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::PTB</th>
43 <td>Implementation quality</td>
48 <td>Performance rank (1 - slowest, 5 - fastest)</td>
53 <td>Max number of guarded (hazard) pointers per thread</td>
54 <td>limited (specifies in GC object ctor)</td>
55 <td>unlimited (dynamically allocated when needed)</td>
58 <td>Max number of retired pointers<sup>1</sup></td>
63 <td>Array of retired pointers</td>
64 <td>preallocated for each thread, limited in size</td>
65 <td>global for the entire process, unlimited (dynamically allocated when needed)</td>
68 <td>Support direct pointer to item of lock-free container (useful for iterators)</td>
69 <td>not supported</td>
70 <td>not supported</td>
74 <sup>1</sup>Unbounded count of retired pointer means a possibility of memory exhaustion.
77 /// Different safe memory reclamation schemas (garbage collectors)
78 /** @ingroup cds_garbage_collector
80 This namespace specifies different safe memory reclamation (SMR) algorithms.
81 See \ref cds_garbage_collector "Garbage collectors"
85 /// Michael's Hazard Pointers reclamation schema
88 - [2002] Maged M.Michael "Safe memory reclamation for dynamic lock-freeobjects using atomic reads and writes"
89 - [2003] Maged M.Michael "Hazard Pointers: Safe memory reclamation for lock-free objects"
90 - [2004] Andrei Alexandrescy, Maged Michael "Lock-free Data Structures with Hazard Pointers"
93 The cds::gc::hzp namespace and its members are internal representation of Hazard Pointer GC and should not be used directly.
94 Use cds::gc::HP class in your code.
96 Hazard Pointer garbage collector is a singleton. The main user-level part of Hazard Pointer schema is
97 GC class and its nested classes. Before use any HP-related class you must initialize HP garbage collector
98 by contructing cds::gc::HP object in beginning of your main().
99 See cds::gc::HP class for explanation.
104 /// Hazard pointer record of the thread
106 The structure of type "single writer - multiple reader": only the owner thread may write to this structure
107 other threads have read-only access.
110 HPAllocator<hazard_pointer> m_hzp ; ///< array of hazard pointers. Implicit \ref CDS_DEFAULT_ALLOCATOR dependency
111 retired_vector m_arrRetired ; ///< Retired pointer array
114 HPRec( const cds::gc::hzp::GarbageCollector& HzpMgr ) ; // inline
118 /// Clears all hazard pointers
124 } // namespace details
126 /// GarbageCollector::Scan phase strategy
128 See GarbageCollector::Scan for explanation
131 classic, ///< classic scan as described in Michael's works (see GarbageCollector::classic_scan)
132 inplace ///< inplace scan without allocation (see GarbageCollector::inplace_scan)
135 /// Hazard Pointer singleton
137 Safe memory reclamation schema by Michael "Hazard Pointers"
140 \li [2002] Maged M.Michael "Safe memory reclamation for dynamic lock-freeobjects using atomic reads and writes"
141 \li [2003] Maged M.Michael "Hazard Pointers: Safe memory reclamation for lock-free objects"
142 \li [2004] Andrei Alexandrescy, Maged Michael "Lock-free Data Structures with Hazard Pointers"
145 class CDS_EXPORT_API GarbageCollector
148 typedef cds::atomicity::event_counter event_counter ; ///< event counter type
150 /// Internal GC statistics
151 struct InternalState {
152 size_t nHPCount ; ///< HP count per thread (const)
153 size_t nMaxThreadCount ; ///< Max thread count (const)
154 size_t nMaxRetiredPtrCount ; ///< Max retired pointer count per thread (const)
155 size_t nHPRecSize ; ///< Size of HP record, bytes (const)
157 size_t nHPRecAllocated ; ///< Count of HP record allocations
158 size_t nHPRecUsed ; ///< Count of HP record used
159 size_t nTotalRetiredPtrCount ; ///< Current total count of retired pointers
160 size_t nRetiredPtrInFreeHPRecs ; ///< Count of retired pointer in free (unused) HP records
162 event_counter::value_type evcAllocHPRec ; ///< Count of HPRec allocations
163 event_counter::value_type evcRetireHPRec ; ///< Count of HPRec retire events
164 event_counter::value_type evcAllocNewHPRec; ///< Count of new HPRec allocations from heap
165 event_counter::value_type evcDeleteHPRec ; ///< Count of HPRec deletions
167 event_counter::value_type evcScanCall ; ///< Count of Scan calling
168 event_counter::value_type evcHelpScanCall ; ///< Count of HelpScan calling
169 event_counter::value_type evcScanFromHelpScan;///< Count of Scan calls from HelpScan
171 event_counter::value_type evcDeletedNode ; ///< Count of deleting of retired objects
172 event_counter::value_type evcDeferredNode ; ///< Count of objects that cannot be deleted in Scan phase because of a hazard_pointer guards it
175 /// No GarbageCollector object is created
176 CDS_DECLARE_EXCEPTION( HZPManagerEmpty, "Global Hazard Pointer GarbageCollector is NULL" );
178 /// Not enough required Hazard Pointer count
179 CDS_DECLARE_EXCEPTION( HZPTooMany, "Not enough required Hazard Pointer count" );
182 /// Internal GC statistics
184 event_counter m_AllocHPRec ; ///< Count of HPRec allocations
185 event_counter m_RetireHPRec ; ///< Count of HPRec retire events
186 event_counter m_AllocNewHPRec ; ///< Count of new HPRec allocations from heap
187 event_counter m_DeleteHPRec ; ///< Count of HPRec deletions
189 event_counter m_ScanCallCount ; ///< Count of Scan calling
190 event_counter m_HelpScanCallCount ; ///< Count of HelpScan calling
191 event_counter m_CallScanFromHelpScan ; ///< Count of Scan calls from HelpScan
193 event_counter m_DeletedNode ; ///< Count of retired objects deleting
194 event_counter m_DeferredNode ; ///< Count of objects that cannot be deleted in Scan phase because of a hazard_pointer guards it
197 /// Internal list of cds::gc::hzp::details::HPRec
198 struct hplist_node: public details::HPRec
200 hplist_node * m_pNextNode ; ///< next hazard ptr record in list
201 atomics::atomic<OS::ThreadId> m_idOwner ; ///< Owner thread id; 0 - the record is free (not owned)
202 atomics::atomic<bool> m_bFree ; ///< true if record if free (not owned)
205 hplist_node( const GarbageCollector& HzpMgr )
207 m_pNextNode( nullptr ),
208 m_idOwner( OS::c_NullThreadId ),
214 assert( m_idOwner.load( atomics::memory_order_relaxed ) == OS::c_NullThreadId );
215 assert( m_bFree.load(atomics::memory_order_relaxed) );
220 atomics::atomic<hplist_node *> m_pListHead ; ///< Head of GC list
222 static GarbageCollector * m_pHZPManager ; ///< GC instance pointer
224 Statistics m_Stat ; ///< Internal statistics
225 bool m_bStatEnabled ; ///< true - statistics enabled
227 const size_t m_nHazardPointerCount ; ///< max count of thread's hazard pointer
228 const size_t m_nMaxThreadCount ; ///< max count of thread
229 const size_t m_nMaxRetiredPtrCount ; ///< max count of retired ptr per thread
230 scan_type m_nScanType ; ///< scan type (see \ref scan_type enum)
236 size_t nHazardPtrCount = 0, ///< Hazard pointer count per thread
237 size_t nMaxThreadCount = 0, ///< Max count of thread
238 size_t nMaxRetiredPtrCount = 0, ///< Capacity of the array of retired objects
239 scan_type nScanType = inplace ///< Scan type (see \ref scan_type enum)
245 /// Allocate new HP record
246 hplist_node * NewHPRec();
248 /// Permanently deletes HPrecord \p pNode
250 Caveat: for performance reason this function is defined as inline and cannot be called directly
252 void DeleteHPRec( hplist_node * pNode );
254 /// Permanently deletes retired pointer \p p
256 Caveat: for performance reason this function is defined as inline and cannot be called directly
258 void DeletePtr( details::retired_ptr& p );
261 void detachAllThread();
265 /// Creates GarbageCollector singleton
267 GC is the singleton. If GC instance is not exist then the function creates the instance.
268 Otherwise it does nothing.
270 The Michael's HP reclamation schema depends of three parameters:
272 \p nHazardPtrCount - HP pointer count per thread. Usually it is small number (2-4) depending from
273 the data structure algorithms. By default, if \p nHazardPtrCount = 0,
274 the function uses maximum of HP count for CDS library.
276 \p nMaxThreadCount - max count of thread with using HP GC in your application. Default is 100.
278 \p nMaxRetiredPtrCount - capacity of array of retired pointers for each thread. Must be greater than
279 \p nHazardPtrCount * \p nMaxThreadCount.
280 Default is 2 * \p nHazardPtrCount * \p nMaxThreadCount.
282 static void CDS_STDCALL Construct(
283 size_t nHazardPtrCount = 0, ///< Hazard pointer count per thread
284 size_t nMaxThreadCount = 0, ///< Max count of simultaneous working thread in your application
285 size_t nMaxRetiredPtrCount = 0, ///< Capacity of the array of retired objects for the thread
286 scan_type nScanType = inplace ///< Scan type (see \ref scan_type enum)
289 /// Destroys global instance of GarbageCollector
291 The parameter \p bDetachAll should be used carefully: if its value is \p true,
292 then the destroying GC automatically detaches all attached threads. This feature
293 can be useful when you have no control over the thread termination, for example,
294 when \p libcds is injected into existing external thread.
296 static void CDS_STDCALL Destruct(
297 bool bDetachAll = false ///< Detach all threads
300 /// Returns pointer to GarbageCollector instance
301 static GarbageCollector& instance()
303 if ( !m_pHZPManager )
304 throw HZPManagerEmpty();
305 return *m_pHZPManager;
308 /// Checks if global GC object is constructed and may be used
311 return m_pHZPManager != nullptr;
314 /// Returns max Hazard Pointer count defined in construction time
315 size_t getHazardPointerCount() const { return m_nHazardPointerCount; }
317 /// Returns max thread count defined in construction time
318 size_t getMaxThreadCount() const { return m_nMaxThreadCount; }
320 /// Returns max size of retired objects array. It is defined in construction time
321 size_t getMaxRetiredPtrCount() const { return m_nMaxRetiredPtrCount; }
323 // Internal statistics
325 /// Get internal statistics
326 InternalState& getInternalState(InternalState& stat) const;
328 /// Checks if internal statistics enabled
329 bool isStatisticsEnabled() const { return m_bStatEnabled; }
331 /// Enables/disables internal statistics
332 bool enableStatistics( bool bEnable )
334 bool bEnabled = m_bStatEnabled;
335 m_bStatEnabled = bEnable;
339 /// Checks that required hazard pointer count \p nRequiredCount is less or equal then max hazard pointer count
341 If \p nRequiredCount > getHazardPointerCount() then the exception HZPTooMany is thrown
343 static void checkHPCount( unsigned int nRequiredCount )
345 if ( instance().getHazardPointerCount() < nRequiredCount )
349 /// Get current scan strategy
350 scan_type getScanType() const
355 /// Set current scan strategy
356 /** @anchor hzp_gc_setScanType
357 Scan strategy changing is allowed on the fly.
360 scan_type nScanType ///< new scan strategy
363 m_nScanType = nScanType;
366 public: // Internals for threads
368 /// Allocates Hazard Pointer GC record. For internal use only
369 details::HPRec * AllocateHPRec();
371 /// Free HP record. For internal use only
372 void RetireHPRec( details::HPRec * pRec );
374 /// The main garbage collecting function
376 This function is called internally by ThreadGC object when upper bound of thread's list of reclaimed pointers
379 There are the following scan algorithm:
380 - \ref hzp_gc_classic_scan "classic_scan" allocates memory for internal use
381 - \ref hzp_gc_inplace_scan "inplace_scan" does not allocate any memory
383 Use \ref hzp_gc_setScanType "setScanType" member function to setup appropriate scan algorithm.
385 void Scan( details::HPRec * pRec )
387 switch ( m_nScanType ) {
389 inplace_scan( pRec );
392 assert(false) ; // Forgotten something?..
394 classic_scan( pRec );
399 /// Helper scan routine
401 The function guarantees that every node that is eligible for reuse is eventually freed, barring
402 thread failures. To do so, after executing Scan, a thread executes a HelpScan,
403 where it checks every HP record. If an HP record is inactive, the thread moves all "lost" reclaimed pointers
404 to thread's list of reclaimed pointers.
406 The function is called internally by Scan.
408 void HelpScan( details::HPRec * pThis );
411 /// Classic scan algorithm
412 /** @anchor hzp_gc_classic_scan
413 Classical scan algorithm as described in Michael's paper.
415 A scan includes four stages. The first stage involves scanning the array HP for non-null values.
416 Whenever a non-null value is encountered, it is inserted in a local list of currently protected pointer.
417 Only stage 1 accesses shared variables. The following stages operate only on private variables.
419 The second stage of a scan involves sorting local list of protected pointers to allow
420 binary search in the third stage.
422 The third stage of a scan involves checking each reclaimed node
423 against the pointers in local list of protected pointers. If the binary search yields
424 no match, the node is freed. Otherwise, it cannot be deleted now and must kept in thread's list
425 of reclaimed pointers.
427 The forth stage prepares new thread's private list of reclaimed pointers
428 that could not be freed during the current scan, where they remain until the next scan.
430 This algorithm allocates memory for internal HP array.
432 This function is called internally by ThreadGC object when upper bound of thread's list of reclaimed pointers
435 void classic_scan( details::HPRec * pRec );
437 /// In-place scan algorithm
438 /** @anchor hzp_gc_inplace_scan
439 Unlike the \ref hzp_gc_classic_scan "classic_scan" algorithm, \p inplace_scan does not allocate any memory.
440 All operations are performed in-place.
442 void inplace_scan( details::HPRec * pRec );
445 /// Thread's hazard pointer manager
447 To use Hazard Pointer reclamation schema each thread object must be linked with the object of ThreadGC class
448 that interacts with GarbageCollector global object. The linkage is performed by calling \ref cds_threading "cds::threading::Manager::attachThread()"
449 on the start of each thread that uses HP GC. Before terminating the thread linked to HP GC it is necessary to call
450 \ref cds_threading "cds::threading::Manager::detachThread()".
454 GarbageCollector& m_HzpManager ; ///< Hazard Pointer GC singleton
455 details::HPRec * m_pHzpRec ; ///< Pointer to thread's HZP record
458 /// Default constructor
460 : m_HzpManager( GarbageCollector::instance() ),
464 /// The object is not copy-constructible
465 ThreadGC( ThreadGC const& ) = delete;
472 /// Checks if thread GC is initialized
473 bool isInitialized() const { return m_pHzpRec != nullptr; }
475 /// Initialization. Repeat call is available
479 m_pHzpRec = m_HzpManager.AllocateHPRec();
482 /// Finalization. Repeat call is available
486 details::HPRec * pRec = m_pHzpRec;
488 m_HzpManager.RetireHPRec( pRec );
492 /// Initializes HP guard \p guard
493 details::HPGuard& allocGuard()
496 return m_pHzpRec->m_hzp.alloc();
499 /// Frees HP guard \p guard
500 void freeGuard( details::HPGuard& guard )
503 m_pHzpRec->m_hzp.free( guard );
506 /// Initializes HP guard array \p arr
507 template <size_t Count>
508 void allocGuard( details::HPArray<Count>& arr )
511 m_pHzpRec->m_hzp.alloc( arr );
514 /// Frees HP guard array \p arr
515 template <size_t Count>
516 void freeGuard( details::HPArray<Count>& arr )
519 m_pHzpRec->m_hzp.free( arr );
522 /// Places retired pointer \p and its deleter \p pFunc into thread's array of retired pointer for deferred reclamation
523 template <typename T>
524 void retirePtr( T * p, void (* pFunc)(T *) )
526 retirePtr( details::retired_ptr( reinterpret_cast<void *>( p ), reinterpret_cast<free_retired_ptr_func>( pFunc ) ) );
529 /// Places retired pointer \p into thread's array of retired pointer for deferred reclamation
530 void retirePtr( const details::retired_ptr& p )
532 m_pHzpRec->m_arrRetired.push( p );
534 if ( m_pHzpRec->m_arrRetired.isFull() ) {
535 // Max of retired pointer count is reached. Do scan
543 m_HzpManager.Scan( m_pHzpRec );
544 m_HzpManager.HelpScan( m_pHzpRec );
551 This class encapsulates Hazard Pointer guard to protect a pointer against deletion .
552 It allocates one HP from thread's HP array in constructor and free the HP allocated in destruction time.
557 details::HPGuard& m_hp ; ///< Hazard pointer guarded
558 ThreadGC& m_gc ; ///< Thread GC
562 typedef details::HPGuard::hazard_ptr hazard_ptr ; ///< Hazard pointer type
564 /// Allocates HP guard from \p gc
565 AutoHPGuard( ThreadGC& gc )
566 : m_hp( gc.allocGuard() )
570 /// Allocates HP guard from \p gc and protects the pointer \p p of type \p T
571 template <typename T>
572 AutoHPGuard( ThreadGC& gc, T * p )
573 : m_hp( gc.allocGuard() )
579 /// Frees HP guard. The pointer guarded may be deleted after this.
582 m_gc.freeGuard( m_hp );
585 /// Returns thread GC
586 ThreadGC& getGC() const
591 /// Protects the pointer \p p against reclamation (guards the pointer).
592 template <typename T>
593 T * operator =( T * p )
599 std::nullptr_t operator =(std::nullptr_t)
601 return m_hp = nullptr;
604 hazard_ptr get() const
611 /// Auto-managed array of hazard pointers
613 This class is wrapper around cds::gc::hzp::details::HPArray class.
614 \p Count is the size of HP array
616 template <size_t Count>
617 class AutoHPArray: public details::HPArray<Count>
619 ThreadGC& m_mgr ; ///< Thread GC
622 /// Rebind array for other size \p COUNT2
623 template <size_t Count2>
625 typedef AutoHPArray<Count2> other ; ///< rebinding result
629 /// Allocates array of HP guard from \p mgr
630 AutoHPArray( ThreadGC& mgr )
633 mgr.allocGuard( *this );
636 /// Frees array of HP guard
639 m_mgr.freeGuard( *this );
642 /// Returns thread GC
643 ThreadGC& getGC() const { return m_mgr; }
647 }} // namespace cds::gc
650 #include <cds/gc/hzp/details/hp_inline.h>
652 #if CDS_COMPILER == CDS_COMPILER_MSVC
653 # pragma warning(pop)
656 #endif // #ifndef __CDS_GC_HZP_HZP_H