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 ); } )) {
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 will be inserted into the set iff \p bInsert is \p true.
259 Otherwise, if \p val is found, the functor \p func will be called with the item found.
261 The functor \p Func signature:
264 void operator()( bool bNew, value_type& item, const Q& val );
268 - \p bNew - \p true if the item has been inserted, \p false otherwise
269 - \p item - item of the set
270 - \p val - argument \p key passed into the \p %update() function
272 The functor may change non-key fields of the \p item; however, \p func must guarantee
273 that during changing no any other modifications could be made on this item by concurrent threads.
275 Returns <tt> std::pair<bool, bool> </tt> where \p first is \p true if operation is successfull,
276 i.e. the item has been inserted or updated,
277 \p second is \p true if new item has been added or \p false if the item with key equal to \p val
280 @warning See \ref cds_intrusive_item_creating "insert item troubleshooting"
282 template <typename Q, typename Func>
283 std::pair<bool, bool> update( const Q& val, Func func, bool bInsert = true )
285 scoped_node_ptr sp( node_allocator().New( random_level(), val ));
286 std::pair<bool, bool> bRes = base_class::update( *sp,
287 [&func, &val](bool bNew, node_type& node, node_type&){ func( bNew, node.m_Value, val ); },
289 if ( bRes.first && bRes.second )
295 // Deprecated, use update()
296 template <typename Q, typename Func>
297 std::pair<bool, bool> ensure( const Q& val, Func func )
299 return update( val, func, true );
303 /// Inserts data of type \p value_type created in-place from <tt>std::forward<Args>(args)...</tt>
305 Returns \p true if inserting successful, \p false otherwise.
307 template <typename... Args>
308 bool emplace( Args&&... args )
310 scoped_node_ptr sp( node_allocator().New( random_level(), std::forward<Args>(args)... ));
311 if ( base_class::insert( *sp.get() )) {
318 /// Delete \p key from the set
319 /** \anchor cds_nonintrusive_SkipListSet_erase_val
321 The set item comparator should be able to compare the type \p value_type
324 Return \p true if key is found and deleted, \p false otherwise
326 template <typename Q>
327 bool erase( Q const& key )
329 return base_class::erase( key );
332 /// Deletes the item from the set using \p pred predicate for searching
334 The function is an analog of \ref cds_nonintrusive_SkipListSet_erase_val "erase(Q const&)"
335 but \p pred is used for key comparing.
336 \p Less functor has the interface like \p std::less.
337 \p Less must imply the same element order as the comparator used for building the set.
339 template <typename Q, typename Less>
340 bool erase_with( Q const& key, Less pred )
343 return base_class::erase_with( key, cds::details::predicate_wrapper< node_type, Less, typename maker::value_accessor >() );
346 /// Delete \p key from the set
347 /** \anchor cds_nonintrusive_SkipListSet_erase_func
349 The function searches an item with key \p key, calls \p f functor
350 and deletes the item. If \p key is not found, the functor is not called.
352 The functor \p Func interface:
355 void operator()(value_type const& val);
359 Since the key of \p value_type is not explicitly specified,
360 template parameter \p Q defines the key type to search in the list.
361 The list item comparator should be able to compare the type \p T of list item
364 Return \p true if key is found and deleted, \p false otherwise
366 template <typename Q, typename Func>
367 bool erase( Q const& key, Func f )
369 return base_class::erase( key, [&f]( node_type const& node) { f( node.m_Value ); } );
372 /// Deletes the item from the set using \p pred predicate for searching
374 The function is an analog of \ref cds_nonintrusive_SkipListSet_erase_func "erase(Q const&, Func)"
375 but \p pred is used for key comparing.
376 \p Less functor has the interface like \p std::less.
377 \p Less must imply the same element order as the comparator used for building the set.
379 template <typename Q, typename Less, typename Func>
380 bool erase_with( Q const& key, Less pred, Func f )
383 return base_class::erase_with( key, cds::details::predicate_wrapper< node_type, Less, typename maker::value_accessor >(),
384 [&f]( node_type const& node) { f( node.m_Value ); } );
387 /// Extracts the item from the set with specified \p key
388 /** \anchor cds_nonintrusive_SkipListSet_hp_extract
389 The function searches an item with key equal to \p key in the set,
390 unlinks it from the set, and returns it as \p guarded_ptr.
391 If \p key is not found the function returns an empty guarded pointer.
393 Note the compare functor should accept a parameter of type \p Q that can be not the same as \p value_type.
395 The item extracted is freed automatically by garbage collector \p GC
396 when returned \p guarded_ptr object will be destroyed or released.
397 @note Each \p guarded_ptr object uses the GC's guard that can be limited resource.
401 typedef cds::container::SkipListSet< cds::gc::HP, foo, my_traits > skip_list;
405 skip_list::guarded_ptr gp(theList.extract( 5 ))
410 // Destructor of gp releases internal HP guard and frees the pointer
414 template <typename Q>
415 guarded_ptr extract( Q const& key )
418 base_class::extract_( gp.guard(), key, typename base_class::key_comparator() );
422 /// Extracts the item from the set with comparing functor \p pred
424 The function is an analog of \ref cds_nonintrusive_SkipListSet_hp_extract "extract(Q const&)"
425 but \p pred predicate is used for key comparing.
427 \p Less functor has the semantics like \p std::less but should take arguments of type \ref value_type and \p Q
429 \p pred must imply the same element order as the comparator used for building the set.
431 template <typename Q, typename Less>
432 guarded_ptr extract_with( Q const& key, Less pred )
435 typedef cds::details::predicate_wrapper< node_type, Less, typename maker::value_accessor > wrapped_less;
437 base_class::extract_( gp.guard(), key, cds::opt::details::make_comparator_from_less<wrapped_less>() );
441 /// Extracts an item with minimal key from the set
443 The function searches an item with minimal key, unlinks it, and returns pointer to the item found as \p guarded_ptr.
444 If the skip-list is empty the function returns an empty guarded pointer.
446 The item extracted is freed automatically by garbage collector \p GC
447 when returned \p guarded_ptr object will be destroyed or released.
448 @note Each \p guarded_ptr object uses the GC's guard that can be limited resource.
452 typedef cds::continer::SkipListSet< cds::gc::HP, foo, my_traits > skip_list;
456 skip_list::guarded_ptr gp( theList.extract_min());
461 // Destructor of gp releases internal HP guard and then frees the pointer
465 guarded_ptr extract_min()
468 base_class::extract_min_( gp.guard() );
472 /// Extracts an item with maximal key from the set
474 The function searches an item with maximal key, unlinks it, and returns the pointer to item found as \p guarded_ptr.
475 If the skip-list is empty the function returns an empty guarded pointer.
477 The item found is freed by garbage collector \p GC automatically
478 when returned \p guarded_ptr object will be destroyed or released.
479 @note Each \p guarded_ptr object uses the GC's guard that can be limited resource.
483 typedef cds::container::SkipListSet< cds::gc::HP, foo, my_traits > skip_list;
487 skip_list::guarded_ptr gp( theList.extract_max());
492 // Destructor of gp releases internal HP guard and then frees the pointer
496 guarded_ptr extract_max()
499 base_class::extract_max_( gp.guard() );
504 /** \anchor cds_nonintrusive_SkipListSet_find_func
506 The function searches the item with key equal to \p key and calls the functor \p f for item found.
507 The interface of \p Func functor is:
510 void operator()( value_type& item, Q& key );
513 where \p item is the item found, \p key is the <tt>find</tt> function argument.
515 The functor may change non-key fields of \p item. Note that the functor is only guarantee
516 that \p item cannot be disposed during functor is executing.
517 The functor does not serialize simultaneous access to the set's \p item. If such access is
518 possible you must provide your own synchronization schema on item level to exclude unsafe item modifications.
520 Note the hash functor specified for class \p Traits template parameter
521 should accept a parameter of type \p Q that may be not the same as \p value_type.
523 The function returns \p true if \p key is found, \p false otherwise.
525 template <typename Q, typename Func>
526 bool find( Q& key, Func f )
528 return base_class::find( key, [&f]( node_type& node, Q& v ) { f( node.m_Value, v ); });
531 template <typename Q, typename Func>
532 bool find( Q const& key, Func f )
534 return base_class::find( key, [&f]( node_type& node, Q& v ) { f( node.m_Value, v ); } );
538 /// Finds \p key using \p pred predicate for searching
540 The function is an analog of \ref cds_nonintrusive_SkipListSet_find_func "find(Q&, Func)"
541 but \p pred is used for key comparing.
542 \p Less functor has the interface like \p std::less.
543 \p Less must imply the same element order as the comparator used for building the set.
545 template <typename Q, typename Less, typename Func>
546 bool find_with( Q& 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 ); } );
553 template <typename Q, typename Less, typename Func>
554 bool find_with( Q const& key, Less pred, Func f )
557 return base_class::find_with( key, cds::details::predicate_wrapper< node_type, Less, typename maker::value_accessor >(),
558 [&f]( node_type& node, Q& v ) { f( node.m_Value, v ); } );
563 /** \anchor cds_nonintrusive_SkipListSet_find_val
565 The function searches the item with key equal to \p key
566 and returns \p true if it is found, and \p false otherwise.
568 Note the hash functor specified for class \p Traits template parameter
569 should accept a parameter of type \p Q that may be not the same as \ref value_type.
571 template <typename Q>
572 bool find( Q const& key )
574 return base_class::find( key );
577 /// Finds \p key using \p pred predicate for searching
579 The function is an analog of \ref cds_nonintrusive_SkipListSet_find_val "find(Q const&)"
580 but \p pred is used for key comparing.
581 \p Less functor has the interface like \p std::less.
582 \p Less must imply the same element order as the comparator used for building the set.
584 template <typename Q, typename Less>
585 bool find_with( Q const& key, Less pred )
588 return base_class::find_with( key, cds::details::predicate_wrapper< node_type, Less, typename maker::value_accessor >());
591 /// Finds \p key and return the item found
592 /** \anchor cds_nonintrusive_SkipListSet_hp_get
593 The function searches the item with key equal to \p key
594 and returns a guarded pointer to the item found.
595 If \p key is not found the function returns an empty guarded pointer.
597 It is safe when a concurrent thread erases the item returned in \p result guarded pointer.
598 In this case the item will be freed later by garbage collector \p GC automatically
599 when \p guarded_ptr object will be destroyed or released.
600 @note Each \p guarded_ptr object uses one GC's guard which can be limited resource.
604 typedef cds::container::SkipListSet< cds::gc::HP, foo, my_traits > skip_list;
608 skip_list::guarded_ptr gp( theList.get( 5 ));
609 if ( theList.get( 5 )) {
613 // Destructor of guarded_ptr releases internal HP guard
617 Note the compare functor specified for class \p Traits template parameter
618 should accept a parameter of type \p Q that can be not the same as \p value_type.
620 template <typename Q>
621 guarded_ptr get( Q const& key )
624 base_class::get_with_( gp.guard(), key, typename base_class::key_comparator() );
628 /// Finds \p key and return the item found
630 The function is an analog of \ref cds_nonintrusive_SkipListSet_hp_get "get(Q const&)"
631 but \p pred is used for comparing the keys.
633 \p Less functor has the semantics like \p std::less but should take arguments of type \ref value_type and \p Q
635 \p pred must imply the same element order as the comparator used for building the set.
637 template <typename Q, typename Less>
638 guarded_ptr get_with( Q const& key, Less pred )
641 typedef cds::details::predicate_wrapper< node_type, Less, typename maker::value_accessor > wrapped_less;
643 base_class::get_with_( gp.guard(), key, cds::opt::details::make_comparator_from_less< wrapped_less >());
647 /// Clears the set (not atomic).
649 The function deletes all items from the set.
650 The function is not atomic, thus, in multi-threaded environment with parallel insertions
654 assert( set.empty() );
656 the assertion could be raised.
658 For each item the \ref disposer provided by \p Traits template parameter will be called.
665 /// Checks if the set is empty
668 return base_class::empty();
671 /// Returns item count in the set
673 The value returned depends on item counter type provided by \p Traits template parameter.
674 If it is \p atomicity::empty_item_counter this function always returns 0.
675 Therefore, the function is not suitable for checking the set emptiness, use \p empty()
676 member function for this purpose.
680 return base_class::size();
683 /// Returns const reference to internal statistics
684 stat const& statistics() const
686 return base_class::statistics();
690 }} // namespace cds::container
692 #endif // #ifndef CDSLIB_CONTAINER_IMPL_SKIP_LIST_SET_H