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 typedef typename bucket_type::raw_ptr raw_ptr; ///< Return type of \p get() member function and its derivatives
127 /// Group of \p extract_xxx functions require external locking if underlying ordered list requires that
128 static CDS_CONSTEXPR const bool c_bExtractLockExternal = bucket_type::c_bExtractLockExternal;
131 typedef cds::container::michael_set::implementation_tag implementation_tag;
135 item_counter m_ItemCounter; ///< Item counter
136 hash m_HashFunctor; ///< Hash functor
137 bucket_type * m_Buckets; ///< bucket table
141 const size_t m_nHashBitmask;
146 /// Calculates hash value of \p key
147 template <typename Q>
148 size_t hash_value( Q const& key ) const
150 return m_HashFunctor( key ) & m_nHashBitmask;
153 /// Returns the bucket (ordered list) for \p key
154 template <typename Q>
155 bucket_type& bucket( Q const& key )
157 return m_Buckets[ hash_value( key ) ];
159 template <typename Q>
160 bucket_type const& bucket( Q const& key ) const
162 return m_Buckets[ hash_value( key ) ];
168 The forward iterator for Michael's set is based on \p OrderedList forward iterator and has some features:
169 - it has no post-increment operator
170 - it iterates items in unordered fashion
171 - The iterator cannot be moved across thread boundary since it may contain GC's guard that is thread-private GC data.
172 - Iterator ensures thread-safety even if you delete the item that iterator points to. However, in case of concurrent
173 deleting operations it is no guarantee that you iterate all item in the set.
175 Therefore, the use of iterators in concurrent environment is not good idea. Use the iterator for the concurrent container
176 for debug purpose only.
178 typedef michael_set::details::iterator< bucket_type, false > iterator;
180 /// Const forward iterator
181 typedef michael_set::details::iterator< bucket_type, true > const_iterator;
183 /// Returns a forward iterator addressing the first element in a set
185 For empty set \code begin() == end() \endcode
189 return iterator( m_Buckets[0].begin(), m_Buckets, m_Buckets + bucket_count() );
192 /// Returns an iterator that addresses the location succeeding the last element in a set
194 Do not use the value returned by <tt>end</tt> function to access any item.
195 The returned value can be used only to control reaching the end of the set.
196 For empty set \code begin() == end() \endcode
200 return iterator( m_Buckets[bucket_count() - 1].end(), m_Buckets + bucket_count() - 1, m_Buckets + bucket_count() );
203 /// Returns a forward const iterator addressing the first element in a set
205 const_iterator begin() const
207 return get_const_begin();
209 const_iterator cbegin() const
211 return get_const_begin();
215 /// Returns an const iterator that addresses the location succeeding the last element in a set
217 const_iterator end() const
219 return get_const_end();
221 const_iterator cend() const
223 return get_const_end();
229 const_iterator get_const_begin() const
231 return const_iterator( const_cast<bucket_type const&>(m_Buckets[0]).begin(), m_Buckets, m_Buckets + bucket_count() );
233 const_iterator get_const_end() const
235 return const_iterator( const_cast<bucket_type const&>(m_Buckets[bucket_count() - 1]).end(), m_Buckets + bucket_count() - 1, m_Buckets + bucket_count() );
240 /// Initialize hash set
241 /** @copydetails cds_nonintrusive_MichaelHashSet_hp_ctor
244 size_t nMaxItemCount, ///< estimation of max item count in the hash set
245 size_t nLoadFactor ///< load factor: estimation of max number of items in the bucket
246 ) : m_nHashBitmask( michael_set::details::init_hash_bitmask( nMaxItemCount, nLoadFactor ))
248 // GC and OrderedList::gc must be the same
249 static_assert( std::is_same<gc, typename bucket_type::gc>::value, "GC and OrderedList::gc must be the same");
251 // atomicity::empty_item_counter is not allowed as a item counter
252 static_assert( !std::is_same<item_counter, atomicity::empty_item_counter>::value,
253 "atomicity::empty_item_counter is not allowed as a item counter");
255 m_Buckets = bucket_table_allocator().NewArray( bucket_count() );
258 /// Clears hash set and destroys it
262 bucket_table_allocator().Delete( m_Buckets, bucket_count() );
267 The function creates a node with copy of \p val value
268 and then inserts the node created into the set.
270 The type \p Q should contain as minimum the complete key for the node.
271 The object of \ref value_type should be constructible from a value of type \p Q.
272 In trivial case, \p Q is equal to \ref value_type.
274 The function applies RCU lock internally.
276 Returns \p true if \p val is inserted into the set, \p false otherwise.
278 template <typename Q>
279 bool insert( Q const& val )
281 const bool bRet = bucket( val ).insert( val );
289 The function allows to split creating of new item into two part:
290 - create item with key only
291 - insert new item into the set
292 - if inserting is success, calls \p f functor to initialize value-fields of \p val.
294 The functor signature is:
296 void func( value_type& val );
298 where \p val is the item inserted.
299 The user-defined functor is called only if the inserting is success.
301 The function applies RCU lock internally.
303 @warning For \ref cds_nonintrusive_MichaelList_rcu "MichaelList" as the bucket see \ref cds_intrusive_item_creating "insert item troubleshooting".
304 \ref cds_nonintrusive_LazyList_rcu "LazyList" provides exclusive access to inserted item and does not require any node-level
307 template <typename Q, typename Func>
308 bool insert( Q const& val, Func f )
310 const bool bRet = bucket( val ).insert( val, f );
316 /// Ensures that the item exists in the set
318 The operation performs inserting or changing data with lock-free manner.
320 If the \p val key not found in the set, then the new item created from \p val
321 is inserted into the set. Otherwise, the functor \p func is called with the item found.
322 The functor \p Func signature is:
325 void operator()( bool bNew, value_type& item, const Q& val );
330 - \p bNew - \p true if the item has been inserted, \p false otherwise
331 - \p item - item of the set
332 - \p val - argument \p key passed into the \p ensure function
334 The functor may change non-key fields of the \p item.
336 The function applies RCU lock internally.
338 Returns <tt> std::pair<bool, bool> </tt> where \p first is true if operation is successfull,
339 \p second is true if new item has been added or \p false if the item with \p key
340 already is in the set.
342 @warning For \ref cds_nonintrusive_MichaelList_rcu "MichaelList" as the bucket see \ref cds_intrusive_item_creating "insert item troubleshooting".
343 \ref cds_nonintrusive_LazyList_rcu "LazyList" provides exclusive access to inserted item and does not require any node-level
346 template <typename Q, typename Func>
347 std::pair<bool, bool> ensure( const Q& val, Func func )
349 std::pair<bool, bool> bRet = bucket( val ).ensure( val, func );
350 if ( bRet.first && bRet.second )
355 /// Inserts data of type \p value_type created from \p args
357 Returns \p true if inserting successful, \p false otherwise.
359 The function applies RCU lock internally.
361 template <typename... Args>
362 bool emplace( Args&&... args )
364 bool bRet = bucket( value_type(std::forward<Args>(args)...) ).emplace( std::forward<Args>(args)... );
370 /// Deletes \p key from the set
371 /** \anchor cds_nonintrusive_MichealSet_rcu_erase_val
373 Since the key of MichaelHashSet's item type \p value_type is not explicitly specified,
374 template parameter \p Q defines the key type searching in the list.
375 The set item comparator should be able to compare the type \p value_type
378 RCU \p synchronize method can be called. RCU should not be locked.
380 Return \p true if key is found and deleted, \p false otherwise
382 template <typename Q>
383 bool erase( Q const& key )
385 const bool bRet = bucket( key ).erase( key );
391 /// Deletes the item from the set using \p pred predicate for searching
393 The function is an analog of \ref cds_nonintrusive_MichealSet_rcu_erase_val "erase(Q const&)"
394 but \p pred is used for key comparing.
395 \p Less functor has the interface like \p std::less.
396 \p Less must imply the same element order as the comparator used for building the set.
398 template <typename Q, typename Less>
399 bool erase_with( Q const& key, Less pred )
401 const bool bRet = bucket( key ).erase_with( key, pred );
407 /// Deletes \p key from the set
408 /** \anchor cds_nonintrusive_MichealSet_rcu_erase_func
410 The function searches an item with key \p key, calls \p f functor
411 and deletes the item. If \p key is not found, the functor is not called.
413 The functor \p Func interface:
416 void operator()(value_type const& val);
420 Since the key of %MichaelHashSet's \p value_type is not explicitly specified,
421 template parameter \p Q defines the key type searching in the list.
422 The list item comparator should be able to compare the type \p T of list item
425 RCU \p synchronize method can be called. RCU should not be locked.
427 Return \p true if key is found and deleted, \p false otherwise
429 template <typename Q, typename Func>
430 bool erase( Q const& key, Func f )
432 const bool bRet = bucket( key ).erase( key, f );
438 /// Deletes the item from the set using \p pred predicate for searching
440 The function is an analog of \ref cds_nonintrusive_MichealSet_rcu_erase_func "erase(Q const&, Func)"
441 but \p pred is used for key comparing.
442 \p Less functor has the interface like \p std::less.
443 \p Less must imply the same element order as the comparator used for building the set.
445 template <typename Q, typename Less, typename Func>
446 bool erase_with( Q const& key, Less pred, Func f )
448 const bool bRet = bucket( key ).erase_with( key, pred, f );
454 /// Extracts an item from the set
455 /** \anchor cds_nonintrusive_MichaelHashSet_rcu_extract
456 The function searches an item with key equal to \p key in the set,
457 unlinks it from the set, and returns \ref cds::urcu::exempt_ptr "exempt_ptr" pointer to the item found.
458 If the item with the key equal to \p key is not found the function return an empty \p exempt_ptr.
460 The function just excludes the item from the set and returns a pointer to item found.
461 Depends on \p bucket_type you should or should not lock RCU before calling of this function:
462 - for the set based on \ref cds_nonintrusive_MichaelList_rcu "MichaelList" RCU should not be locked
463 - for the set based on \ref cds_nonintrusive_LazyList_rcu "LazyList" RCU should be locked
464 See ordered list implementation for details.
467 #include <cds/urcu/general_buffered.h>
468 #include <cds/container/michael_list_rcu.h>
469 #include <cds/container/michael_set_rcu.h>
471 typedef cds::urcu::gc< general_buffered<> > rcu;
472 typedef cds::container::MichaelList< rcu, Foo > rcu_michael_list;
473 typedef cds::container::MichaelHashSet< rcu, rcu_michael_list, foo_traits > rcu_michael_set;
475 rcu_michael_set theSet;
478 typename rcu_michael_set::exempt_ptr p;
480 // For MichaelList we should not lock RCU
482 // Note that you must not delete the item found inside the RCU lock
483 p = theSet.extract( 10 );
485 // do something with p
489 // We may safely release p here
490 // release() passes the pointer to RCU reclamation cycle
494 template <typename Q>
495 exempt_ptr extract( Q const& key )
497 exempt_ptr p = bucket( key ).extract( key );
503 /// Extracts an item from the set using \p pred predicate for searching
505 The function is an analog of \p extract(Q const&) but \p pred is used for key comparing.
506 \p Less functor has the interface like \p std::less.
507 \p pred must imply the same element order as the comparator used for building the set.
509 template <typename Q, typename Less>
510 exempt_ptr extract_with( Q const& key, Less pred )
512 exempt_ptr p = bucket( key ).extract_with( key, pred );
518 /// Finds the key \p key
519 /** \anchor cds_nonintrusive_MichealSet_rcu_find_func
521 The function searches the item with key equal to \p key and calls the functor \p f for item found.
522 The interface of \p Func functor is:
525 void operator()( value_type& item, Q& key );
528 where \p item is the item found, \p key is the <tt>find</tt> function argument.
530 The functor may change non-key fields of \p item. Note that the functor is only guarantee
531 that \p item cannot be disposed during functor is executing.
532 The functor does not serialize simultaneous access to the set's \p item. If such access is
533 possible you must provide your own synchronization schema on item level to exclude unsafe item modifications.
535 The \p key argument is non-const since it can be used as \p f functor destination i.e., the functor
536 can modify both arguments.
538 Note the hash functor specified for class \p Traits template parameter
539 should accept a parameter of type \p Q that may be not the same as \p value_type.
541 The function applies RCU lock internally.
543 The function returns \p true if \p key is found, \p false otherwise.
545 template <typename Q, typename Func>
546 bool find( Q& key, Func f )
548 return bucket( key ).find( key, f );
551 template <typename Q, typename Func>
552 bool find( Q const& key, Func f )
554 return bucket( key ).find( key, f );
558 /// Finds the key \p key using \p pred predicate for searching
560 The function is an analog of \ref cds_nonintrusive_MichealSet_rcu_find_func "find(Q&, Func)"
561 but \p pred is used for key comparing.
562 \p Less functor has the interface like \p std::less.
563 \p Less must imply the same element order as the comparator used for building the set.
565 template <typename Q, typename Less, typename Func>
566 bool find_with( Q& key, Less pred, Func f )
568 return bucket( key ).find_with( key, pred, f );
571 template <typename Q, typename Less, typename Func>
572 bool find_with( Q const& key, Less pred, Func f )
574 return bucket( key ).find_with( key, pred, f );
578 /// Finds the key \p key
579 /** \anchor cds_nonintrusive_MichealSet_rcu_find_val
581 The function searches the item with key equal to \p key
582 and returns \p true if it is found, and \p false otherwise.
584 Note the hash functor specified for class \p Traits template parameter
585 should accept a parameter of type \p Q that may be not the same as \p value_type.
587 template <typename Q>
588 bool find( Q const & key )
590 return bucket( key ).find( key );
593 /// Finds the key \p key using \p pred predicate for searching
595 The function is an analog of \ref cds_nonintrusive_MichealSet_rcu_find_val "find(Q const&)"
596 but \p pred is used for key comparing.
597 \p Less functor has the interface like \p std::less.
598 \p Less must imply the same element order as the comparator used for building the set.
600 template <typename Q, typename Less>
601 bool find_with( Q const & key, Less pred )
603 return bucket( key ).find_with( key, pred );
606 /// Finds the key \p key and return the item found
607 /** \anchor cds_nonintrusive_MichaelHashSet_rcu_get
608 The function searches the item with key equal to \p key and returns the pointer to item found.
609 If \p key is not found it returns \p nullptr.
610 Note the type of returned value depends on underlying \p bucket_type.
611 For details, see documentation of ordered list you use.
613 Note the compare functor should accept a parameter of type \p Q that can be not the same as \p value_type.
615 RCU should be locked before call of this function.
616 Returned item is valid only while RCU is locked:
618 typedef cds::container::MichaelHashSet< your_template_parameters > hash_set;
620 typename hash_set::raw_ptr gp;
624 hash_set::rcu_lock lock;
626 gp = theSet.get( 5 );
631 // Unlock RCU by rcu_lock destructor
632 // gp can be reclaimed at any time after RCU has been unlocked
636 template <typename Q>
637 raw_ptr get( Q const& key )
639 return bucket( key ).get( key );
642 /// Finds the key \p key and return the item found
644 The function is an analog of \ref cds_nonintrusive_MichaelHashSet_rcu_get "get(Q const&)"
645 but \p pred is used for comparing the keys.
647 \p Less functor has the semantics like \p std::less but should take arguments of type \ref value_type and \p Q
649 \p pred must imply the same element order as the comparator used for building the set.
651 template <typename Q, typename Less>
652 raw_ptr get_with( Q const& key, Less pred )
654 return bucket( key ).get_with( key, pred );
657 /// Clears the set (not atomic)
660 for ( size_t i = 0; i < bucket_count(); ++i )
661 m_Buckets[i].clear();
662 m_ItemCounter.reset();
665 /// Checks if the set is empty
667 Emptiness is checked by item counting: if item count is zero then the set is empty.
668 Thus, the correct item counting feature is an important part of Michael's set implementation.
675 /// Returns item count in the set
678 return m_ItemCounter;
681 /// Returns the size of hash table
683 Since \p %MichaelHashSet cannot dynamically extend the hash table size,
684 the value returned is an constant depending on object initialization parameters;
685 see MichaelHashSet::MichaelHashSet for explanation.
687 size_t bucket_count() const
689 return m_nHashBitmask + 1;
693 }} // namespace cds::container
695 #endif // ifndef CDSLIB_CONTAINER_MICHAEL_SET_RCU_H