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
242 The Michael's hash set is non-expandable container. You should point the average count of items \p nMaxItemCount
243 when you create an object.
244 \p nLoadFactor parameter defines average count of items per bucket and it should be small number between 1 and 10.
245 Remember, since the bucket implementation is an ordered list, searching in the bucket is linear [<tt>O(nLoadFactor)</tt>].
247 The ctor defines hash table size as rounding <tt>nMaxItemCount / nLoadFactor</tt> up to nearest power of two.
250 size_t nMaxItemCount, ///< estimation of max item count in the hash set
251 size_t nLoadFactor ///< load factor: estimation of max number of items in the bucket
252 ) : m_nHashBitmask( michael_set::details::init_hash_bitmask( nMaxItemCount, nLoadFactor ))
254 // GC and OrderedList::gc must be the same
255 static_assert( std::is_same<gc, typename bucket_type::gc>::value, "GC and OrderedList::gc must be the same");
257 // atomicity::empty_item_counter is not allowed as a item counter
258 static_assert( !std::is_same<item_counter, atomicity::empty_item_counter>::value,
259 "atomicity::empty_item_counter is not allowed as a item counter");
261 m_Buckets = bucket_table_allocator().NewArray( bucket_count() );
264 /// Clears hash set and destroys it
268 bucket_table_allocator().Delete( m_Buckets, bucket_count() );
273 The function creates a node with copy of \p val value
274 and then inserts the node created into the set.
276 The type \p Q should contain as minimum the complete key for the node.
277 The object of \ref value_type should be constructible from a value of type \p Q.
278 In trivial case, \p Q is equal to \ref value_type.
280 The function applies RCU lock internally.
282 Returns \p true if \p val is inserted into the set, \p false otherwise.
284 template <typename Q>
285 bool insert( Q const& val )
287 const bool bRet = bucket( val ).insert( val );
295 The function allows to split creating of new item into two part:
296 - create item with key only
297 - insert new item into the set
298 - if inserting is success, calls \p f functor to initialize value-fields of \p val.
300 The functor signature is:
302 void func( value_type& val );
304 where \p val is the item inserted.
305 The user-defined functor is called only if the inserting is success.
307 The function applies RCU lock internally.
309 @warning For \ref cds_nonintrusive_MichaelList_rcu "MichaelList" as the bucket see \ref cds_intrusive_item_creating "insert item troubleshooting".
310 \ref cds_nonintrusive_LazyList_rcu "LazyList" provides exclusive access to inserted item and does not require any node-level
313 template <typename Q, typename Func>
314 bool insert( Q const& val, Func f )
316 const bool bRet = bucket( val ).insert( val, f );
322 /// Ensures that the item exists in the set
324 The operation performs inserting or changing data with lock-free manner.
326 If the \p val key not found in the set, then the new item created from \p val
327 is inserted into the set. Otherwise, the functor \p func is called with the item found.
328 The functor \p Func signature is:
331 void operator()( bool bNew, value_type& item, const Q& val );
336 - \p bNew - \p true if the item has been inserted, \p false otherwise
337 - \p item - item of the set
338 - \p val - argument \p key passed into the \p ensure function
340 The functor may change non-key fields of the \p item.
342 The function applies RCU lock internally.
344 Returns <tt> std::pair<bool, bool> </tt> where \p first is true if operation is successfull,
345 \p second is true if new item has been added or \p false if the item with \p key
346 already is in the set.
348 @warning For \ref cds_nonintrusive_MichaelList_rcu "MichaelList" as the bucket see \ref cds_intrusive_item_creating "insert item troubleshooting".
349 \ref cds_nonintrusive_LazyList_rcu "LazyList" provides exclusive access to inserted item and does not require any node-level
352 template <typename Q, typename Func>
353 std::pair<bool, bool> ensure( const Q& val, Func func )
355 std::pair<bool, bool> bRet = bucket( val ).ensure( val, func );
356 if ( bRet.first && bRet.second )
361 /// Inserts data of type \p value_type created from \p args
363 Returns \p true if inserting successful, \p false otherwise.
365 The function applies RCU lock internally.
367 template <typename... Args>
368 bool emplace( Args&&... args )
370 bool bRet = bucket( value_type(std::forward<Args>(args)...) ).emplace( std::forward<Args>(args)... );
376 /// Deletes \p key from the set
377 /** \anchor cds_nonintrusive_MichealSet_rcu_erase_val
379 Since the key of MichaelHashSet's item type \p value_type is not explicitly specified,
380 template parameter \p Q defines the key type searching in the list.
381 The set item comparator should be able to compare the type \p value_type
384 RCU \p synchronize method can be called. RCU should not be locked.
386 Return \p true if key is found and deleted, \p false otherwise
388 template <typename Q>
389 bool erase( Q const& key )
391 const bool bRet = bucket( key ).erase( key );
397 /// Deletes the item from the set using \p pred predicate for searching
399 The function is an analog of \ref cds_nonintrusive_MichealSet_rcu_erase_val "erase(Q const&)"
400 but \p pred is used for key comparing.
401 \p Less functor has the interface like \p std::less.
402 \p Less must imply the same element order as the comparator used for building the set.
404 template <typename Q, typename Less>
405 bool erase_with( Q const& key, Less pred )
407 const bool bRet = bucket( key ).erase_with( key, pred );
413 /// Deletes \p key from the set
414 /** \anchor cds_nonintrusive_MichealSet_rcu_erase_func
416 The function searches an item with key \p key, calls \p f functor
417 and deletes the item. If \p key is not found, the functor is not called.
419 The functor \p Func interface:
422 void operator()(value_type const& val);
426 Since the key of %MichaelHashSet's \p value_type is not explicitly specified,
427 template parameter \p Q defines the key type searching in the list.
428 The list item comparator should be able to compare the type \p T of list item
431 RCU \p synchronize method can be called. RCU should not be locked.
433 Return \p true if key is found and deleted, \p false otherwise
435 template <typename Q, typename Func>
436 bool erase( Q const& key, Func f )
438 const bool bRet = bucket( key ).erase( key, f );
444 /// Deletes the item from the set using \p pred predicate for searching
446 The function is an analog of \ref cds_nonintrusive_MichealSet_rcu_erase_func "erase(Q const&, Func)"
447 but \p pred is used for key comparing.
448 \p Less functor has the interface like \p std::less.
449 \p Less must imply the same element order as the comparator used for building the set.
451 template <typename Q, typename Less, typename Func>
452 bool erase_with( Q const& key, Less pred, Func f )
454 const bool bRet = bucket( key ).erase_with( key, pred, f );
460 /// Extracts an item from the set
461 /** \anchor cds_nonintrusive_MichaelHashSet_rcu_extract
462 The function searches an item with key equal to \p key in the set,
463 unlinks it from the set, and returns \ref cds::urcu::exempt_ptr "exempt_ptr" pointer to the item found.
464 If the item with the key equal to \p key is not found the function return an empty \p exempt_ptr.
466 The function just excludes the item from the set and returns a pointer to item found.
467 Depends on \p bucket_type you should or should not lock RCU before calling of this function:
468 - for the set based on \ref cds_nonintrusive_MichaelList_rcu "MichaelList" RCU should not be locked
469 - for the set based on \ref cds_nonintrusive_LazyList_rcu "LazyList" RCU should be locked
470 See ordered list implementation for details.
473 #include <cds/urcu/general_buffered.h>
474 #include <cds/container/michael_list_rcu.h>
475 #include <cds/container/michael_set_rcu.h>
477 typedef cds::urcu::gc< general_buffered<> > rcu;
478 typedef cds::container::MichaelList< rcu, Foo > rcu_michael_list;
479 typedef cds::container::MichaelHashSet< rcu, rcu_michael_list, foo_traits > rcu_michael_set;
481 rcu_michael_set theSet;
484 typename rcu_michael_set::exempt_ptr p;
486 // For MichaelList we should not lock RCU
488 // Note that you must not delete the item found inside the RCU lock
489 p = theSet.extract( 10 );
491 // do something with p
495 // We may safely release p here
496 // release() passes the pointer to RCU reclamation cycle
500 template <typename Q>
501 exempt_ptr extract( Q const& key )
503 exempt_ptr p = bucket( key ).extract( key );
509 /// Extracts an item from the set using \p pred predicate for searching
511 The function is an analog of \p extract(Q const&) but \p pred is used for key comparing.
512 \p Less functor has the interface like \p std::less.
513 \p pred must imply the same element order as the comparator used for building the set.
515 template <typename Q, typename Less>
516 exempt_ptr extract_with( Q const& key, Less pred )
518 exempt_ptr p = bucket( key ).extract_with( key, pred );
524 /// Finds the key \p key
525 /** \anchor cds_nonintrusive_MichealSet_rcu_find_func
527 The function searches the item with key equal to \p key and calls the functor \p f for item found.
528 The interface of \p Func functor is:
531 void operator()( value_type& item, Q& key );
534 where \p item is the item found, \p key is the <tt>find</tt> function argument.
536 The functor may change non-key fields of \p item. Note that the functor is only guarantee
537 that \p item cannot be disposed during functor is executing.
538 The functor does not serialize simultaneous access to the set's \p item. If such access is
539 possible you must provide your own synchronization schema on item level to exclude unsafe item modifications.
541 The \p key argument is non-const since it can be used as \p f functor destination i.e., the functor
542 can modify both arguments.
544 Note the hash functor specified for class \p Traits template parameter
545 should accept a parameter of type \p Q that may be not the same as \p value_type.
547 The function applies RCU lock internally.
549 The function returns \p true if \p key is found, \p false otherwise.
551 template <typename Q, typename Func>
552 bool find( Q& key, Func f )
554 return bucket( key ).find( key, f );
557 template <typename Q, typename Func>
558 bool find( Q const& key, Func f )
560 return bucket( key ).find( key, f );
564 /// Finds the key \p key using \p pred predicate for searching
566 The function is an analog of \ref cds_nonintrusive_MichealSet_rcu_find_func "find(Q&, Func)"
567 but \p pred is used for key comparing.
568 \p Less functor has the interface like \p std::less.
569 \p Less must imply the same element order as the comparator used for building the set.
571 template <typename Q, typename Less, typename Func>
572 bool find_with( Q& key, Less pred, Func f )
574 return bucket( key ).find_with( key, pred, f );
577 template <typename Q, typename Less, typename Func>
578 bool find_with( Q const& key, Less pred, Func f )
580 return bucket( key ).find_with( key, pred, f );
584 /// Finds the key \p key
585 /** \anchor cds_nonintrusive_MichealSet_rcu_find_val
587 The function searches the item with key equal to \p key
588 and returns \p true if it is found, and \p false otherwise.
590 Note the hash functor specified for class \p Traits template parameter
591 should accept a parameter of type \p Q that may be not the same as \p value_type.
593 template <typename Q>
594 bool find( Q const & key )
596 return bucket( key ).find( key );
599 /// Finds the key \p key using \p pred predicate for searching
601 The function is an analog of \ref cds_nonintrusive_MichealSet_rcu_find_val "find(Q const&)"
602 but \p pred is used for key comparing.
603 \p Less functor has the interface like \p std::less.
604 \p Less must imply the same element order as the comparator used for building the set.
606 template <typename Q, typename Less>
607 bool find_with( Q const & key, Less pred )
609 return bucket( key ).find_with( key, pred );
612 /// Finds the key \p key and return the item found
613 /** \anchor cds_nonintrusive_MichaelHashSet_rcu_get
614 The function searches the item with key equal to \p key and returns the pointer to item found.
615 If \p key is not found it returns \p nullptr.
616 Note the type of returned value depends on underlying \p bucket_type.
617 For details, see documentation of ordered list you use.
619 Note the compare functor should accept a parameter of type \p Q that can be not the same as \p value_type.
621 RCU should be locked before call of this function.
622 Returned item is valid only while RCU is locked:
624 typedef cds::container::MichaelHashSet< your_template_parameters > hash_set;
626 typename hash_set::raw_ptr gp;
630 hash_set::rcu_lock lock;
632 gp = theSet.get( 5 );
637 // Unlock RCU by rcu_lock destructor
638 // gp can be reclaimed at any time after RCU has been unlocked
642 template <typename Q>
643 raw_ptr get( Q const& key )
645 return bucket( key ).get( key );
648 /// Finds the key \p key and return the item found
650 The function is an analog of \ref cds_nonintrusive_MichaelHashSet_rcu_get "get(Q const&)"
651 but \p pred is used for comparing the keys.
653 \p Less functor has the semantics like \p std::less but should take arguments of type \ref value_type and \p Q
655 \p pred must imply the same element order as the comparator used for building the set.
657 template <typename Q, typename Less>
658 raw_ptr get_with( Q const& key, Less pred )
660 return bucket( key ).get_with( key, pred );
663 /// Clears the set (not atomic)
666 for ( size_t i = 0; i < bucket_count(); ++i )
667 m_Buckets[i].clear();
668 m_ItemCounter.reset();
671 /// Checks if the set is empty
673 Emptiness is checked by item counting: if item count is zero then the set is empty.
674 Thus, the correct item counting feature is an important part of Michael's set implementation.
681 /// Returns item count in the set
684 return m_ItemCounter;
687 /// Returns the size of hash table
689 Since \p %MichaelHashSet cannot dynamically extend the hash table size,
690 the value returned is an constant depending on object initialization parameters;
691 see MichaelHashSet::MichaelHashSet for explanation.
693 size_t bucket_count() const
695 return m_nHashBitmask + 1;
699 }} // namespace cds::container
701 #endif // ifndef CDSLIB_CONTAINER_MICHAEL_SET_RCU_H