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_INTRUSIVE_MICHAEL_SET_RCU_H
32 #define CDSLIB_INTRUSIVE_MICHAEL_SET_RCU_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, \ref cds_urcu_desc "RCU" specialization
40 /** @ingroup cds_intrusive_map
41 \anchor cds_intrusive_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 bucket for hash set, for example, MichaelList, 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, default is \p michael_set::traits.
58 Instead of defining \p Traits struct you can use option-based syntax with \p michael_set::make_traits metafunction.
61 Before including <tt><cds/intrusive/michael_set_rcu.h></tt> you should include appropriate RCU header file,
62 see \ref cds_urcu_gc "RCU type" for list of existing RCU class and corresponding header files.
63 For example, for \ref cds_urcu_general_buffered_gc "general-purpose buffered RCU" you should include:
65 #include <cds/urcu/general_buffered.h>
66 #include <cds/intrusive/michael_list_rcu.h>
67 #include <cds/intrusive/michael_set_rcu.h>
70 // Hash functor for struct Foo
72 size_t operator()( Foo const& foo ) const { return ... }
75 // Now, you can declare Michael's list for type Foo and default traits:
76 typedef cds::intrusive::MichaelList<cds::urcu::gc< general_buffered<> >, Foo > rcu_michael_list;
78 // Declare Michael's set with MichaelList as bucket type
79 typedef cds::intrusive::MichaelSet<
80 cds::urcu::gc< general_buffered<> >,
82 cds::intrusive::michael_set::make_traits<
83 cds::opt::::hash< foo_hash >
87 // Declares hash set for 1000000 items with load factor 2
88 rcu_michael_set theSet( 1000000, 2 );
90 // Now you can use theSet object in many threads without any synchronization.
96 #ifdef CDS_DOXYGEN_INVOKED
97 class Traits = michael_set::traits
102 class MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >
105 typedef cds::urcu::gc< RCU > gc; ///< RCU schema
106 typedef OrderedList bucket_type; ///< type of ordered list used as a bucket implementation
107 typedef Traits traits; ///< Set traits
109 typedef typename bucket_type::value_type value_type ; ///< type of value stored in the list
110 typedef typename bucket_type::key_comparator key_comparator ; ///< key comparing functor
111 typedef typename bucket_type::disposer disposer ; ///< Node disposer functor
113 /// Hash functor for \ref value_type and all its derivatives that you use
114 typedef typename cds::opt::v::hash_selector< typename traits::hash >::type hash;
115 typedef typename traits::item_counter item_counter; ///< Item counter type
117 /// Bucket table allocator
118 typedef cds::details::Allocator< bucket_type, typename traits::allocator > bucket_table_allocator;
120 typedef typename bucket_type::rcu_lock rcu_lock; ///< RCU scoped lock
121 typedef typename bucket_type::exempt_ptr exempt_ptr; ///< pointer to extracted node
122 typedef typename bucket_type::raw_ptr raw_ptr; ///< Return type of \p get() member function and its derivatives
123 /// Group of \p extract_xxx functions require external locking if underlying ordered list requires that
124 static CDS_CONSTEXPR const bool c_bExtractLockExternal = bucket_type::c_bExtractLockExternal;
127 item_counter m_ItemCounter; ///< Item counter
128 hash m_HashFunctor; ///< Hash functor
129 bucket_type * m_Buckets; ///< bucket table
133 const size_t m_nHashBitmask;
138 /// Calculates hash value of \p key
139 template <typename Q>
140 size_t hash_value( Q const& key ) const
142 return m_HashFunctor( key ) & m_nHashBitmask;
145 /// Returns the bucket (ordered list) for \p key
146 template <typename Q>
147 bucket_type& bucket( Q const& key )
149 return m_Buckets[ hash_value( key ) ];
151 template <typename Q>
152 bucket_type const& bucket( Q const& key ) const
154 return m_Buckets[ hash_value( key ) ];
159 ///@name Forward iterators (thread-safe under RCU lock)
163 The forward iterator for Michael's set is based on \p OrderedList forward iterator and has some features:
164 - it has no post-increment operator
165 - it iterates items in unordered fashion
167 You may safely use iterators in multi-threaded environment only under RCU lock.
168 Otherwise, a crash is possible if another thread deletes the element the iterator points to.
170 The iterator interface:
174 // Default constructor
178 iterator( iterator const& src );
180 // Dereference operator
181 value_type * operator ->() const;
183 // Dereference operator
184 value_type& operator *() const;
186 // Preincrement operator
187 iterator& operator ++();
189 // Assignment operator
190 iterator& operator = (iterator const& src);
192 // Equality operators
193 bool operator ==(iterator const& i ) const;
194 bool operator !=(iterator const& i ) const;
198 typedef michael_set::details::iterator< bucket_type, false > iterator;
200 /// Const forward iterator
202 For iterator's features and requirements see \ref iterator
204 typedef michael_set::details::iterator< bucket_type, true > const_iterator;
206 /// Returns a forward iterator addressing the first element in a set
208 For empty set \code begin() == end() \endcode
212 return iterator( m_Buckets[0].begin(), m_Buckets, m_Buckets + bucket_count() );
215 /// Returns an iterator that addresses the location succeeding the last element in a set
217 Do not use the value returned by <tt>end</tt> function to access any item.
218 The returned value can be used only to control reaching the end of the set.
219 For empty set \code begin() == end() \endcode
223 return iterator( m_Buckets[bucket_count() - 1].end(), m_Buckets + bucket_count() - 1, m_Buckets + bucket_count() );
226 /// Returns a forward const iterator addressing the first element in a set
227 const_iterator begin() const
232 /// Returns a forward const iterator addressing the first element in a set
233 const_iterator cbegin() const
235 return const_iterator( m_Buckets[0].cbegin(), m_Buckets, m_Buckets + bucket_count() );
238 /// Returns an const iterator that addresses the location succeeding the last element in a set
239 const_iterator end() const
244 /// Returns an const iterator that addresses the location succeeding the last element in a set
245 const_iterator cend() const
247 return const_iterator( m_Buckets[bucket_count() - 1].cend(), m_Buckets + bucket_count() - 1, m_Buckets + bucket_count() );
252 /// Initialize hash set
254 The Michael's hash set is an unbounded container, but its hash table is non-expandable.
255 At construction time you should pass estimated maximum item count and a load factor.
256 The load factor is average size of one bucket - a small number between 1 and 10.
257 The bucket is an ordered single-linked list, the complexity of searching in the bucket is linear <tt>O(nLoadFactor)</tt>.
258 The constructor defines hash table size as rounding <tt>nMaxItemCount / nLoadFactor</tt> up to nearest power of two.
261 size_t nMaxItemCount, ///< estimation of max item count in the hash set
262 size_t nLoadFactor ///< load factor: average size of the bucket
263 ) : m_nHashBitmask( michael_set::details::init_hash_bitmask( nMaxItemCount, nLoadFactor ))
265 // GC and OrderedList::gc must be the same
266 static_assert( std::is_same<gc, typename bucket_type::gc>::value, "GC and OrderedList::gc must be the same");
268 // atomicity::empty_item_counter is not allowed as a item counter
269 static_assert( !std::is_same<item_counter, atomicity::empty_item_counter>::value,
270 "atomicity::empty_item_counter is not allowed as a item counter");
272 m_Buckets = bucket_table_allocator().NewArray( bucket_count() );
275 /// Clear hash set and destroy it
279 bucket_table_allocator().Delete( m_Buckets, bucket_count() );
284 The function inserts \p val in the set if it does not contain
285 an item with key equal to \p val.
287 Returns \p true if \p val is placed into the set, \p false otherwise.
289 bool insert( value_type& val )
291 bool bRet = bucket( val ).insert( val );
299 This function is intended for derived non-intrusive containers.
301 The function allows to split creating of new item into two part:
302 - create item with key only
303 - insert new item into the set
304 - if inserting is success, calls \p f functor to initialize value-field of \p val.
306 The functor signature is:
308 void func( value_type& val );
310 where \p val is the item inserted.
311 The user-defined functor is called only if the inserting is success.
313 @warning For \ref cds_intrusive_MichaelList_rcu "MichaelList" as the bucket see \ref cds_intrusive_item_creating "insert item troubleshooting".
314 \ref cds_intrusive_LazyList_rcu "LazyList" provides exclusive access to inserted item and does not require any node-level
317 template <typename Func>
318 bool insert( value_type& val, Func f )
320 bool bRet = bucket( val ).insert( val, f );
326 /// Updates the element
328 The operation performs inserting or changing data with lock-free manner.
330 If the item \p val not found in the set, then \p val is inserted iff \p bAllowInsert is \p true.
331 Otherwise, the functor \p func is called with item found.
332 The functor signature is:
335 void operator()( bool bNew, value_type& item, value_type& val );
339 - \p bNew - \p true if the item has been inserted, \p false otherwise
340 - \p item - item of the set
341 - \p val - argument \p val passed into the \p %update() function
342 If new item has been inserted (i.e. \p bNew is \p true) then \p item and \p val arguments
343 refers to the same thing.
345 The functor may change non-key fields of the \p item.
347 Returns <tt> std::pair<bool, bool> </tt> where \p first is \p true if operation is successful,
348 \p second is \p true if new item has been added or \p false if the item with \p key
349 already is in the set.
351 @warning For \ref cds_intrusive_MichaelList_hp "MichaelList" as the bucket see \ref cds_intrusive_item_creating "insert item troubleshooting".
352 \ref cds_intrusive_LazyList_hp "LazyList" provides exclusive access to inserted item and does not require any node-level
355 template <typename Func>
356 std::pair<bool, bool> update( value_type& val, Func func, bool bAllowInsert = true )
358 std::pair<bool, bool> bRet = bucket( val ).update( val, func, bAllowInsert );
364 template <typename Func>
365 CDS_DEPRECATED("ensure() is deprecated, use update()")
366 std::pair<bool, bool> ensure( value_type& val, Func func )
368 return update( val, func, true );
372 /// Unlinks the item \p val from the set
374 The function searches the item \p val in the set and unlink it from the set
375 if it is found and is equal to \p val.
377 The function returns \p true if success and \p false otherwise.
379 bool unlink( value_type& val )
381 bool bRet = bucket( val ).unlink( val );
387 /// Deletes the item from the set
388 /** \anchor cds_intrusive_MichaelHashSet_rcu_erase
389 The function searches an item with key equal to \p key in the set,
390 unlinks it from the set, and returns \p true.
391 If the item with key equal to \p key is not found the function return \p false.
393 Note the hash functor should accept a parameter of type \p Q that may be not the same as \p value_type.
395 template <typename Q>
396 bool erase( Q const& key )
398 if ( bucket( key ).erase( key )) {
405 /// Deletes the item from the set using \p pred predicate for searching
407 The function is an analog of \ref cds_intrusive_MichaelHashSet_rcu_erase "erase(Q const&)"
408 but \p pred is used for key comparing.
409 \p Less functor has the interface like \p std::less.
410 \p pred must imply the same element order as the comparator used for building the set.
412 template <typename Q, typename Less>
413 bool erase_with( Q const& key, Less pred )
415 if ( bucket( key ).erase_with( key, pred )) {
422 /// Deletes the item from the set
423 /** \anchor cds_intrusive_MichaelHashSet_rcu_erase_func
424 The function searches an item with key equal to \p key in the set,
425 call \p f functor with item found, and unlinks it from the set.
426 The \ref disposer specified in \p OrderedList class template parameter is called
427 by garbage collector \p GC asynchronously.
429 The \p Func interface is
432 void operator()( value_type const& item );
436 If the item with key equal to \p key is not found the function return \p false.
438 Note the hash functor should accept a parameter of type \p Q that can be not the same as \p value_type.
440 template <typename Q, typename Func>
441 bool erase( const Q& key, Func f )
443 if ( bucket( key ).erase( key, f )) {
450 /// Deletes the item from the set using \p pred predicate for searching
452 The function is an analog of \ref cds_intrusive_MichaelHashSet_rcu_erase_func "erase(Q const&)"
453 but \p pred is used for key comparing.
454 \p Less functor has the interface like \p std::less.
455 \p pred must imply the same element order as the comparator used for building the set.
457 template <typename Q, typename Less, typename Func>
458 bool erase_with( const Q& key, Less pred, Func f )
460 if ( bucket( key ).erase_with( key, pred, f )) {
467 /// Extracts an item from the set
468 /** \anchor cds_intrusive_MichaelHashSet_rcu_extract
469 The function searches an item with key equal to \p key in the set,
470 unlinks it from the set, and returns \ref cds::urcu::exempt_ptr "exempt_ptr" pointer to the item found.
471 If the item with the key equal to \p key is not found the function returns an empty \p exempt_ptr.
473 Depends on \p bucket_type you should or should not lock RCU before calling of this function:
474 - for the set based on \ref cds_intrusive_MichaelList_rcu "MichaelList" RCU should not be locked
475 - for the set based on \ref cds_intrusive_LazyList_rcu "LazyList" RCU should be locked
477 See ordered list implementation for details.
480 #include <cds/urcu/general_buffered.h>
481 #include <cds/intrusive/michael_list_rcu.h>
482 #include <cds/intrusive/michael_set_rcu.h>
484 typedef cds::urcu::gc< general_buffered<> > rcu;
485 typedef cds::intrusive::MichaelList< rcu, Foo > rcu_michael_list;
486 typedef cds::intrusive::MichaelHashSet< rcu, rcu_michael_list, foo_traits > rcu_michael_set;
488 rcu_michael_set theSet;
491 typename rcu_michael_set::exempt_ptr p;
493 // For MichaelList we should not lock RCU
495 // Now, you can apply extract function
496 // Note that you must not delete the item found inside the RCU lock
497 p = theSet.extract( 10 )
499 // do something with p
503 // We may safely release p here
504 // release() passes the pointer to RCU reclamation cycle:
505 // it invokes RCU retire_ptr function with the disposer you provided for rcu_michael_list.
509 template <typename Q>
510 exempt_ptr extract( Q const& key )
512 exempt_ptr p( bucket( key ).extract( key ) );
518 /// Extracts an item from the set using \p pred predicate for searching
520 The function is an analog of \p extract(Q const&) but \p pred is used for key comparing.
521 \p Less functor has the interface like \p std::less.
522 \p pred must imply the same element order as the comparator used for building the set.
524 template <typename Q, typename Less>
525 exempt_ptr extract_with( Q const& key, Less pred )
527 exempt_ptr p( bucket( key ).extract_with( key, pred ) );
533 /// Checks whether the set contains \p key
536 The function searches the item with key equal to \p key
537 and returns \p true if the key is found, and \p false otherwise.
539 Note the hash functor specified for class \p Traits template parameter
540 should accept a parameter of type \p Q that can be not the same as \p value_type.
542 template <typename Q>
543 bool contains( Q const& key )
545 return bucket( key ).contains( key );
548 template <typename Q>
549 CDS_DEPRECATED("use contains()")
550 bool find( Q const& key )
552 return contains( key );
556 /// Checks whether the set contains \p key using \p pred predicate for searching
558 The function is an analog of <tt>contains( key )</tt> but \p pred is used for key comparing.
559 \p Less functor has the interface like \p std::less.
560 \p Less must imply the same element order as the comparator used for building the set.
562 template <typename Q, typename Less>
563 bool contains( Q const& key, Less pred )
565 return bucket( key ).contains( key, pred );
568 template <typename Q, typename Less>
569 CDS_DEPRECATED("use contains()")
570 bool find_with( Q const& key, Less pred )
572 return contains( key, pred );
576 /// Find the key \p key
577 /** \anchor cds_intrusive_MichaelHashSet_rcu_find_func
578 The function searches the item with key equal to \p key and calls the functor \p f for item found.
579 The interface of \p Func functor is:
582 void operator()( value_type& item, Q& key );
585 where \p item is the item found, \p key is the <tt>find</tt> function argument.
587 The functor can change non-key fields of \p item.
588 The functor does not serialize simultaneous access to the set \p item. If such access is
589 possible you must provide your own synchronization schema on item level to exclude unsafe item modifications.
591 The \p key argument is non-const since it can be used as \p f functor destination i.e., the functor
592 can modify both arguments.
594 Note the hash functor specified for class \p Traits template parameter
595 should accept a parameter of type \p Q that can be not the same as \p value_type.
597 The function returns \p true if \p key is found, \p false otherwise.
599 template <typename Q, typename Func>
600 bool find( Q& key, Func f )
602 return bucket( key ).find( key, f );
605 template <typename Q, typename Func>
606 bool find( Q const& key, Func f )
608 return bucket( key ).find( key, f );
612 /// Finds the key \p key using \p pred predicate for searching
614 The function is an analog of \ref cds_intrusive_MichaelHashSet_rcu_find_func "find(Q&, Func)"
615 but \p pred is used for key comparing.
616 \p Less functor has the interface like \p std::less.
617 \p pred must imply the same element order as the comparator used for building the set.
619 template <typename Q, typename Less, typename Func>
620 bool find_with( Q& key, Less pred, Func f )
622 return bucket( key ).find_with( key, pred, f );
625 template <typename Q, typename Less, typename Func>
626 bool find_with( Q const& key, Less pred, Func f )
628 return bucket( key ).find_with( key, pred, f );
632 /// Finds the key \p key and return the item found
633 /** \anchor cds_intrusive_MichaelHashSet_rcu_get
634 The function searches the item with key equal to \p key and returns the pointer to item found.
635 If \p key is not found it returns \p nullptr.
636 Note the type of returned value depends on underlying \p bucket_type.
637 For details, see documentation of ordered list you use.
639 Note the compare functor should accept a parameter of type \p Q that can be not the same as \p value_type.
641 RCU should be locked before call of this function.
642 Returned item is valid only while RCU is locked:
644 typedef cds::intrusive::MichaelHashSet< your_template_parameters > hash_set;
647 // Result of get() call
648 typename hash_set::raw_ptr ptr;
651 hash_set::rcu_lock lock;
653 ptr = theSet.get( 5 );
658 // Unlock RCU by rcu_lock destructor
659 // ptr can be reclaimed by disposer at any time after RCU has been unlocked
663 template <typename Q>
664 raw_ptr get( Q const& key )
666 return bucket( key ).get( key );
669 /// Finds the key \p key and return the item found
671 The function is an analog of \ref cds_intrusive_MichaelHashSet_rcu_get "get(Q const&)"
672 but \p pred is used for comparing the keys.
674 \p Less functor has the semantics like \p std::less but should take arguments of type \ref value_type and \p Q
676 \p pred must imply the same element order as the comparator used for building the set.
678 template <typename Q, typename Less>
679 raw_ptr get_with( Q const& key, Less pred )
681 return bucket( key ).get_with( key, pred );
684 /// Clears the set (non-atomic)
686 The function unlink all items from the set.
687 The function is not atomic. It cleans up each bucket and then resets the item counter to zero.
688 If there are a thread that performs insertion while \p clear is working the result is undefined in general case:
689 <tt> empty() </tt> may return \p true but the set may contain item(s).
690 Therefore, \p clear may be used only for debugging purposes.
692 For each item the \p disposer is called after unlinking.
696 for ( size_t i = 0; i < bucket_count(); ++i )
697 m_Buckets[i].clear();
698 m_ItemCounter.reset();
702 /// Checks if the set is empty
704 Emptiness is checked by item counting: if item count is zero then the set is empty.
705 Thus, the correct item counting feature is an important part of Michael's set implementation.
712 /// Returns item count in the set
715 return m_ItemCounter;
718 /// Returns the size of hash table
720 Since %MichaelHashSet cannot dynamically extend the hash table size,
721 the value returned is an constant depending on object initialization parameters;
722 see \ref cds_intrusive_MichaelHashSet_hp "MichaelHashSet" for explanation.
724 size_t bucket_count() const
726 return m_nHashBitmask + 1;
731 }} // namespace cds::intrusive
733 #endif // #ifndef CDSLIB_INTRUSIVE_MICHAEL_SET_NOGC_H