3 #ifndef CDSLIB_CONTAINER_MICHAEL_SET_RCU_H
4 #define CDSLIB_CONTAINER_MICHAEL_SET_RCU_H
6 #include <cds/container/details/michael_set_base.h>
7 #include <cds/details/allocator.h>
9 namespace cds { namespace container {
11 /// Michael's hash set (template specialization for \ref cds_urcu_desc "RCU")
12 /** @ingroup cds_nonintrusive_set
13 \anchor cds_nonintrusive_MichaelHashSet_rcu
16 - [2002] Maged Michael "High performance dynamic lock-free hash tables and list-based sets"
18 Michael's hash table algorithm is based on lock-free ordered list and it is very simple.
19 The main structure is an array \p T of size \p M. Each element in \p T is basically a pointer
20 to a hash bucket, implemented as a singly linked list. The array of buckets cannot be dynamically expanded.
21 However, each bucket may contain unbounded number of items.
23 Template parameters are:
24 - \p RCU - one of \ref cds_urcu_gc "RCU type"
25 - \p OrderedList - ordered list implementation used as the bucket for hash set, for example,
26 \ref cds_nonintrusive_MichaelList_rcu "MichaelList".
27 The ordered list implementation specifies the type \p T stored in the hash-set,
28 the comparison functor for the type \p T and other features specific for
30 - \p Traits - set traits, default is michael_set::traits.
31 Instead of defining \p Traits struct you may use option-based syntax with michael_set::make_traits metafunction.
33 About hash functor see \ref cds_nonintrusive_MichaelHashSet_hash_functor "MichaelSet hash functor".
37 Suppose, we have the following type \p Foo that we want to store in your \p %MichaelHashSet:
40 int nKey ; // key field
41 int nVal ; // value field
45 To use \p %MichaelHashSet for \p Foo values, you should first choose suitable ordered list class
46 that will be used as a bucket for the set. We will cds::urcu::general_buffered<> RCU type and
47 MichaelList as a bucket type.
48 You should include RCU-related header file (<tt>cds/urcu/general_buffered.h</tt> in this example)
49 before including <tt>cds/container/michael_set_rcu.h</tt>.
50 Also, for ordered list we should develop a comparator for our \p Foo struct.
52 #include <cds/urcu/general_buffered.h>
53 #include <cds/container/michael_list_rcu.h>
54 #include <cds/container/michael_set_rcu.h>
56 namespace cc = cds::container;
60 int operator ()(Foo const& v1, Foo const& v2 ) const
62 if ( std::less( v1.nKey, v2.nKey ))
64 return std::less(v2.nKey, v1.nKey) ? 1 : 0;
69 typedef cc::MichaelList< cds::urcu::gc< cds::urcu::general_buffered<> >, Foo,
70 typename cc::michael_list::make_traits<
71 cc::opt::compare< Foo_cmp > // item comparator option
75 // Hash functor for Foo
77 size_t operator ()( int i ) const
79 return std::hash( i );
81 size_t operator()( Foo const& i ) const
83 return std::hash( i.nKey );
88 // Note that \p RCU template parameter of ordered list must be equal \p RCU for the set.
89 typedef cc::MichaelHashSet< cds::urcu::gc< cds::urcu::general_buffered<> >, bucket_list,
90 cc::michael_set::make_traits<
91 cc::opt::hash< foo_hash >
101 #ifdef CDS_DOXYGEN_INVOKED
102 class Traits = michael_set::traits
107 class MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >
110 typedef cds::urcu::gc< RCU > gc; ///< RCU used as garbage collector
111 typedef OrderedList bucket_type; ///< type of ordered list to be used as a bucket implementation
112 typedef Traits traits; ///< Set traits
114 typedef typename bucket_type::value_type value_type; ///< type of value to be stored in the list
115 typedef typename bucket_type::key_comparator key_comparator; ///< key comparing functor
117 /// Hash functor for \ref value_type and all its derivatives that you use
118 typedef typename cds::opt::v::hash_selector< typename traits::hash >::type hash;
119 typedef typename traits::item_counter item_counter; ///< Item counter type
121 /// Bucket table allocator
122 typedef cds::details::Allocator< bucket_type, typename traits::allocator > bucket_table_allocator;
124 typedef typename bucket_type::rcu_lock rcu_lock; ///< RCU scoped lock
125 typedef typename bucket_type::exempt_ptr exempt_ptr; ///< pointer to extracted node
126 /// Group of \p extract_xxx functions require external locking if underlying ordered list requires that
127 static CDS_CONSTEXPR const bool c_bExtractLockExternal = bucket_type::c_bExtractLockExternal;
130 item_counter m_ItemCounter; ///< Item counter
131 hash m_HashFunctor; ///< Hash functor
132 bucket_type * m_Buckets; ///< bucket table
136 const size_t m_nHashBitmask;
141 /// Calculates hash value of \p key
142 template <typename Q>
143 size_t hash_value( Q const& key ) const
145 return m_HashFunctor( key ) & m_nHashBitmask;
148 /// Returns the bucket (ordered list) for \p key
149 template <typename Q>
150 bucket_type& bucket( Q const& key )
152 return m_Buckets[ hash_value( key ) ];
154 template <typename Q>
155 bucket_type const& bucket( Q const& key ) const
157 return m_Buckets[ hash_value( key ) ];
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
166 - The iterator cannot be moved across thread boundary since it may contain GC's guard that is thread-private GC data.
167 - Iterator ensures thread-safety even if you delete the item that iterator points to. However, in case of concurrent
168 deleting operations it is no guarantee that you iterate all item in the set.
170 Therefore, the use of iterators in concurrent environment is not good idea. Use the iterator for the concurrent container
171 for debug purpose only.
173 typedef michael_set::details::iterator< bucket_type, false > iterator;
175 /// Const forward 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
200 const_iterator begin() const
202 return get_const_begin();
204 const_iterator cbegin() const
206 return get_const_begin();
210 /// Returns an const iterator that addresses the location succeeding the last element in a set
212 const_iterator end() const
214 return get_const_end();
216 const_iterator cend() const
218 return get_const_end();
224 const_iterator get_const_begin() const
226 return const_iterator( const_cast<bucket_type const&>(m_Buckets[0]).begin(), m_Buckets, m_Buckets + bucket_count() );
228 const_iterator get_const_end() const
230 return const_iterator( const_cast<bucket_type const&>(m_Buckets[bucket_count() - 1]).end(), m_Buckets + bucket_count() - 1, m_Buckets + bucket_count() );
235 /// Initialize hash set
236 /** @copydetails cds_nonintrusive_MichaelHashSet_hp_ctor
239 size_t nMaxItemCount, ///< estimation of max item count in the hash set
240 size_t nLoadFactor ///< load factor: estimation of max number of items in the bucket
241 ) : m_nHashBitmask( michael_set::details::init_hash_bitmask( nMaxItemCount, nLoadFactor ))
243 // GC and OrderedList::gc must be the same
244 static_assert( std::is_same<gc, typename bucket_type::gc>::value, "GC and OrderedList::gc must be the same");
246 // atomicity::empty_item_counter is not allowed as a item counter
247 static_assert( !std::is_same<item_counter, atomicity::empty_item_counter>::value,
248 "atomicity::empty_item_counter is not allowed as a item counter");
250 m_Buckets = bucket_table_allocator().NewArray( bucket_count() );
253 /// Clears hash set and destroys it
257 bucket_table_allocator().Delete( m_Buckets, bucket_count() );
262 The function creates a node with copy of \p val value
263 and then inserts the node created into the set.
265 The type \p Q should contain as minimum the complete key for the node.
266 The object of \ref value_type should be constructible from a value of type \p Q.
267 In trivial case, \p Q is equal to \ref value_type.
269 The function applies RCU lock internally.
271 Returns \p true if \p val is inserted into the set, \p false otherwise.
273 template <typename Q>
274 bool insert( Q const& val )
276 const bool bRet = bucket( val ).insert( val );
284 The function allows to split creating of new item into two part:
285 - create item with key only
286 - insert new item into the set
287 - if inserting is success, calls \p f functor to initialize value-fields of \p val.
289 The functor signature is:
291 void func( value_type& val );
293 where \p val is the item inserted.
294 The user-defined functor is called only if the inserting is success.
296 The function applies RCU lock internally.
298 @warning For \ref cds_nonintrusive_MichaelList_rcu "MichaelList" as the bucket see \ref cds_intrusive_item_creating "insert item troubleshooting".
299 \ref cds_nonintrusive_LazyList_rcu "LazyList" provides exclusive access to inserted item and does not require any node-level
302 template <typename Q, typename Func>
303 bool insert( Q const& val, Func f )
305 const bool bRet = bucket( val ).insert( val, f );
311 /// Ensures that the item exists in the set
313 The operation performs inserting or changing data with lock-free manner.
315 If the \p val key not found in the set, then the new item created from \p val
316 is inserted into the set. Otherwise, the functor \p func is called with the item found.
317 The functor \p Func signature is:
320 void operator()( bool bNew, value_type& item, const Q& val );
325 - \p bNew - \p true if the item has been inserted, \p false otherwise
326 - \p item - item of the set
327 - \p val - argument \p key passed into the \p ensure function
329 The functor may change non-key fields of the \p item.
331 The function applies RCU lock internally.
333 Returns <tt> std::pair<bool, bool> </tt> where \p first is true if operation is successfull,
334 \p second is true if new item has been added or \p false if the item with \p key
335 already is in the set.
337 @warning For \ref cds_nonintrusive_MichaelList_rcu "MichaelList" as the bucket see \ref cds_intrusive_item_creating "insert item troubleshooting".
338 \ref cds_nonintrusive_LazyList_rcu "LazyList" provides exclusive access to inserted item and does not require any node-level
341 template <typename Q, typename Func>
342 std::pair<bool, bool> ensure( const Q& val, Func func )
344 std::pair<bool, bool> bRet = bucket( val ).ensure( val, func );
345 if ( bRet.first && bRet.second )
350 /// Inserts data of type \p value_type created from \p args
352 Returns \p true if inserting successful, \p false otherwise.
354 The function applies RCU lock internally.
356 template <typename... Args>
357 bool emplace( Args&&... args )
359 bool bRet = bucket( value_type(std::forward<Args>(args)...) ).emplace( std::forward<Args>(args)... );
365 /// Deletes \p key from the set
366 /** \anchor cds_nonintrusive_MichealSet_rcu_erase_val
368 Since the key of MichaelHashSet's item type \p value_type is not explicitly specified,
369 template parameter \p Q defines the key type searching in the list.
370 The set item comparator should be able to compare the type \p value_type
373 RCU \p synchronize method can be called. RCU should not be locked.
375 Return \p true if key is found and deleted, \p false otherwise
377 template <typename Q>
378 bool erase( Q const& key )
380 const bool bRet = bucket( key ).erase( key );
386 /// Deletes the item from the set using \p pred predicate for searching
388 The function is an analog of \ref cds_nonintrusive_MichealSet_rcu_erase_val "erase(Q const&)"
389 but \p pred is used for key comparing.
390 \p Less functor has the interface like \p std::less.
391 \p Less must imply the same element order as the comparator used for building the set.
393 template <typename Q, typename Less>
394 bool erase_with( Q const& key, Less pred )
396 const bool bRet = bucket( key ).erase_with( key, pred );
402 /// Deletes \p key from the set
403 /** \anchor cds_nonintrusive_MichealSet_rcu_erase_func
405 The function searches an item with key \p key, calls \p f functor
406 and deletes the item. If \p key is not found, the functor is not called.
408 The functor \p Func interface:
411 void operator()(value_type const& val);
415 Since the key of %MichaelHashSet's \p value_type is not explicitly specified,
416 template parameter \p Q defines the key type searching in the list.
417 The list item comparator should be able to compare the type \p T of list item
420 RCU \p synchronize method can be called. RCU should not be locked.
422 Return \p true if key is found and deleted, \p false otherwise
424 template <typename Q, typename Func>
425 bool erase( Q const& key, Func f )
427 const bool bRet = bucket( key ).erase( key, f );
433 /// Deletes the item from the set using \p pred predicate for searching
435 The function is an analog of \ref cds_nonintrusive_MichealSet_rcu_erase_func "erase(Q const&, Func)"
436 but \p pred is used for key comparing.
437 \p Less functor has the interface like \p std::less.
438 \p Less must imply the same element order as the comparator used for building the set.
440 template <typename Q, typename Less, typename Func>
441 bool erase_with( Q const& key, Less pred, Func f )
443 const bool bRet = bucket( key ).erase_with( key, pred, f );
449 /// Extracts an item from the set
450 /** \anchor cds_nonintrusive_MichaelHashSet_rcu_extract
451 The function searches an item with key equal to \p key in the set,
452 unlinks it from the set, and returns \ref cds::urcu::exempt_ptr "exempt_ptr" pointer to the item found.
453 If the item with the key equal to \p key is not found the function return an empty \p exempt_ptr.
455 @note The function does NOT call RCU read-side lock or synchronization,
456 and does NOT dispose the item found. It just excludes the item from the set
457 and returns a pointer to item found.
458 You should lock RCU before calling of the function, and you should synchronize RCU
459 outside the RCU lock to free extracted item
462 #include <cds/urcu/general_buffered.h>
463 #include <cds/container/michael_list_rcu.h>
464 #include <cds/container/michael_set_rcu.h>
466 typedef cds::urcu::gc< general_buffered<> > rcu;
467 typedef cds::container::MichaelList< rcu, Foo > rcu_michael_list;
468 typedef cds::container::MichaelHashSet< rcu, rcu_michael_list, foo_traits > rcu_michael_set;
470 rcu_michael_set theSet;
473 rcu_michael_set::exempt_ptr p;
475 // first, we should lock RCU
476 rcu_michael_set::rcu_lock lock;
478 // Now, you can apply extract function
479 // Note that you must not delete the item found inside the RCU lock
480 p = theSet.extract( 10 );
482 // do something with p
487 // We may safely release p here
488 // release() passes the pointer to RCU reclamation cycle
492 template <typename Q>
493 exempt_ptr extract( Q const& key )
495 exempt_ptr p = bucket( key ).extract( key );
501 /// Extracts an item from the set using \p pred predicate for searching
503 The function is an analog of \p extract(Q const&) but \p pred is used for key comparing.
504 \p Less functor has the interface like \p std::less.
505 \p pred must imply the same element order as the comparator used for building the set.
507 template <typename Q, typename Less>
508 exempt_ptr extract_with( Q const& key, Less pred )
510 exempt_ptr p = bucket( key ).extract_with( key, pred );
516 /// Finds the key \p key
517 /** \anchor cds_nonintrusive_MichealSet_rcu_find_func
519 The function searches the item with key equal to \p key and calls the functor \p f for item found.
520 The interface of \p Func functor is:
523 void operator()( value_type& item, Q& key );
526 where \p item is the item found, \p key is the <tt>find</tt> function argument.
528 The functor may change non-key fields of \p item. Note that the functor is only guarantee
529 that \p item cannot be disposed during functor is executing.
530 The functor does not serialize simultaneous access to the set's \p item. If such access is
531 possible you must provide your own synchronization schema on item level to exclude unsafe item modifications.
533 The \p key argument is non-const since it can be used as \p f functor destination i.e., the functor
534 can modify both arguments.
536 Note the hash functor specified for class \p Traits template parameter
537 should accept a parameter of type \p Q that may be not the same as \p value_type.
539 The function applies RCU lock internally.
541 The function returns \p true if \p key is found, \p false otherwise.
543 template <typename Q, typename Func>
544 bool find( Q& key, Func f ) const
546 return bucket( key ).find( key, f );
549 template <typename Q, typename Func>
550 bool find( Q const& key, Func f ) const
552 return bucket( key ).find( key, f );
556 /// Finds the key \p key using \p pred predicate for searching
558 The function is an analog of \ref cds_nonintrusive_MichealSet_rcu_find_func "find(Q&, Func)"
559 but \p pred is used for key comparing.
560 \p Less functor has the interface like \p std::less.
561 \p Less must imply the same element order as the comparator used for building the set.
563 template <typename Q, typename Less, typename Func>
564 bool find_with( Q& key, Less pred, Func f ) const
566 return bucket( key ).find_with( key, pred, f );
569 template <typename Q, typename Less, typename Func>
570 bool find_with( Q const& key, Less pred, Func f ) const
572 return bucket( key ).find_with( key, pred, f );
576 /// Finds the key \p key
577 /** \anchor cds_nonintrusive_MichealSet_rcu_find_val
579 The function searches the item with key equal to \p key
580 and returns \p true if it is found, and \p false otherwise.
582 Note the hash functor specified for class \p Traits template parameter
583 should accept a parameter of type \p Q that may be not the same as \p value_type.
585 template <typename Q>
586 bool find( Q const & key ) const
588 return bucket( key ).find( key );
591 /// Finds the key \p key using \p pred predicate for searching
593 The function is an analog of \ref cds_nonintrusive_MichealSet_rcu_find_val "find(Q const&)"
594 but \p pred is used for key comparing.
595 \p Less functor has the interface like \p std::less.
596 \p Less must imply the same element order as the comparator used for building the set.
598 template <typename Q, typename Less>
599 bool find_with( Q const & key, Less pred ) const
601 return bucket( key ).find_with( key, pred );
604 /// Finds the key \p key and return the item found
605 /** \anchor cds_nonintrusive_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.
609 Note the compare functor should accept a parameter of type \p Q that can be not the same as \p value_type.
611 RCU should be locked before call of this function.
612 Returned item is valid only while RCU is locked:
614 typedef cds::container::MichaelHashSet< your_template_parameters > hash_set;
619 hash_set::rcu_lock lock;
621 foo * pVal = theSet.get( 5 );
626 // Unlock RCU by rcu_lock destructor
627 // pVal can be freed at any time after RCU has been unlocked
631 template <typename Q>
632 value_type * get( Q const& key ) const
634 return bucket( key ).get( key );
637 /// Finds the key \p key and return the item found
639 The function is an analog of \ref cds_nonintrusive_MichaelHashSet_rcu_get "get(Q const&)"
640 but \p pred is used for comparing the keys.
642 \p Less functor has the semantics like \p std::less but should take arguments of type \ref value_type and \p Q
644 \p pred must imply the same element order as the comparator used for building the set.
646 template <typename Q, typename Less>
647 value_type * get_with( Q const& key, Less pred ) const
649 return bucket( key ).get_with( key, pred );
652 /// Clears the set (not atomic)
655 for ( size_t i = 0; i < bucket_count(); ++i )
656 m_Buckets[i].clear();
657 m_ItemCounter.reset();
660 /// Checks if the set is empty
662 Emptiness is checked by item counting: if item count is zero then the set is empty.
663 Thus, the correct item counting feature is an important part of Michael's set implementation.
670 /// Returns item count in the set
673 return m_ItemCounter;
676 /// Returns the size of hash table
678 Since \p %MichaelHashSet cannot dynamically extend the hash table size,
679 the value returned is an constant depending on object initialization parameters;
680 see MichaelHashSet::MichaelHashSet for explanation.
682 size_t bucket_count() const
684 return m_nHashBitmask + 1;
688 }} // namespace cds::container
690 #endif // ifndef CDSLIB_CONTAINER_MICHAEL_SET_RCU_H