3 #ifndef __CDS_CONTAINER_SKIP_LIST_SET_RCU_H
4 #define __CDS_CONTAINER_SKIP_LIST_SET_RCU_H
6 #include <cds/intrusive/skip_list_rcu.h>
7 #include <cds/container/details/make_skip_list_set.h>
9 namespace cds { namespace container {
11 /// Lock-free skip-list set (template specialization for \ref cds_urcu_desc "RCU")
12 /** @ingroup cds_nonintrusive_set
13 \anchor cds_nonintrusive_SkipListSet_rcu
15 The implementation of well-known probabilistic data structure called skip-list
16 invented by W.Pugh in his papers:
17 - [1989] W.Pugh Skip Lists: A Probabilistic Alternative to Balanced Trees
18 - [1990] W.Pugh A Skip List Cookbook
20 A skip-list is a probabilistic data structure that provides expected logarithmic
21 time search without the need of rebalance. The skip-list is a collection of sorted
22 linked list. Nodes are ordered by key. Each node is linked into a subset of the lists.
23 Each list has a level, ranging from 0 to 32. The bottom-level list contains
24 all the nodes, and each higher-level list is a sublist of the lower-level lists.
25 Each node is created with a random top level (with a random height), and belongs
26 to all lists up to that level. The probability that a node has the height 1 is 1/2.
27 The probability that a node has the height N is 1/2 ** N (more precisely,
28 the distribution depends on an random generator provided, but our generators
31 The lock-free variant of skip-list is implemented according to book
32 - [2008] M.Herlihy, N.Shavit "The Art of Multiprocessor Programming",
33 chapter 14.4 "A Lock-Free Concurrent Skiplist"
36 - \p RCU - one of \ref cds_urcu_gc "RCU type".
37 - \p T - type to be stored in the list.
38 - \p Traits - type traits. See skip_list::type_traits for explanation.
40 It is possible to declare option-based list with cds::container::skip_list::make_traits metafunction istead of \p Traits template
42 Template argument list \p Options of cds::container::skip_list::make_traits metafunction are:
43 - opt::compare - key comparison functor. No default functor is provided.
44 If the option is not specified, the opt::less is used.
45 - opt::less - specifies binary predicate used for key comparison. Default is \p std::less<T>.
46 - opt::item_counter - the type of item counting feature. Default is \ref atomicity::empty_item_counter that is no item counting.
47 - opt::memory_model - C++ memory ordering model. Can be opt::v::relaxed_ordering (relaxed memory model, the default)
48 or opt::v::sequential_consistent (sequentially consisnent memory model).
49 - skip_list::random_level_generator - random level generator. Can be skip_list::xorshift, skip_list::turbo_pascal or
50 user-provided one. See skip_list::random_level_generator option description for explanation.
51 Default is \p %skip_list::turbo_pascal.
52 - opt::allocator - allocator for skip-list node. Default is \ref CDS_DEFAULT_ALLOCATOR.
53 - opt::back_off - back-off strategy used. If the option is not specified, the cds::backoff::Default is used.
54 - opt::stat - internal statistics. Available types: skip_list::stat, skip_list::empty_stat (the default)
55 - opt::rcu_check_deadlock - a deadlock checking policy. Default is opt::v::rcu_throw_deadlock
57 @note Before including <tt><cds/container/skip_list_set_rcu.h></tt> you should include appropriate RCU header file,
58 see \ref cds_urcu_gc "RCU type" for list of existing RCU class and corresponding header files.
62 The class supports a forward iterator (\ref iterator and \ref const_iterator).
63 The iteration is ordered.
65 You may iterate over skip-list set items only under RCU lock.
66 Only in this case the iterator is thread-safe since
67 while RCU is locked any set's item cannot be reclaimed.
69 The requirement of RCU lock during iterating means that deletion of the elements (i.e. \ref erase)
72 @warning The iterator object cannot be passed between threads
74 Example how to use skip-list set iterators:
76 // First, you should include the header for RCU type you have chosen
77 #include <cds/urcu/general_buffered.h>
78 #include <cds/container/skip_list_set_rcu.h>
80 typedef cds::urcu::gc< cds::urcu::general_buffered<> > rcu_type;
86 // Traits for your skip-list.
87 // At least, you should define cds::opt::less or cds::opt::compare for Foo struct
88 struct my_traits: public cds::continer::skip_list::type_traits
92 typedef cds::container::SkipListSet< rcu_type, Foo, my_traits > my_skiplist_set;
94 my_skiplist_set theSet;
100 // Apply RCU locking manually
101 typename rcu_type::scoped_lock sl;
103 for ( auto it = theList.begin(); it != theList.end(); ++it ) {
107 // rcu_type::scoped_lock destructor releases RCU lock implicitly
111 \warning Due to concurrent nature of skip-list set it is not guarantee that you can iterate
112 all elements in the set: any concurrent deletion can exclude the element
113 pointed by the iterator from the set, and your iteration can be terminated
114 before end of the set. Therefore, such iteration is more suitable for debugging purposes
116 The iterator class supports the following minimalistic interface:
123 iterator( iterator const& s);
125 value_type * operator ->() const;
126 value_type& operator *() const;
129 iterator& operator ++();
132 iterator& operator = (const iterator& src);
134 bool operator ==(iterator const& i ) const;
135 bool operator !=(iterator const& i ) const;
138 Note, the iterator object returned by \ref end, \p cend member functions points to \p nullptr and should not be dereferenced.
143 #ifdef CDS_DOXYGEN_INVOKED
144 typename Traits = skip_list::type_traits
149 class SkipListSet< cds::urcu::gc< RCU >, T, Traits >:
150 #ifdef CDS_DOXYGEN_INVOKED
151 protected intrusive::SkipListSet< cds::urcu::gc< RCU >, T, Traits >
153 protected details::make_skip_list_set< cds::urcu::gc< RCU >, T, Traits >::type
157 typedef details::make_skip_list_set< cds::urcu::gc< RCU >, T, Traits > maker;
158 typedef typename maker::type base_class;
161 typedef typename base_class::gc gc ; ///< Garbage collector used
162 typedef T value_type ; ///< Value type stored in the set
163 typedef Traits options ; ///< Options specified
165 typedef typename base_class::back_off back_off ; ///< Back-off strategy used
166 typedef typename options::allocator allocator_type ; ///< Allocator type used for allocate/deallocate the skip-list nodes
167 typedef typename base_class::item_counter item_counter ; ///< Item counting policy used
168 typedef typename maker::key_comparator key_comparator ; ///< key compare functor
169 typedef typename base_class::memory_model memory_model ; ///< Memory ordering. See cds::opt::memory_model option
170 typedef typename options::random_level_generator random_level_generator ; ///< random level generator
171 typedef typename options::stat stat ; ///< internal statistics type
172 typedef typename options::rcu_check_deadlock rcu_check_deadlock ; ///< Deadlock checking policy
176 typedef typename maker::node_type node_type;
177 typedef typename maker::node_allocator node_allocator;
179 typedef std::unique_ptr< node_type, typename maker::node_deallocator > scoped_node_ptr;
183 typedef typename base_class::rcu_lock rcu_lock; ///< RCU scoped lock
184 /// Group of \p extract_xxx functions do not require external locking
185 static CDS_CONSTEXPR const bool c_bExtractLockExternal = base_class::c_bExtractLockExternal;
187 /// pointer to extracted node
188 typedef cds::urcu::exempt_ptr< gc, node_type, value_type, typename maker::intrusive_traits::disposer > exempt_ptr;
192 unsigned int random_level()
194 return base_class::random_level();
197 value_type * to_value_ptr( node_type * pNode ) const CDS_NOEXCEPT
199 return pNode ? &pNode->m_Value : nullptr;
209 /// Destructor destroys the set object
215 typedef skip_list::details::iterator< typename base_class::iterator > iterator;
217 /// Const iterator type
218 typedef skip_list::details::iterator< typename base_class::const_iterator > const_iterator;
220 /// Returns a forward iterator addressing the first element in a set
223 return iterator( base_class::begin() );
226 /// Returns a forward const iterator addressing the first element in a set
228 const_iterator begin() const
230 return const_iterator( base_class::begin() );
232 const_iterator cbegin() const
234 return const_iterator( base_class::cbegin() );
238 /// Returns a forward iterator that addresses the location succeeding the last element in a set.
241 return iterator( base_class::end() );
244 /// Returns a forward const iterator that addresses the location succeeding the last element in a set.
246 const_iterator end() const
248 return const_iterator( base_class::end() );
250 const_iterator cend() const
252 return const_iterator( base_class::cend() );
259 The function creates a node with copy of \p val value
260 and then inserts the node created into the set.
262 The type \p Q should contain as minimum the complete key for the node.
263 The object of \ref value_type should be constructible from a value of type \p Q.
264 In trivial case, \p Q is equal to \ref value_type.
266 RCU \p synchronize method can be called. RCU should not be locked.
268 Returns \p true if \p val is inserted into the set, \p false otherwise.
270 template <typename Q>
271 bool insert( Q const& val )
273 scoped_node_ptr sp( node_allocator().New( random_level(), val ));
274 if ( base_class::insert( *sp.get() )) {
283 The function allows to split creating of new item into two part:
284 - create item with key only
285 - insert new item into the set
286 - if inserting is success, calls \p f functor to initialize value-fields of \p val.
288 The functor signature is:
290 void func( value_type& val );
292 where \p val is the item inserted. User-defined functor \p f should guarantee that during changing
293 \p val no any other changes could be made on this set's item by concurrent threads.
294 The user-defined functor is called only if the inserting is success.
296 RCU \p synchronize method can be called. RCU should not be locked.
298 template <typename Q, typename Func>
299 bool insert( Q const& val, Func f )
301 scoped_node_ptr sp( node_allocator().New( random_level(), val ));
302 if ( base_class::insert( *sp.get(), [&f]( node_type& val ) { f( val.m_Value ); } )) {
309 /// Ensures that the item exists in the set
311 The operation performs inserting or changing data with lock-free manner.
313 If the \p val key not found in the set, then the new item created from \p val
314 is inserted into the set. Otherwise, the functor \p func is called with the item found.
315 The functor \p Func should be a function with signature:
317 void func( bool bNew, value_type& item, const Q& val );
322 void operator()( bool bNew, value_type& item, const Q& val );
327 - \p bNew - \p true if the item has been inserted, \p false otherwise
328 - \p item - item of the set
329 - \p val - argument \p key passed into the \p ensure function
331 The functor may change non-key fields of the \p item; however, \p func must guarantee
332 that during changing no any other modifications could be made on this item by concurrent threads.
334 RCU \p synchronize method can be called. RCU should not be locked.
336 Returns <tt> std::pair<bool, bool> </tt> where \p first is true if operation is successfull,
337 \p second is true if new item has been added or \p false if the item with \p key
338 already is in the set.
340 template <typename Q, typename Func>
341 std::pair<bool, bool> ensure( const Q& val, Func func )
343 scoped_node_ptr sp( node_allocator().New( random_level(), val ));
344 std::pair<bool, bool> bRes = base_class::ensure( *sp,
345 [&func, &val](bool bNew, node_type& node, node_type&){ func( bNew, node.m_Value, val ); });
346 if ( bRes.first && bRes.second )
351 /// Inserts data of type \ref value_type constructed with <tt>std::forward<Args>(args)...</tt>
353 Returns \p true if inserting successful, \p false otherwise.
355 RCU \p synchronize method can be called. RCU should not be locked.
357 template <typename... Args>
358 bool emplace( Args&&... args )
360 scoped_node_ptr sp( node_allocator().New( random_level(), std::forward<Args>(args)... ));
361 if ( base_class::insert( *sp.get() )) {
368 /// Delete \p key from the set
369 /** \anchor cds_nonintrusive_SkipListSet_rcu_erase_val
371 The item comparator should be able to compare the type \p value_type
374 RCU \p synchronize method can be called. RCU should not be locked.
376 Return \p true if key is found and deleted, \p false otherwise
378 template <typename Q>
379 bool erase( Q const& key )
381 return base_class::erase( key );
384 /// Deletes the item from the set using \p pred predicate for searching
386 The function is an analog of \ref cds_nonintrusive_SkipListSet_rcu_erase_val "erase(Q const&)"
387 but \p pred is used for key comparing.
388 \p Less functor has the interface like \p std::less.
389 \p Less must imply the same element order as the comparator used for building the set.
391 template <typename Q, typename Less>
392 bool erase_with( Q const& key, Less pred )
394 return base_class::erase_with( key, cds::details::predicate_wrapper< node_type, Less, typename maker::value_accessor >());
397 /// Delete \p key from the set
398 /** \anchor cds_nonintrusive_SkipListSet_rcu_erase_func
400 The function searches an item with key \p key, calls \p f functor
401 and deletes the item. If \p key is not found, the functor is not called.
403 The functor \p Func interface:
406 void operator()(value_type const& val);
410 Since the key of MichaelHashSet's \p value_type is not explicitly specified,
411 template parameter \p Q defines the key type searching in the list.
412 The list item comparator should be able to compare the type \p T of list item
415 RCU \p synchronize method can be called. RCU should not be locked.
417 Return \p true if key is found and deleted, \p false otherwise
421 template <typename Q, typename Func>
422 bool erase( Q const& key, Func f )
424 return base_class::erase( key, [&f]( node_type const& node) { f( node.m_Value ); } );
427 /// Deletes the item from the set using \p pred predicate for searching
429 The function is an analog of \ref cds_nonintrusive_SkipListSet_rcu_erase_func "erase(Q const&, Func)"
430 but \p pred is used for key comparing.
431 \p Less functor has the interface like \p std::less.
432 \p Less must imply the same element order as the comparator used for building the set.
434 template <typename Q, typename Less, typename Func>
435 bool erase_with( Q const& key, Less pred, Func f )
437 return base_class::erase_with( key, cds::details::predicate_wrapper< node_type, Less, typename maker::value_accessor >(),
438 [&f]( node_type const& node) { f( node.m_Value ); } );
441 /// Extracts the item from the set with specified \p key
442 /** \anchor cds_nonintrusive_SkipListSet_rcu_extract
443 The function searches an item with key equal to \p key in the set,
444 unlinks it from the set, and returns it in \p result parameter.
445 If the item with key equal to \p key is not found the function returns \p false.
447 Note the compare functor from \p Traits class' template argument
448 should accept a parameter of type \p Q that can be not the same as \p value_type.
450 RCU \p synchronize method can be called. RCU should NOT be locked.
451 The function does not free the item found.
452 The item will be implicitly freed when \p result object is destroyed or when
453 <tt>result.release()</tt> is called, see \p cds::urcu::exempt_ptr for explanation.
454 @note Before reusing \p result object you should call its \p release() method.
456 template <typename Q>
457 bool extract( exempt_ptr& result, Q const& key )
459 return base_class::do_extract( result, key );
462 /// Extracts the item from the set with comparing functor \p pred
464 The function is an analog of \ref cds_nonintrusive_SkipListSet_rcu_extract "extract(exempt_ptr&, Q const&)"
465 but \p pred predicate is used for key comparing.
466 \p Less has the semantics like \p std::less.
467 \p pred must imply the same element order as the comparator used for building the set.
469 template <typename Q, typename Less>
470 bool extract_with( exempt_ptr& result, Q const& key, Less pred )
472 return base_class::do_extract_with( result, key, cds::details::predicate_wrapper< node_type, Less, typename maker::value_accessor >());
475 /// Extracts an item with minimal key from the set
477 The function searches an item with minimal key, unlinks it, and returns the item found in \p result parameter.
478 If the skip-list is empty the function returns \p false.
480 RCU \p synchronize method can be called. RCU should NOT be locked.
481 The function does not free the item found.
482 The item will be implicitly freed when \p result object is destroyed or when
483 <tt>result.release()</tt> is called, see cds::urcu::exempt_ptr for explanation.
484 @note Before reusing \p result object you should call its \p release() method.
486 bool extract_min( exempt_ptr& result )
488 return base_class::do_extract_min(result);
491 /// Extracts an item with maximal key from the set
493 The function searches an item with maximal key, unlinks it from the set, and returns the item found
494 in \p result parameter. If the skip-list is empty the function returns \p false.
496 RCU \p synchronize method can be called. RCU should NOT be locked.
497 The function does not free the item found.
498 The item will be implicitly freed when \p result object is destroyed or when
499 <tt>result.release()</tt> is called, see cds::urcu::exempt_ptr for explanation.
500 @note Before reusing \p result object you should call its \p release() method.
502 bool extract_max(exempt_ptr& result)
504 return base_class::do_extract_max(result);
507 /// Find the key \p val
509 @anchor cds_nonintrusive_SkipListSet_rcu_find_func
511 The function searches the item with key equal to \p val and calls the functor \p f for item found.
512 The interface of \p Func functor is:
515 void operator()( value_type& item, Q& val );
518 where \p item is the item found, \p val is the <tt>find</tt> function argument.
520 The functor may change non-key fields of \p item. Note that the functor is only guarantee
521 that \p item cannot be disposed during functor is executing.
522 The functor does not serialize simultaneous access to the set's \p item. If such access is
523 possible you must provide your own synchronization schema on item level to exclude unsafe item modifications.
525 The \p val argument is non-const since it can be used as \p f functor destination i.e., the functor
526 can modify both arguments.
528 Note the hash functor specified for class \p Traits template parameter
529 should accept a parameter of type \p Q that may be not the same as \p value_type.
531 The function applies RCU lock internally.
533 The function returns \p true if \p val is found, \p false otherwise.
535 template <typename Q, typename Func>
536 bool find( Q& val, Func f )
538 return base_class::find( val, [&f]( node_type& node, Q& v ) { f( node.m_Value, v ); });
541 /// Finds the key \p val using \p pred predicate for searching
543 The function is an analog of \ref cds_nonintrusive_SkipListSet_rcu_find_func "find(Q&, Func)"
544 but \p pred is used for key comparing.
545 \p Less functor has the interface like \p std::less.
546 \p Less must imply the same element order as the comparator used for building the set.
548 template <typename Q, typename Less, typename Func>
549 bool find_with( Q& val, Less pred, Func f )
551 return base_class::find_with( val, cds::details::predicate_wrapper< node_type, Less, typename maker::value_accessor >(),
552 [&f]( node_type& node, Q& v ) { f( node.m_Value, v ); } );
555 /// Find the key \p val
556 /** @anchor cds_nonintrusive_SkipListSet_rcu_find_cfunc
558 The function searches the item with key equal to \p val and calls the functor \p f for item found.
559 The interface of \p Func functor is:
562 void operator()( value_type& item, Q const& val );
565 where \p item is the item found, \p val is the <tt>find</tt> function argument.
567 The functor may change non-key fields of \p item. Note that the functor is only guarantee
568 that \p item cannot be disposed during functor is executing.
569 The functor does not serialize simultaneous access to the set's \p item. If such access is
570 possible you must provide your own synchronization schema on item level to exclude unsafe item modifications.
572 Note the hash functor specified for class \p Traits template parameter
573 should accept a parameter of type \p Q that may be not the same as \p value_type.
575 The function applies RCU lock internally.
577 The function returns \p true if \p val is found, \p false otherwise.
579 template <typename Q, typename Func>
580 bool find( Q const& val, Func f )
582 return base_class::find( val, [&f]( node_type& node, Q const& v ) { f( node.m_Value, v ); });
585 /// Finds the key \p val using \p pred predicate for searching
587 The function is an analog of \ref cds_nonintrusive_SkipListSet_rcu_find_cfunc "find(Q const&, Func)"
588 but \p pred is used for key comparing.
589 \p Less functor has the semantics like \p std::less.
590 \p Less must imply the same element order as the comparator used for building the set.
592 template <typename Q, typename Less, typename Func>
593 bool find_with( Q const& val, Less pred, Func f )
595 return base_class::find_with( val, cds::details::predicate_wrapper< node_type, Less, typename maker::value_accessor >(),
596 [&f]( node_type& node, Q const& v ) { f( node.m_Value, v ); } );
599 /// Find the key \p val
600 /** @anchor cds_nonintrusive_SkipListSet_rcu_find_val
602 The function searches the item with key equal to \p val
603 and returns \p true if it is found, and \p false otherwise.
605 Note the hash functor specified for class \p Traits template parameter
606 should accept a parameter of type \p Q that may be not the same as \ref value_type.
608 The function applies RCU lock internally.
610 template <typename Q>
611 bool find( Q const & val )
613 return base_class::find( val );
616 /// Finds the key \p val using \p pred predicate for searching
618 The function is an analog of \ref cds_nonintrusive_SkipListSet_rcu_find_val "find(Q const&)"
619 but \p pred is used for key comparing.
620 \p Less functor has the interface like \p std::less.
621 \p Less must imply the same element order as the comparator used for building the set.
623 template <typename Q, typename Less>
624 bool find_with( Q const& val, Less pred )
626 return base_class::find_with( val, cds::details::predicate_wrapper< node_type, Less, typename maker::value_accessor >());
629 /// Finds \p key and return the item found
630 /** \anchor cds_nonintrusive_SkipListSet_rcu_get
631 The function searches the item with key equal to \p key and returns the pointer to item found.
632 If \p key is not found it returns \p nullptr.
634 Note the compare functor in \p Traits class' template argument
635 should accept a parameter of type \p Q that can be not the same as \p value_type.
637 RCU should be locked before call of this function.
638 Returned item is valid only while RCU is locked:
640 typedef cds::container::SkipListSet< cds::urcu::gc< cds::urcu::general_buffered<> >, foo, my_traits > skip_list;
645 skip_list::rcu_lock lock;
647 foo * pVal = theList.get( 5 );
651 // Unlock RCU by rcu_lock destructor
652 // pVal can be freed at any time after RCU unlocking
656 After RCU unlocking the \p %force_dispose member function can be called manually,
657 see \ref force_dispose for explanation.
659 template <typename Q>
660 value_type * get( Q const& key )
662 return to_value_ptr( base_class::get( key ));
665 /// Finds the key \p val and return the item found
667 The function is an analog of \ref cds_nonintrusive_SkipListSet_rcu_get "get(Q const&)"
668 but \p pred is used for comparing the keys.
670 \p Less functor has the semantics like \p std::less but should take arguments of type \ref value_type and \p Q
672 \p pred must imply the same element order as the comparator used for building the set.
674 template <typename Q, typename Less>
675 value_type * get_with( Q const& val, Less pred )
677 return to_value_ptr( base_class::get_with( val, cds::details::predicate_wrapper< node_type, Less, typename maker::value_accessor >() ));
680 /// Clears the set (non-atomic).
682 The function deletes all items from the set.
683 The function is not atomic, thus, in multi-threaded environment with parallel insertions
687 assert( set.empty() );
689 the assertion could be raised.
691 For each item the \ref disposer provided by \p Traits template parameter will be called.
698 /// Checks if the set is empty
701 return base_class::empty();
704 /// Returns item count in the set
706 The value returned depends on item counter type provided by \p Traits template parameter.
707 If it is atomicity::empty_item_counter this function always returns 0.
708 Therefore, the function is not suitable for checking the set emptiness, use \ref empty
709 member function for this purpose.
713 return base_class::size();
716 /// Returns const reference to internal statistics
717 stat const& statistics() const
719 return base_class::statistics();
722 /// Clears internal list of ready-to-delete items passing them to RCU reclamation cycle
724 See \ref cds_intrusive_SkipListSet_rcu_force_dispose "intrusive SkipListSet" for explanation
728 return base_class::force_dispose();
732 }} // namespace cds::container
734 #endif // #ifndef __CDS_CONTAINER_SKIP_LIST_SET_RCU_H