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 )
398 for (unsigned int i = 0; i <= m_nEpochBitmask; ++i )
399 m_pEpochFree[i].store( nullptr, atomics::memory_order_relaxed );
408 for ( block * pBlock = m_pBlockListHead.load(atomics::memory_order_relaxed); pBlock; pBlock = p ) {
409 p = pBlock->pNext.load( atomics::memory_order_relaxed );
413 epoch_array_alloc().Delete( m_pEpochFree, m_nEpochBitmask + 1 );
416 /// Increments current epoch
417 void inc_epoch() CDS_NOEXCEPT
419 m_nCurEpoch.fetch_add( 1, atomics::memory_order_acq_rel );
422 /// Allocates the new retired pointer
423 retired_ptr_node& alloc()
428 pItem = m_pEpochFree[ nEpoch = current_epoch() ].load(atomics::memory_order_acquire);
431 if ( m_pEpochFree[nEpoch].compare_exchange_weak( pItem,
432 pItem->m_pNextFree.load(atomics::memory_order_acquire),
433 atomics::memory_order_acquire, atomics::memory_order_relaxed ))
439 // Epoch free list is empty
440 // Alloc from global free list
442 pItem = m_pGlobalFreeHead.load( atomics::memory_order_relaxed );
448 // pItem is changed by compare_exchange_weak
449 } while ( !m_pGlobalFreeHead.compare_exchange_weak( pItem,
450 pItem->m_pNextFree.load(atomics::memory_order_acquire),
451 atomics::memory_order_acquire, atomics::memory_order_relaxed ));
454 CDS_STRICT_DO( pItem->m_pNextFree.store( nullptr, atomics::memory_order_relaxed ));
458 /// Allocates and initializes new retired pointer
459 retired_ptr_node& alloc( const retired_ptr& p )
461 retired_ptr_node& node = alloc();
466 /// Places the list [pHead, pTail] of retired pointers to pool (frees retired pointers)
468 The list is linked on the m_pNextFree field
470 void free_range( retired_ptr_node * pHead, retired_ptr_node * pTail ) CDS_NOEXCEPT
472 assert( pHead != nullptr );
473 assert( pTail != nullptr );
478 pCurHead = m_pEpochFree[nEpoch = next_epoch()].load(atomics::memory_order_acquire);
479 pTail->m_pNextFree.store( pCurHead, atomics::memory_order_release );
480 } while ( !m_pEpochFree[nEpoch].compare_exchange_weak( pCurHead, pHead, atomics::memory_order_release, atomics::memory_order_relaxed ));
484 /// Uninitialized guard
487 friend class dhp::ThreadGC;
489 details::guard_data * m_pGuard ; ///< Pointer to guard data
492 /// Initialize empty guard.
493 CDS_CONSTEXPR guard() CDS_NOEXCEPT
494 : m_pGuard( nullptr )
497 /// Copy-ctor is disabled
498 guard( guard const& ) = delete;
500 /// Move-ctor is disabled
501 guard( guard&& ) = delete;
503 /// Object destructor, does nothing
504 ~guard() CDS_NOEXCEPT
507 /// Get current guarded pointer
508 void * get( atomics::memory_order order = atomics::memory_order_acquire ) const CDS_NOEXCEPT
510 assert( m_pGuard != nullptr );
511 return m_pGuard->pPost.load( order );
514 /// Guards pointer \p p
515 void set( void * p, atomics::memory_order order = atomics::memory_order_release ) CDS_NOEXCEPT
517 assert( m_pGuard != nullptr );
518 m_pGuard->pPost.store( p, order );
522 void clear( atomics::memory_order order = atomics::memory_order_relaxed ) CDS_NOEXCEPT
524 assert( m_pGuard != nullptr );
525 m_pGuard->pPost.store( nullptr, order );
528 /// Guards pointer \p p
529 template <typename T>
530 T * operator =(T * p) CDS_NOEXCEPT
532 set( reinterpret_cast<void *>( const_cast<T *>(p) ));
536 std::nullptr_t operator=(std::nullptr_t) CDS_NOEXCEPT
542 public: // for ThreadGC.
544 GCC cannot compile code for template versions of ThreadGC::allocGuard/freeGuard,
545 the compiler produces error: 'cds::gc::dhp::details::guard_data* cds::gc::dhp::details::guard::m_pGuard' is protected
546 despite the fact that ThreadGC is declared as friend for guard class.
547 Therefore, we have to add set_guard/get_guard public functions
550 void set_guard( details::guard_data * pGuard ) CDS_NOEXCEPT
552 assert( m_pGuard == nullptr );
556 /// Get current guard data
557 details::guard_data * get_guard() CDS_NOEXCEPT
561 /// Get current guard data
562 details::guard_data * get_guard() const CDS_NOEXCEPT
567 details::guard_data * release_guard() CDS_NOEXCEPT
569 details::guard_data * p = m_pGuard;
574 bool is_initialized() const
576 return m_pGuard != nullptr;
580 } // namespace details
584 This class represents auto guard: ctor allocates a guard from guard pool,
585 dtor returns the guard back to the pool of free guard.
587 class Guard: public details::guard
589 typedef details::guard base_class;
590 friend class ThreadGC;
592 /// Allocates a guard from \p gc GC. \p gc must be ThreadGC object of current thread
593 Guard(); // inline in dhp_impl.h
595 /// Returns guard allocated back to pool of free guards
596 ~Guard(); // inline in dhp_impl.h
598 /// Guards pointer \p p
599 template <typename T>
600 T * operator =(T * p) CDS_NOEXCEPT
602 return base_class::operator =<T>( p );
605 std::nullptr_t operator=(std::nullptr_t) CDS_NOEXCEPT
607 return base_class::operator =(nullptr);
613 This class represents array of auto guards: ctor allocates \p Count guards from guard pool,
614 dtor returns the guards allocated back to the pool.
616 template <size_t Count>
619 details::guard m_arr[Count] ; ///< array of guard
620 const static size_t c_nCapacity = Count ; ///< Array capacity (equal to \p Count template parameter)
623 /// Rebind array for other size \p OtherCount
624 template <size_t OtherCount>
626 typedef GuardArray<OtherCount> other ; ///< rebinding result
630 /// Allocates array of guards from \p gc which must be the ThreadGC object of current thread
631 GuardArray(); // inline in dhp_impl.h
633 /// The object is not copy-constructible
634 GuardArray( GuardArray const& ) = delete;
636 /// The object is not move-constructible
637 GuardArray( GuardArray&& ) = delete;
639 /// Returns guards allocated back to pool
640 ~GuardArray(); // inline in dh_impl.h
642 /// Returns the capacity of array
643 CDS_CONSTEXPR size_t capacity() const CDS_NOEXCEPT
648 /// Returns reference to the guard of index \p nIndex (0 <= \p nIndex < \p Count)
649 details::guard& operator []( size_t nIndex ) CDS_NOEXCEPT
651 assert( nIndex < capacity() );
652 return m_arr[nIndex];
655 /// Returns reference to the guard of index \p nIndex (0 <= \p nIndex < \p Count) [const version]
656 const details::guard& operator []( size_t nIndex ) const CDS_NOEXCEPT
658 assert( nIndex < capacity() );
659 return m_arr[nIndex];
662 /// Set the guard \p nIndex. 0 <= \p nIndex < \p Count
663 template <typename T>
664 void set( size_t nIndex, T * p ) CDS_NOEXCEPT
666 assert( nIndex < capacity() );
667 m_arr[nIndex].set( p );
670 /// Clears (sets to \p nullptr) the guard \p nIndex
671 void clear( size_t nIndex ) CDS_NOEXCEPT
673 assert( nIndex < capacity() );
674 m_arr[nIndex].clear();
677 /// Clears all guards in the array
678 void clearAll() CDS_NOEXCEPT
680 for ( size_t i = 0; i < capacity(); ++i )
685 /// Memory manager (Garbage collector)
686 class CDS_EXPORT_API GarbageCollector
689 friend class ThreadGC;
691 /// Internal GC statistics
694 atomics::atomic<size_t> m_nGuardCount ; ///< Total guard count
695 atomics::atomic<size_t> m_nFreeGuardCount ; ///< Count of free guard
699 , m_nFreeGuardCount(0)
704 /// Exception "No GarbageCollector object is created"
705 class not_initialized : public std::runtime_error
710 : std::runtime_error( "Global DHP GarbageCollector is not initialized" )
715 /// Internal GC statistics
718 size_t m_nGuardCount ; ///< Total guard count
719 size_t m_nFreeGuardCount ; ///< Count of free guard
724 , m_nFreeGuardCount(0)
727 InternalState& operator =( internal_stat const& s )
729 m_nGuardCount = s.m_nGuardCount.load(atomics::memory_order_relaxed);
730 m_nFreeGuardCount = s.m_nFreeGuardCount.load(atomics::memory_order_relaxed);
738 static GarbageCollector * m_pManager ; ///< GC global instance
740 atomics::atomic<size_t> m_nLiberateThreshold; ///< Max size of retired pointer buffer to call \p scan()
741 const size_t m_nInitialThreadGuardCount; ///< Initial count of guards allocated for ThreadGC
743 details::guard_allocator<> m_GuardPool ; ///< Guard pool
744 details::retired_ptr_pool<> m_RetiredAllocator ; ///< Pool of free retired pointers
745 details::retired_ptr_buffer m_RetiredBuffer ; ///< Retired pointer buffer for liberating
747 internal_stat m_stat ; ///< Internal statistics
748 bool m_bStatEnabled ; ///< Internal Statistics enabled
751 /// Initializes DHP memory manager singleton
753 This member function creates and initializes DHP global object.
754 The function should be called before using CDS data structure based on cds::gc::DHP GC. Usually,
755 this member function is called in the \p main() function. See cds::gc::dhp for example.
756 After calling of this function you may use CDS data structures based on cds::gc::DHP.
759 - \p nLiberateThreshold - \p scan() threshold. When count of retired pointers reaches this value,
760 the \ref dhp_gc_liberate "scan()" member function would be called for freeing retired pointers.
761 If \p nLiberateThreshold <= 1, \p scan() would called after each \ref dhp_gc_retirePtr "retirePtr" call.
762 - \p nInitialThreadGuardCount - initial count of guard allocated for ThreadGC. When a thread
763 is initialized the GC allocates local guard pool for the thread from common guard pool.
764 By perforce the local thread's guard pool is grown automatically from common pool.
765 When the thread terminated its guard pool is backed to common GC's pool.
766 - \p nEpochCount: internally, DHP memory manager uses epoch-based schema to solve
767 ABA problem for internal data. \p nEpochCount specifies the epoch count,
768 i.e. the count of simultaneously working threads that remove the elements
769 of DHP-based concurrent data structure. Default value is 8.
772 static void CDS_STDCALL Construct(
773 size_t nLiberateThreshold = 1024
774 , size_t nInitialThreadGuardCount = 8
775 , size_t nEpochCount = 8
778 /// Destroys DHP memory manager
780 The member function destroys DHP global object. After calling of this function you may \b NOT
781 use CDS data structures based on cds::gc::DHP. Usually, the \p Destruct function is called
782 at the end of your \p main(). See cds::gc::dhp for example.
784 static void CDS_STDCALL Destruct();
786 /// Returns pointer to GarbageCollector instance
788 If DHP GC is not initialized, \p not_initialized exception is thrown
790 static GarbageCollector& instance()
792 if ( m_pManager == nullptr )
793 throw not_initialized();
797 /// Checks if global GC object is constructed and may be used
798 static bool isUsed() CDS_NOEXCEPT
800 return m_pManager != nullptr;
805 /// Internal interface
807 /// Allocates a guard
808 details::guard_data * allocGuard()
810 return m_GuardPool.alloc();
813 /// Frees guard \p g for reusing in future
814 void freeGuard(details::guard_data * pGuard )
816 m_GuardPool.free( pGuard );
819 /// Allocates guard list for a thread.
820 details::guard_data * allocGuardList( size_t nCount )
822 return m_GuardPool.allocList( nCount );
825 /// Frees thread's guard list pointed by \p pList
826 void freeGuardList( details::guard_data * pList )
828 m_GuardPool.freeList( pList );
831 /// Places retired pointer \p and its deleter \p pFunc into thread's array of retired pointer for deferred reclamation
832 /**@anchor dhp_gc_retirePtr
834 template <typename T>
835 void retirePtr( T * p, void (* pFunc)(T *) )
837 retirePtr( retired_ptr( reinterpret_cast<void *>( p ), reinterpret_cast<free_retired_ptr_func>( pFunc ) ) );
840 /// Places retired pointer \p into thread's array of retired pointer for deferred reclamation
841 void retirePtr( retired_ptr const& p )
843 if ( m_RetiredBuffer.push( m_RetiredAllocator.alloc(p)) >= m_nLiberateThreshold.load(atomics::memory_order_relaxed) )
848 /// Liberate function
849 /** @anchor dhp_gc_liberate
850 The main function of Dynamic Hazard Pointer algorithm. It tries to free retired pointers if they are not
851 trapped by any guard.
857 /// Get internal statistics
858 InternalState& getInternalState(InternalState& stat) const
860 return stat = m_stat;
863 /// Checks if internal statistics enabled
864 bool isStatisticsEnabled() const
866 return m_bStatEnabled;
869 /// Enables/disables internal statistics
870 bool enableStatistics( bool bEnable )
872 bool bEnabled = m_bStatEnabled;
873 m_bStatEnabled = bEnable;
878 GarbageCollector( size_t nLiberateThreshold, size_t nInitialThreadGuardCount, size_t nEpochCount );
884 To use Dynamic Hazard Pointer reclamation schema each thread object must be linked with the object of ThreadGC class
885 that interacts with GarbageCollector global object. The linkage is performed by calling \ref cds_threading "cds::threading::Manager::attachThread()"
886 on the start of each thread that uses DHP GC. Before terminating the thread linked to DHP GC it is necessary to call
887 \ref cds_threading "cds::threading::Manager::detachThread()".
889 The ThreadGC object maintains two list:
890 \li Thread guard list: the list of thread-local guards (linked by \p pThreadNext field)
891 \li Free guard list: the list of thread-local free guards (linked by \p pNextFree field)
892 Free guard list is a subset of thread guard list.
896 GarbageCollector& m_gc ; ///< reference to GC singleton
897 details::guard_data * m_pList ; ///< Local list of guards owned by the thread
898 details::guard_data * m_pFree ; ///< The list of free guard from m_pList
901 /// Default constructor
903 : m_gc( GarbageCollector::instance() )
908 /// The object is not copy-constructible
909 ThreadGC( ThreadGC const& ) = delete;
911 /// Dtor calls fini()
917 /// Initialization. Repeat call is available
922 m_pFree = m_gc.allocGuardList( m_gc.m_nInitialThreadGuardCount );
926 /// Finalization. Repeat call is available
930 m_gc.freeGuardList( m_pList );
937 /// Initializes guard \p g
938 void allocGuard( dhp::details::guard& g )
940 assert( m_pList != nullptr );
943 g.m_pGuard = m_pFree;
944 m_pFree = m_pFree->pNextFree.load( atomics::memory_order_relaxed );
947 g.m_pGuard = m_gc.allocGuard();
948 g.m_pGuard->pThreadNext = m_pList;
949 m_pList = g.m_pGuard;
955 void freeGuard( dhp::details::guard& g )
957 assert( m_pList != nullptr );
959 g.m_pGuard->pPost.store( nullptr, atomics::memory_order_relaxed );
960 g.m_pGuard->pNextFree.store( m_pFree, atomics::memory_order_relaxed );
961 m_pFree = g.m_pGuard;
962 g.m_pGuard = nullptr;
966 /// Initializes guard array \p arr
967 template <size_t Count>
968 void allocGuard( GuardArray<Count>& arr )
970 assert( m_pList != nullptr );
973 while ( m_pFree && nCount < Count ) {
974 arr[nCount].set_guard( m_pFree );
975 m_pFree = m_pFree->pNextFree.load(atomics::memory_order_relaxed);
979 while ( nCount < Count ) {
980 details::guard& g = arr[nCount++];
981 g.set_guard( m_gc.allocGuard() );
982 g.get_guard()->pThreadNext = m_pList;
983 m_pList = g.get_guard();
987 /// Frees guard array \p arr
988 template <size_t Count>
989 void freeGuard( GuardArray<Count>& arr )
991 assert( m_pList != nullptr );
993 details::guard_data * pGuard;
994 for ( size_t i = 0; i < Count - 1; ++i ) {
995 pGuard = arr[i].get_guard();
996 pGuard->pPost.store( nullptr, atomics::memory_order_relaxed );
997 pGuard->pNextFree.store( arr[i+1].get_guard(), atomics::memory_order_relaxed );
999 pGuard = arr[Count-1].get_guard();
1000 pGuard->pPost.store( nullptr, atomics::memory_order_relaxed );
1001 pGuard->pNextFree.store( m_pFree, atomics::memory_order_relaxed );
1002 m_pFree = arr[0].get_guard();
1005 /// Places retired pointer \p and its deleter \p pFunc into list of retired pointer for deferred reclamation
1006 template <typename T>
1007 void retirePtr( T * p, void (* pFunc)(T *) )
1009 m_gc.retirePtr( p, pFunc );
1012 /// Run retiring cycle
1019 }} // namespace cds::gc
1022 #if CDS_COMPILER == CDS_COMPILER_MSVC
1023 # pragma warning(pop)
1026 #endif // #ifndef CDSLIB_GC_DETAILS_DHP_H