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 typedef michael_set::details::iterator< bucket_type, false > iterator;
172 /// Const forward iterator
174 For iterator's features and requirements see \ref iterator
176 typedef michael_set::details::iterator< bucket_type, true > const_iterator;
178 /// Returns a forward iterator addressing the first element in a set
180 For empty set \code begin() == end() \endcode
184 return iterator( m_Buckets[0].begin(), m_Buckets, m_Buckets + bucket_count() );
187 /// Returns an iterator that addresses the location succeeding the last element in a set
189 Do not use the value returned by <tt>end</tt> function to access any item.
190 The returned value can be used only to control reaching the end of the set.
191 For empty set \code begin() == end() \endcode
195 return iterator( m_Buckets[bucket_count() - 1].end(), m_Buckets + bucket_count() - 1, m_Buckets + bucket_count() );
198 /// Returns a forward const iterator addressing the first element in a set
199 const_iterator begin() const
204 /// Returns a forward const iterator addressing the first element in a set
205 const_iterator cbegin() const
207 return const_iterator( m_Buckets[0].cbegin(), m_Buckets, m_Buckets + bucket_count() );
210 /// Returns an const iterator that addresses the location succeeding the last element in a set
211 const_iterator end() const
216 /// Returns an const iterator that addresses the location succeeding the last element in a set
217 const_iterator cend() const
219 return const_iterator( m_Buckets[bucket_count() - 1].cend(), m_Buckets + bucket_count() - 1, m_Buckets + bucket_count() );
224 /// Initialize hash set
226 The Michael's hash set is an unbounded container, but its hash table is non-expandable.
227 At construction time you should pass estimated maximum item count and a load factor.
228 The load factor is average size of one bucket - a small number between 1 and 10.
229 The bucket is an ordered single-linked list, the complexity of searching in the bucket is linear <tt>O(nLoadFactor)</tt>.
230 The constructor defines hash table size as rounding <tt>nMaxItemCount / nLoadFactor</tt> up to nearest power of two.
233 size_t nMaxItemCount, ///< estimation of max item count in the hash set
234 size_t nLoadFactor ///< load factor: average size of the bucket
235 ) : m_nHashBitmask( michael_set::details::init_hash_bitmask( nMaxItemCount, nLoadFactor ))
237 // GC and OrderedList::gc must be the same
238 static_assert( std::is_same<gc, typename bucket_type::gc>::value, "GC and OrderedList::gc must be the same");
240 // atomicity::empty_item_counter is not allowed as a item counter
241 static_assert( !std::is_same<item_counter, atomicity::empty_item_counter>::value,
242 "atomicity::empty_item_counter is not allowed as a item counter");
244 m_Buckets = bucket_table_allocator().NewArray( bucket_count() );
247 /// Clear hash set and destroy it
251 bucket_table_allocator().Delete( m_Buckets, bucket_count() );
256 The function inserts \p val in the set if it does not contain
257 an item with key equal to \p val.
259 Returns \p true if \p val is placed into the set, \p false otherwise.
261 bool insert( value_type& val )
263 bool bRet = bucket( val ).insert( val );
271 This function is intended for derived non-intrusive containers.
273 The function allows to split creating of new item into two part:
274 - create item with key only
275 - insert new item into the set
276 - if inserting is success, calls \p f functor to initialize value-field of \p val.
278 The functor signature is:
280 void func( value_type& val );
282 where \p val is the item inserted.
283 The user-defined functor is called only if the inserting is success.
285 @warning For \ref cds_intrusive_MichaelList_rcu "MichaelList" as the bucket see \ref cds_intrusive_item_creating "insert item troubleshooting".
286 \ref cds_intrusive_LazyList_rcu "LazyList" provides exclusive access to inserted item and does not require any node-level
289 template <typename Func>
290 bool insert( value_type& val, Func f )
292 bool bRet = bucket( val ).insert( val, f );
298 /// Updates the element
300 The operation performs inserting or changing data with lock-free manner.
302 If the item \p val not found in the set, then \p val is inserted iff \p bAllowInsert is \p true.
303 Otherwise, the functor \p func is called with item found.
304 The functor signature is:
307 void operator()( bool bNew, value_type& item, value_type& val );
311 - \p bNew - \p true if the item has been inserted, \p false otherwise
312 - \p item - item of the set
313 - \p val - argument \p val passed into the \p %update() function
314 If new item has been inserted (i.e. \p bNew is \p true) then \p item and \p val arguments
315 refers to the same thing.
317 The functor may change non-key fields of the \p item.
319 Returns <tt> std::pair<bool, bool> </tt> where \p first is \p true if operation is successfull,
320 \p second is \p true if new item has been added or \p false if the item with \p key
321 already is in the set.
323 @warning For \ref cds_intrusive_MichaelList_hp "MichaelList" as the bucket see \ref cds_intrusive_item_creating "insert item troubleshooting".
324 \ref cds_intrusive_LazyList_hp "LazyList" provides exclusive access to inserted item and does not require any node-level
327 template <typename Func>
328 std::pair<bool, bool> update( value_type& val, Func func, bool bAllowInsert = true )
330 std::pair<bool, bool> bRet = bucket( val ).update( val, func, bAllowInsert );
336 template <typename Func>
337 CDS_DEPRECATED("ensure() is deprecated, use update()")
338 std::pair<bool, bool> ensure( value_type& val, Func func )
340 return update( val, func, true );
344 /// Unlinks the item \p val from the set
346 The function searches the item \p val in the set and unlink it from the set
347 if it is found and is equal to \p val.
349 The function returns \p true if success and \p false otherwise.
351 bool unlink( value_type& val )
353 bool bRet = bucket( val ).unlink( val );
359 /// Deletes the item from the set
360 /** \anchor cds_intrusive_MichaelHashSet_rcu_erase
361 The function searches an item with key equal to \p key in the set,
362 unlinks it from the set, and returns \p true.
363 If the item with key equal to \p key is not found the function return \p false.
365 Note the hash functor should accept a parameter of type \p Q that may be not the same as \p value_type.
367 template <typename Q>
368 bool erase( Q const& key )
370 if ( bucket( key ).erase( key )) {
377 /// Deletes the item from the set using \p pred predicate for searching
379 The function is an analog of \ref cds_intrusive_MichaelHashSet_rcu_erase "erase(Q const&)"
380 but \p pred is used for key comparing.
381 \p Less functor has the interface like \p std::less.
382 \p pred must imply the same element order as the comparator used for building the set.
384 template <typename Q, typename Less>
385 bool erase_with( Q const& key, Less pred )
387 if ( bucket( key ).erase_with( key, pred )) {
394 /// Deletes the item from the set
395 /** \anchor cds_intrusive_MichaelHashSet_rcu_erase_func
396 The function searches an item with key equal to \p key in the set,
397 call \p f functor with item found, and unlinks it from the set.
398 The \ref disposer specified in \p OrderedList class template parameter is called
399 by garbage collector \p GC asynchronously.
401 The \p Func interface is
404 void operator()( value_type const& item );
408 If the item with key equal to \p key is not found the function return \p false.
410 Note the hash functor should accept a parameter of type \p Q that can be not the same as \p value_type.
412 template <typename Q, typename Func>
413 bool erase( const Q& key, Func f )
415 if ( bucket( key ).erase( key, f )) {
422 /// Deletes the item from the set using \p pred predicate for searching
424 The function is an analog of \ref cds_intrusive_MichaelHashSet_rcu_erase_func "erase(Q const&)"
425 but \p pred is used for key comparing.
426 \p Less functor has the interface like \p std::less.
427 \p pred must imply the same element order as the comparator used for building the set.
429 template <typename Q, typename Less, typename Func>
430 bool erase_with( const Q& key, Less pred, Func f )
432 if ( bucket( key ).erase_with( key, pred, f )) {
439 /// Extracts an item from the set
440 /** \anchor cds_intrusive_MichaelHashSet_rcu_extract
441 The function searches an item with key equal to \p key in the set,
442 unlinks it from the set, and returns \ref cds::urcu::exempt_ptr "exempt_ptr" pointer to the item found.
443 If the item with the key equal to \p key is not found the function returns an empty \p exempt_ptr.
445 Depends on \p bucket_type you should or should not lock RCU before calling of this function:
446 - for the set based on \ref cds_intrusive_MichaelList_rcu "MichaelList" RCU should not be locked
447 - for the set based on \ref cds_intrusive_LazyList_rcu "LazyList" RCU should be locked
449 See ordered list implementation for details.
452 #include <cds/urcu/general_buffered.h>
453 #include <cds/intrusive/michael_list_rcu.h>
454 #include <cds/intrusive/michael_set_rcu.h>
456 typedef cds::urcu::gc< general_buffered<> > rcu;
457 typedef cds::intrusive::MichaelList< rcu, Foo > rcu_michael_list;
458 typedef cds::intrusive::MichaelHashSet< rcu, rcu_michael_list, foo_traits > rcu_michael_set;
460 rcu_michael_set theSet;
463 typename rcu_michael_set::exempt_ptr p;
465 // For MichaelList we should not lock RCU
467 // Now, you can apply extract function
468 // Note that you must not delete the item found inside the RCU lock
469 p = theSet.extract( 10 )
471 // do something with p
475 // We may safely release p here
476 // release() passes the pointer to RCU reclamation cycle:
477 // it invokes RCU retire_ptr function with the disposer you provided for rcu_michael_list.
481 template <typename Q>
482 exempt_ptr extract( Q const& key )
484 exempt_ptr p( bucket( key ).extract( key ) );
490 /// Extracts an item from the set using \p pred predicate for searching
492 The function is an analog of \p extract(Q const&) but \p pred is used for key comparing.
493 \p Less functor has the interface like \p std::less.
494 \p pred must imply the same element order as the comparator used for building the set.
496 template <typename Q, typename Less>
497 exempt_ptr extract_with( Q const& key, Less pred )
499 exempt_ptr p( bucket( key ).extract_with( key, pred ) );
505 /// Checks whether the set contains \p key
508 The function searches the item with key equal to \p key
509 and returns \p true if the key is found, and \p false otherwise.
511 Note the hash functor specified for class \p Traits template parameter
512 should accept a parameter of type \p Q that can be not the same as \p value_type.
514 template <typename Q>
515 bool contains( Q const& key )
517 return bucket( key ).contains( key );
520 template <typename Q>
521 CDS_DEPRECATED("use contains()")
522 bool find( Q const& key )
524 return contains( key );
528 /// Checks whether the set contains \p key using \p pred predicate for searching
530 The function is an analog of <tt>contains( key )</tt> but \p pred is used for key comparing.
531 \p Less functor has the interface like \p std::less.
532 \p Less must imply the same element order as the comparator used for building the set.
534 template <typename Q, typename Less>
535 bool contains( Q const& key, Less pred )
537 return bucket( key ).contains( key, pred );
540 template <typename Q, typename Less>
541 CDS_DEPRECATED("use contains()")
542 bool find_with( Q const& key, Less pred )
544 return contains( key, pred );
548 /// Find the key \p key
549 /** \anchor cds_intrusive_MichaelHashSet_rcu_find_func
550 The function searches the item with key equal to \p key and calls the functor \p f for item found.
551 The interface of \p Func functor is:
554 void operator()( value_type& item, Q& key );
557 where \p item is the item found, \p key is the <tt>find</tt> function argument.
559 The functor can change non-key fields of \p item.
560 The functor does not serialize simultaneous access to the set \p item. If such access is
561 possible you must provide your own synchronization schema on item level to exclude unsafe item modifications.
563 The \p key argument is non-const since it can be used as \p f functor destination i.e., the functor
564 can modify both arguments.
566 Note the hash functor specified for class \p Traits template parameter
567 should accept a parameter of type \p Q that can be not the same as \p value_type.
569 The function returns \p true if \p key is found, \p false otherwise.
571 template <typename Q, typename Func>
572 bool find( Q& key, Func f )
574 return bucket( key ).find( key, f );
577 template <typename Q, typename Func>
578 bool find( Q const& key, Func f )
580 return bucket( key ).find( key, f );
584 /// Finds the key \p key using \p pred predicate for searching
586 The function is an analog of \ref cds_intrusive_MichaelHashSet_rcu_find_func "find(Q&, Func)"
587 but \p pred is used for key comparing.
588 \p Less functor has the interface like \p std::less.
589 \p pred must imply the same element order as the comparator used for building the set.
591 template <typename Q, typename Less, typename Func>
592 bool find_with( Q& key, Less pred, Func f )
594 return bucket( key ).find_with( key, pred, f );
597 template <typename Q, typename Less, typename Func>
598 bool find_with( Q const& key, Less pred, Func f )
600 return bucket( key ).find_with( key, pred, f );
604 /// Finds the key \p key and return the item found
605 /** \anchor cds_intrusive_MichaelHashSet_rcu_get
606 The function searches the item with key equal to \p key and returns the pointer to item found.
607 If \p key is not found it returns \p nullptr.
608 Note the type of returned value depends on underlying \p bucket_type.
609 For details, see documentation of ordered list you use.
611 Note the compare functor should accept a parameter of type \p Q that can be not the same as \p value_type.
613 RCU should be locked before call of this function.
614 Returned item is valid only while RCU is locked:
616 typedef cds::intrusive::MichaelHashSet< your_template_parameters > hash_set;
619 // Result of get() call
620 typename hash_set::raw_ptr ptr;
623 hash_set::rcu_lock lock;
625 ptr = theSet.get( 5 );
630 // Unlock RCU by rcu_lock destructor
631 // ptr can be reclaimed by disposer at any time after RCU has been unlocked
635 template <typename Q>
636 raw_ptr get( Q const& key )
638 return bucket( key ).get( key );
641 /// Finds the key \p key and return the item found
643 The function is an analog of \ref cds_intrusive_MichaelHashSet_rcu_get "get(Q const&)"
644 but \p pred is used for comparing the keys.
646 \p Less functor has the semantics like \p std::less but should take arguments of type \ref value_type and \p Q
648 \p pred must imply the same element order as the comparator used for building the set.
650 template <typename Q, typename Less>
651 raw_ptr get_with( Q const& key, Less pred )
653 return bucket( key ).get_with( key, pred );
656 /// Clears the set (non-atomic)
658 The function unlink all items from the set.
659 The function is not atomic. It cleans up each bucket and then resets the item counter to zero.
660 If there are a thread that performs insertion while \p clear is working the result is undefined in general case:
661 <tt> empty() </tt> may return \p true but the set may contain item(s).
662 Therefore, \p clear may be used only for debugging purposes.
664 For each item the \p disposer is called after unlinking.
668 for ( size_t i = 0; i < bucket_count(); ++i )
669 m_Buckets[i].clear();
670 m_ItemCounter.reset();
674 /// Checks if the set is empty
676 Emptiness is checked by item counting: if item count is zero then the set is empty.
677 Thus, the correct item counting feature is an important part of Michael's set implementation.
684 /// Returns item count in the set
687 return m_ItemCounter;
690 /// Returns the size of hash table
692 Since %MichaelHashSet cannot dynamically extend the hash table size,
693 the value returned is an constant depending on object initialization parameters;
694 see \ref cds_intrusive_MichaelHashSet_hp "MichaelHashSet" for explanation.
696 size_t bucket_count() const
698 return m_nHashBitmask + 1;
703 }} // namespace cds::intrusive
705 #endif // #ifndef CDSLIB_INTRUSIVE_MICHAEL_SET_NOGC_H