3 #ifndef __CDS_GC_HZP_HZP_H
4 #define __CDS_GC_HZP_HZP_H
7 #include <cds/cxx11_atomic.h>
8 #include <cds/os/thread.h>
9 #include <cds/gc/exception.h>
10 #include <cds/gc/hzp/details/hp_fwd.h>
11 #include <cds/gc/hzp/details/hp_alloc.h>
12 #include <cds/gc/hzp/details/hp_retired.h>
14 #if CDS_COMPILER == CDS_COMPILER_MSVC
15 # pragma warning(push)
16 // warning C4251: 'cds::gc::hzp::GarbageCollector::m_pListHead' : class 'cds::cxx11_atomic::atomic<T>'
17 // needs to have dll-interface to be used by clients of class 'cds::gc::hzp::GarbageCollector'
18 # pragma warning(disable: 4251)
23 2007.12.24 khizmax Add statistics and CDS_GATHER_HAZARDPTR_STAT macro
24 2008.03.06 khizmax Refactoring: implementation of HazardPtrMgr is moved to hazardptr.cpp
25 2008.03.08 khizmax Remove HazardPtrMgr singleton. Now you must initialize/destroy HazardPtrMgr calling
26 HazardPtrMgr::Construct / HazardPtrMgr::Destruct before use (usually in main() function).
27 2008.12.06 khizmax Refactoring. Changes class name, namespace hierarchy, all helper defs have been moved to details namespace
28 2010.01.27 khizmax Introducing memory order constraint
33 @page cds_garbage_collectors_comparison GC comparison
34 @ingroup cds_garbage_collector
40 <th>%cds::gc::HRC</th>
41 <th>%cds::gc::PTB</th>
44 <td>Implementation quality</td>
50 <td>Performance rank (1 - slowest, 5 - fastest)</td>
56 <td>Max number of guarded (hazard) pointers per thread</td>
57 <td>limited (specifies in GC object ctor)</td>
58 <td>limited (specifies in GC object ctor)</td>
59 <td>unlimited (dynamically allocated when needed)</td>
62 <td>Max number of retired pointers<sup>1</sup></td>
68 <td>Array of retired pointers</td>
69 <td>preallocated for each thread, limited in size</td>
70 <td>preallocated for each thread, limited in size</td>
71 <td>global for the entire process, unlimited (dynamically allocated when needed)</td>
74 <td>Support direct pointer to item of lock-free container (useful for iterators)</td>
75 <td>not supported</td>
76 <td>potentially supported (not implemented)</td>
77 <td>not supported</td>
81 <sup>1</sup>Unbounded count of retired pointer means a possibility of memory exhaustion.
84 /// Different safe memory reclamation schemas (garbage collectors)
85 /** @ingroup cds_garbage_collector
87 This namespace specifies different safe memory reclamation (SMR) algorithms.
88 See \ref cds_garbage_collector "Garbage collectors"
92 /// Michael's Hazard Pointers reclamation schema
95 - [2002] Maged M.Michael "Safe memory reclamation for dynamic lock-freeobjects using atomic reads and writes"
96 - [2003] Maged M.Michael "Hazard Pointers: Safe memory reclamation for lock-free objects"
97 - [2004] Andrei Alexandrescy, Maged Michael "Lock-free Data Structures with Hazard Pointers"
100 The cds::gc::hzp namespace and its members are internal representation of Hazard Pointer GC and should not be used directly.
101 Use cds::gc::HP class in your code.
103 Hazard Pointer garbage collector is a singleton. The main user-level part of Hazard Pointer schema is
104 GC class and its nested classes. Before use any HP-related class you must initialize HP garbage collector
105 by contructing cds::gc::HP object in beginning of your main().
106 See cds::gc::HP class for explanation.
111 /// Hazard pointer record of the thread
113 The structure of type "single writer - multiple reader": only the owner thread may write to this structure
114 other threads have read-only access.
117 HPAllocator<hazard_pointer> m_hzp ; ///< array of hazard pointers. Implicit \ref CDS_DEFAULT_ALLOCATOR dependency
118 retired_vector m_arrRetired ; ///< Retired pointer array
121 HPRec( const cds::gc::hzp::GarbageCollector& HzpMgr ) ; // inline
125 /// Clears all hazard pointers
131 } // namespace details
133 /// GarbageCollector::Scan phase strategy
135 See GarbageCollector::Scan for explanation
138 classic, ///< classic scan as described in Michael's works (see GarbageCollector::classic_scan)
139 inplace ///< inplace scan without allocation (see GarbageCollector::inplace_scan)
142 /// Hazard Pointer singleton
144 Safe memory reclamation schema by Michael "Hazard Pointers"
147 \li [2002] Maged M.Michael "Safe memory reclamation for dynamic lock-freeobjects using atomic reads and writes"
148 \li [2003] Maged M.Michael "Hazard Pointers: Safe memory reclamation for lock-free objects"
149 \li [2004] Andrei Alexandrescy, Maged Michael "Lock-free Data Structures with Hazard Pointers"
152 class CDS_EXPORT_API GarbageCollector
155 typedef cds::atomicity::event_counter event_counter ; ///< event counter type
157 /// Internal GC statistics
158 struct InternalState {
159 size_t nHPCount ; ///< HP count per thread (const)
160 size_t nMaxThreadCount ; ///< Max thread count (const)
161 size_t nMaxRetiredPtrCount ; ///< Max retired pointer count per thread (const)
162 size_t nHPRecSize ; ///< Size of HP record, bytes (const)
164 size_t nHPRecAllocated ; ///< Count of HP record allocations
165 size_t nHPRecUsed ; ///< Count of HP record used
166 size_t nTotalRetiredPtrCount ; ///< Current total count of retired pointers
167 size_t nRetiredPtrInFreeHPRecs ; ///< Count of retired pointer in free (unused) HP records
169 event_counter::value_type evcAllocHPRec ; ///< Count of HPRec allocations
170 event_counter::value_type evcRetireHPRec ; ///< Count of HPRec retire events
171 event_counter::value_type evcAllocNewHPRec; ///< Count of new HPRec allocations from heap
172 event_counter::value_type evcDeleteHPRec ; ///< Count of HPRec deletions
174 event_counter::value_type evcScanCall ; ///< Count of Scan calling
175 event_counter::value_type evcHelpScanCall ; ///< Count of HelpScan calling
176 event_counter::value_type evcScanFromHelpScan;///< Count of Scan calls from HelpScan
178 event_counter::value_type evcDeletedNode ; ///< Count of deleting of retired objects
179 event_counter::value_type evcDeferredNode ; ///< Count of objects that cannot be deleted in Scan phase because of a hazard_pointer guards it
182 /// No GarbageCollector object is created
183 CDS_DECLARE_EXCEPTION( HZPManagerEmpty, "Global Hazard Pointer GarbageCollector is NULL" );
185 /// Not enough required Hazard Pointer count
186 CDS_DECLARE_EXCEPTION( HZPTooMany, "Not enough required Hazard Pointer count" );
189 /// Internal GC statistics
191 event_counter m_AllocHPRec ; ///< Count of HPRec allocations
192 event_counter m_RetireHPRec ; ///< Count of HPRec retire events
193 event_counter m_AllocNewHPRec ; ///< Count of new HPRec allocations from heap
194 event_counter m_DeleteHPRec ; ///< Count of HPRec deletions
196 event_counter m_ScanCallCount ; ///< Count of Scan calling
197 event_counter m_HelpScanCallCount ; ///< Count of HelpScan calling
198 event_counter m_CallScanFromHelpScan ; ///< Count of Scan calls from HelpScan
200 event_counter m_DeletedNode ; ///< Count of retired objects deleting
201 event_counter m_DeferredNode ; ///< Count of objects that cannot be deleted in Scan phase because of a hazard_pointer guards it
204 /// Internal list of cds::gc::hzp::details::HPRec
205 struct hplist_node: public details::HPRec
207 hplist_node * m_pNextNode ; ///< next hazard ptr record in list
208 atomics::atomic<OS::ThreadId> m_idOwner ; ///< Owner thread id; 0 - the record is free (not owned)
209 atomics::atomic<bool> m_bFree ; ///< true if record if free (not owned)
212 hplist_node( const GarbageCollector& HzpMgr )
214 m_pNextNode( nullptr ),
215 m_idOwner( OS::c_NullThreadId ),
221 assert( m_idOwner.load( atomics::memory_order_relaxed ) == OS::c_NullThreadId );
222 assert( m_bFree.load(atomics::memory_order_relaxed) );
227 atomics::atomic<hplist_node *> m_pListHead ; ///< Head of GC list
229 static GarbageCollector * m_pHZPManager ; ///< GC instance pointer
231 Statistics m_Stat ; ///< Internal statistics
232 bool m_bStatEnabled ; ///< true - statistics enabled
234 const size_t m_nHazardPointerCount ; ///< max count of thread's hazard pointer
235 const size_t m_nMaxThreadCount ; ///< max count of thread
236 const size_t m_nMaxRetiredPtrCount ; ///< max count of retired ptr per thread
237 scan_type m_nScanType ; ///< scan type (see \ref scan_type enum)
243 size_t nHazardPtrCount = 0, ///< Hazard pointer count per thread
244 size_t nMaxThreadCount = 0, ///< Max count of thread
245 size_t nMaxRetiredPtrCount = 0, ///< Capacity of the array of retired objects
246 scan_type nScanType = inplace ///< Scan type (see \ref scan_type enum)
252 /// Allocate new HP record
253 hplist_node * NewHPRec();
255 /// Permanently deletes HPrecord \p pNode
257 Caveat: for performance reason this function is defined as inline and cannot be called directly
259 void DeleteHPRec( hplist_node * pNode );
261 /// Permanently deletes retired pointer \p p
263 Caveat: for performance reason this function is defined as inline and cannot be called directly
265 void DeletePtr( details::retired_ptr& p );
268 void detachAllThread();
272 /// Creates GarbageCollector singleton
274 GC is the singleton. If GC instance is not exist then the function creates the instance.
275 Otherwise it does nothing.
277 The Michael's HP reclamation schema depends of three parameters:
279 \p nHazardPtrCount - HP pointer count per thread. Usually it is small number (2-4) depending from
280 the data structure algorithms. By default, if \p nHazardPtrCount = 0,
281 the function uses maximum of HP count for CDS library.
283 \p nMaxThreadCount - max count of thread with using HP GC in your application. Default is 100.
285 \p nMaxRetiredPtrCount - capacity of array of retired pointers for each thread. Must be greater than
286 \p nHazardPtrCount * \p nMaxThreadCount.
287 Default is 2 * \p nHazardPtrCount * \p nMaxThreadCount.
289 static void CDS_STDCALL Construct(
290 size_t nHazardPtrCount = 0, ///< Hazard pointer count per thread
291 size_t nMaxThreadCount = 0, ///< Max count of simultaneous working thread in your application
292 size_t nMaxRetiredPtrCount = 0, ///< Capacity of the array of retired objects for the thread
293 scan_type nScanType = inplace ///< Scan type (see \ref scan_type enum)
296 /// Destroys global instance of GarbageCollector
298 The parameter \p bDetachAll should be used carefully: if its value is \p true,
299 then the destroying GC automatically detaches all attached threads. This feature
300 can be useful when you have no control over the thread termination, for example,
301 when \p libcds is injected into existing external thread.
303 static void CDS_STDCALL Destruct(
304 bool bDetachAll = false ///< Detach all threads
307 /// Returns pointer to GarbageCollector instance
308 static GarbageCollector& instance()
310 if ( !m_pHZPManager )
311 throw HZPManagerEmpty();
312 return *m_pHZPManager;
315 /// Checks if global GC object is constructed and may be used
318 return m_pHZPManager != nullptr;
321 /// Returns max Hazard Pointer count defined in construction time
322 size_t getHazardPointerCount() const { return m_nHazardPointerCount; }
324 /// Returns max thread count defined in construction time
325 size_t getMaxThreadCount() const { return m_nMaxThreadCount; }
327 /// Returns max size of retired objects array. It is defined in construction time
328 size_t getMaxRetiredPtrCount() const { return m_nMaxRetiredPtrCount; }
330 // Internal statistics
332 /// Get internal statistics
333 InternalState& getInternalState(InternalState& stat) const;
335 /// Checks if internal statistics enabled
336 bool isStatisticsEnabled() const { return m_bStatEnabled; }
338 /// Enables/disables internal statistics
339 bool enableStatistics( bool bEnable )
341 bool bEnabled = m_bStatEnabled;
342 m_bStatEnabled = bEnable;
346 /// Checks that required hazard pointer count \p nRequiredCount is less or equal then max hazard pointer count
348 If \p nRequiredCount > getHazardPointerCount() then the exception HZPTooMany is thrown
350 static void checkHPCount( unsigned int nRequiredCount )
352 if ( instance().getHazardPointerCount() < nRequiredCount )
356 /// Get current scan strategy
357 scan_type getScanType() const
362 /// Set current scan strategy
363 /** @anchor hzp_gc_setScanType
364 Scan strategy changing is allowed on the fly.
367 scan_type nScanType ///< new scan strategy
370 m_nScanType = nScanType;
373 public: // Internals for threads
375 /// Allocates Hazard Pointer GC record. For internal use only
376 details::HPRec * AllocateHPRec();
378 /// Free HP record. For internal use only
379 void RetireHPRec( details::HPRec * pRec );
381 /// The main garbage collecting function
383 This function is called internally by ThreadGC object when upper bound of thread's list of reclaimed pointers
386 There are the following scan algorithm:
387 - \ref hzp_gc_classic_scan "classic_scan" allocates memory for internal use
388 - \ref hzp_gc_inplace_scan "inplace_scan" does not allocate any memory
390 Use \ref hzp_gc_setScanType "setScanType" member function to setup appropriate scan algorithm.
392 void Scan( details::HPRec * pRec )
394 switch ( m_nScanType ) {
396 inplace_scan( pRec );
399 assert(false) ; // Forgotten something?..
401 classic_scan( pRec );
406 /// Helper scan routine
408 The function guarantees that every node that is eligible for reuse is eventually freed, barring
409 thread failures. To do so, after executing Scan, a thread executes a HelpScan,
410 where it checks every HP record. If an HP record is inactive, the thread moves all "lost" reclaimed pointers
411 to thread's list of reclaimed pointers.
413 The function is called internally by Scan.
415 void HelpScan( details::HPRec * pThis );
418 /// Classic scan algorithm
419 /** @anchor hzp_gc_classic_scan
420 Classical scan algorithm as described in Michael's paper.
422 A scan includes four stages. The first stage involves scanning the array HP for non-null values.
423 Whenever a non-null value is encountered, it is inserted in a local list of currently protected pointer.
424 Only stage 1 accesses shared variables. The following stages operate only on private variables.
426 The second stage of a scan involves sorting local list of protected pointers to allow
427 binary search in the third stage.
429 The third stage of a scan involves checking each reclaimed node
430 against the pointers in local list of protected pointers. If the binary search yields
431 no match, the node is freed. Otherwise, it cannot be deleted now and must kept in thread's list
432 of reclaimed pointers.
434 The forth stage prepares new thread's private list of reclaimed pointers
435 that could not be freed during the current scan, where they remain until the next scan.
437 This algorithm allocates memory for internal HP array.
439 This function is called internally by ThreadGC object when upper bound of thread's list of reclaimed pointers
442 void classic_scan( details::HPRec * pRec );
444 /// In-place scan algorithm
445 /** @anchor hzp_gc_inplace_scan
446 Unlike the \ref hzp_gc_classic_scan "classic_scan" algorithm, \p inplace_scan does not allocate any memory.
447 All operations are performed in-place.
449 void inplace_scan( details::HPRec * pRec );
452 /// Thread's hazard pointer manager
454 To use Hazard Pointer reclamation schema each thread object must be linked with the object of ThreadGC class
455 that interacts with GarbageCollector global object. The linkage is performed by calling \ref cds_threading "cds::threading::Manager::attachThread()"
456 on the start of each thread that uses HP GC. Before terminating the thread linked to HP GC it is necessary to call
457 \ref cds_threading "cds::threading::Manager::detachThread()".
461 GarbageCollector& m_HzpManager ; ///< Hazard Pointer GC singleton
462 details::HPRec * m_pHzpRec ; ///< Pointer to thread's HZP record
465 /// Default constructor
467 : m_HzpManager( GarbageCollector::instance() ),
471 /// The object is not copy-constructible
472 ThreadGC( ThreadGC const& ) = delete;
479 /// Checks if thread GC is initialized
480 bool isInitialized() const { return m_pHzpRec != nullptr; }
482 /// Initialization. Repeat call is available
486 m_pHzpRec = m_HzpManager.AllocateHPRec();
489 /// Finalization. Repeat call is available
493 details::HPRec * pRec = m_pHzpRec;
495 m_HzpManager.RetireHPRec( pRec );
499 /// Initializes HP guard \p guard
500 details::HPGuard& allocGuard()
503 return m_pHzpRec->m_hzp.alloc();
506 /// Frees HP guard \p guard
507 void freeGuard( details::HPGuard& guard )
510 m_pHzpRec->m_hzp.free( guard );
513 /// Initializes HP guard array \p arr
514 template <size_t Count>
515 void allocGuard( details::HPArray<Count>& arr )
518 m_pHzpRec->m_hzp.alloc( arr );
521 /// Frees HP guard array \p arr
522 template <size_t Count>
523 void freeGuard( details::HPArray<Count>& arr )
526 m_pHzpRec->m_hzp.free( arr );
529 /// Places retired pointer \p and its deleter \p pFunc into thread's array of retired pointer for deferred reclamation
530 template <typename T>
531 void retirePtr( T * p, void (* pFunc)(T *) )
533 retirePtr( details::retired_ptr( reinterpret_cast<void *>( p ), reinterpret_cast<free_retired_ptr_func>( pFunc ) ) );
536 /// Places retired pointer \p into thread's array of retired pointer for deferred reclamation
537 void retirePtr( const details::retired_ptr& p )
539 m_pHzpRec->m_arrRetired.push( p );
541 if ( m_pHzpRec->m_arrRetired.isFull() ) {
542 // Max of retired pointer count is reached. Do scan
550 m_HzpManager.Scan( m_pHzpRec );
551 m_HzpManager.HelpScan( m_pHzpRec );
558 This class encapsulates Hazard Pointer guard to protect a pointer against deletion .
559 It allocates one HP from thread's HP array in constructor and free the HP allocated in destruction time.
564 details::HPGuard& m_hp ; ///< Hazard pointer guarded
565 ThreadGC& m_gc ; ///< Thread GC
569 typedef details::HPGuard::hazard_ptr hazard_ptr ; ///< Hazard pointer type
571 /// Allocates HP guard from \p gc
572 AutoHPGuard( ThreadGC& gc )
573 : m_hp( gc.allocGuard() )
577 /// Allocates HP guard from \p gc and protects the pointer \p p of type \p T
578 template <typename T>
579 AutoHPGuard( ThreadGC& gc, T * p )
580 : m_hp( gc.allocGuard() )
586 /// Frees HP guard. The pointer guarded may be deleted after this.
589 m_gc.freeGuard( m_hp );
592 /// Returns thread GC
593 ThreadGC& getGC() const
598 /// Protects the pointer \p p against reclamation (guards the pointer).
599 template <typename T>
600 T * operator =( T * p )
606 std::nullptr_t operator =(std::nullptr_t)
608 return m_hp = nullptr;
611 hazard_ptr get() const
618 /// Auto-managed array of hazard pointers
620 This class is wrapper around cds::gc::hzp::details::HPArray class.
621 \p Count is the size of HP array
623 template <size_t Count>
624 class AutoHPArray: public details::HPArray<Count>
626 ThreadGC& m_mgr ; ///< Thread GC
629 /// Rebind array for other size \p COUNT2
630 template <size_t Count2>
632 typedef AutoHPArray<Count2> other ; ///< rebinding result
636 /// Allocates array of HP guard from \p mgr
637 AutoHPArray( ThreadGC& mgr )
640 mgr.allocGuard( *this );
643 /// Frees array of HP guard
646 m_mgr.freeGuard( *this );
649 /// Returns thread GC
650 ThreadGC& getGC() const { return m_mgr; }
654 }} // namespace cds::gc
657 #include <cds/gc/hzp/details/hp_inline.h>
659 #if CDS_COMPILER == CDS_COMPILER_MSVC
660 # pragma warning(pop)
663 #endif // #ifndef __CDS_GC_HZP_HZP_H