3 #ifndef __CDS_GC_DETAILS_DHP_H
4 #define __CDS_GC_DETAILS_DHP_H
6 #include <mutex> // unique_lock
7 #include <cds/cxx11_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 /// Result of \ref dhp_gc_privatve "privatize" function.
274 The \p privatize function returns retired node list as \p first and the size of that list as \p second.
276 typedef std::pair<retired_ptr_node *, size_t> privatize_result;
278 /// Gets current list of retired pointer and clears the list
279 /**@anchor dhp_gc_privatve
281 privatize_result privatize() CDS_NOEXCEPT
283 privatize_result res;
284 res.first = m_pHead.exchange( nullptr, atomics::memory_order_acq_rel );
286 // Item counter is needed only as a threshold for \p scan() function
287 // So, we may clear the item counter without synchronization with m_pHead
288 res.second = m_nItemCount.exchange( 0, atomics::memory_order_relaxed );
292 /// Returns current size of buffer (approximate)
293 size_t size() const CDS_NOEXCEPT
295 return m_nItemCount.load(atomics::memory_order_relaxed);
299 /// Pool of retired pointers
301 The class acts as an allocator of retired node.
302 Retired pointers are linked in the lock-free list.
304 template <class Alloc = CDS_DEFAULT_ALLOCATOR>
305 class retired_ptr_pool {
307 typedef retired_ptr_node item;
309 /// Count of items in block
310 static const size_t m_nItemPerBlock = 1024 / sizeof(item) - 1;
314 block * pNext ; ///< next block
315 item items[m_nItemPerBlock] ; ///< item array
318 atomics::atomic<block *> m_pBlockListHead ; ///< head of of allocated block list
320 // To solve ABA problem we use epoch-based approach
321 static const unsigned int c_nEpochCount = 4 ; ///< Max epoch count
322 atomics::atomic<unsigned int> m_nCurEpoch ; ///< Current epoch
323 atomics::atomic<item *> m_pEpochFree[c_nEpochCount] ; ///< List of free item per epoch
324 atomics::atomic<item *> m_pGlobalFreeHead ; ///< Head of unallocated item list
326 cds::details::Allocator< block, Alloc > m_BlockAllocator ; ///< block allocator
331 // allocate new block
332 block * pNew = m_BlockAllocator.New();
334 // link items within the block
335 item * pLastItem = pNew->items + m_nItemPerBlock - 1;
336 for ( item * pItem = pNew->items; pItem != pLastItem; ++pItem ) {
337 pItem->m_pNextFree = pItem + 1;
338 CDS_STRICT_DO( pItem->m_pNext = nullptr );
341 // link new block to block list
343 block * pHead = m_pBlockListHead.load(atomics::memory_order_acquire);
346 // pHead is changed by compare_exchange_weak
347 } while ( !m_pBlockListHead.compare_exchange_weak( pHead, pNew, atomics::memory_order_release, atomics::memory_order_relaxed ));
350 // link block's items to free list
352 item * pHead = m_pGlobalFreeHead.load(atomics::memory_order_acquire);
354 pLastItem->m_pNextFree = pHead;
355 // pHead is changed by compare_exchange_weak
356 } while ( !m_pGlobalFreeHead.compare_exchange_weak( pHead, pNew->items, atomics::memory_order_release, atomics::memory_order_relaxed ));
360 unsigned int current_epoch() const CDS_NOEXCEPT
362 return m_nCurEpoch.load(atomics::memory_order_acquire) & (c_nEpochCount - 1);
365 unsigned int next_epoch() const CDS_NOEXCEPT
367 return (m_nCurEpoch.load(atomics::memory_order_acquire) - 1) & (c_nEpochCount - 1);
372 : m_pBlockListHead( nullptr )
374 , m_pGlobalFreeHead( nullptr )
376 for (unsigned int i = 0; i < sizeof(m_pEpochFree)/sizeof(m_pEpochFree[0]); ++i )
377 m_pEpochFree[i].store( nullptr, atomics::memory_order_relaxed );
385 for ( block * pBlock = m_pBlockListHead.load(atomics::memory_order_relaxed); pBlock; pBlock = p ) {
387 m_BlockAllocator.Delete( pBlock );
391 /// Increments current epoch
392 void inc_epoch() CDS_NOEXCEPT
394 m_nCurEpoch.fetch_add( 1, atomics::memory_order_acq_rel );
397 /// Allocates new retired pointer
398 retired_ptr_node& alloc()
403 pItem = m_pEpochFree[ nEpoch = current_epoch() ].load(atomics::memory_order_acquire);
406 if ( m_pEpochFree[nEpoch].compare_exchange_weak( pItem, pItem->m_pNextFree, atomics::memory_order_release, atomics::memory_order_relaxed ))
410 // Epoch free list is empty
411 // Alloc from global free list
413 pItem = m_pGlobalFreeHead.load( atomics::memory_order_acquire );
419 // pItem is changed by compare_exchange_weak
420 } while ( !m_pGlobalFreeHead.compare_exchange_weak( pItem, pItem->m_pNextFree, atomics::memory_order_release, atomics::memory_order_relaxed ));
423 CDS_STRICT_DO( pItem->m_pNextFree = nullptr );
427 /// Allocates and initializes new retired pointer
428 retired_ptr_node& alloc( const retired_ptr& p )
430 retired_ptr_node& node = alloc();
435 /// Places the list (pHead, pTail) of retired pointers to pool (frees retired pointers)
437 The list is linked on the m_pNextFree field
439 void free_range( retired_ptr_node * pHead, retired_ptr_node * pTail ) CDS_NOEXCEPT
441 assert( pHead != nullptr );
442 assert( pTail != nullptr );
447 pCurHead = m_pEpochFree[nEpoch = next_epoch()].load(atomics::memory_order_acquire);
448 pTail->m_pNextFree = pCurHead;
449 } while ( !m_pEpochFree[nEpoch].compare_exchange_weak( pCurHead, pHead, atomics::memory_order_release, atomics::memory_order_relaxed ));
453 /// Uninitialized guard
456 friend class dhp::ThreadGC;
458 details::guard_data * m_pGuard ; ///< Pointer to guard data
461 /// Initialize empty guard.
462 CDS_CONSTEXPR guard() CDS_NOEXCEPT
463 : m_pGuard( nullptr )
466 /// Ñopy-ctor is disabled
467 guard( guard const& ) = delete;
469 /// Move-ctor is disabled
470 guard( guard&& ) = delete;
472 /// Object destructor, does nothing
473 ~guard() CDS_NOEXCEPT
476 /// Get current guarded pointer
477 void * get( atomics::memory_order order = atomics::memory_order_acquire ) const CDS_NOEXCEPT
479 assert( m_pGuard != nullptr );
480 return m_pGuard->pPost.load( order );
483 /// Guards pointer \p p
484 void set( void * p, atomics::memory_order order = atomics::memory_order_release ) CDS_NOEXCEPT
486 assert( m_pGuard != nullptr );
487 m_pGuard->pPost.store( p, order );
491 void clear( atomics::memory_order order = atomics::memory_order_relaxed ) CDS_NOEXCEPT
493 assert( m_pGuard != nullptr );
494 m_pGuard->pPost.store( nullptr, order );
497 /// Guards pointer \p p
498 template <typename T>
499 T * operator =(T * p) CDS_NOEXCEPT
501 set( reinterpret_cast<void *>( const_cast<T *>(p) ));
505 std::nullptr_t operator=(std::nullptr_t) CDS_NOEXCEPT
511 public: // for ThreadGC.
513 GCC cannot compile code for template versions of ThreasGC::allocGuard/freeGuard,
514 the compiler produces error:
\91cds::gc::dhp::details::guard_data* cds::gc::dhp::details::guard::m_pGuard
\92 is protected
515 despite the fact that ThreadGC is declared as friend for guard class.
516 Therefore, we have to add set_guard/get_guard public functions
519 void set_guard( details::guard_data * pGuard ) CDS_NOEXCEPT
521 assert( m_pGuard == nullptr );
525 /// Get current guard data
526 details::guard_data * get_guard() CDS_NOEXCEPT
530 /// Get current guard data
531 details::guard_data * get_guard() const CDS_NOEXCEPT
536 details::guard_data * release_guard() CDS_NOEXCEPT
538 details::guard_data * p = m_pGuard;
543 bool is_initialized() const
545 return m_pGuard != nullptr;
549 } // namespace details
553 This class represents auto guard: ctor allocates a guard from guard pool,
554 dtor returns the guard back to the pool of free guard.
556 class Guard: public details::guard
558 typedef details::guard base_class;
559 friend class ThreadGC;
561 ThreadGC& m_gc ; ///< ThreadGC object of current thread
563 /// Allocates a guard from \p gc GC. \p gc must be ThreadGC object of current thread
564 Guard( ThreadGC& gc );
566 /// Returns guard allocated back to pool of free guards
567 ~Guard(); // inline after GarbageCollector
569 /// Returns DHP GC object
570 ThreadGC& getGC() CDS_NOEXCEPT
575 /// Guards pointer \p p
576 template <typename T>
577 T * operator =(T * p) CDS_NOEXCEPT
579 return base_class::operator =<T>( p );
582 std::nullptr_t operator=(std::nullptr_t) CDS_NOEXCEPT
584 return base_class::operator =(nullptr);
590 This class represents array of auto guards: ctor allocates \p Count guards from guard pool,
591 dtor returns the guards allocated back to the pool.
593 template <size_t Count>
596 details::guard m_arr[Count] ; ///< array of guard
597 ThreadGC& m_gc ; ///< ThreadGC object of current thread
598 const static size_t c_nCapacity = Count ; ///< Array capacity (equal to \p Count template parameter)
601 /// Rebind array for other size \p OtherCount
602 template <size_t OtherCount>
604 typedef GuardArray<OtherCount> other ; ///< rebinding result
608 /// Allocates array of guards from \p gc which must be the ThreadGC object of current thread
609 GuardArray( ThreadGC& gc ); // inline below
611 /// The object is not default-constructible
612 GuardArray() = delete;
614 /// The object is not copy-constructible
615 GuardArray( GuardArray const& ) = delete;
617 /// Returns guards allocated back to pool
618 ~GuardArray(); // inline below
620 /// Returns the capacity of array
621 CDS_CONSTEXPR size_t capacity() const CDS_NOEXCEPT
626 /// Returns DHP ThreadGC object
627 ThreadGC& getGC() 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 CDS_DECLARE_EXCEPTION( DHPManagerEmpty, "Global DHP GarbageCollector is NULL" );
691 /// Internal GC statistics
694 size_t m_nGuardCount ; ///< Total guard count
695 size_t m_nFreeGuardCount ; ///< Count of free guard
699 , m_nFreeGuardCount(0)
702 InternalState& operator =( internal_stat const& s )
704 m_nGuardCount = s.m_nGuardCount.load(atomics::memory_order_relaxed);
705 m_nFreeGuardCount = s.m_nFreeGuardCount.load(atomics::memory_order_relaxed);
712 static GarbageCollector * m_pManager ; ///< GC global instance
714 details::guard_allocator<> m_GuardPool ; ///< Guard pool
715 details::retired_ptr_pool<> m_RetiredAllocator ; ///< Pool of free retired pointers
716 details::retired_ptr_buffer m_RetiredBuffer ; ///< Retired pointer buffer for liberating
718 atomics::atomic<size_t> m_nLiberateThreshold; ///< Max size of retired pointer buffer to call \p scan()
719 const size_t m_nInitialThreadGuardCount; ///< Initial count of guards allocated for ThreadGC
721 internal_stat m_stat ; ///< Internal statistics
722 bool m_bStatEnabled ; ///< Internal Statistics enabled
725 /// Initializes DHP memory manager singleton
727 This member function creates and initializes DHP global object.
728 The function should be called before using CDS data structure based on cds::gc::DHP GC. Usually,
729 this member function is called in the \p main() function. See cds::gc::dhp for example.
730 After calling of this function you may use CDS data structures based on cds::gc::DHP.
733 \li \p nLiberateThreshold - \p scan() threshold. When count of retired pointers reaches this value,
734 the \ref dhp_gc_liberate "scan()" member function would be called for freeing retired pointers.
735 If \p nLiberateThreshold <= 1, \p scan() would called after each \ref dhp_gc_retirePtr "retirePtr" call.
736 \li \p nInitialThreadGuardCount - initial count of guard allocated for ThreadGC. When a thread
737 is initialized the GC allocates local guard pool for the thread from common guard pool.
738 By perforce the local thread's guard pool is grown automatically from common pool.
739 When the thread terminated its guard pool is backed to common GC's pool.
742 static void CDS_STDCALL Construct(
743 size_t nLiberateThreshold = 1024
744 , size_t nInitialThreadGuardCount = 8
747 /// Destroys DHP memory manager
749 The member function destroys DHP global object. After calling of this function you may \b NOT
750 use CDS data structures based on cds::gc::DHP. Usually, the \p Destruct function is called
751 at the end of your \p main(). See cds::gc::dhp for example.
753 static void CDS_STDCALL Destruct();
755 /// Returns pointer to GarbageCollector instance
757 If DHP GC is not initialized, \p DHPManagerEmpty exception is thrown
759 static GarbageCollector& instance()
761 if ( m_pManager == nullptr )
762 throw DHPManagerEmpty();
766 /// Checks if global GC object is constructed and may be used
767 static bool isUsed() CDS_NOEXCEPT
769 return m_pManager != nullptr;
774 /// Internal interface
776 /// Allocates a guard
777 details::guard_data * allocGuard()
779 return m_GuardPool.alloc();
782 /// Frees guard \p g for reusing in future
783 void freeGuard(details::guard_data * pGuard )
785 m_GuardPool.free( pGuard );
788 /// Allocates guard list for a thread.
789 details::guard_data * allocGuardList( size_t nCount )
791 return m_GuardPool.allocList( nCount );
794 /// Frees thread's guard list pointed by \p pList
795 void freeGuardList( details::guard_data * pList )
797 m_GuardPool.freeList( pList );
800 /// Places retired pointer \p and its deleter \p pFunc into thread's array of retired pointer for deferred reclamation
801 /**@anchor dhp_gc_retirePtr
803 template <typename T>
804 void retirePtr( T * p, void (* pFunc)(T *) )
806 retirePtr( retired_ptr( reinterpret_cast<void *>( p ), reinterpret_cast<free_retired_ptr_func>( pFunc ) ) );
809 /// Places retired pointer \p into thread's array of retired pointer for deferred reclamation
810 void retirePtr( retired_ptr const& p )
812 if ( m_RetiredBuffer.push( m_RetiredAllocator.alloc(p)) >= m_nLiberateThreshold.load(atomics::memory_order_relaxed) )
817 /// Liberate function
818 /** @anchor dhp_gc_liberate
819 The main function of Dynamic Hazard Pointer algorithm. It tries to free retired pointers if they are not
820 trapped by any guard.
826 /// Get internal statistics
827 InternalState& getInternalState(InternalState& stat) const
829 return stat = m_stat;
832 /// Checks if internal statistics enabled
833 bool isStatisticsEnabled() const
835 return m_bStatEnabled;
838 /// Enables/disables internal statistics
839 bool enableStatistics( bool bEnable )
841 bool bEnabled = m_bStatEnabled;
842 m_bStatEnabled = bEnable;
847 GarbageCollector( size_t nLiberateThreshold, size_t nInitialThreadGuardCount );
853 To use Dynamic Hazard Pointer reclamation schema each thread object must be linked with the object of ThreadGC class
854 that interacts with GarbageCollector global object. The linkage is performed by calling \ref cds_threading "cds::threading::Manager::attachThread()"
855 on the start of each thread that uses DHP GC. Before terminating the thread linked to DHP GC it is necessary to call
856 \ref cds_threading "cds::threading::Manager::detachThread()".
858 The ThreadGC object maintains two list:
859 \li Thread guard list: the list of thread-local guards (linked by \p pThreadNext field)
860 \li Free guard list: the list of thread-local free guards (linked by \p pNextFree field)
861 Free guard list is a subset of thread guard list.
865 GarbageCollector& m_gc ; ///< reference to GC singleton
866 details::guard_data * m_pList ; ///< Local list of guards owned by the thread
867 details::guard_data * m_pFree ; ///< The list of free guard from m_pList
870 /// Default constructor
872 : m_gc( GarbageCollector::instance() )
877 /// The object is not copy-constructible
878 ThreadGC( ThreadGC const& ) = delete;
880 /// Dtor calls fini()
886 /// Initialization. Repeat call is available
891 m_pFree = m_gc.allocGuardList( m_gc.m_nInitialThreadGuardCount );
895 /// Finalization. Repeat call is available
899 m_gc.freeGuardList( m_pList );
906 /// Initializes guard \p g
907 void allocGuard( dhp::details::guard& g )
909 assert( m_pList != nullptr );
912 g.m_pGuard = m_pFree;
913 m_pFree = m_pFree->pNextFree.load( atomics::memory_order_relaxed );
916 g.m_pGuard = m_gc.allocGuard();
917 g.m_pGuard->pThreadNext = m_pList;
918 m_pList = g.m_pGuard;
924 void freeGuard( dhp::details::guard& g )
926 assert( m_pList != nullptr );
928 g.m_pGuard->pPost.store( nullptr, atomics::memory_order_relaxed );
929 g.m_pGuard->pNextFree.store( m_pFree, atomics::memory_order_relaxed );
930 m_pFree = g.m_pGuard;
931 g.m_pGuard = nullptr;
935 /// Initializes guard array \p arr
936 template <size_t Count>
937 void allocGuard( GuardArray<Count>& arr )
939 assert( m_pList != nullptr );
942 while ( m_pFree && nCount < Count ) {
943 arr[nCount].set_guard( m_pFree );
944 m_pFree = m_pFree->pNextFree.load(atomics::memory_order_relaxed);
948 while ( nCount < Count ) {
949 details::guard& g = arr[nCount++];
950 g.set_guard( m_gc.allocGuard() );
951 g.get_guard()->pThreadNext = m_pList;
952 m_pList = g.get_guard();
956 /// Frees guard array \p arr
957 template <size_t Count>
958 void freeGuard( GuardArray<Count>& arr )
960 assert( m_pList != nullptr );
962 details::guard_data * pGuard;
963 for ( size_t i = 0; i < Count - 1; ++i ) {
964 pGuard = arr[i].get_guard();
965 pGuard->pPost.store( nullptr, atomics::memory_order_relaxed );
966 pGuard->pNextFree.store( arr[i+1].get_guard(), atomics::memory_order_relaxed );
968 pGuard = arr[Count-1].get_guard();
969 pGuard->pPost.store( nullptr, atomics::memory_order_relaxed );
970 pGuard->pNextFree.store( m_pFree, atomics::memory_order_relaxed );
971 m_pFree = arr[0].get_guard();
974 /// Places retired pointer \p and its deleter \p pFunc into list of retired pointer for deferred reclamation
975 template <typename T>
976 void retirePtr( T * p, void (* pFunc)(T *) )
978 m_gc.retirePtr( p, pFunc );
987 //////////////////////////////////////////////////////////
990 inline Guard::Guard(ThreadGC& gc)
993 getGC().allocGuard( *this );
995 inline Guard::~Guard()
997 getGC().freeGuard( *this );
1000 template <size_t Count>
1001 inline GuardArray<Count>::GuardArray( ThreadGC& gc )
1004 getGC().allocGuard( *this );
1006 template <size_t Count>
1007 inline GuardArray<Count>::~GuardArray()
1009 getGC().freeGuard( *this );
1013 }} // namespace cds::gc
1016 #if CDS_COMPILER == CDS_COMPILER_MSVC
1017 # pragma warning(pop)
1020 #endif // #ifndef __CDS_GC_DETAILS_DHP_H