3 #ifndef __CDS_INTRUSIVE_MSQUEUE_H
4 #define __CDS_INTRUSIVE_MSQUEUE_H
7 #include <cds/intrusive/details/single_link_struct.h>
8 #include <cds/cxx11_atomic.h>
10 namespace cds { namespace intrusive {
12 /// MSQueue related definitions
13 /** @ingroup cds_intrusive_helper
20 - GC - garbage collector used
21 - Tag - a \ref cds_intrusive_hook_tag "tag"
23 template <class GC, typename Tag = opt::none >
24 using node = cds::intrusive::single_link::node< GC, Tag > ;
29 - opt::gc - garbage collector used.
30 - opt::tag - a \ref cds_intrusive_hook_tag "tag"
32 template < typename... Options >
33 using base_hook = cds::intrusive::single_link::base_hook< Options...>;
37 \p MemberOffset specifies offset in bytes of \ref node member into your structure.
38 Use \p offsetof macro to define \p MemberOffset
41 - opt::gc - garbage collector used.
42 - opt::tag - a \ref cds_intrusive_hook_tag "tag"
44 template < size_t MemberOffset, typename... Options >
45 using member_hook = cds::intrusive::single_link::member_hook< MemberOffset, Options... >;
49 \p NodeTraits defines type traits for node.
50 See \ref node_traits for \p NodeTraits interface description
53 - opt::gc - garbage collector used.
54 - opt::tag - a \ref cds_intrusive_hook_tag "tag"
56 template <typename NodeTraits, typename... Options >
57 using traits_hook = cds::intrusive::single_link::traits_hook< NodeTraits, Options... >;
59 /// Queue internal statistics. May be used for debugging or profiling
61 Template argument \p Counter defines type of counter.
62 Default is \p cds::atomicity::event_counter, that is weak, i.e. it is not guaranteed
63 strict event counting.
64 You may use stronger type of counter like as \p cds::atomicity::item_counter,
65 or even integral type, for example, \p int.
67 template <typename Counter = cds::atomicity::event_counter >
70 typedef Counter counter_type; ///< Counter type
72 counter_type m_EnqueueCount ; ///< Enqueue call count
73 counter_type m_DequeueCount ; ///< Dequeue call count
74 counter_type m_EnqueueRace ; ///< Count of enqueue race conditions encountered
75 counter_type m_DequeueRace ; ///< Count of dequeue race conditions encountered
76 counter_type m_AdvanceTailError ; ///< Count of "advance tail failed" events
77 counter_type m_BadTail ; ///< Count of events "Tail is not pointed to the last item in the queue"
79 /// Register enqueue call
80 void onEnqueue() { ++m_EnqueueCount; }
81 /// Register dequeue call
82 void onDequeue() { ++m_DequeueCount; }
83 /// Register enqueue race event
84 void onEnqueueRace() { ++m_EnqueueRace; }
85 /// Register dequeue race event
86 void onDequeueRace() { ++m_DequeueRace; }
87 /// Register "advance tail failed" event
88 void onAdvanceTailFailed() { ++m_AdvanceTailError; }
89 /// Register event "Tail is not pointed to last item in the queue"
90 void onBadTail() { ++m_BadTail; }
95 m_EnqueueCount.reset();
96 m_DequeueCount.reset();
97 m_EnqueueRace.reset();
98 m_DequeueRace.reset();
99 m_AdvanceTailError.reset();
103 stat& operator +=( stat const& s )
105 m_EnqueueCount += s.m_EnqueueCount.get();
106 m_DequeueCount += s.m_DequeueCount.get();
107 m_EnqueueRace += s.m_EnqueueRace.get();
108 m_DequeueRace += s.m_DequeueRace.get();
109 m_AdvanceTailError += s.m_AdvanceTailError.get();
110 m_BadTail += s.m_BadTail.get();
117 /// Dummy queue statistics - no counting is performed, no overhead. Support interface like \p msqueue::stat
123 void onEnqueueRace() {}
124 void onDequeueRace() {}
125 void onAdvanceTailFailed() {}
129 empty_stat& operator +=( empty_stat const& s )
136 /// MSQueue default type traits
139 /// Back-off strategy
140 typedef cds::backoff::empty back_off;
142 /// Hook, possible types are \p msqueue::base_hook, \p msqueue::member_hook, \p msqueue::traits_hook
143 typedef msqueue::base_hook<> hook;
145 /// The functor used for dispose removed items. Default is \p opt::v::empty_disposer. This option is used for dequeuing
146 typedef opt::v::empty_disposer disposer;
148 /// Item counting feature; by default, disabled. Use \p cds::atomicity::item_counter to enable item counting
149 typedef atomicity::empty_item_counter item_counter;
151 /// Internal statistics (by default, disabled)
153 Possible option value are: \p msqueue::stat, \p msqueue::empty_stat (the default),
154 user-provided class that supports \p %msqueue::stat interface.
156 typedef msqueue::empty_stat stat;
158 /// C++ memory ordering model
160 Can be \p opt::v::relaxed_ordering (relaxed memory model, the default)
161 or \p opt::v::sequential_consistent (sequentially consisnent memory model).
163 typedef opt::v::relaxed_ordering memory_model;
165 /// Link checking, see \p cds::opt::link_checker
166 static CDS_CONSTEXPR const opt::link_check_type link_checker = opt::debug_check_link;
168 /// Alignment for internal queue data. Default is \p opt::cache_line_alignment
169 enum { alignment = opt::cache_line_alignment };
172 /// Metafunction converting option list to \p msqueue::traits
174 This is a wrapper for <tt> cds::opt::make_options< type_traits, Options...> </tt>
175 Supported \p Options are:
177 - opt::hook - hook used. Possible hooks are: \p msqueue::base_hook, \p msqueue::member_hook, \p msqueue::traits_hook.
178 If the option is not specified, \p %msqueue::base_hook<> is used.
179 - opt::back_off - back-off strategy used, default is \p cds::backoff::empty.
180 - opt::disposer - the functor used for dispose removed items. Default is \p opt::v::empty_disposer. This option is used
182 - opt::link_checker - the type of node's link fields checking. Default is \p opt::debug_check_link
183 - opt::item_counter - the type of item counting feature. Default is \p cds::atomicity::empty_item_counter (item counting disabled)
184 To enable item counting use \p cds::atomicity::item_counter
185 - opt::stat - the type to gather internal statistics.
186 Possible statistics types are: \p msqueue::stat, \p msqueue::empty_stat, user-provided class that supports \p %msqueue::stat interface.
187 Default is \p %msqueue::empty_stat (internal statistics disabled).
188 - opt::alignment - the alignment for internal queue data. Default is \p opt::cache_line_alignment
189 - opt::memory_model - C++ memory ordering model. Can be \p opt::v::relaxed_ordering (relaxed memory model, the default)
190 or \p opt::v::sequential_consistent (sequentially consisnent memory model).
192 Example: declare \p %MSQueue with item counting and internal statistics
194 typedef cds::intrusive::MSQueue< cds::gc::HP, Foo,
195 typename cds::intrusive::msqueue::make_traits<
196 cds::intrusive::opt:hook< cds::intrusive::msqueue::base_hook< cds::opt::gc<cds:gc::HP> >>,
197 cds::opt::item_counte< cds::atomicity::item_counter >,
198 cds::opt::stat< cds::intrusive::msqueue::stat<> >
203 template <typename... Options>
205 # ifdef CDS_DOXYGEN_INVOKED
206 typedef implementation_defined type; ///< Metafunction result
208 typedef typename cds::opt::make_options<
209 typename cds::opt::find_type_traits< traits, Options... >::type
216 } // namespace msqueue
218 /// Michael & Scott's intrusive lock-free queue
219 /** @ingroup cds_intrusive_queue
220 Implementation of well-known Michael & Scott's queue algorithm:
221 - [1998] Maged Michael, Michael Scott "Simple, fast, and practical non-blocking and blocking concurrent queue algorithms"
224 - \p GC - garbage collector type: \p gc::HP, \p gc::DHP
225 - \p T - type of value to be stored in the queue. A value of type \p T must be derived from \p msqueue::node for \p msqueue::base_hook,
226 or it should have a member of type \p %msqueue::node for \p msqueue::member_hook,
227 or it should be convertible to \p %msqueue::node for \p msqueue::traits_hook.
228 - \p Traits - queue traits, default is \p msqueue::traits. You can use \p msqueue::make_traits
229 metafunction to make your traits or just derive your traits from \p %msqueue::traits:
231 struct myTraits: public cds::intrusive::msqueue::traits {
232 typedef cds::intrusive::msqueue::stat<> stat;
233 typedef cds::atomicity::item_counter item_counter;
235 typedef cds::intrusive::MSQueue< cds::gc::HP, Foo, myTraits > myQueue;
237 // Equivalent make_traits example:
238 typedef cds::intrusive::MSQueue< cds::gc::HP, Foo,
239 typename cds::intrusive::msqueue::make_traits<
240 cds::opt::stat< cds::intrusive::msqueue::stat<> >,
241 cds::opt::item_counter< cds::atomicity::item_counter >
246 \par About item disposing
247 The Michael & Scott's queue algo has a key feature: even if the queue is empty it contains one item that is "dummy" one from
248 the standpoint of the algo. See \p dequeue() function for explanation.
252 #include <cds/intrusive/msqueue.h>
253 #include <cds/gc/hp.h>
255 namespace ci = cds::inrtusive;
256 typedef cds::gc::HP hp_gc;
258 // MSQueue with Hazard Pointer garbage collector, base hook + item disposer:
259 struct Foo: public ci::msqueue::node< hp_gc >
265 // Disposer for Foo struct just deletes the object passed in
267 void operator()( Foo * p )
273 // Declare traits for the queue
274 struct myTraits: public ci::msqueue::traits {
276 ci::msqueue::base_hook< ci::opt::gc<hp_gc> >
278 ,ci::opt::disposer< fooDisposer >
281 // At least, declare the queue type
282 typedef ci::MSQueue< hp_gc, Foo, myTraits > fooQueue;
285 // MSQueue with Hazard Pointer garbage collector,
286 // member hook + item disposer + item counter,
287 // without alignment of internal queue data
288 // Use msqueue::make_traits
293 ci::msqueue::node< hp_gc > hMember;
296 typedef ci::MSQueue< hp_gc,
298 typename ci::msqueue::make_traits<
300 ci::msqueue::member_hook<
301 offsetof(Bar, hMember)
305 ,ci::opt::disposer< fooDisposer >
306 ,cds::opt::item_counter< cds::atomicity::item_counter >
307 ,cds::opt::alignment< cds::opt::no_special_alignment >
312 template <typename GC, typename T, typename Traits>
316 typedef GC gc; ///< Garbage collector
317 typedef T value_type; ///< type of value stored in the queue
318 typedef Traits traits; ///< Queue traits
320 typedef typename traits::hook hook; ///< hook type
321 typedef typename hook::node_type node_type; ///< node type
322 typedef typename traits::disposer disposer; ///< disposer used
323 typedef typename get_node_traits< value_type, node_type, hook>::type node_traits; ///< node traits
324 typedef typename single_link::get_link_checker< node_type, traits::link_checker >::type link_checker; ///< link checker
326 typedef typename traits::back_off back_off; ///< back-off strategy
327 typedef typename traits::item_counter item_counter; ///< Item counter class
328 typedef typename traits::stat stat; ///< Internal statistics
329 typedef typename traits::memory_model memory_model; ///< Memory ordering. See \p cds::opt::memory_model option
331 /// Rebind template arguments
332 template <typename GC2, typename T2, typename Traits2>
334 typedef MSQueue< GC2, T2, Traits2 > other; ///< Rebinding result
337 static CDS_CONSTEXPR const size_t m_nHazardPtrCount = 2; ///< Count of hazard pointer required for the algorithm
342 // GC and node_type::gc must be the same
343 static_assert((std::is_same<gc, typename node_type::gc>::value), "GC and node_type::gc must be the same");
345 typedef intrusive::node_to_value<MSQueue> node_to_value;
346 typedef typename opt::details::alignment_setter< typename node_type::atomic_node_ptr, traits::alignment >::type aligned_node_ptr;
347 typedef typename opt::details::alignment_setter< node_type, traits::alignment >::type dummy_node_type;
349 aligned_node_ptr m_pHead ; ///< Queue's head pointer
350 aligned_node_ptr m_pTail ; ///< Queue's tail pointer
351 dummy_node_type m_Dummy ; ///< dummy node
352 item_counter m_ItemCounter ; ///< Item counter
353 stat m_Stat ; ///< Internal statistics
357 struct dequeue_result {
358 typename gc::template GuardArray<2> guards;
364 bool do_dequeue( dequeue_result& res )
371 h = res.guards.protect( 0, m_pHead, node_to_value() );
372 pNext = h->m_pNext.load( memory_model::memory_order_relaxed );
373 res.guards.assign( 1, node_to_value()( pNext ));
374 if ( m_pHead.load(memory_model::memory_order_acquire) != h )
377 if ( pNext == nullptr )
378 return false ; // empty queue
380 node_type * t = m_pTail.load(memory_model::memory_order_acquire);
382 // It is needed to help enqueue
383 m_pTail.compare_exchange_strong( t, pNext, memory_model::memory_order_release, atomics::memory_order_relaxed );
388 if ( m_pHead.compare_exchange_strong( h, pNext, memory_model::memory_order_release, atomics::memory_order_relaxed ))
391 m_Stat.onDequeueRace();
403 static void clear_links( node_type * pNode )
405 pNode->m_pNext.store( nullptr, memory_model::memory_order_release );
408 void dispose_result( dequeue_result& res )
410 dispose_node( res.pHead );
413 void dispose_node( node_type * p )
415 // Note about the dummy node:
416 // We cannot clear m_Dummy here since it leads to ABA.
417 // On the other hand, we cannot use deferred clear_links( &m_Dummy ) call via
418 // HP retiring cycle since m_Dummy is member of MSQueue and may be destroyed
419 // before HP retiring cycle invocation.
420 // So, we will never clear m_Dummy
422 struct disposer_thunk {
423 void operator()( value_type * p ) const
425 assert( p != nullptr );
426 MSQueue::clear_links( node_traits::to_node_ptr( p ) );
432 gc::template retire<disposer_thunk>( node_traits::to_value_ptr( p ) );
437 /// Initializes empty queue
439 : m_pHead( &m_Dummy )
440 , m_pTail( &m_Dummy )
443 /// Destructor clears the queue
445 Since the Michael & Scott queue contains at least one item even
446 if the queue is empty, the destructor may call item disposer.
452 node_type * pHead = m_pHead.load(memory_model::memory_order_relaxed);
454 assert( pHead != nullptr );
455 assert( pHead == m_pTail.load(memory_model::memory_order_relaxed) );
457 m_pHead.store( nullptr, memory_model::memory_order_relaxed );
458 m_pTail.store( nullptr, memory_model::memory_order_relaxed );
460 dispose_node( pHead );
463 /// Enqueues \p val value into the queue.
464 /** @anchor cds_intrusive_MSQueue_enqueue
465 The function always returns \p true.
467 bool enqueue( value_type& val )
469 node_type * pNew = node_traits::to_node_ptr( val );
470 link_checker::is_empty( pNew );
472 typename gc::Guard guard;
477 t = guard.protect( m_pTail, node_to_value() );
479 node_type * pNext = t->m_pNext.load(memory_model::memory_order_acquire);
480 if ( pNext != nullptr ) {
481 // Tail is misplaced, advance it
482 m_pTail.compare_exchange_weak( t, pNext, memory_model::memory_order_release, atomics::memory_order_relaxed );
487 node_type * tmp = nullptr;
488 if ( t->m_pNext.compare_exchange_strong( tmp, pNew, memory_model::memory_order_release, atomics::memory_order_relaxed ))
491 m_Stat.onEnqueueRace();
497 if ( !m_pTail.compare_exchange_strong( t, pNew, memory_model::memory_order_acq_rel, atomics::memory_order_relaxed ))
498 m_Stat.onAdvanceTailFailed();
502 /// Dequeues a value from the queue
503 /** @anchor cds_intrusive_MSQueue_dequeue
504 If the queue is empty the function returns \p nullptr.
507 The queue algorithm has following feature: when \p %dequeue() is called,
508 the item returning is still queue's top, and previous top is disposed:
511 before dequeuing Dequeue after dequeuing
512 +------------------+ +------------------+
513 Top ->| Item 1 | -> Dispose Item 1 | Item 2 | <- Top
514 +------------------+ +------------------+
515 | Item 2 | -> Return Item 2 | ... |
520 \p %dequeue() function returns Item 2, that becomes new top of queue, and calls
521 the disposer for Item 1, that was queue's top on function entry.
522 Thus, you cannot manually delete item returned because it is still included in
523 item sequence and it has valuable link field that must not be zeroed.
524 The item should be deleted only in garbage collector retire cycle using the disposer.
526 value_type * dequeue()
530 if ( do_dequeue( res )) {
531 dispose_result( res );
533 return node_traits::to_value_ptr( *res.pNext );
538 /// Synonym for \ref cds_intrusive_MSQueue_enqueue "enqueue()" function
539 bool push( value_type& val )
541 return enqueue( val );
544 /// Synonym for \ref cds_intrusive_MSQueue_dequeue "dequeue()" function
550 /// Checks if the queue is empty
553 typename gc::Guard guard;
554 return guard.protect( m_pHead, node_to_value() )->m_pNext.load( memory_model::memory_order_relaxed ) == nullptr;
559 The function repeatedly calls \p dequeue() until it returns \p nullptr.
560 The disposer defined in template \p Traits is called for each item
561 that can be safely disposed.
568 /// Returns queue's item count
570 The value returned depends on \p msqueue::traits::item_counter. For \p atomicity::empty_item_counter,
571 this function always returns 0.
573 @note Even if you use real item counter and it returns 0, this fact is not mean that the queue
574 is empty. To check queue emptyness use \p empty() method.
578 return m_ItemCounter.value();
581 /// Returns reference to internal statistics
582 stat const& statistics() const
588 }} // namespace cds::intrusive
590 #endif // #ifndef __CDS_INTRUSIVE_MSQUEUE_H