3 #ifndef CDSLIB_GC_DETAILS_DHP_H
4 #define CDSLIB_GC_DETAILS_DHP_H
6 #include <mutex> // unique_lock
7 #include <cds/algo/atomic.h>
8 #include <cds/algo/int_algo.h>
9 #include <cds/gc/details/retired_ptr.h>
10 #include <cds/details/aligned_allocator.h>
11 #include <cds/details/allocator.h>
12 #include <cds/sync/spinlock.h>
14 #if CDS_COMPILER == CDS_COMPILER_MSVC
15 # pragma warning(push)
16 # pragma warning(disable:4251) // C4251: 'identifier' : class 'type' needs to have dll-interface to be used by clients of class 'type2'
20 namespace cds { namespace gc {
22 /// Dynamic Hazard Pointer reclamation schema
24 The cds::gc::dhp namespace and its members are internal representation of the GC and should not be used directly.
25 Use cds::gc::DHP class in your code.
27 Dynamic Hazard Pointer (DHP) garbage collector is a singleton. The main user-level part of DHP schema is
28 GC class and its nested classes. Before use any DHP-related class you must initialize DHP garbage collector
29 by contructing cds::gc::DHP object in beginning of your main().
30 See cds::gc::DHP class for explanation.
32 \par Implementation issues
33 The global list of free guards (\p cds::gc::dhp::details::guard_allocator) is protected by a spin-lock (i.e. serialized).
34 It seems that this solution should not introduce significant performance bottleneck, because each thread has its own set
35 of guards allocated from the global list of free guards and the access to the global list is occurred only when
36 all thread's guard is busy. In this case the thread allocates a next block of guards from the global list.
37 Guards allocated for the thread is push back to the global list only when the thread terminates.
41 // Forward declarations
43 template <size_t Count> class GuardArray;
45 class GarbageCollector;
47 /// Retired pointer type
48 typedef cds::gc::details::retired_ptr retired_ptr;
50 using cds::gc::details::free_retired_ptr_func;
52 /// Details of Dynamic Hazard Pointer algorithm
55 // Forward declaration
58 /// Retired pointer buffer node
59 struct retired_ptr_node {
60 retired_ptr m_ptr ; ///< retired pointer
61 atomics::atomic<retired_ptr_node *> m_pNext ; ///< next retired pointer in buffer
62 atomics::atomic<retired_ptr_node *> m_pNextFree ; ///< next item in free list of \p retired_ptr_node
65 /// Internal guard representation
67 typedef void * guarded_ptr; ///< type of value guarded
69 atomics::atomic<guarded_ptr> pPost; ///< pointer guarded
70 atomics::atomic<guard_data *> pGlobalNext; ///< next item of global list of allocated guards
71 atomics::atomic<guard_data *> pNextFree; ///< pointer to the next item in global or thread-local free-list
73 guard_data * pThreadNext; ///< next item of thread's local list of guards
75 guard_data() CDS_NOEXCEPT
77 , pGlobalNext( nullptr )
78 , pNextFree( nullptr )
79 , pThreadNext( nullptr )
82 void init() CDS_NOEXCEPT
84 pPost.store( nullptr, atomics::memory_order_relaxed );
87 /// Checks if the guard is free, that is, it does not contain any pointer guarded
88 bool isFree() const CDS_NOEXCEPT
90 return pPost.load( atomics::memory_order_acquire ) == nullptr;
95 template <class Alloc = CDS_DEFAULT_ALLOCATOR>
98 cds::details::Allocator<details::guard_data> m_GuardAllocator ; ///< guard allocator
100 atomics::atomic<guard_data *> m_GuardList; ///< Head of allocated guard list (linked by guard_data::pGlobalNext field)
101 atomics::atomic<guard_data *> m_FreeGuardList; ///< Head of free guard list (linked by guard_data::pNextFree field)
102 cds::sync::spin m_freeListLock; ///< Access to m_FreeGuardList
105 Unfortunately, access to the list of free guard is lock-based.
106 Lock-free manipulations with guard free-list are ABA-prone.
107 TODO: working with m_FreeGuardList in lock-free manner.
111 /// Allocates new guard from the heap. The function uses aligned allocator
112 guard_data * allocNew()
114 //TODO: the allocator should make block allocation
116 details::guard_data * pGuard = m_GuardAllocator.New();
118 // Link guard to the list
119 // m_GuardList is an accumulating list and it cannot support concurrent deletion,
120 // so, ABA problem is impossible for it
121 details::guard_data * pHead = m_GuardList.load( atomics::memory_order_acquire );
123 pGuard->pGlobalNext.store( pHead, atomics::memory_order_relaxed );
124 // pHead is changed by compare_exchange_weak
125 } while ( !m_GuardList.compare_exchange_weak( pHead, pGuard, atomics::memory_order_release, atomics::memory_order_relaxed ));
133 guard_allocator() CDS_NOEXCEPT
134 : m_GuardList( nullptr )
135 , m_FreeGuardList( nullptr )
142 for ( guard_data * pData = m_GuardList.load( atomics::memory_order_relaxed ); pData != nullptr; pData = pNext ) {
143 pNext = pData->pGlobalNext.load( atomics::memory_order_relaxed );
144 m_GuardAllocator.Delete( pData );
148 /// Allocates a guard from free list or from heap if free list is empty
151 // Try to pop a guard from free-list
152 details::guard_data * pGuard;
155 std::unique_lock<cds::sync::spin> al( m_freeListLock );
156 pGuard = m_FreeGuardList.load(atomics::memory_order_relaxed);
158 m_FreeGuardList.store( pGuard->pNextFree.load(atomics::memory_order_relaxed), atomics::memory_order_relaxed );
167 /// Frees guard \p pGuard
169 The function places the guard \p pGuard into free-list
171 void free( guard_data * pGuard ) CDS_NOEXCEPT
173 pGuard->pPost.store( nullptr, atomics::memory_order_relaxed );
175 std::unique_lock<cds::sync::spin> al( m_freeListLock );
176 pGuard->pNextFree.store( m_FreeGuardList.load(atomics::memory_order_relaxed), atomics::memory_order_relaxed );
177 m_FreeGuardList.store( pGuard, atomics::memory_order_relaxed );
180 /// Allocates list of guard
182 The list returned is linked by guard's \p pThreadNext and \p pNextFree fields.
184 cds::gc::dhp::ThreadGC supporting method
186 guard_data * allocList( size_t nCount )
188 assert( nCount != 0 );
196 // The guard list allocated is private for the thread,
197 // so, we can use relaxed memory order
199 guard_data * p = alloc();
200 pLast->pNextFree.store( pLast->pThreadNext = p, atomics::memory_order_relaxed );
204 pLast->pNextFree.store( pLast->pThreadNext = nullptr, atomics::memory_order_relaxed );
209 /// Frees list of guards
211 The list \p pList is linked by guard's \p pThreadNext field.
213 cds::gc::dhp::ThreadGC supporting method
215 void freeList( guard_data * pList ) CDS_NOEXCEPT
217 assert( pList != nullptr );
219 guard_data * pLast = pList;
220 while ( pLast->pThreadNext ) {
221 pLast->pPost.store( nullptr, atomics::memory_order_relaxed );
223 pLast->pNextFree.store( p = pLast->pThreadNext, atomics::memory_order_relaxed );
227 std::unique_lock<cds::sync::spin> al( m_freeListLock );
228 pLast->pNextFree.store( m_FreeGuardList.load(atomics::memory_order_relaxed), atomics::memory_order_relaxed );
229 m_FreeGuardList.store( pList, atomics::memory_order_relaxed );
232 /// Returns the list's head of guards allocated
233 guard_data * begin() CDS_NOEXCEPT
235 return m_GuardList.load(atomics::memory_order_acquire);
239 /// Retired pointer buffer
241 The buffer of retired nodes ready for liberating.
242 When size of buffer exceeds a threshold the GC calls \p scan() procedure to free
245 class retired_ptr_buffer
247 atomics::atomic<retired_ptr_node *> m_pHead ; ///< head of buffer
248 atomics::atomic<size_t> m_nItemCount; ///< buffer's item count
251 retired_ptr_buffer() CDS_NOEXCEPT
256 ~retired_ptr_buffer() CDS_NOEXCEPT
258 assert( m_pHead.load( atomics::memory_order_relaxed ) == nullptr );
261 /// Pushes new node into the buffer. Returns current buffer size
262 size_t push( retired_ptr_node& node ) CDS_NOEXCEPT
264 retired_ptr_node * pHead = m_pHead.load(atomics::memory_order_acquire);
266 node.m_pNext.store( pHead, atomics::memory_order_relaxed );
267 // pHead is changed by compare_exchange_weak
268 } while ( !m_pHead.compare_exchange_weak( pHead, &node, atomics::memory_order_release, atomics::memory_order_relaxed ));
270 return m_nItemCount.fetch_add( 1, atomics::memory_order_relaxed ) + 1;
273 /// Pushes [pFirst, pLast] list linked by pNext field.
274 size_t push_list( retired_ptr_node* pFirst, retired_ptr_node* pLast, size_t nSize )
279 retired_ptr_node * pHead = m_pHead.load( atomics::memory_order_acquire );
281 pLast->m_pNext.store( pHead, atomics::memory_order_relaxed );
282 // pHead is changed by compare_exchange_weak
283 } while ( !m_pHead.compare_exchange_weak( pHead, pFirst, atomics::memory_order_release, atomics::memory_order_relaxed ) );
285 return m_nItemCount.fetch_add( nSize, atomics::memory_order_relaxed ) + 1;
288 /// Result of \ref dhp_gc_privatize "privatize" function.
290 The \p privatize function returns retired node list as \p first and the size of that list as \p second.
292 typedef std::pair<retired_ptr_node *, size_t> privatize_result;
294 /// Gets current list of retired pointer and clears the list
295 /**@anchor dhp_gc_privatize
297 privatize_result privatize() CDS_NOEXCEPT
299 privatize_result res;
301 // Item counter is needed only as a threshold for \p scan() function
302 // So, we may clear the item counter without synchronization with m_pHead
303 res.second = m_nItemCount.exchange( 0, atomics::memory_order_relaxed );
305 res.first = m_pHead.exchange( nullptr, atomics::memory_order_acq_rel );
310 /// Returns current size of buffer (approximate)
311 size_t size() const CDS_NOEXCEPT
313 return m_nItemCount.load(atomics::memory_order_relaxed);
317 /// Pool of retired pointers
319 The class acts as an allocator of retired node.
320 Retired pointers are linked in the lock-free list.
322 template <class Alloc = CDS_DEFAULT_ALLOCATOR>
323 class retired_ptr_pool {
325 typedef retired_ptr_node item;
327 /// Count of items in block
328 static const size_t m_nItemPerBlock = 1024 / sizeof(item) - 1;
332 atomics::atomic<block *> pNext; ///< next block
333 item items[m_nItemPerBlock]; ///< item array
336 atomics::atomic<block *> m_pBlockListHead; ///< head of of allocated block list
338 // To solve ABA problem we use epoch-based approach
339 unsigned int const m_nEpochBitmask; ///< Epoch bitmask (log2( m_nEpochCount))
340 atomics::atomic<unsigned int> m_nCurEpoch; ///< Current epoch
341 atomics::atomic<item *>* m_pEpochFree; ///< List of free item per epoch
342 atomics::atomic<item *> m_pGlobalFreeHead; ///< Head of unallocated item list
344 typedef cds::details::Allocator< block, Alloc > block_allocator;
345 typedef cds::details::Allocator< atomics::atomic<item *>, Alloc > epoch_array_alloc;
350 // allocate new block
351 block * pNew = block_allocator().New();
353 // link items within the block
354 item * pLastItem = pNew->items + m_nItemPerBlock - 1;
355 for ( item * pItem = pNew->items; pItem != pLastItem; ++pItem ) {
356 pItem->m_pNextFree.store( pItem + 1, atomics::memory_order_release );
357 CDS_STRICT_DO( pItem->m_pNext.store( nullptr, atomics::memory_order_relaxed ));
360 // links new block to the block list
362 block * pHead = m_pBlockListHead.load(atomics::memory_order_relaxed);
364 pNew->pNext.store( pHead, atomics::memory_order_relaxed );
365 // pHead is changed by compare_exchange_weak
366 } while ( !m_pBlockListHead.compare_exchange_weak( pHead, pNew, atomics::memory_order_relaxed, atomics::memory_order_relaxed ));
369 // links block's items to the free list
371 item * pHead = m_pGlobalFreeHead.load(atomics::memory_order_relaxed);
373 pLastItem->m_pNextFree.store( pHead, atomics::memory_order_release );
374 // pHead is changed by compare_exchange_weak
375 } while ( !m_pGlobalFreeHead.compare_exchange_weak( pHead, pNew->items, atomics::memory_order_release, atomics::memory_order_relaxed ));
379 unsigned int current_epoch() const CDS_NOEXCEPT
381 return m_nCurEpoch.load(atomics::memory_order_acquire) & m_nEpochBitmask;
384 unsigned int next_epoch() const CDS_NOEXCEPT
386 return (m_nCurEpoch.load(atomics::memory_order_acquire) - 1) & m_nEpochBitmask;
390 retired_ptr_pool( unsigned int nEpochCount = 8 )
391 : m_pBlockListHead( nullptr )
392 , m_nEpochBitmask( static_cast<unsigned int>(beans::ceil2(nEpochCount)) - 1 )
394 , m_pEpochFree( epoch_array_alloc().NewArray( m_nEpochBitmask + 1))
395 , m_pGlobalFreeHead( nullptr )
399 for (unsigned int i = 0; i <= m_nEpochBitmask; ++i )
400 m_pEpochFree[i].store( nullptr, atomics::memory_order_relaxed );
409 for ( block * pBlock = m_pBlockListHead.load(atomics::memory_order_relaxed); pBlock; pBlock = p ) {
410 p = pBlock->pNext.load( atomics::memory_order_relaxed );
414 epoch_array_alloc().Delete( m_pEpochFree, m_nEpochBitmask + 1 );
417 /// Increments current epoch
418 void inc_epoch() CDS_NOEXCEPT
420 m_nCurEpoch.fetch_add( 1, atomics::memory_order_acq_rel );
423 /// Allocates the new retired pointer
424 retired_ptr_node& alloc()
429 pItem = m_pEpochFree[ nEpoch = current_epoch() ].load(atomics::memory_order_acquire);
432 if ( m_pEpochFree[nEpoch].compare_exchange_weak( pItem,
433 pItem->m_pNextFree.load(atomics::memory_order_acquire),
434 atomics::memory_order_acquire, atomics::memory_order_relaxed ))
440 // Epoch free list is empty
441 // Alloc from global free list
443 pItem = m_pGlobalFreeHead.load( atomics::memory_order_relaxed );
449 // pItem is changed by compare_exchange_weak
450 } while ( !m_pGlobalFreeHead.compare_exchange_weak( pItem,
451 pItem->m_pNextFree.load(atomics::memory_order_acquire),
452 atomics::memory_order_acquire, atomics::memory_order_relaxed ));
455 CDS_STRICT_DO( pItem->m_pNextFree.store( nullptr, atomics::memory_order_relaxed ));
459 /// Allocates and initializes new retired pointer
460 retired_ptr_node& alloc( const retired_ptr& p )
462 retired_ptr_node& node = alloc();
467 /// Places the list [pHead, pTail] of retired pointers to pool (frees retired pointers)
469 The list is linked on the m_pNextFree field
471 void free_range( retired_ptr_node * pHead, retired_ptr_node * pTail ) CDS_NOEXCEPT
473 assert( pHead != nullptr );
474 assert( pTail != nullptr );
479 pCurHead = m_pEpochFree[nEpoch = next_epoch()].load(atomics::memory_order_acquire);
480 pTail->m_pNextFree.store( pCurHead, atomics::memory_order_release );
481 } while ( !m_pEpochFree[nEpoch].compare_exchange_weak( pCurHead, pHead, atomics::memory_order_release, atomics::memory_order_relaxed ));
485 /// Uninitialized guard
488 friend class dhp::ThreadGC;
490 details::guard_data * m_pGuard ; ///< Pointer to guard data
493 /// Initialize empty guard.
494 CDS_CONSTEXPR guard() CDS_NOEXCEPT
495 : m_pGuard( nullptr )
498 /// Copy-ctor is disabled
499 guard( guard const& ) = delete;
501 /// Move-ctor is disabled
502 guard( guard&& ) = delete;
504 /// Object destructor, does nothing
505 ~guard() CDS_NOEXCEPT
508 /// Get current guarded pointer
509 void * get( atomics::memory_order order = atomics::memory_order_acquire ) const CDS_NOEXCEPT
511 assert( m_pGuard != nullptr );
512 return m_pGuard->pPost.load( order );
515 /// Guards pointer \p p
516 void set( void * p, atomics::memory_order order = atomics::memory_order_release ) CDS_NOEXCEPT
518 assert( m_pGuard != nullptr );
519 m_pGuard->pPost.store( p, order );
523 void clear( atomics::memory_order order = atomics::memory_order_relaxed ) CDS_NOEXCEPT
525 assert( m_pGuard != nullptr );
526 m_pGuard->pPost.store( nullptr, order );
529 /// Guards pointer \p p
530 template <typename T>
531 T * operator =(T * p) CDS_NOEXCEPT
533 set( reinterpret_cast<void *>( const_cast<T *>(p) ));
537 std::nullptr_t operator=(std::nullptr_t) CDS_NOEXCEPT
543 public: // for ThreadGC.
545 GCC cannot compile code for template versions of ThreadGC::allocGuard/freeGuard,
546 the compiler produces error: 'cds::gc::dhp::details::guard_data* cds::gc::dhp::details::guard::m_pGuard' is protected
547 despite the fact that ThreadGC is declared as friend for guard class.
548 Therefore, we have to add set_guard/get_guard public functions
551 void set_guard( details::guard_data * pGuard ) CDS_NOEXCEPT
553 assert( m_pGuard == nullptr );
557 /// Get current guard data
558 details::guard_data * get_guard() CDS_NOEXCEPT
562 /// Get current guard data
563 details::guard_data * get_guard() const CDS_NOEXCEPT
568 details::guard_data * release_guard() CDS_NOEXCEPT
570 details::guard_data * p = m_pGuard;
575 bool is_initialized() const
577 return m_pGuard != nullptr;
581 } // namespace details
585 This class represents auto guard: ctor allocates a guard from guard pool,
586 dtor returns the guard back to the pool of free guard.
588 class Guard: public details::guard
590 typedef details::guard base_class;
591 friend class ThreadGC;
593 /// Allocates a guard from \p gc GC. \p gc must be ThreadGC object of current thread
594 Guard(); // inline in dhp_impl.h
596 /// Returns guard allocated back to pool of free guards
597 ~Guard(); // inline in dhp_impl.h
599 /// Guards pointer \p p
600 template <typename T>
601 T * operator =(T * p) CDS_NOEXCEPT
603 return base_class::operator =<T>( p );
606 std::nullptr_t operator=(std::nullptr_t) CDS_NOEXCEPT
608 return base_class::operator =(nullptr);
614 This class represents array of auto guards: ctor allocates \p Count guards from guard pool,
615 dtor returns the guards allocated back to the pool.
617 template <size_t Count>
620 details::guard m_arr[Count] ; ///< array of guard
621 const static size_t c_nCapacity = Count ; ///< Array capacity (equal to \p Count template parameter)
624 /// Rebind array for other size \p OtherCount
625 template <size_t OtherCount>
627 typedef GuardArray<OtherCount> other ; ///< rebinding result
631 /// Allocates array of guards from \p gc which must be the ThreadGC object of current thread
632 GuardArray(); // inline in dhp_impl.h
634 /// The object is not copy-constructible
635 GuardArray( GuardArray const& ) = delete;
637 /// The object is not move-constructible
638 GuardArray( GuardArray&& ) = delete;
640 /// Returns guards allocated back to pool
641 ~GuardArray(); // inline in dh_impl.h
643 /// Returns the capacity of array
644 CDS_CONSTEXPR size_t capacity() const CDS_NOEXCEPT
649 /// Returns reference to the guard of index \p nIndex (0 <= \p nIndex < \p Count)
650 details::guard& operator []( size_t nIndex ) CDS_NOEXCEPT
652 assert( nIndex < capacity() );
653 return m_arr[nIndex];
656 /// Returns reference to the guard of index \p nIndex (0 <= \p nIndex < \p Count) [const version]
657 const details::guard& operator []( size_t nIndex ) const CDS_NOEXCEPT
659 assert( nIndex < capacity() );
660 return m_arr[nIndex];
663 /// Set the guard \p nIndex. 0 <= \p nIndex < \p Count
664 template <typename T>
665 void set( size_t nIndex, T * p ) CDS_NOEXCEPT
667 assert( nIndex < capacity() );
668 m_arr[nIndex].set( p );
671 /// Clears (sets to \p nullptr) the guard \p nIndex
672 void clear( size_t nIndex ) CDS_NOEXCEPT
674 assert( nIndex < capacity() );
675 m_arr[nIndex].clear();
678 /// Clears all guards in the array
679 void clearAll() CDS_NOEXCEPT
681 for ( size_t i = 0; i < capacity(); ++i )
686 /// Memory manager (Garbage collector)
687 class CDS_EXPORT_API GarbageCollector
690 friend class ThreadGC;
692 /// Internal GC statistics
695 atomics::atomic<size_t> m_nGuardCount ; ///< Total guard count
696 atomics::atomic<size_t> m_nFreeGuardCount ; ///< Count of free guard
700 , m_nFreeGuardCount(0)
705 /// Exception "No GarbageCollector object is created"
706 class not_initialized : public std::runtime_error
711 : std::runtime_error( "Global DHP GarbageCollector is not initialized" )
716 /// Internal GC statistics
719 size_t m_nGuardCount ; ///< Total guard count
720 size_t m_nFreeGuardCount ; ///< Count of free guard
725 , m_nFreeGuardCount(0)
728 InternalState& operator =( internal_stat const& s )
730 m_nGuardCount = s.m_nGuardCount.load(atomics::memory_order_relaxed);
731 m_nFreeGuardCount = s.m_nFreeGuardCount.load(atomics::memory_order_relaxed);
739 static GarbageCollector * m_pManager ; ///< GC global instance
741 atomics::atomic<size_t> m_nLiberateThreshold; ///< Max size of retired pointer buffer to call \p scan()
742 const size_t m_nInitialThreadGuardCount; ///< Initial count of guards allocated for ThreadGC
744 details::guard_allocator<> m_GuardPool ; ///< Guard pool
745 details::retired_ptr_pool<> m_RetiredAllocator ; ///< Pool of free retired pointers
746 details::retired_ptr_buffer m_RetiredBuffer ; ///< Retired pointer buffer for liberating
748 internal_stat m_stat ; ///< Internal statistics
749 bool m_bStatEnabled ; ///< Internal Statistics enabled
752 /// Initializes DHP memory manager singleton
754 This member function creates and initializes DHP global object.
755 The function should be called before using CDS data structure based on cds::gc::DHP GC. Usually,
756 this member function is called in the \p main() function. See cds::gc::dhp for example.
757 After calling of this function you may use CDS data structures based on cds::gc::DHP.
760 - \p nLiberateThreshold - \p scan() threshold. When count of retired pointers reaches this value,
761 the \ref dhp_gc_liberate "scan()" member function would be called for freeing retired pointers.
762 If \p nLiberateThreshold <= 1, \p scan() would called after each \ref dhp_gc_retirePtr "retirePtr" call.
763 - \p nInitialThreadGuardCount - initial count of guard allocated for ThreadGC. When a thread
764 is initialized the GC allocates local guard pool for the thread from common guard pool.
765 By perforce the local thread's guard pool is grown automatically from common pool.
766 When the thread terminated its guard pool is backed to common GC's pool.
767 - \p nEpochCount: internally, DHP memory manager uses epoch-based schema to solve
768 ABA problem for internal data. \p nEpochCount specifies the epoch count,
770 i.e. the count of simultaneously working threads that remove the elements
771 of DHP-based concurrent data structure. Default value is 8.
774 static void CDS_STDCALL Construct(
775 size_t nLiberateThreshold = 1024
776 , size_t nInitialThreadGuardCount = 8
777 , size_t nEpochCount = 8
780 /// Destroys DHP memory manager
782 The member function destroys DHP global object. After calling of this function you may \b NOT
783 use CDS data structures based on cds::gc::DHP. Usually, the \p Destruct function is called
784 at the end of your \p main(). See cds::gc::dhp for example.
786 static void CDS_STDCALL Destruct();
788 /// Returns pointer to GarbageCollector instance
790 If DHP GC is not initialized, \p not_initialized exception is thrown
792 static GarbageCollector& instance()
794 if ( m_pManager == nullptr )
795 throw not_initialized();
799 /// Checks if global GC object is constructed and may be used
800 static bool isUsed() CDS_NOEXCEPT
802 return m_pManager != nullptr;
807 /// Internal interface
809 /// Allocates a guard
810 details::guard_data * allocGuard()
812 return m_GuardPool.alloc();
815 /// Frees guard \p g for reusing in future
816 void freeGuard(details::guard_data * pGuard )
818 m_GuardPool.free( pGuard );
821 /// Allocates guard list for a thread.
822 details::guard_data * allocGuardList( size_t nCount )
824 return m_GuardPool.allocList( nCount );
827 /// Frees thread's guard list pointed by \p pList
828 void freeGuardList( details::guard_data * pList )
830 m_GuardPool.freeList( pList );
833 /// Places retired pointer \p and its deleter \p pFunc into thread's array of retired pointer for deferred reclamation
834 /**@anchor dhp_gc_retirePtr
836 template <typename T>
837 void retirePtr( T * p, void (* pFunc)(T *) )
839 retirePtr( retired_ptr( reinterpret_cast<void *>( p ), reinterpret_cast<free_retired_ptr_func>( pFunc ) ) );
842 /// Places retired pointer \p into thread's array of retired pointer for deferred reclamation
843 void retirePtr( retired_ptr const& p )
845 if ( m_RetiredBuffer.push( m_RetiredAllocator.alloc(p)) >= m_nLiberateThreshold.load(atomics::memory_order_relaxed) )
850 /// Liberate function
851 /** @anchor dhp_gc_liberate
852 The main function of Dynamic Hazard Pointer algorithm. It tries to free retired pointers if they are not
853 trapped by any guard.
859 /// Get internal statistics
860 InternalState& getInternalState(InternalState& stat) const
862 return stat = m_stat;
865 /// Checks if internal statistics enabled
866 bool isStatisticsEnabled() const
868 return m_bStatEnabled;
871 /// Enables/disables internal statistics
872 bool enableStatistics( bool bEnable )
874 bool bEnabled = m_bStatEnabled;
875 m_bStatEnabled = bEnable;
880 GarbageCollector( size_t nLiberateThreshold, size_t nInitialThreadGuardCount, size_t nEpochCount );
886 To use Dynamic Hazard Pointer reclamation schema each thread object must be linked with the object of ThreadGC class
887 that interacts with GarbageCollector global object. The linkage is performed by calling \ref cds_threading "cds::threading::Manager::attachThread()"
888 on the start of each thread that uses DHP GC. Before terminating the thread linked to DHP GC it is necessary to call
889 \ref cds_threading "cds::threading::Manager::detachThread()".
891 The ThreadGC object maintains two list:
892 \li Thread guard list: the list of thread-local guards (linked by \p pThreadNext field)
893 \li Free guard list: the list of thread-local free guards (linked by \p pNextFree field)
894 Free guard list is a subset of thread guard list.
898 GarbageCollector& m_gc ; ///< reference to GC singleton
899 details::guard_data * m_pList ; ///< Local list of guards owned by the thread
900 details::guard_data * m_pFree ; ///< The list of free guard from m_pList
903 /// Default constructor
905 : m_gc( GarbageCollector::instance() )
910 /// The object is not copy-constructible
911 ThreadGC( ThreadGC const& ) = delete;
913 /// Dtor calls fini()
919 /// Initialization. Repeat call is available
924 m_pFree = m_gc.allocGuardList( m_gc.m_nInitialThreadGuardCount );
928 /// Finalization. Repeat call is available
932 m_gc.freeGuardList( m_pList );
939 /// Initializes guard \p g
940 void allocGuard( dhp::details::guard& g )
942 assert( m_pList != nullptr );
945 g.m_pGuard = m_pFree;
946 m_pFree = m_pFree->pNextFree.load( atomics::memory_order_relaxed );
949 g.m_pGuard = m_gc.allocGuard();
950 g.m_pGuard->pThreadNext = m_pList;
951 m_pList = g.m_pGuard;
957 void freeGuard( dhp::details::guard& g )
959 assert( m_pList != nullptr );
961 g.m_pGuard->pPost.store( nullptr, atomics::memory_order_relaxed );
962 g.m_pGuard->pNextFree.store( m_pFree, atomics::memory_order_relaxed );
963 m_pFree = g.m_pGuard;
964 g.m_pGuard = nullptr;
968 /// Initializes guard array \p arr
969 template <size_t Count>
970 void allocGuard( GuardArray<Count>& arr )
972 assert( m_pList != nullptr );
975 while ( m_pFree && nCount < Count ) {
976 arr[nCount].set_guard( m_pFree );
977 m_pFree = m_pFree->pNextFree.load(atomics::memory_order_relaxed);
981 while ( nCount < Count ) {
982 details::guard& g = arr[nCount++];
983 g.set_guard( m_gc.allocGuard() );
984 g.get_guard()->pThreadNext = m_pList;
985 m_pList = g.get_guard();
989 /// Frees guard array \p arr
990 template <size_t Count>
991 void freeGuard( GuardArray<Count>& arr )
993 assert( m_pList != nullptr );
995 details::guard_data * pGuard;
996 for ( size_t i = 0; i < Count - 1; ++i ) {
997 pGuard = arr[i].get_guard();
998 pGuard->pPost.store( nullptr, atomics::memory_order_relaxed );
999 pGuard->pNextFree.store( arr[i+1].get_guard(), atomics::memory_order_relaxed );
1001 pGuard = arr[Count-1].get_guard();
1002 pGuard->pPost.store( nullptr, atomics::memory_order_relaxed );
1003 pGuard->pNextFree.store( m_pFree, atomics::memory_order_relaxed );
1004 m_pFree = arr[0].get_guard();
1007 /// Places retired pointer \p and its deleter \p pFunc into list of retired pointer for deferred reclamation
1008 template <typename T>
1009 void retirePtr( T * p, void (* pFunc)(T *) )
1011 m_gc.retirePtr( p, pFunc );
1014 /// Run retiring cycle
1021 }} // namespace cds::gc
1024 #if CDS_COMPILER == CDS_COMPILER_MSVC
1025 # pragma warning(pop)
1028 #endif // #ifndef CDSLIB_GC_DETAILS_DHP_H