3 #ifndef CDSLIB_CONTAINER_IMPL_SKIP_LIST_SET_H
4 #define CDSLIB_CONTAINER_IMPL_SKIP_LIST_SET_H
6 #include <cds/details/binary_functor_wrapper.h>
7 #include <cds/container/details/guarded_ptr_cast.h>
9 namespace cds { namespace container {
11 /// Lock-free skip-list set
12 /** @ingroup cds_nonintrusive_set
13 \anchor cds_nonintrusive_SkipListSet_hp
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 GC - Garbage collector used.
37 - \p T - type to be stored in the list.
38 - \p Traits - set traits, default is \p skip_list::traits.
39 It is possible to declare option-based list with \p cds::container::skip_list::make_traits metafunction
40 istead of \p Traits template argument.
42 @warning The skip-list requires up to 67 hazard pointers that may be critical for some GCs for which
43 the guard count is limited (like as \p gc::HP). Those GCs should be explicitly initialized with
44 hazard pointer enough: \code cds::gc::HP myhp( 67 ) \endcode. Otherwise an run-time exception may be raised
45 when you try to create skip-list object.
47 @note There are several specializations of \p %SkipListSet for each \p GC. You should include:
48 - <tt><cds/container/skip_list_set_hp.h></tt> for \p gc::HP garbage collector
49 - <tt><cds/container/skip_list_set_dhp.h></tt> for \p gc::DHP garbage collector
50 - <tt><cds/container/skip_list_set_rcu.h></tt> for \ref cds_nonintrusive_SkipListSet_rcu "RCU type"
51 - <tt><cds/container/skip_list_set_nogc.h></tt> for \ref cds_nonintrusive_SkipListSet_nogc "non-deletable SkipListSet"
55 The class supports a forward iterator (\ref iterator and \ref const_iterator).
56 The iteration is ordered.
57 The iterator object is thread-safe: the element pointed by the iterator object is guarded,
58 so, the element cannot be reclaimed while the iterator object is alive.
59 However, passing an iterator object between threads is dangerous.
61 \warning Due to concurrent nature of skip-list set it is not guarantee that you can iterate
62 all elements in the set: any concurrent deletion can exclude the element
63 pointed by the iterator from the set, and your iteration can be terminated
64 before end of the set. Therefore, such iteration is more suitable for debugging purpose only
66 Remember, each iterator object requires 2 additional hazard pointers, that may be
67 a limited resource for \p GC like \p gc::HP (for \p gc::DHP the count of
70 The iterator class supports the following minimalistic interface:
77 iterator( iterator const& s);
79 value_type * operator ->() const;
80 value_type& operator *() const;
83 iterator& operator ++();
86 iterator& operator = (const iterator& src);
88 bool operator ==(iterator const& i ) const;
89 bool operator !=(iterator const& i ) const;
92 Note, the iterator object returned by \p end(), \p cend() member functions points to \p nullptr and should not be dereferenced.
97 #ifdef CDS_DOXYGEN_INVOKED
98 typename Traits = skip_list::traits
104 #ifdef CDS_DOXYGEN_INVOKED
105 protected intrusive::SkipListSet< GC, T, Traits >
107 protected details::make_skip_list_set< GC, T, Traits >::type
111 typedef details::make_skip_list_set< GC, T, Traits > maker;
112 typedef typename maker::type base_class;
115 typedef GC gc; ///< Garbage collector used
116 typedef T value_type; ///< @anchor cds_containewr_SkipListSet_value_type Value type to be stored in the set
117 typedef Traits traits; ///< Options specified
119 typedef typename base_class::back_off back_off; ///< Back-off strategy
120 typedef typename traits::allocator allocator_type; ///< Allocator type used for allocate/deallocate the skip-list nodes
121 typedef typename base_class::item_counter item_counter; ///< Item counting policy used
122 typedef typename maker::key_comparator key_comparator; ///< key comparison functor
123 typedef typename base_class::memory_model memory_model; ///< Memory ordering. See cds::opt::memory_model option
124 typedef typename traits::random_level_generator random_level_generator; ///< random level generator
125 typedef typename traits::stat stat; ///< internal statistics type
128 typedef cds::container::skip_list::implementation_tag implementation_tag;
133 typedef typename maker::node_type node_type;
134 typedef typename maker::node_allocator node_allocator;
136 typedef std::unique_ptr< node_type, typename maker::node_deallocator > scoped_node_ptr;
141 typedef typename gc::template guarded_ptr< node_type, value_type, details::guarded_ptr_cast_set<node_type, value_type> > guarded_ptr;
145 unsigned int random_level()
147 return base_class::random_level();
157 /// Destructor destroys the set object
163 typedef skip_list::details::iterator< typename base_class::iterator > iterator;
165 /// Const iterator type
166 typedef skip_list::details::iterator< typename base_class::const_iterator > const_iterator;
168 /// Returns a forward iterator addressing the first element in a set
171 return iterator( base_class::begin() );
174 /// Returns a forward const iterator addressing the first element in a set
175 const_iterator begin() const
177 return const_iterator( base_class::begin() );
180 /// Returns a forward const iterator addressing the first element in a set
181 const_iterator cbegin() const
183 return const_iterator( base_class::cbegin() );
186 /// Returns a forward iterator that addresses the location succeeding the last element in a set.
189 return iterator( base_class::end() );
192 /// Returns a forward const iterator that addresses the location succeeding the last element in a set.
193 const_iterator end() const
195 return const_iterator( base_class::end() );
198 /// Returns a forward const iterator that addresses the location succeeding the last element in a set.
199 const_iterator cend() const
201 return const_iterator( base_class::cend() );
207 The function creates a node with copy of \p val value
208 and then inserts the node created into the set.
210 The type \p Q should contain as minimum the complete key for the node.
211 The object of \ref value_type should be constructible from a value of type \p Q.
212 In trivial case, \p Q is equal to \ref value_type.
214 Returns \p true if \p val is inserted into the set, \p false otherwise.
216 template <typename Q>
217 bool insert( Q const& val )
219 scoped_node_ptr sp( node_allocator().New( random_level(), val ));
220 if ( base_class::insert( *sp.get() )) {
229 The function allows to split creating of new item into two part:
230 - create item with key only
231 - insert new item into the set
232 - if inserting is success, calls \p f functor to initialize value-fields of \p val.
234 The functor signature is:
236 void func( value_type& val );
238 where \p val is the item inserted. User-defined functor \p f should guarantee that during changing
239 \p val no any other changes could be made on this set's item by concurrent threads.
240 The user-defined functor is called only if the inserting is success.
242 template <typename Q, typename Func>
243 bool insert( Q const& val, Func f )
245 scoped_node_ptr sp( node_allocator().New( random_level(), val ));
246 if ( base_class::insert( *sp.get(), [&f]( node_type& val ) { f( val.m_Value ); } )) {
253 /// Ensures that the item exists in the set
255 The operation performs inserting or changing data with lock-free manner.
257 If the \p val key not found in the set, then the new item created from \p val
258 is inserted into the set. Otherwise, the functor \p func is called with the item found.
259 The functor \p Func should be a function with signature:
261 void func( bool bNew, value_type& item, const Q& val );
266 void operator()( bool bNew, value_type& item, const Q& val );
271 - \p bNew - \p true if the item has been inserted, \p false otherwise
272 - \p item - item of the set
273 - \p val - argument \p key passed into the \p %ensure() function
275 The functor may change non-key fields of the \p item; however, \p func must guarantee
276 that during changing no any other modifications could be made on this item by concurrent threads.
278 Returns <tt> std::pair<bool, bool> </tt> where \p first is true if operation is successfull,
279 \p second is true if new item has been added or \p false if the item with \p key
280 already is in the set.
282 @warning See \ref cds_intrusive_item_creating "insert item troubleshooting"
284 template <typename Q, typename Func>
285 std::pair<bool, bool> ensure( const Q& val, Func func )
287 scoped_node_ptr sp( node_allocator().New( random_level(), val ));
288 std::pair<bool, bool> bRes = base_class::ensure( *sp,
289 [&func, &val](bool bNew, node_type& node, node_type&){ func( bNew, node.m_Value, val ); });
290 if ( bRes.first && bRes.second )
295 /// Inserts data of type \p value_type created in-place from <tt>std::forward<Args>(args)...</tt>
297 Returns \p true if inserting successful, \p false otherwise.
299 template <typename... Args>
300 bool emplace( Args&&... args )
302 scoped_node_ptr sp( node_allocator().New( random_level(), std::forward<Args>(args)... ));
303 if ( base_class::insert( *sp.get() )) {
310 /// Delete \p key from the set
311 /** \anchor cds_nonintrusive_SkipListSet_erase_val
313 The set item comparator should be able to compare the type \p value_type
316 Return \p true if key is found and deleted, \p false otherwise
318 template <typename Q>
319 bool erase( Q const& key )
321 return base_class::erase( key );
324 /// Deletes the item from the set using \p pred predicate for searching
326 The function is an analog of \ref cds_nonintrusive_SkipListSet_erase_val "erase(Q const&)"
327 but \p pred is used for key comparing.
328 \p Less functor has the interface like \p std::less.
329 \p Less must imply the same element order as the comparator used for building the set.
331 template <typename Q, typename Less>
332 bool erase_with( Q const& key, Less pred )
335 return base_class::erase_with( key, cds::details::predicate_wrapper< node_type, Less, typename maker::value_accessor >() );
338 /// Delete \p key from the set
339 /** \anchor cds_nonintrusive_SkipListSet_erase_func
341 The function searches an item with key \p key, calls \p f functor
342 and deletes the item. If \p key is not found, the functor is not called.
344 The functor \p Func interface:
347 void operator()(value_type const& val);
351 Since the key of \p value_type is not explicitly specified,
352 template parameter \p Q defines the key type to search in the list.
353 The list item comparator should be able to compare the type \p T of list item
356 Return \p true if key is found and deleted, \p false otherwise
358 template <typename Q, typename Func>
359 bool erase( Q const& key, Func f )
361 return base_class::erase( key, [&f]( node_type const& node) { f( node.m_Value ); } );
364 /// Deletes the item from the set using \p pred predicate for searching
366 The function is an analog of \ref cds_nonintrusive_SkipListSet_erase_func "erase(Q const&, Func)"
367 but \p pred is used for key comparing.
368 \p Less functor has the interface like \p std::less.
369 \p Less must imply the same element order as the comparator used for building the set.
371 template <typename Q, typename Less, typename Func>
372 bool erase_with( Q const& key, Less pred, Func f )
375 return base_class::erase_with( key, cds::details::predicate_wrapper< node_type, Less, typename maker::value_accessor >(),
376 [&f]( node_type const& node) { f( node.m_Value ); } );
379 /// Extracts the item from the set with specified \p key
380 /** \anchor cds_nonintrusive_SkipListSet_hp_extract
381 The function searches an item with key equal to \p key in the set,
382 unlinks it from the set, and returns it as \p guarded_ptr.
383 If \p key is not found the function returns an empty guarded pointer.
385 Note the compare functor should accept a parameter of type \p Q that can be not the same as \p value_type.
387 The item extracted is freed automatically by garbage collector \p GC
388 when returned \p guarded_ptr object will be destroyed or released.
389 @note Each \p guarded_ptr object uses the GC's guard that can be limited resource.
393 typedef cds::container::SkipListSet< cds::gc::HP, foo, my_traits > skip_list;
397 skip_list::guarded_ptr gp(theList.extract( 5 ))
402 // Destructor of gp releases internal HP guard and frees the pointer
406 template <typename Q>
407 guarded_ptr extract( Q const& key )
410 base_class::extract_( gp.guard(), key, typename base_class::key_comparator() );
414 /// Extracts the item from the set with comparing functor \p pred
416 The function is an analog of \ref cds_nonintrusive_SkipListSet_hp_extract "extract(Q const&)"
417 but \p pred predicate is used for key comparing.
419 \p Less functor has the semantics like \p std::less but should take arguments of type \ref value_type and \p Q
421 \p pred must imply the same element order as the comparator used for building the set.
423 template <typename Q, typename Less>
424 guarded_ptr extract_with( Q const& key, Less pred )
427 typedef cds::details::predicate_wrapper< node_type, Less, typename maker::value_accessor > wrapped_less;
429 base_class::extract_( gp.guard(), key, cds::opt::details::make_comparator_from_less<wrapped_less>() );
433 /// Extracts an item with minimal key from the set
435 The function searches an item with minimal key, unlinks it, and returns pointer to the item found as \p guarded_ptr.
436 If the skip-list is empty the function returns an empty guarded pointer.
438 The item extracted is freed automatically by garbage collector \p GC
439 when returned \p guarded_ptr object will be destroyed or released.
440 @note Each \p guarded_ptr object uses the GC's guard that can be limited resource.
444 typedef cds::continer::SkipListSet< cds::gc::HP, foo, my_traits > skip_list;
448 skip_list::guarded_ptr gp( theList.extract_min());
453 // Destructor of gp releases internal HP guard and then frees the pointer
457 guarded_ptr extract_min()
460 base_class::extract_min_( gp.guard() );
464 /// Extracts an item with maximal key from the set
466 The function searches an item with maximal key, unlinks it, and returns the pointer to item found as \p guarded_ptr.
467 If the skip-list is empty the function returns an empty guarded pointer.
469 The item found is freed by garbage collector \p GC automatically
470 when returned \p guarded_ptr object will be destroyed or released.
471 @note Each \p guarded_ptr object uses the GC's guard that can be limited resource.
475 typedef cds::container::SkipListSet< cds::gc::HP, foo, my_traits > skip_list;
479 skip_list::guarded_ptr gp( theList.extract_max());
484 // Destructor of gp releases internal HP guard and then frees the pointer
488 guarded_ptr extract_max()
491 base_class::extract_max_( gp.guard() );
496 /** \anchor cds_nonintrusive_SkipListSet_find_func
498 The function searches the item with key equal to \p key and calls the functor \p f for item found.
499 The interface of \p Func functor is:
502 void operator()( value_type& item, Q& key );
505 where \p item is the item found, \p key is the <tt>find</tt> function argument.
507 The functor may change non-key fields of \p item. Note that the functor is only guarantee
508 that \p item cannot be disposed during functor is executing.
509 The functor does not serialize simultaneous access to the set's \p item. If such access is
510 possible you must provide your own synchronization schema on item level to exclude unsafe item modifications.
512 Note the hash functor specified for class \p Traits template parameter
513 should accept a parameter of type \p Q that may be not the same as \p value_type.
515 The function returns \p true if \p key is found, \p false otherwise.
517 template <typename Q, typename Func>
518 bool find( Q& key, Func f )
520 return base_class::find( key, [&f]( node_type& node, Q& v ) { f( node.m_Value, v ); });
523 template <typename Q, typename Func>
524 bool find( Q const& key, Func f )
526 return base_class::find( key, [&f]( node_type& node, Q& v ) { f( node.m_Value, v ); } );
530 /// Finds \p key using \p pred predicate for searching
532 The function is an analog of \ref cds_nonintrusive_SkipListSet_find_func "find(Q&, Func)"
533 but \p pred is used for key comparing.
534 \p Less functor has the interface like \p std::less.
535 \p Less must imply the same element order as the comparator used for building the set.
537 template <typename Q, typename Less, typename Func>
538 bool find_with( Q& key, Less pred, Func f )
541 return base_class::find_with( key, cds::details::predicate_wrapper< node_type, Less, typename maker::value_accessor >(),
542 [&f]( node_type& node, Q& v ) { f( node.m_Value, v ); } );
545 template <typename Q, typename Less, typename Func>
546 bool find_with( Q const& key, Less pred, Func f )
549 return base_class::find_with( key, cds::details::predicate_wrapper< node_type, Less, typename maker::value_accessor >(),
550 [&f]( node_type& node, Q& v ) { f( node.m_Value, v ); } );
555 /** \anchor cds_nonintrusive_SkipListSet_find_val
557 The function searches the item with key equal to \p key
558 and returns \p true if it is found, and \p false otherwise.
560 Note the hash functor specified for class \p Traits template parameter
561 should accept a parameter of type \p Q that may be not the same as \ref value_type.
563 template <typename Q>
564 bool find( Q const& key )
566 return base_class::find( key );
569 /// Finds \p key using \p pred predicate for searching
571 The function is an analog of \ref cds_nonintrusive_SkipListSet_find_val "find(Q const&)"
572 but \p pred is used for key comparing.
573 \p Less functor has the interface like \p std::less.
574 \p Less must imply the same element order as the comparator used for building the set.
576 template <typename Q, typename Less>
577 bool find_with( Q const& key, Less pred )
580 return base_class::find_with( key, cds::details::predicate_wrapper< node_type, Less, typename maker::value_accessor >());
583 /// Finds \p key and return the item found
584 /** \anchor cds_nonintrusive_SkipListSet_hp_get
585 The function searches the item with key equal to \p key
586 and returns a guarded pointer to the item found.
587 If \p key is not found the function returns an empty guarded pointer.
589 It is safe when a concurrent thread erases the item returned in \p result guarded pointer.
590 In this case the item will be freed later by garbage collector \p GC automatically
591 when \p guarded_ptr object will be destroyed or released.
592 @note Each \p guarded_ptr object uses one GC's guard which can be limited resource.
596 typedef cds::container::SkipListSet< cds::gc::HP, foo, my_traits > skip_list;
600 skip_list::guarded_ptr gp( theList.get( 5 ));
601 if ( theList.get( 5 )) {
605 // Destructor of guarded_ptr releases internal HP guard
609 Note the compare functor specified for class \p Traits template parameter
610 should accept a parameter of type \p Q that can be not the same as \p value_type.
612 template <typename Q>
613 guarded_ptr get( Q const& key )
616 base_class::get_with_( gp.guard(), key, typename base_class::key_comparator() );
620 /// Finds \p key and return the item found
622 The function is an analog of \ref cds_nonintrusive_SkipListSet_hp_get "get(Q const&)"
623 but \p pred is used for comparing the keys.
625 \p Less functor has the semantics like \p std::less but should take arguments of type \ref value_type and \p Q
627 \p pred must imply the same element order as the comparator used for building the set.
629 template <typename Q, typename Less>
630 guarded_ptr get_with( Q const& key, Less pred )
633 typedef cds::details::predicate_wrapper< node_type, Less, typename maker::value_accessor > wrapped_less;
635 base_class::get_with_( gp.guard(), key, cds::opt::details::make_comparator_from_less< wrapped_less >());
639 /// Clears the set (not atomic).
641 The function deletes all items from the set.
642 The function is not atomic, thus, in multi-threaded environment with parallel insertions
646 assert( set.empty() );
648 the assertion could be raised.
650 For each item the \ref disposer provided by \p Traits template parameter will be called.
657 /// Checks if the set is empty
660 return base_class::empty();
663 /// Returns item count in the set
665 The value returned depends on item counter type provided by \p Traits template parameter.
666 If it is \p atomicity::empty_item_counter this function always returns 0.
667 Therefore, the function is not suitable for checking the set emptiness, use \p empty()
668 member function for this purpose.
672 return base_class::size();
675 /// Returns const reference to internal statistics
676 stat const& statistics() const
678 return base_class::statistics();
682 }} // namespace cds::container
684 #endif // #ifndef CDSLIB_CONTAINER_IMPL_SKIP_LIST_SET_H