3 #ifndef __CDS_CONTAINER_IMPL_SKIP_LIST_MAP_H
4 #define __CDS_CONTAINER_IMPL_SKIP_LIST_MAP_H
6 #include <cds/details/functor_wrapper.h>
7 #include <cds/gc/guarded_ptr.h>
8 #include <cds/container/details/guarded_ptr_cast.h>
10 namespace cds { namespace container {
12 /// Lock-free skip-list map
13 /** @ingroup cds_nonintrusive_map
14 \anchor cds_nonintrusive_SkipListMap_hp
16 The implementation of well-known probabilistic data structure called skip-list
17 invented by W.Pugh in his papers:
18 - [1989] W.Pugh Skip Lists: A Probabilistic Alternative to Balanced Trees
19 - [1990] W.Pugh A Skip List Cookbook
21 A skip-list is a probabilistic data structure that provides expected logarithmic
22 time search without the need of rebalance. The skip-list is a collection of sorted
23 linked list. Nodes are ordered by key. Each node is linked into a subset of the lists.
24 Each list has a level, ranging from 0 to 32. The bottom-level list contains
25 all the nodes, and each higher-level list is a sublist of the lower-level lists.
26 Each node is created with a random top level (with a random height), and belongs
27 to all lists up to that level. The probability that a node has the height 1 is 1/2.
28 The probability that a node has the height N is 1/2 ** N (more precisely,
29 the distribution depends on an random generator provided, but our generators
32 The lock-free variant of skip-list is implemented according to book
33 - [2008] M.Herlihy, N.Shavit "The Art of Multiprocessor Programming",
34 chapter 14.4 "A Lock-Free Concurrent Skiplist"
37 - \p GC - Garbage collector used.
38 - \p K - type of a key to be stored in the list.
39 - \p T - type of a value to be stored in the list.
40 - \p Traits - type traits. See skip_list::type_traits for explanation.
42 It is possible to declare option-based list with cds::container::skip_list::make_traits metafunction istead of \p Traits template
44 Template argument list \p Options of cds::container::skip_list::make_traits metafunction are:
45 - opt::compare - key compare functor. No default functor is provided.
46 If the option is not specified, the opt::less is used.
47 - opt::less - specifies binary predicate used for key comparison. Default is \p std::less<K>.
48 - opt::item_counter - the type of item counting feature. Default is \ref atomicity::empty_item_counter that is no item counting.
49 - opt::memory_model - C++ memory ordering model. Can be opt::v::relaxed_ordering (relaxed memory model, the default)
50 or opt::v::sequential_consistent (sequentially consisnent memory model).
51 - skip_list::random_level_generator - random level generator. Can be skip_list::xorshift, skip_list::turbo_pascal or
52 user-provided one. See skip_list::random_level_generator option description for explanation.
53 Default is \p %skip_list::turbo_pascal.
54 - opt::allocator - allocator for skip-list node. Default is \ref CDS_DEFAULT_ALLOCATOR.
55 - opt::back_off - back-off strategy used. If the option is not specified, the cds::backoff::Default is used.
56 - opt::stat - internal statistics. Available types: skip_list::stat, skip_list::empty_stat (the default)
58 Like STL map class, %SkipListMap stores its key-value pair as <tt>std:pair< K const, T></tt>.
60 \warning The skip-list requires up to 67 hazard pointers that may be critical for some GCs for which
61 the guard count is limited (like as gc::HP, gc::HRC). Those GCs should be explicitly initialized with
62 hazard pointer enough: \code cds::gc::HP myhp( 67 ) \endcode. Otherwise an run-time exception may be raised
63 when you try to create skip-list object.
65 \note There are several specializations of \p %SkipListMap for each \p GC. You should include:
66 - <tt><cds/container/skip_list_map_hp.h></tt> for gc::HP garbage collector
67 - <tt><cds/container/skip_list_map_ptb.h></tt> for gc::PTB garbage collector
68 - <tt><cds/container/skip_list_map_rcu.h></tt> for \ref cds_nonintrusive_SkipListMap_rcu "RCU type"
69 - <tt><cds/container/skip_list_map_nogc.h></tt> for \ref cds_nonintrusive_SkipListMap_nogc "non-deletable SkipListMap"
73 The class supports a forward iterator (\ref iterator and \ref const_iterator).
74 The iteration is ordered.
75 The iterator object is thread-safe: the element pointed by the iterator object is guarded,
76 so, the element cannot be reclaimed while the iterator object is alive.
77 However, passing an iterator object between threads is dangerous.
79 \warning Due to concurrent nature of skip-list map it is not guarantee that you can iterate
80 all elements in the map: any concurrent deletion can exclude the element
81 pointed by the iterator from the map, and your iteration can be terminated
82 before end of the map. Therefore, such iteration is more suitable for debugging purpose only
84 Remember, each iterator object requires 2 additional hazard pointers, that may be
85 a limited resource for \p GC like as gc::HP and gc::HRC (however, for gc::PTB the count of
88 The iterator class supports the following minimalistic interface:
95 iterator( iterator const& s);
97 value_type * operator ->() const;
98 value_type& operator *() const;
101 iterator& operator ++();
104 iterator& operator = (const iterator& src);
106 bool operator ==(iterator const& i ) const;
107 bool operator !=(iterator const& i ) const;
110 Note, the iterator object returned by \ref end, \ cend member functions points to \p nullptr and should not be dereferenced.
117 #ifdef CDS_DOXYGEN_INVOKED
118 typename Traits = skip_list::type_traits
124 #ifdef CDS_DOXYGEN_INVOKED
125 protected intrusive::SkipListSet< GC, std::pair<Key const, T>, Traits >
127 protected details::make_skip_list_map< GC, Key, T, Traits >::type
131 typedef details::make_skip_list_map< GC, Key, T, Traits > maker;
132 typedef typename maker::type base_class;
135 typedef typename base_class::gc gc ; ///< Garbage collector used
136 typedef Key key_type ; ///< Key type
137 typedef T mapped_type ; ///< Mapped type
138 # ifdef CDS_DOXYGEN_INVOKED
139 typedef std::pair< K const, T> value_type ; ///< Value type stored in the map
141 typedef typename maker::value_type value_type;
143 typedef Traits options ; ///< Options specified
145 typedef typename base_class::back_off back_off ; ///< Back-off strategy used
146 typedef typename options::allocator allocator_type ; ///< Allocator type used for allocate/deallocate the skip-list nodes
147 typedef typename base_class::item_counter item_counter ; ///< Item counting policy used
148 typedef typename maker::key_comparator key_comparator ; ///< key comparison functor
149 typedef typename base_class::memory_model memory_model ; ///< Memory ordering. See cds::opt::memory_model option
150 typedef typename options::random_level_generator random_level_generator ; ///< random level generator
151 typedef typename options::stat stat ; ///< internal statistics type
155 typedef typename maker::node_type node_type;
156 typedef typename maker::node_allocator node_allocator;
158 typedef std::unique_ptr< node_type, typename maker::node_deallocator > scoped_node_ptr;
164 typedef cds::gc::guarded_ptr< gc, node_type, value_type, details::guarded_ptr_cast_set<node_type, value_type> > guarded_ptr;
168 unsigned int random_level()
170 return base_class::random_level();
180 /// Destructor destroys the set object
186 typedef skip_list::details::iterator< typename base_class::iterator > iterator;
188 /// Const iterator type
189 typedef skip_list::details::iterator< typename base_class::const_iterator > const_iterator;
191 /// Returns a forward iterator addressing the first element in a map
194 return iterator( base_class::begin() );
197 /// Returns a forward const iterator addressing the first element in a map
199 const_iterator begin() const
203 const_iterator cbegin()
205 return const_iterator( base_class::cbegin() );
209 /// Returns a forward iterator that addresses the location succeeding the last element in a map.
212 return iterator( base_class::end() );
215 /// Returns a forward const iterator that addresses the location succeeding the last element in a map.
217 const_iterator end() const
221 const_iterator cend()
223 return const_iterator( base_class::cend() );
228 /// Inserts new node with key and default value
230 The function creates a node with \p key and default value, and then inserts the node created into the map.
233 - The \ref key_type should be constructible from a value of type \p K.
234 In trivial case, \p K is equal to \ref key_type.
235 - The \ref mapped_type should be default-constructible.
237 Returns \p true if inserting successful, \p false otherwise.
239 template <typename K>
240 bool insert( K const& key )
242 return insert_key( key, [](value_type&){} );
247 The function creates a node with copy of \p val value
248 and then inserts the node created into the map.
251 - The \ref key_type should be constructible from \p key of type \p K.
252 - The \ref value_type should be constructible from \p val of type \p V.
254 Returns \p true if \p val is inserted into the set, \p false otherwise.
256 template <typename K, typename V>
257 bool insert( K const& key, V const& val )
259 return insert_key( key, [&val](value_type& item) { item.second = val ; } );
262 /// Inserts new node and initialize it by a functor
264 This function inserts new node with key \p key and if inserting is successful then it calls
265 \p func functor with signature
268 void operator()( value_type& item );
272 The argument \p item of user-defined functor \p func is the reference
273 to the map's item inserted:
274 - <tt>item.first</tt> is a const reference to item's key that cannot be changed.
275 - <tt>item.second</tt> is a reference to item's value that may be changed.
277 The user-defined functor can be passed by reference using \p std::ref
278 and it is called only if inserting is successful.
280 The key_type should be constructible from value of type \p K.
282 The function allows to split creating of new item into two part:
283 - create item from \p key;
284 - insert new item into the map;
285 - if inserting is successful, initialize the value of item by calling \p func functor
287 This can be useful if complete initialization of object of \p value_type is heavyweight and
288 it is preferable that the initialization should be completed only if inserting is successful.
290 template <typename K, typename Func>
291 bool insert_key( const K& key, Func func )
293 scoped_node_ptr pNode( node_allocator().New( random_level(), key ));
294 if ( base_class::insert( *pNode, [&func]( node_type& item ) { func( item.m_Value ); } )) {
301 /// For key \p key inserts data of type \ref value_type constructed with <tt>std::forward<Args>(args)...</tt>
303 Returns \p true if inserting successful, \p false otherwise.
305 template <typename K, typename... Args>
306 bool emplace( K&& key, Args&&... args )
308 scoped_node_ptr pNode( node_allocator().New( random_level(), std::forward<K>(key), std::forward<Args>(args)... ));
309 if ( base_class::insert( *pNode )) {
316 /// Ensures that the \p key exists in the map
318 The operation performs inserting or changing data with lock-free manner.
320 If the \p key not found in the map, then the new item created from \p key
321 is inserted into the map (note that in this case the \ref key_type should be
322 constructible from type \p K).
323 Otherwise, the functor \p func is called with item found.
324 The functor \p Func may be a function with signature:
326 void func( bool bNew, value_type& item );
331 void operator()( bool bNew, value_type& item );
336 - \p bNew - \p true if the item has been inserted, \p false otherwise
337 - \p item - item of the list
339 The functor may change any fields of the \p item.second that is \ref value_type.
341 You may pass \p func argument by reference using \p std::ref
343 Returns <tt> std::pair<bool, bool> </tt> where \p first is true if operation is successfull,
344 \p second is true if new item has been added or \p false if the item with \p key
345 already is in the list.
347 template <typename K, typename Func>
348 std::pair<bool, bool> ensure( K const& key, Func func )
350 scoped_node_ptr pNode( node_allocator().New( random_level(), key ));
351 std::pair<bool, bool> res = base_class::ensure( *pNode,
352 [&func](bool bNew, node_type& item, node_type const& ){ func( bNew, item.m_Value ); }
354 if ( res.first && res.second )
359 /// Delete \p key from the map
360 /** \anchor cds_nonintrusive_SkipListMap_erase_val
362 Return \p true if \p key is found and deleted, \p false otherwise
364 template <typename K>
365 bool erase( K const& key )
367 return base_class::erase(key);
370 /// Deletes the item from the map using \p pred predicate for searching
372 The function is an analog of \ref cds_nonintrusive_SkipListMap_erase_val "erase(K const&)"
373 but \p pred is used for key comparing.
374 \p Less functor has the interface like \p std::less.
375 \p Less must imply the same element order as the comparator used for building the map.
377 template <typename K, typename Less>
378 bool erase_with( K const& key, Less pred )
380 return base_class::erase_with( key, cds::details::predicate_wrapper< node_type, Less, typename maker::key_accessor >());
383 /// Delete \p key from the map
384 /** \anchor cds_nonintrusive_SkipListMap_erase_func
386 The function searches an item with key \p key, calls \p f functor
387 and deletes the item. If \p key is not found, the functor is not called.
389 The functor \p Func interface:
392 void operator()(value_type& item) { ... }
395 The functor may be passed by reference using <tt>boost:ref</tt>
397 Return \p true if key is found and deleted, \p false otherwise
399 template <typename K, typename Func>
400 bool erase( K const& key, Func f )
402 return base_class::erase( key, [&f]( node_type& node) { f( node.m_Value ); } );
405 /// Deletes the item from the map using \p pred predicate for searching
407 The function is an analog of \ref cds_nonintrusive_SkipListMap_erase_func "erase(K const&, Func)"
408 but \p pred is used for key comparing.
409 \p Less functor has the interface like \p std::less.
410 \p Less must imply the same element order as the comparator used for building the map.
412 template <typename K, typename Less, typename Func>
413 bool erase_with( K const& key, Less pred, Func f )
415 return base_class::erase_with( key,
416 cds::details::predicate_wrapper< node_type, Less, typename maker::key_accessor >(),
417 [&f]( node_type& node) { f( node.m_Value ); } );
420 /// Extracts the item from the map with specified \p key
421 /** \anchor cds_nonintrusive_SkipListMap_hp_extract
422 The function searches an item with key equal to \p key in the map,
423 unlinks it from the map, and returns it in \p ptr parameter.
424 If the item with key equal to \p key is not found the function returns \p false.
426 Note the compare functor should accept a parameter of type \p K that can be not the same as \p key_type.
428 The item extracted is freed automatically by garbage collector \p GC
429 when returned \ref guarded_ptr object will be destroyed or released.
430 @note Each \p guarded_ptr object uses the GC's guard that can be limited resource.
434 typedef cds::container::SkipListMap< cds::gc::HP, int, foo, my_traits > skip_list;
438 skip_list::guarded_ptr gp;
439 if ( theList.extract( gp, 5 ) ) {
443 // Destructor of gp releases internal HP guard and frees the pointer
447 template <typename K>
448 bool extract( guarded_ptr& ptr, K const& key )
450 return base_class::extract_( ptr.guard(), key, typename base_class::key_comparator() );
453 /// Extracts the item from the map with comparing functor \p pred
455 The function is an analog of \ref cds_nonintrusive_SkipListMap_hp_extract "extract(K const&)"
456 but \p pred predicate is used for key comparing.
458 \p Less functor has the semantics like \p std::less but should take arguments of type \ref key_type and \p K
460 \p pred must imply the same element order as the comparator used for building the map.
462 template <typename K, typename Less>
463 bool extract_with( guarded_ptr& ptr, K const& key, Less pred )
465 typedef cds::details::predicate_wrapper< node_type, Less, typename maker::key_accessor > wrapped_less;
466 return base_class::extract_( ptr.guard(), key, cds::opt::details::make_comparator_from_less<wrapped_less>() );
469 /// Extracts an item with minimal key from the map
471 The function searches an item with minimal key, unlinks it, and returns the item found in \p ptr parameter.
472 If the skip-list is empty the function returns \p false.
474 The item extracted is freed automatically by garbage collector \p GC
475 when returned \ref guarded_ptr object will be destroyed or released.
476 @note Each \p guarded_ptr object uses the GC's guard that can be limited resource.
480 typedef cds::continer::SkipListMap< cds::gc::HP, int, foo, my_traits > skip_list;
484 skip_list::guarded_ptr gp;
485 if ( theList.extract_min( gp )) {
489 // Destructor of gp releases internal HP guard and then frees the pointer
493 bool extract_min( guarded_ptr& ptr)
495 return base_class::extract_min_( ptr.guard() );
498 /// Extracts an item with maximal key from the map
500 The function searches an item with maximal key, unlinks it, and returns the pointer to item found in \p ptr parameter.
501 If the skip-list is empty the function returns empty \p guarded_ptr.
503 The item found is freed by garbage collector \p GC automatically
504 when returned \ref guarded_ptr object will be destroyed or released.
505 @note Each \p guarded_ptr object uses the GC's guard that can be limited resource.
509 typedef cds::container::SkipListMap< cds::gc::HP, int, foo, my_traits > skip_list;
513 skip_list::guarded_ptr gp;
514 if ( theList.extract_max( gp )) {
518 // Destructor of gp releases internal HP guard and then frees the pointer
522 bool extract_max( guarded_ptr& dest )
524 return base_class::extract_max_( dest.guard() );
527 /// Find the key \p key
528 /** \anchor cds_nonintrusive_SkipListMap_find_cfunc
530 The function searches the item with key equal to \p key and calls the functor \p f for item found.
531 The interface of \p Func functor is:
534 void operator()( value_type& item );
537 where \p item is the item found.
539 You can pass \p f argument by reference using \p std::ref
541 The functor may change \p item.second.
543 The function returns \p true if \p key is found, \p false otherwise.
545 template <typename K, typename Func>
546 bool find( K const& key, Func f )
548 return base_class::find( key, [&f](node_type& item, K const& ) { f( item.m_Value );});
551 /// Finds the key \p val using \p pred predicate for searching
553 The function is an analog of \ref cds_nonintrusive_SkipListMap_find_cfunc "find(K const&, Func)"
554 but \p pred is used for key comparing.
555 \p Less functor has the interface like \p std::less.
556 \p Less must imply the same element order as the comparator used for building the map.
558 template <typename K, typename Less, typename Func>
559 bool find_with( K const& key, Less pred, Func f )
561 return base_class::find_with( key,
562 cds::details::predicate_wrapper< node_type, Less, typename maker::key_accessor >(),
563 [&f](node_type& item, K const& ) { f( item.m_Value );});
566 /// Find the key \p key
567 /** \anchor cds_nonintrusive_SkipListMap_find_val
569 The function searches the item with key equal to \p key
570 and returns \p true if it is found, and \p false otherwise.
572 template <typename K>
573 bool find( K const& key )
575 return base_class::find( key );
578 /// Finds the key \p val using \p pred predicate for searching
580 The function is an analog of \ref cds_nonintrusive_SkipListMap_find_val "find(K const&)"
581 but \p pred is used for key comparing.
582 \p Less functor has the interface like \p std::less.
583 \p Less must imply the same element order as the comparator used for building the map.
585 template <typename K, typename Less>
586 bool find_with( K const& key, Less pred )
588 return base_class::find_with( key, cds::details::predicate_wrapper< node_type, Less, typename maker::key_accessor >() );
591 /// Finds the key \p key and return the item found
592 /** \anchor cds_nonintrusive_SkipListMap_hp_get
593 The function searches the item with key equal to \p key
594 and assigns the item found to guarded pointer \p ptr.
595 The function returns \p true if \p key is found, and \p false otherwise.
596 If \p key is not found the \p ptr parameter is not changed.
598 It is safe when a concurrent thread erases the item returned in \p ptr guarded pointer.
599 In this case the item will be freed later by garbage collector \p GC automatically
600 when \p guarded_ptr object will be destroyed or released.
601 @note Each \p guarded_ptr object uses one GC's guard which can be limited resource.
605 typedef cds::container::SkipListMap< cds::gc::HP, int, foo, my_traits > skip_list;
609 skip_list::guarded_ptr gp;
610 if ( theList.get( gp, 5 ) ) {
614 // Destructor of guarded_ptr releases internal HP guard
618 Note the compare functor specified for class \p Traits template parameter
619 should accept a parameter of type \p K that can be not the same as \p value_type.
621 template <typename K>
622 bool get( guarded_ptr& ptr, K const& key )
624 return base_class::get_with_( ptr.guard(), key, typename base_class::key_comparator() );
627 /// Finds the key \p key and return the item found
629 The function is an analog of \ref cds_nonintrusive_SkipListMap_hp_get "get( guarded_ptr& ptr, K const&)"
630 but \p pred is used for comparing the keys.
632 \p Less functor has the semantics like \p std::less but should take arguments of type \ref key_type and \p K
634 \p pred must imply the same element order as the comparator used for building the map.
636 template <typename K, typename Less>
637 bool get_with( guarded_ptr& ptr, K const& key, Less pred )
639 typedef cds::details::predicate_wrapper< node_type, Less, typename maker::key_accessor > wrapped_less;
640 return base_class::get_with_( ptr.guard(), key, cds::opt::details::make_comparator_from_less< wrapped_less >());
649 /// Checks if the map is empty
651 Emptiness is checked by item counting: if item count is zero then the map is empty.
655 return base_class::empty();
658 /// Returns item count in the map
661 return base_class::size();
664 /// Returns const reference to internal statistics
665 stat const& statistics() const
667 return base_class::statistics();
671 }} // namespace cds::container
673 #endif // #ifndef __CDS_CONTAINER_IMPL_SKIP_LIST_MAP_H