3 #ifndef __CDS_GC_DETAILS_DHP_H
4 #define __CDS_GC_DETAILS_DHP_H
6 #include <mutex> // unique_lock
7 #include <cds/algo/atomic.h>
8 #include <cds/gc/details/retired_ptr.h>
9 #include <cds/details/aligned_allocator.h>
10 #include <cds/details/allocator.h>
11 #include <cds/lock/spinlock.h>
13 #if CDS_COMPILER == CDS_COMPILER_MSVC
14 # pragma warning(push)
15 # pragma warning(disable:4251) // C4251: 'identifier' : class 'type' needs to have dll-interface to be used by clients of class 'type2'
19 namespace cds { namespace gc {
21 /// Dynamic Hazard Pointer reclamation schema
23 The cds::gc::dhp namespace and its members are internal representation of the GC and should not be used directly.
24 Use cds::gc::DHP class in your code.
26 Dynamic Hazard Pointer (DHP) garbage collector is a singleton. The main user-level part of DHP schema is
27 GC class and its nested classes. Before use any DHP-related class you must initialize DHP garbage collector
28 by contructing cds::gc::DHP object in beginning of your main().
29 See cds::gc::DHP class for explanation.
31 \par Implementation issues
32 The global list of free guards (\p cds::gc::dhp::details::guard_allocator) is protected by a spin-lock (i.e. serialized).
33 It seems that this solution should not introduce significant performance bottleneck, because each thread has its own set
34 of guards allocated from the global list of free guards and the access to the global list is occurred only when
35 all thread's guard is busy. In this case the thread allocates a next block of guards from the global list.
36 Guards allocated for the thread is push back to the global list only when the thread terminates.
40 // Forward declarations
42 template <size_t Count> class GuardArray;
44 class GarbageCollector;
46 /// Retired pointer type
47 typedef cds::gc::details::retired_ptr retired_ptr;
49 using cds::gc::details::free_retired_ptr_func;
51 /// Details of Dynamic Hazard Pointer algorithm
54 // Forward declaration
57 /// Retired pointer buffer node
58 struct retired_ptr_node {
59 retired_ptr m_ptr ; ///< retired pointer
60 retired_ptr_node * m_pNext ; ///< next retired pointer in buffer
61 retired_ptr_node * m_pNextFree ; ///< next item in free list of retired_ptr_node
64 /// Internal guard representation
66 typedef void * guarded_ptr; ///< type of value guarded
68 atomics::atomic<guarded_ptr> pPost; ///< pointer guarded
69 atomics::atomic<guard_data *> pGlobalNext; ///< next item of global list of allocated guards
70 atomics::atomic<guard_data *> pNextFree; ///< pointer to the next item in global or thread-local free-list
72 guard_data * pThreadNext; ///< next item of thread's local list of guards
74 guard_data() CDS_NOEXCEPT
76 , pGlobalNext( nullptr )
77 , pNextFree( nullptr )
78 , pThreadNext( nullptr )
81 void init() CDS_NOEXCEPT
83 pPost.store( nullptr, atomics::memory_order_relaxed );
86 /// Checks if the guard is free, that is, it does not contain any pointer guarded
87 bool isFree() const CDS_NOEXCEPT
89 return pPost.load( atomics::memory_order_acquire ) == nullptr;
94 template <class Alloc = CDS_DEFAULT_ALLOCATOR>
97 cds::details::Allocator<details::guard_data> m_GuardAllocator ; ///< guard allocator
99 atomics::atomic<guard_data *> m_GuardList ; ///< Head of allocated guard list (linked by guard_data::pGlobalNext field)
100 atomics::atomic<guard_data *> m_FreeGuardList ; ///< Head of free guard list (linked by guard_data::pNextFree field)
101 SpinLock m_freeListLock ; ///< Access to m_FreeGuardList
104 Unfortunately, access to the list of free guard is lock-based.
105 Lock-free manipulations with guard free-list are ABA-prone.
106 TODO: working with m_FreeGuardList in lock-free manner.
110 /// Allocates new guard from the heap. The function uses aligned allocator
111 guard_data * allocNew()
113 //TODO: the allocator should make block allocation
115 details::guard_data * pGuard = m_GuardAllocator.New();
117 // Link guard to the list
118 // m_GuardList is an accumulating list and it cannot support concurrent deletion,
119 // so, ABA problem is impossible for it
120 details::guard_data * pHead = m_GuardList.load( atomics::memory_order_acquire );
122 pGuard->pGlobalNext.store( pHead, atomics::memory_order_relaxed );
123 // pHead is changed by compare_exchange_weak
124 } while ( !m_GuardList.compare_exchange_weak( pHead, pGuard, atomics::memory_order_release, atomics::memory_order_relaxed ));
132 guard_allocator() CDS_NOEXCEPT
133 : m_GuardList( nullptr )
134 , m_FreeGuardList( nullptr )
141 for ( guard_data * pData = m_GuardList.load( atomics::memory_order_relaxed ); pData != nullptr; pData = pNext ) {
142 pNext = pData->pGlobalNext.load( atomics::memory_order_relaxed );
143 m_GuardAllocator.Delete( pData );
147 /// Allocates a guard from free list or from heap if free list is empty
150 // Try to pop a guard from free-list
151 details::guard_data * pGuard;
154 std::unique_lock<SpinLock> al( m_freeListLock );
155 pGuard = m_FreeGuardList.load(atomics::memory_order_relaxed);
157 m_FreeGuardList.store( pGuard->pNextFree.load(atomics::memory_order_relaxed), atomics::memory_order_relaxed );
166 /// Frees guard \p pGuard
168 The function places the guard \p pGuard into free-list
170 void free( guard_data * pGuard ) CDS_NOEXCEPT
172 pGuard->pPost.store( nullptr, atomics::memory_order_relaxed );
174 std::unique_lock<SpinLock> al( m_freeListLock );
175 pGuard->pNextFree.store( m_FreeGuardList.load(atomics::memory_order_relaxed), atomics::memory_order_relaxed );
176 m_FreeGuardList.store( pGuard, atomics::memory_order_relaxed );
179 /// Allocates list of guard
181 The list returned is linked by guard's \p pThreadNext and \p pNextFree fields.
183 cds::gc::dhp::ThreadGC supporting method
185 guard_data * allocList( size_t nCount )
187 assert( nCount != 0 );
195 // The guard list allocated is private for the thread,
196 // so, we can use relaxed memory order
198 guard_data * p = alloc();
199 pLast->pNextFree.store( pLast->pThreadNext = p, atomics::memory_order_relaxed );
203 pLast->pNextFree.store( pLast->pThreadNext = nullptr, atomics::memory_order_relaxed );
208 /// Frees list of guards
210 The list \p pList is linked by guard's \p pThreadNext field.
212 cds::gc::dhp::ThreadGC supporting method
214 void freeList( guard_data * pList ) CDS_NOEXCEPT
216 assert( pList != nullptr );
218 guard_data * pLast = pList;
219 while ( pLast->pThreadNext ) {
220 pLast->pPost.store( nullptr, atomics::memory_order_relaxed );
222 pLast->pNextFree.store( p = pLast->pThreadNext, atomics::memory_order_relaxed );
226 std::unique_lock<SpinLock> al( m_freeListLock );
227 pLast->pNextFree.store( m_FreeGuardList.load(atomics::memory_order_relaxed), atomics::memory_order_relaxed );
228 m_FreeGuardList.store( pList, atomics::memory_order_relaxed );
231 /// Returns the list's head of guards allocated
232 guard_data * begin() CDS_NOEXCEPT
234 return m_GuardList.load(atomics::memory_order_acquire);
238 /// Retired pointer buffer
240 The buffer of retired nodes ready for liberating.
241 When size of buffer exceeds a threshold the GC calls \p scan() procedure to free
244 class retired_ptr_buffer
246 atomics::atomic<retired_ptr_node *> m_pHead ; ///< head of buffer
247 atomics::atomic<size_t> m_nItemCount; ///< buffer's item count
250 retired_ptr_buffer() CDS_NOEXCEPT
255 ~retired_ptr_buffer() CDS_NOEXCEPT
257 assert( m_pHead.load( atomics::memory_order_relaxed ) == nullptr );
260 /// Pushes new node into the buffer. Returns current buffer size
261 size_t push( retired_ptr_node& node ) CDS_NOEXCEPT
263 retired_ptr_node * pHead = m_pHead.load(atomics::memory_order_acquire);
265 node.m_pNext = pHead;
266 // pHead is changed by compare_exchange_weak
267 } while ( !m_pHead.compare_exchange_weak( pHead, &node, atomics::memory_order_release, atomics::memory_order_relaxed ));
269 return m_nItemCount.fetch_add( 1, atomics::memory_order_relaxed ) + 1;
272 /// Pushes [pFirst, pLast] list linked by pNext field.
273 size_t push_list( retired_ptr_node* pFirst, retired_ptr_node* pLast, size_t nSize )
278 retired_ptr_node * pHead = m_pHead.load( atomics::memory_order_acquire );
280 pLast->m_pNext = pHead;
281 // pHead is changed by compare_exchange_weak
282 } while ( !m_pHead.compare_exchange_weak( pHead, pFirst, atomics::memory_order_release, atomics::memory_order_relaxed ) );
284 return m_nItemCount.fetch_add( nSize, atomics::memory_order_relaxed ) + 1;
287 /// Result of \ref dhp_gc_privatve "privatize" function.
289 The \p privatize function returns retired node list as \p first and the size of that list as \p second.
291 typedef std::pair<retired_ptr_node *, size_t> privatize_result;
293 /// Gets current list of retired pointer and clears the list
294 /**@anchor dhp_gc_privatve
296 privatize_result privatize() CDS_NOEXCEPT
298 privatize_result res;
299 res.first = m_pHead.exchange( nullptr, atomics::memory_order_acq_rel );
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 );
307 /// Returns current size of buffer (approximate)
308 size_t size() const CDS_NOEXCEPT
310 return m_nItemCount.load(atomics::memory_order_relaxed);
314 /// Pool of retired pointers
316 The class acts as an allocator of retired node.
317 Retired pointers are linked in the lock-free list.
319 template <class Alloc = CDS_DEFAULT_ALLOCATOR>
320 class retired_ptr_pool {
322 typedef retired_ptr_node item;
324 /// Count of items in block
325 static const size_t m_nItemPerBlock = 1024 / sizeof(item) - 1;
329 block * pNext; ///< next block
330 item items[m_nItemPerBlock]; ///< item array
333 atomics::atomic<block *> m_pBlockListHead; ///< head of of allocated block list
335 // To solve ABA problem we use epoch-based approach
336 static const unsigned int c_nEpochCount = 4; ///< Max epoch count
337 atomics::atomic<unsigned int> m_nCurEpoch; ///< Current epoch
338 atomics::atomic<item *> m_pEpochFree[c_nEpochCount]; ///< List of free item per epoch
339 atomics::atomic<item *> m_pGlobalFreeHead; ///< Head of unallocated item list
341 cds::details::Allocator< block, Alloc > m_BlockAllocator ; ///< block allocator
346 // allocate new block
347 block * pNew = m_BlockAllocator.New();
349 // link items within the block
350 item * pLastItem = pNew->items + m_nItemPerBlock - 1;
351 for ( item * pItem = pNew->items; pItem != pLastItem; ++pItem ) {
352 pItem->m_pNextFree = pItem + 1;
353 CDS_STRICT_DO( pItem->m_pNext = nullptr );
356 // links new block to the block list
358 block * pHead = m_pBlockListHead.load(atomics::memory_order_acquire);
361 // pHead is changed by compare_exchange_weak
362 } while ( !m_pBlockListHead.compare_exchange_weak( pHead, pNew, atomics::memory_order_release, atomics::memory_order_relaxed ));
365 // links block's items to the free list
367 item * pHead = m_pGlobalFreeHead.load(atomics::memory_order_acquire);
369 pLastItem->m_pNextFree = pHead;
370 // pHead is changed by compare_exchange_weak
371 } while ( !m_pGlobalFreeHead.compare_exchange_weak( pHead, pNew->items, atomics::memory_order_release, atomics::memory_order_relaxed ));
375 unsigned int current_epoch() const CDS_NOEXCEPT
377 return m_nCurEpoch.load(atomics::memory_order_acquire) & (c_nEpochCount - 1);
380 unsigned int next_epoch() const CDS_NOEXCEPT
382 return (m_nCurEpoch.load(atomics::memory_order_acquire) - 1) & (c_nEpochCount - 1);
387 : m_pBlockListHead( nullptr )
389 , m_pGlobalFreeHead( nullptr )
391 for (unsigned int i = 0; i < sizeof(m_pEpochFree)/sizeof(m_pEpochFree[0]); ++i )
392 m_pEpochFree[i].store( nullptr, atomics::memory_order_relaxed );
400 for ( block * pBlock = m_pBlockListHead.load(atomics::memory_order_relaxed); pBlock; pBlock = p ) {
402 m_BlockAllocator.Delete( pBlock );
406 /// Increments current epoch
407 void inc_epoch() CDS_NOEXCEPT
409 m_nCurEpoch.fetch_add( 1, atomics::memory_order_acq_rel );
412 /// Allocates the new retired pointer
413 retired_ptr_node& alloc()
418 pItem = m_pEpochFree[ nEpoch = current_epoch() ].load(atomics::memory_order_acquire);
421 if ( m_pEpochFree[nEpoch].compare_exchange_weak( pItem, pItem->m_pNextFree, atomics::memory_order_release, atomics::memory_order_relaxed ))
425 // Epoch free list is empty
426 // Alloc from global free list
428 pItem = m_pGlobalFreeHead.load( atomics::memory_order_acquire );
434 // pItem is changed by compare_exchange_weak
435 } while ( !m_pGlobalFreeHead.compare_exchange_weak( pItem, pItem->m_pNextFree, atomics::memory_order_release, atomics::memory_order_relaxed ));
438 CDS_STRICT_DO( pItem->m_pNextFree = nullptr );
442 /// Allocates and initializes new retired pointer
443 retired_ptr_node& alloc( const retired_ptr& p )
445 retired_ptr_node& node = alloc();
450 /// Places the list [pHead, pTail] of retired pointers to pool (frees retired pointers)
452 The list is linked on the m_pNextFree field
454 void free_range( retired_ptr_node * pHead, retired_ptr_node * pTail ) CDS_NOEXCEPT
456 assert( pHead != nullptr );
457 assert( pTail != nullptr );
462 pCurHead = m_pEpochFree[nEpoch = next_epoch()].load(atomics::memory_order_acquire);
463 pTail->m_pNextFree = pCurHead;
464 } while ( !m_pEpochFree[nEpoch].compare_exchange_weak( pCurHead, pHead, atomics::memory_order_release, atomics::memory_order_relaxed ));
468 /// Uninitialized guard
471 friend class dhp::ThreadGC;
473 details::guard_data * m_pGuard ; ///< Pointer to guard data
476 /// Initialize empty guard.
477 CDS_CONSTEXPR guard() CDS_NOEXCEPT
478 : m_pGuard( nullptr )
481 /// Ñopy-ctor is disabled
482 guard( guard const& ) = delete;
484 /// Move-ctor is disabled
485 guard( guard&& ) = delete;
487 /// Object destructor, does nothing
488 ~guard() CDS_NOEXCEPT
491 /// Get current guarded pointer
492 void * get( atomics::memory_order order = atomics::memory_order_acquire ) const CDS_NOEXCEPT
494 assert( m_pGuard != nullptr );
495 return m_pGuard->pPost.load( order );
498 /// Guards pointer \p p
499 void set( void * p, atomics::memory_order order = atomics::memory_order_release ) CDS_NOEXCEPT
501 assert( m_pGuard != nullptr );
502 m_pGuard->pPost.store( p, order );
506 void clear( atomics::memory_order order = atomics::memory_order_relaxed ) CDS_NOEXCEPT
508 assert( m_pGuard != nullptr );
509 m_pGuard->pPost.store( nullptr, order );
512 /// Guards pointer \p p
513 template <typename T>
514 T * operator =(T * p) CDS_NOEXCEPT
516 set( reinterpret_cast<void *>( const_cast<T *>(p) ));
520 std::nullptr_t operator=(std::nullptr_t) CDS_NOEXCEPT
526 public: // for ThreadGC.
528 GCC cannot compile code for template versions of ThreasGC::allocGuard/freeGuard,
529 the compiler produces error:
\91cds::gc::dhp::details::guard_data* cds::gc::dhp::details::guard::m_pGuard
\92 is protected
530 despite the fact that ThreadGC is declared as friend for guard class.
531 Therefore, we have to add set_guard/get_guard public functions
534 void set_guard( details::guard_data * pGuard ) CDS_NOEXCEPT
536 assert( m_pGuard == nullptr );
540 /// Get current guard data
541 details::guard_data * get_guard() CDS_NOEXCEPT
545 /// Get current guard data
546 details::guard_data * get_guard() const CDS_NOEXCEPT
551 details::guard_data * release_guard() CDS_NOEXCEPT
553 details::guard_data * p = m_pGuard;
558 bool is_initialized() const
560 return m_pGuard != nullptr;
564 } // namespace details
568 This class represents auto guard: ctor allocates a guard from guard pool,
569 dtor returns the guard back to the pool of free guard.
571 class Guard: public details::guard
573 typedef details::guard base_class;
574 friend class ThreadGC;
576 /// Allocates a guard from \p gc GC. \p gc must be ThreadGC object of current thread
577 Guard(); // inline in dhp_impl.h
579 /// Returns guard allocated back to pool of free guards
580 ~Guard(); // inline in dhp_impl.h
582 /// Guards pointer \p p
583 template <typename T>
584 T * operator =(T * p) CDS_NOEXCEPT
586 return base_class::operator =<T>( p );
589 std::nullptr_t operator=(std::nullptr_t) CDS_NOEXCEPT
591 return base_class::operator =(nullptr);
597 This class represents array of auto guards: ctor allocates \p Count guards from guard pool,
598 dtor returns the guards allocated back to the pool.
600 template <size_t Count>
603 details::guard m_arr[Count] ; ///< array of guard
604 const static size_t c_nCapacity = Count ; ///< Array capacity (equal to \p Count template parameter)
607 /// Rebind array for other size \p OtherCount
608 template <size_t OtherCount>
610 typedef GuardArray<OtherCount> other ; ///< rebinding result
614 /// Allocates array of guards from \p gc which must be the ThreadGC object of current thread
615 GuardArray(); // inline in dhp_impl.h
617 /// The object is not copy-constructible
618 GuardArray( GuardArray const& ) = delete;
620 /// The object is not move-constructible
621 GuardArray( GuardArray&& ) = delete;
623 /// Returns guards allocated back to pool
624 ~GuardArray(); // inline in dh_impl.h
626 /// Returns the capacity of array
627 CDS_CONSTEXPR size_t capacity() const CDS_NOEXCEPT
632 /// Returns reference to the guard of index \p nIndex (0 <= \p nIndex < \p Count)
633 details::guard& operator []( size_t nIndex ) CDS_NOEXCEPT
635 assert( nIndex < capacity() );
636 return m_arr[nIndex];
639 /// Returns reference to the guard of index \p nIndex (0 <= \p nIndex < \p Count) [const version]
640 const details::guard& operator []( size_t nIndex ) const CDS_NOEXCEPT
642 assert( nIndex < capacity() );
643 return m_arr[nIndex];
646 /// Set the guard \p nIndex. 0 <= \p nIndex < \p Count
647 template <typename T>
648 void set( size_t nIndex, T * p ) CDS_NOEXCEPT
650 assert( nIndex < capacity() );
651 m_arr[nIndex].set( p );
654 /// Clears (sets to \p nullptr) the guard \p nIndex
655 void clear( size_t nIndex ) CDS_NOEXCEPT
657 assert( nIndex < capacity() );
658 m_arr[nIndex].clear();
661 /// Clears all guards in the array
662 void clearAll() CDS_NOEXCEPT
664 for ( size_t i = 0; i < capacity(); ++i )
669 /// Memory manager (Garbage collector)
670 class CDS_EXPORT_API GarbageCollector
673 friend class ThreadGC;
675 /// Internal GC statistics
678 atomics::atomic<size_t> m_nGuardCount ; ///< Total guard count
679 atomics::atomic<size_t> m_nFreeGuardCount ; ///< Count of free guard
683 , m_nFreeGuardCount(0)
688 /// Exception "No GarbageCollector object is created"
689 class not_initialized : public std::runtime_error
694 : std::runtime_error( "Global DHP GarbageCollector is not initialized" )
699 /// Internal GC statistics
702 size_t m_nGuardCount ; ///< Total guard count
703 size_t m_nFreeGuardCount ; ///< Count of free guard
708 , m_nFreeGuardCount(0)
711 InternalState& operator =( internal_stat const& s )
713 m_nGuardCount = s.m_nGuardCount.load(atomics::memory_order_relaxed);
714 m_nFreeGuardCount = s.m_nFreeGuardCount.load(atomics::memory_order_relaxed);
722 static GarbageCollector * m_pManager ; ///< GC global instance
724 details::guard_allocator<> m_GuardPool ; ///< Guard pool
725 details::retired_ptr_pool<> m_RetiredAllocator ; ///< Pool of free retired pointers
726 details::retired_ptr_buffer m_RetiredBuffer ; ///< Retired pointer buffer for liberating
728 atomics::atomic<size_t> m_nLiberateThreshold; ///< Max size of retired pointer buffer to call \p scan()
729 const size_t m_nInitialThreadGuardCount; ///< Initial count of guards allocated for ThreadGC
731 internal_stat m_stat ; ///< Internal statistics
732 bool m_bStatEnabled ; ///< Internal Statistics enabled
735 /// Initializes DHP memory manager singleton
737 This member function creates and initializes DHP global object.
738 The function should be called before using CDS data structure based on cds::gc::DHP GC. Usually,
739 this member function is called in the \p main() function. See cds::gc::dhp for example.
740 After calling of this function you may use CDS data structures based on cds::gc::DHP.
743 \li \p nLiberateThreshold - \p scan() threshold. When count of retired pointers reaches this value,
744 the \ref dhp_gc_liberate "scan()" member function would be called for freeing retired pointers.
745 If \p nLiberateThreshold <= 1, \p scan() would called after each \ref dhp_gc_retirePtr "retirePtr" call.
746 \li \p nInitialThreadGuardCount - initial count of guard allocated for ThreadGC. When a thread
747 is initialized the GC allocates local guard pool for the thread from common guard pool.
748 By perforce the local thread's guard pool is grown automatically from common pool.
749 When the thread terminated its guard pool is backed to common GC's pool.
752 static void CDS_STDCALL Construct(
753 size_t nLiberateThreshold = 1024
754 , size_t nInitialThreadGuardCount = 8
757 /// Destroys DHP memory manager
759 The member function destroys DHP global object. After calling of this function you may \b NOT
760 use CDS data structures based on cds::gc::DHP. Usually, the \p Destruct function is called
761 at the end of your \p main(). See cds::gc::dhp for example.
763 static void CDS_STDCALL Destruct();
765 /// Returns pointer to GarbageCollector instance
767 If DHP GC is not initialized, \p not_initialized exception is thrown
769 static GarbageCollector& instance()
771 if ( m_pManager == nullptr )
772 throw not_initialized();
776 /// Checks if global GC object is constructed and may be used
777 static bool isUsed() CDS_NOEXCEPT
779 return m_pManager != nullptr;
784 /// Internal interface
786 /// Allocates a guard
787 details::guard_data * allocGuard()
789 return m_GuardPool.alloc();
792 /// Frees guard \p g for reusing in future
793 void freeGuard(details::guard_data * pGuard )
795 m_GuardPool.free( pGuard );
798 /// Allocates guard list for a thread.
799 details::guard_data * allocGuardList( size_t nCount )
801 return m_GuardPool.allocList( nCount );
804 /// Frees thread's guard list pointed by \p pList
805 void freeGuardList( details::guard_data * pList )
807 m_GuardPool.freeList( pList );
810 /// Places retired pointer \p and its deleter \p pFunc into thread's array of retired pointer for deferred reclamation
811 /**@anchor dhp_gc_retirePtr
813 template <typename T>
814 void retirePtr( T * p, void (* pFunc)(T *) )
816 retirePtr( retired_ptr( reinterpret_cast<void *>( p ), reinterpret_cast<free_retired_ptr_func>( pFunc ) ) );
819 /// Places retired pointer \p into thread's array of retired pointer for deferred reclamation
820 void retirePtr( retired_ptr const& p )
822 if ( m_RetiredBuffer.push( m_RetiredAllocator.alloc(p)) >= m_nLiberateThreshold.load(atomics::memory_order_relaxed) )
827 /// Liberate function
828 /** @anchor dhp_gc_liberate
829 The main function of Dynamic Hazard Pointer algorithm. It tries to free retired pointers if they are not
830 trapped by any guard.
836 /// Get internal statistics
837 InternalState& getInternalState(InternalState& stat) const
839 return stat = m_stat;
842 /// Checks if internal statistics enabled
843 bool isStatisticsEnabled() const
845 return m_bStatEnabled;
848 /// Enables/disables internal statistics
849 bool enableStatistics( bool bEnable )
851 bool bEnabled = m_bStatEnabled;
852 m_bStatEnabled = bEnable;
857 GarbageCollector( size_t nLiberateThreshold, size_t nInitialThreadGuardCount );
863 To use Dynamic Hazard Pointer reclamation schema each thread object must be linked with the object of ThreadGC class
864 that interacts with GarbageCollector global object. The linkage is performed by calling \ref cds_threading "cds::threading::Manager::attachThread()"
865 on the start of each thread that uses DHP GC. Before terminating the thread linked to DHP GC it is necessary to call
866 \ref cds_threading "cds::threading::Manager::detachThread()".
868 The ThreadGC object maintains two list:
869 \li Thread guard list: the list of thread-local guards (linked by \p pThreadNext field)
870 \li Free guard list: the list of thread-local free guards (linked by \p pNextFree field)
871 Free guard list is a subset of thread guard list.
875 GarbageCollector& m_gc ; ///< reference to GC singleton
876 details::guard_data * m_pList ; ///< Local list of guards owned by the thread
877 details::guard_data * m_pFree ; ///< The list of free guard from m_pList
880 /// Default constructor
882 : m_gc( GarbageCollector::instance() )
887 /// The object is not copy-constructible
888 ThreadGC( ThreadGC const& ) = delete;
890 /// Dtor calls fini()
896 /// Initialization. Repeat call is available
901 m_pFree = m_gc.allocGuardList( m_gc.m_nInitialThreadGuardCount );
905 /// Finalization. Repeat call is available
909 m_gc.freeGuardList( m_pList );
916 /// Initializes guard \p g
917 void allocGuard( dhp::details::guard& g )
919 assert( m_pList != nullptr );
922 g.m_pGuard = m_pFree;
923 m_pFree = m_pFree->pNextFree.load( atomics::memory_order_relaxed );
926 g.m_pGuard = m_gc.allocGuard();
927 g.m_pGuard->pThreadNext = m_pList;
928 m_pList = g.m_pGuard;
934 void freeGuard( dhp::details::guard& g )
936 assert( m_pList != nullptr );
938 g.m_pGuard->pPost.store( nullptr, atomics::memory_order_relaxed );
939 g.m_pGuard->pNextFree.store( m_pFree, atomics::memory_order_relaxed );
940 m_pFree = g.m_pGuard;
941 g.m_pGuard = nullptr;
945 /// Initializes guard array \p arr
946 template <size_t Count>
947 void allocGuard( GuardArray<Count>& arr )
949 assert( m_pList != nullptr );
952 while ( m_pFree && nCount < Count ) {
953 arr[nCount].set_guard( m_pFree );
954 m_pFree = m_pFree->pNextFree.load(atomics::memory_order_relaxed);
958 while ( nCount < Count ) {
959 details::guard& g = arr[nCount++];
960 g.set_guard( m_gc.allocGuard() );
961 g.get_guard()->pThreadNext = m_pList;
962 m_pList = g.get_guard();
966 /// Frees guard array \p arr
967 template <size_t Count>
968 void freeGuard( GuardArray<Count>& arr )
970 assert( m_pList != nullptr );
972 details::guard_data * pGuard;
973 for ( size_t i = 0; i < Count - 1; ++i ) {
974 pGuard = arr[i].get_guard();
975 pGuard->pPost.store( nullptr, atomics::memory_order_relaxed );
976 pGuard->pNextFree.store( arr[i+1].get_guard(), atomics::memory_order_relaxed );
978 pGuard = arr[Count-1].get_guard();
979 pGuard->pPost.store( nullptr, atomics::memory_order_relaxed );
980 pGuard->pNextFree.store( m_pFree, atomics::memory_order_relaxed );
981 m_pFree = arr[0].get_guard();
984 /// Places retired pointer \p and its deleter \p pFunc into list of retired pointer for deferred reclamation
985 template <typename T>
986 void retirePtr( T * p, void (* pFunc)(T *) )
988 m_gc.retirePtr( p, pFunc );
991 /// Run retiring cycle
998 }} // namespace cds::gc
1001 #if CDS_COMPILER == CDS_COMPILER_MSVC
1002 # pragma warning(pop)
1005 #endif // #ifndef __CDS_GC_DETAILS_DHP_H