3 #ifndef __CDS_CONTAINER_SEGMENTED_QUEUE_H
4 #define __CDS_CONTAINER_SEGMENTED_QUEUE_H
7 #include <functional> // ref
8 #include <cds/intrusive/segmented_queue.h>
9 #include <cds/details/trivial_assign.h>
11 namespace cds { namespace container {
13 /// SegmentedQueue -related declarations
14 namespace segmented_queue {
16 # ifdef CDS_DOXYGEN_INVOKED
17 /// SegmentedQueue internal statistics
18 typedef cds::intrusive::segmented_queue::stat stat;
20 using cds::intrusive::segmented_queue::stat;
23 /// SegmentedQueue empty internal statistics (no overhead)
24 typedef cds::intrusive::segmented_queue::empty_stat empty_stat;
26 /// SegmentedQueue default type traits
29 /// Item allocator. Default is \ref CDS_DEFAULT_ALLOCATOR
30 typedef CDS_DEFAULT_ALLOCATOR node_allocator;
32 /// Item counter, default is atomicity::item_counter
34 The item counting is an essential part of segmented queue algorithm.
35 The \p empty() member function is based on checking <tt>size() == 0</tt>.
36 Therefore, dummy item counter like atomicity::empty_item_counter is not the proper counter.
38 typedef atomicity::item_counter item_counter;
40 /// Internal statistics, possible predefined types are \ref stat, \ref empty_stat (the default)
41 typedef segmented_queue::empty_stat stat;
43 /// Memory model, default is opt::v::relaxed_ordering. See cds::opt::memory_model for the full list of possible types
44 typedef opt::v::relaxed_ordering memory_model;
46 /// Alignment of critical data, default is cache line alignment. See cds::opt::alignment option specification
47 enum { alignment = opt::cache_line_alignment };
49 /// Segment allocator. Default is \ref CDS_DEFAULT_ALLOCATOR
50 typedef CDS_DEFAULT_ALLOCATOR allocator;
52 /// Lock type used to maintain an internal list of allocated segments
53 typedef cds::lock::Spin lock_type;
55 /// Random \ref cds::opt::permutation_generator "permutation generator" for sequence [0, quasi_factor)
56 typedef cds::opt::v::random2_permutation<int> permutation_generator;
59 /// Metafunction converting option list to traits for SegmentedQueue
61 The metafunction can be useful if a few fields in \p segmented_queue::traits should be changed.
64 typedef cds::container::segmented_queue::make_traits<
65 cds::opt::item_counter< cds::atomicity::item_counter >
66 >::type my_segmented_queue_traits;
68 This code creates \p %SegmentedQueue type traits with item counting feature,
69 all other \p segmented_queue::traits members left unchanged.
72 - \p opt::node_allocator - node allocator.
73 - \p opt::stat - internal statistics, possible type: \p segmented_queue::stat, \p segmented_queue::empty_stat (the default)
74 - \p opt::item_counter - item counting feature. Note that \p atomicity::empty_item_counetr is not suitable
76 - \p opt::memory_model - memory model, default is \p opt::v::relaxed_ordering.
77 See option description for the full list of possible models
78 - \p opt::alignment - the alignment of critical data, see option description for explanation
79 - \p opt::allocator - the allocator used to maintain segments.
80 - \p opt::lock_type - a mutual exclusion lock type used to maintain internal list of allocated
81 segments. Default is \p cds::opt::Spin, \p std::mutex is also suitable.
82 - \p opt::permutation_generator - a random permutation generator for sequence [0, quasi_factor),
83 default is \p cds::opt::v::random2_permutation<int>
85 template <typename... Options>
87 # ifdef CDS_DOXYGEN_INVOKED
88 typedef implementation_defined type ; ///< Metafunction result
90 typedef typename cds::opt::make_options<
91 typename cds::opt::find_type_traits< traits, Options... >::type
97 } // namespace segmented_queue
102 template <typename GC, typename T, typename Traits>
103 struct make_segmented_queue
106 typedef T value_type;
107 typedef Traits original_type_traits;
109 typedef cds::details::Allocator< T, typename original_type_traits::node_allocator > cxx_node_allocator;
110 struct node_disposer {
111 void operator()( T * p )
113 cxx_node_allocator().Delete( p );
117 struct intrusive_type_traits: public original_type_traits
119 typedef node_disposer disposer;
122 typedef cds::intrusive::SegmentedQueue< gc, value_type, intrusive_type_traits > type;
125 } // namespace details
129 /** @ingroup cds_nonintrusive_queue
131 The queue is based on work
132 - [2010] Afek, Korland, Yanovsky "Quasi-Linearizability: relaxed consistency for improved concurrency"
134 In this paper the authors offer a relaxed version of linearizability, so-called quasi-linearizability,
135 that preserves some of the intuition, provides a flexible way to control the level of relaxation
136 and supports th implementation of more concurrent and scalable data structure.
137 Intuitively, the linearizability requires each run to be equivalent in some sense to a serial run
138 of the algorithm. This equivalence to some serial run imposes strong synchronization requirements
139 that in many cases results in limited scalability and synchronization bottleneck.
141 The general idea is that the queue maintains a linked list of segments, each segment is an array of
142 nodes in the size of the quasi factor, and each node has a deleted boolean marker, which states
143 if it has been dequeued. Each producer iterates over last segment in the linked list in some random
144 permutation order. Whet it finds an empty cell it performs a CAS operation attempting to enqueue its
145 new element. In case the entire segment has been scanned and no available cell is found (implying
146 that the segment is full), then it attempts to add a new segment to the list.
148 The dequeue operation is similar: the consumer iterates over the first segment in the linked list
149 in some random permutation order. When it finds an item which has not yet been dequeued, it performs
150 CAS on its deleted marker in order to "delete" it, if succeeded this item is considered dequeued.
151 In case the entire segment was scanned and all the nodes have already been dequeued (implying that
152 the segment is empty), then it attempts to remove this segment from the linked list and starts
153 the same process on the next segment. If there is no next segment, the queue is considered empty.
155 Based on the fact that most of the time threads do not add or remove segments, most of the work
156 is done in parallel on different cells in the segments. This ensures a controlled contention
157 depending on the segment size, which is quasi factor.
159 The segmented queue is an <i>unfair</i> queue since it violates the strong FIFO order but no more than
160 quasi factor. It means that the consumer dequeues any item from the current first segment.
163 - \p GC - a garbage collector, possible types are cds::gc::HP, cds::gc::PTB
164 - \p T - the type of values stored in the queue
165 - \p Traits - queue type traits, default is \p segmented_queue::type_traits.
166 \p segmented_queue::make_traits metafunction can be used to construct your
169 template <class GC, typename T, typename Traits = segmented_queue::traits >
170 class SegmentedQueue:
171 #ifdef CDS_DOXYGEN_INVOKED
172 public cds::intrusive::SegmentedQueue< GC, T, Traits >
174 public details::make_segmented_queue< GC, T, Traits >::type
178 typedef details::make_segmented_queue< GC, T, Traits > maker;
179 typedef typename maker::type base_class;
182 typedef GC gc; ///< Garbage collector
183 typedef T value_type; ///< type of the value stored in the queue
184 typedef Traits traits; ///< Queue traits
186 typedef typename traits::node_allocator node_allocator; ///< Node allocator
187 typedef typename base_class::memory_model memory_model; ///< Memory ordering. See cds::opt::memory_model option
188 typedef typename base_class::item_counter item_counter; ///< Item counting policy, see cds::opt::item_counter option setter
189 typedef typename base_class::stat stat ; ///< Internal statistics policy
190 typedef typename base_class::lock_type lock_type ; ///< Type of mutex for maintaining an internal list of allocated segments.
191 typedef typename base_class::permutation_generator permutation_generator; ///< Random permutation generator for sequence [0, quasi-factor)
193 static const size_t m_nHazardPtrCount = base_class::m_nHazardPtrCount ; ///< Count of hazard pointer required for the algorithm
197 typedef typename maker::cxx_node_allocator cxx_node_allocator;
198 typedef std::unique_ptr< value_type, typename maker::node_disposer > scoped_node_ptr;
200 static value_type * alloc_node( value_type const& v )
202 return cxx_node_allocator().New( v );
205 static value_type * alloc_node()
207 return cxx_node_allocator().New();
210 template <typename... Args>
211 static value_type * alloc_node_move( Args&&... args )
213 return cxx_node_allocator().MoveNew( std::forward<Args>( args )... );
218 /// Initializes the empty queue
220 size_t nQuasiFactor ///< Quasi factor. If it is not a power of 2 it is rounded up to nearest power of 2. Minimum is 2.
222 : base_class( nQuasiFactor )
225 /// Clears the queue and deletes all internal data
229 /// Inserts a new element at last segment of the queue
231 The function makes queue node in dynamic memory calling copy constructor for \p val
232 and then it calls intrusive::SEgmentedQueue::enqueue.
233 Returns \p true if success, \p false otherwise.
235 bool enqueue( value_type const& val )
237 scoped_node_ptr p( alloc_node(val) );
238 if ( base_class::enqueue( *p ) ) {
245 /// Enqueues data to the queue using a functor
247 \p Func is a functor called to create node.
248 The functor \p f takes one argument - a reference to a new node of type \ref value_type :
250 cds::container::SegmentedQueue< cds::gc::HP, Foo > myQueue;
252 myQueue.enqueue_with( [&bar]( Foo& dest ) { dest = bar; } );
255 template <typename Func>
256 bool enqueue_with( Func f )
258 scoped_node_ptr p( alloc_node() );
260 if ( base_class::enqueue( *p ) ) {
268 /// Synonym for \p enqueue() member function
269 bool push( value_type const& val )
271 return enqueue( val );
274 /// Synonym for \p enqueue_with() member function
275 template <typename Func>
276 bool push_with( Func f )
278 return enqueue_with( f );
281 /// Enqueues data of type \ref value_type constructed with <tt>std::forward<Args>(args)...</tt>
282 template <typename... Args>
283 bool emplace( Args&&... args )
285 scoped_node_ptr p( alloc_node_move( std::forward<Args>(args)... ) );
286 if ( base_class::enqueue( *p )) {
293 /// Dequeues a value from the queue
295 If queue is not empty, the function returns \p true, \p dest contains copy of
296 dequeued value. The assignment operator for type \ref value_type is invoked.
297 If queue is empty, the function returns \p false, \p dest is unchanged.
299 bool dequeue( value_type& dest )
301 return dequeue_with( [&dest]( value_type& src ) { dest = src; });
304 /// Dequeues a value using a functor
306 \p Func is a functor called to copy dequeued value.
307 The functor takes one argument - a reference to removed node:
309 cds:container::MSQueue< cds::gc::HP, Foo > myQueue;
311 myQueue.dequeue_with( [&bar]( Foo& src ) { bar = std::move( src );});
313 The functor is called only if the queue is not empty.
315 template <typename Func>
316 bool dequeue_with( Func f )
318 value_type * p = base_class::dequeue();
321 gc::template retire< typename maker::node_disposer >( p );
327 /// Synonym for \p dequeue_with() function
328 template <typename Func>
329 bool pop_with( Func f )
331 return dequeue_with( f );
334 /// Synonym for \p dequeue() function
335 bool pop( value_type& dest )
337 return dequeue( dest );
340 /// Checks if the queue is empty
342 The original segmented queue algorithm does not allow to check emptiness accurately
343 because \p empty() is unlinearizable.
344 This function tests queue's emptiness checking <tt>size() == 0</tt>,
345 so, the item counting feature is an essential part of queue's algorithm.
349 return base_class::empty();
354 The function repeatedly calls \ref dequeue until it returns \p nullptr.
355 The disposer specified in \p Traits template argument is called for each removed item.
362 /// Returns queue's item count
365 return base_class::size();
368 /// Returns reference to internal statistics
370 The type of internal statistics is specified by \p Traits template argument.
372 const stat& statistics() const
374 return base_class::statistics();
377 /// Returns quasi factor, a power-of-two number
378 size_t quasi_factor() const
380 return base_class::quasi_factor();
384 }} // namespace cds::container
386 #endif // #ifndef __CDS_CONTAINER_SEGMENTED_QUEUE_H