing the keys.
741 \p Less functor has the semantics like \p std::less but should take arguments of type \ref value_type and \p Q
743 \p pred must imply the same element order as the comparator used for building the set.
745 template <typename Q, typename Less>
746 raw_ptr get_with( Q const& key, Less pred )
748 return bucket( key ).get_with( key, pred );
751 /// Clears the set (not atomic)
754 for ( size_t i = 0; i < bucket_count(); ++i )
755 m_Buckets[i].clear();
756 m_ItemCounter.reset();
759 /// Checks if the set is empty
761 Emptiness is checked by item counting: if item count is zero then the set is empty.
762 Thus, the correct item counting feature is an important part of Michael's set implementation.
769 /// Returns item count in the set
772 return m_ItemCounter;
775 /// Returns the size of hash table
777 Since \p %MichaelHashSet cannot dynamically extend the hash table size,
778 the value returned is an constant depending on object initialization parameters;
779 see MichaelHashSet::MichaelHashSet for explanation.
781 size_t bucket_count() const
783 return m_nHashBitmask + 1;
787 }} // namespace cds::container
789 #endif // ifndef CDSLIB_CONTAINER_MICHAEL_SET_RCU_H