3 #ifndef CDSLIB_CONTAINER_SEGMENTED_QUEUE_H
4 #define CDSLIB_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 /// Padding of segment data, default is no special padding
50 /** @copydetails cds::intrusive::segmented_queue::traits::padding
52 enum { padding = cds::intrusive::segmented_queue::traits::padding };
54 /// Segment allocator. Default is \ref CDS_DEFAULT_ALLOCATOR
55 typedef CDS_DEFAULT_ALLOCATOR allocator;
57 /// Lock type used to maintain an internal list of allocated segments
58 typedef cds::sync::spin lock_type;
60 /// Random \ref cds::opt::permutation_generator "permutation generator" for sequence [0, quasi_factor)
61 typedef cds::opt::v::random2_permutation<int> permutation_generator;
64 /// Metafunction converting option list to traits for SegmentedQueue
66 The metafunction can be useful if a few fields in \p segmented_queue::traits should be changed.
69 typedef cds::container::segmented_queue::make_traits<
70 cds::opt::item_counter< cds::atomicity::item_counter >
71 >::type my_segmented_queue_traits;
73 This code creates \p %SegmentedQueue type traits with item counting feature,
74 all other \p segmented_queue::traits members left unchanged.
77 - \p opt::node_allocator - node allocator.
78 - \p opt::stat - internal statistics, possible type: \p segmented_queue::stat, \p segmented_queue::empty_stat (the default)
79 - \p opt::item_counter - item counting feature. Note that \p atomicity::empty_item_counetr is not suitable
81 - \p opt::memory_model - memory model, default is \p opt::v::relaxed_ordering.
82 See option description for the full list of possible models
83 - \p opt::alignment - the alignment of critical data, see option description for explanation
84 - \p opt::padding - the padding of segment data, default no special padding.
85 See \p traits::padding for explanation.
86 - \p opt::allocator - the allocator used to maintain segments.
87 - \p opt::lock_type - a mutual exclusion lock type used to maintain internal list of allocated
88 segments. Default is \p cds::opt::Spin, \p std::mutex is also suitable.
89 - \p opt::permutation_generator - a random permutation generator for sequence [0, quasi_factor),
90 default is \p cds::opt::v::random2_permutation<int>
92 template <typename... Options>
94 # ifdef CDS_DOXYGEN_INVOKED
95 typedef implementation_defined type ; ///< Metafunction result
97 typedef typename cds::opt::make_options<
98 typename cds::opt::find_type_traits< traits, Options... >::type
104 } // namespace segmented_queue
109 template <typename GC, typename T, typename Traits>
110 struct make_segmented_queue
113 typedef T value_type;
114 typedef Traits original_type_traits;
116 typedef cds::details::Allocator< T, typename original_type_traits::node_allocator > cxx_node_allocator;
117 struct node_disposer {
118 void operator()( T * p )
120 cxx_node_allocator().Delete( p );
124 struct intrusive_type_traits: public original_type_traits
126 typedef node_disposer disposer;
129 typedef cds::intrusive::SegmentedQueue< gc, value_type, intrusive_type_traits > type;
132 } // namespace details
136 /** @ingroup cds_nonintrusive_queue
138 The queue is based on work
139 - [2010] Afek, Korland, Yanovsky "Quasi-Linearizability: relaxed consistency for improved concurrency"
141 In this paper the authors offer a relaxed version of linearizability, so-called quasi-linearizability,
142 that preserves some of the intuition, provides a flexible way to control the level of relaxation
143 and supports th implementation of more concurrent and scalable data structure.
144 Intuitively, the linearizability requires each run to be equivalent in some sense to a serial run
145 of the algorithm. This equivalence to some serial run imposes strong synchronization requirements
146 that in many cases results in limited scalability and synchronization bottleneck.
148 The general idea is that the queue maintains a linked list of segments, each segment is an array of
149 nodes in the size of the quasi factor, and each node has a deleted boolean marker, which states
150 if it has been dequeued. Each producer iterates over last segment in the linked list in some random
151 permutation order. Whet it finds an empty cell it performs a CAS operation attempting to enqueue its
152 new element. In case the entire segment has been scanned and no available cell is found (implying
153 that the segment is full), then it attempts to add a new segment to the list.
155 The dequeue operation is similar: the consumer iterates over the first segment in the linked list
156 in some random permutation order. When it finds an item which has not yet been dequeued, it performs
157 CAS on its deleted marker in order to "delete" it, if succeeded this item is considered dequeued.
158 In case the entire segment was scanned and all the nodes have already been dequeued (implying that
159 the segment is empty), then it attempts to remove this segment from the linked list and starts
160 the same process on the next segment. If there is no next segment, the queue is considered empty.
162 Based on the fact that most of the time threads do not add or remove segments, most of the work
163 is done in parallel on different cells in the segments. This ensures a controlled contention
164 depending on the segment size, which is quasi factor.
166 The segmented queue is an <i>unfair</i> queue since it violates the strong FIFO order but no more than
167 quasi factor. It means that the consumer dequeues any item from the current first segment.
170 - \p GC - a garbage collector, possible types are cds::gc::HP, cds::gc::DHP
171 - \p T - the type of values stored in the queue
172 - \p Traits - queue type traits, default is \p segmented_queue::traits.
173 \p segmented_queue::make_traits metafunction can be used to construct your
176 template <class GC, typename T, typename Traits = segmented_queue::traits >
177 class SegmentedQueue:
178 #ifdef CDS_DOXYGEN_INVOKED
179 public cds::intrusive::SegmentedQueue< GC, T, Traits >
181 public details::make_segmented_queue< GC, T, Traits >::type
185 typedef details::make_segmented_queue< GC, T, Traits > maker;
186 typedef typename maker::type base_class;
189 typedef GC gc; ///< Garbage collector
190 typedef T value_type; ///< type of the value stored in the queue
191 typedef Traits traits; ///< Queue traits
193 typedef typename traits::node_allocator node_allocator; ///< Node allocator
194 typedef typename base_class::memory_model memory_model; ///< Memory ordering. See cds::opt::memory_model option
195 typedef typename base_class::item_counter item_counter; ///< Item counting policy, see cds::opt::item_counter option setter
196 typedef typename base_class::stat stat ; ///< Internal statistics policy
197 typedef typename base_class::lock_type lock_type ; ///< Type of mutex for maintaining an internal list of allocated segments.
198 typedef typename base_class::permutation_generator permutation_generator; ///< Random permutation generator for sequence [0, quasi-factor)
200 static const size_t m_nHazardPtrCount = base_class::m_nHazardPtrCount ; ///< Count of hazard pointer required for the algorithm
204 typedef typename maker::cxx_node_allocator cxx_node_allocator;
205 typedef std::unique_ptr< value_type, typename maker::node_disposer > scoped_node_ptr;
207 static value_type * alloc_node( value_type const& v )
209 return cxx_node_allocator().New( v );
212 static value_type * alloc_node()
214 return cxx_node_allocator().New();
217 template <typename... Args>
218 static value_type * alloc_node_move( Args&&... args )
220 return cxx_node_allocator().MoveNew( std::forward<Args>( args )... );
225 /// Initializes the empty queue
227 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.
229 : base_class( nQuasiFactor )
232 /// Clears the queue and deletes all internal data
236 /// Inserts a new element at last segment of the queue
238 The function makes queue node in dynamic memory calling copy constructor for \p val
239 and then it calls intrusive::SEgmentedQueue::enqueue.
240 Returns \p true if success, \p false otherwise.
242 bool enqueue( value_type const& val )
244 scoped_node_ptr p( alloc_node(val) );
245 if ( base_class::enqueue( *p ) ) {
252 /// Enqueues data to the queue using a functor
254 \p Func is a functor called to create node.
255 The functor \p f takes one argument - a reference to a new node of type \ref value_type :
257 cds::container::SegmentedQueue< cds::gc::HP, Foo > myQueue;
259 myQueue.enqueue_with( [&bar]( Foo& dest ) { dest = bar; } );
262 template <typename Func>
263 bool enqueue_with( Func f )
265 scoped_node_ptr p( alloc_node() );
267 if ( base_class::enqueue( *p ) ) {
275 /// Synonym for \p enqueue() member function
276 bool push( value_type const& val )
278 return enqueue( val );
281 /// Synonym for \p enqueue_with() member function
282 template <typename Func>
283 bool push_with( Func f )
285 return enqueue_with( f );
288 /// Enqueues data of type \ref value_type constructed with <tt>std::forward<Args>(args)...</tt>
289 template <typename... Args>
290 bool emplace( Args&&... args )
292 scoped_node_ptr p( alloc_node_move( std::forward<Args>(args)... ) );
293 if ( base_class::enqueue( *p )) {
300 /// Dequeues a value from the queue
302 If queue is not empty, the function returns \p true, \p dest contains copy of
303 dequeued value. The assignment operator for type \ref value_type is invoked.
304 If queue is empty, the function returns \p false, \p dest is unchanged.
306 bool dequeue( value_type& dest )
308 return dequeue_with( [&dest]( value_type& src ) { dest = src; });
311 /// Dequeues a value using a functor
313 \p Func is a functor called to copy dequeued value.
314 The functor takes one argument - a reference to removed node:
316 cds:container::MSQueue< cds::gc::HP, Foo > myQueue;
318 myQueue.dequeue_with( [&bar]( Foo& src ) { bar = std::move( src );});
320 The functor is called only if the queue is not empty.
322 template <typename Func>
323 bool dequeue_with( Func f )
325 value_type * p = base_class::dequeue();
328 gc::template retire< typename maker::node_disposer >( p );
334 /// Synonym for \p dequeue_with() function
335 template <typename Func>
336 bool pop_with( Func f )
338 return dequeue_with( f );
341 /// Synonym for \p dequeue() function
342 bool pop( value_type& dest )
344 return dequeue( dest );
347 /// Checks if the queue is empty
349 The original segmented queue algorithm does not allow to check emptiness accurately
350 because \p empty() is unlinearizable.
351 This function tests queue's emptiness checking <tt>size() == 0</tt>,
352 so, the item counting feature is an essential part of queue's algorithm.
356 return base_class::empty();
361 The function repeatedly calls \ref dequeue until it returns \p nullptr.
362 The disposer specified in \p Traits template argument is called for each removed item.
369 /// Returns queue's item count
372 return base_class::size();
375 /// Returns reference to internal statistics
377 The type of internal statistics is specified by \p Traits template argument.
379 const stat& statistics() const
381 return base_class::statistics();
384 /// Returns quasi factor, a power-of-two number
385 size_t quasi_factor() const
387 return base_class::quasi_factor();
391 }} // namespace cds::container
393 #endif // #ifndef CDSLIB_CONTAINER_SEGMENTED_QUEUE_H