src/hp_gc.cpp

   1 //$$CDS-header$$
   2
   3 /*
   4     File: hzp_gc.cpp
   5
   6     Hazard Pointers memory reclamation strategy implementation
   7
   8     Editions:
   9         2008.02.10    Maxim.Khiszinsky    Created
  10 */
  11
  12 #include <cds/gc/details/hp.h>
  13
  14 #include <algorithm>    // std::sort
  15 #include "hp_const.h"
  16
  17 #define    CDS_HAZARDPTR_STATISTIC( _x )    if ( m_bStatEnabled ) { _x; }
  18
  19 namespace cds { namespace gc {
  20     namespace hp {
  21
  22         /// Max array size of retired pointers
  23         static const size_t c_nMaxRetireNodeCount = c_nHazardPointerPerThread * c_nMaxThreadCount * 2;
  24
  25         GarbageCollector *    GarbageCollector::m_pHZPManager = nullptr;
  26
  27         void CDS_STDCALL GarbageCollector::Construct( size_t nHazardPtrCount, size_t nMaxThreadCount, size_t nMaxRetiredPtrCount, scan_type nScanType )
  28         {
  29             if ( !m_pHZPManager ) {
  30                 m_pHZPManager = new GarbageCollector( nHazardPtrCount, nMaxThreadCount, nMaxRetiredPtrCount, nScanType );
  31             }
  32         }
  33
  34         void CDS_STDCALL GarbageCollector::Destruct( bool bDetachAll )
  35         {
  36             if ( m_pHZPManager ) {
  37                 if ( bDetachAll )
  38                     m_pHZPManager->detachAllThread();
  39
  40                 delete m_pHZPManager;
  41                 m_pHZPManager = nullptr;
  42             }
  43         }
  44
  45         GarbageCollector::GarbageCollector(
  46             size_t nHazardPtrCount,
  47             size_t nMaxThreadCount,
  48             size_t nMaxRetiredPtrCount,
  49             scan_type nScanType
  50         )
  51             : m_pListHead( nullptr )
  52             ,m_bStatEnabled( true )
  53             ,m_nHazardPointerCount( nHazardPtrCount == 0 ? c_nHazardPointerPerThread : nHazardPtrCount )
  54             ,m_nMaxThreadCount( nMaxThreadCount == 0 ? c_nMaxThreadCount : nMaxThreadCount )
  55             ,m_nMaxRetiredPtrCount( nMaxRetiredPtrCount > c_nMaxRetireNodeCount ? nMaxRetiredPtrCount : c_nMaxRetireNodeCount )
  56             ,m_nScanType( nScanType )
  57         {}
  58
  59         GarbageCollector::~GarbageCollector()
  60         {
  61             CDS_DEBUG_ONLY( const cds::OS::ThreadId nullThreadId = cds::OS::c_NullThreadId; )
  62             CDS_DEBUG_ONLY( const cds::OS::ThreadId mainThreadId = cds::OS::getCurrentThreadId() ;)
  63
  64             hplist_node * pHead = m_pListHead.load( atomics::memory_order_relaxed );
  65             m_pListHead.store( nullptr, atomics::memory_order_relaxed );
  66
  67             hplist_node * pNext = nullptr;
  68             for ( hplist_node * hprec = pHead; hprec; hprec = pNext ) {
  69                 assert( hprec->m_idOwner.load( atomics::memory_order_relaxed ) == nullThreadId
  70                     || hprec->m_idOwner.load( atomics::memory_order_relaxed ) == mainThreadId
  71                     || !cds::OS::isThreadAlive( hprec->m_idOwner.load( atomics::memory_order_relaxed ) )
  72                 );
  73                 details::retired_vector& vect = hprec->m_arrRetired;
  74                 details::retired_vector::iterator itRetired = vect.begin();
  75                 details::retired_vector::iterator itRetiredEnd = vect.end();
  76                 while ( itRetired != itRetiredEnd ) {
  77                     DeletePtr( *itRetired );
  78                     ++itRetired;
  79                 }
  80                 vect.clear();
  81                 pNext = hprec->m_pNextNode;
  82                 hprec->m_bFree.store( true, atomics::memory_order_relaxed );
  83                 DeleteHPRec( hprec );
  84             }
  85         }
  86
  87         inline GarbageCollector::hplist_node * GarbageCollector::NewHPRec()
  88         {
  89             CDS_HAZARDPTR_STATISTIC( ++m_Stat.m_AllocNewHPRec );
  90             return new hplist_node( *this );
  91         }
  92
  93         inline void GarbageCollector::DeleteHPRec( hplist_node * pNode )
  94         {
  95             CDS_HAZARDPTR_STATISTIC( ++m_Stat.m_DeleteHPRec );
  96             assert( pNode->m_arrRetired.size() == 0 );
  97             delete pNode;
  98         }
  99
 100         inline void GarbageCollector::DeletePtr( details::retired_ptr& p )
 101         {
 102             CDS_HAZARDPTR_STATISTIC( ++m_Stat.m_DeletedNode );
 103             p.free();
 104         }
 105
 106         details::hp_record * GarbageCollector::alloc_hp_record()
 107         {
 108             CDS_HAZARDPTR_STATISTIC( ++m_Stat.m_AllocHPRec );
 109
 110             hplist_node * hprec;
 111             const cds::OS::ThreadId nullThreadId = cds::OS::c_NullThreadId;
 112             const cds::OS::ThreadId curThreadId  = cds::OS::getCurrentThreadId();
 113
 114             // First try to reuse a retired (non-active) HP record
 115             for ( hprec = m_pListHead.load( atomics::memory_order_acquire ); hprec; hprec = hprec->m_pNextNode ) {
 116                 cds::OS::ThreadId thId = nullThreadId;
 117                 if ( !hprec->m_idOwner.compare_exchange_strong( thId, curThreadId, atomics::memory_order_seq_cst, atomics::memory_order_relaxed ) )
 118                     continue;
 119                 hprec->m_bFree.store( false, atomics::memory_order_release );
 120                 return hprec;
 121             }
 122
 123             // No HP records available for reuse
 124             // Allocate and push a new HP record
 125             hprec = NewHPRec();
 126             hprec->m_idOwner.store( curThreadId, atomics::memory_order_relaxed );
 127             hprec->m_bFree.store( false, atomics::memory_order_relaxed );
 128
 129             atomics::atomic_thread_fence( atomics::memory_order_release );
 130
 131             hplist_node * pOldHead = m_pListHead.load( atomics::memory_order_acquire );
 132             do {
 133                 hprec->m_pNextNode = pOldHead;
 134             } while ( !m_pListHead.compare_exchange_weak( pOldHead, hprec, atomics::memory_order_release, atomics::memory_order_relaxed ));
 135
 136             return hprec;
 137         }
 138
 139         void GarbageCollector::free_hp_record( details::hp_record * pRec )
 140         {
 141             assert( pRec != nullptr );
 142             CDS_HAZARDPTR_STATISTIC( ++m_Stat.m_RetireHPRec );
 143
 144             pRec->clear();
 145             Scan( pRec );
 146             hplist_node * pNode = static_cast<hplist_node *>( pRec );
 147             pNode->m_idOwner.store( cds::OS::c_NullThreadId, atomics::memory_order_release );
 148         }
 149
 150         void GarbageCollector::detachAllThread()
 151         {
 152             hplist_node * pNext = nullptr;
 153             const cds::OS::ThreadId nullThreadId = cds::OS::c_NullThreadId;
 154             for ( hplist_node * hprec = m_pListHead.load(atomics::memory_order_acquire); hprec; hprec = pNext ) {
 155                 pNext = hprec->m_pNextNode;
 156                 if ( hprec->m_idOwner.load(atomics::memory_order_relaxed) != nullThreadId ) {
 157                     free_hp_record( hprec );
 158                 }
 159             }
 160         }
 161
 162         void GarbageCollector::classic_scan( details::hp_record * pRec )
 163         {
 164             CDS_HAZARDPTR_STATISTIC( ++m_Stat.m_ScanCallCount );
 165
 166             std::vector< void * >   plist;
 167             plist.reserve( m_nMaxThreadCount * m_nHazardPointerCount );
 168             assert( plist.size() == 0 );
 169
 170             // Stage 1: Scan HP list and insert non-null values in plist
 171
 172             hplist_node * pNode = m_pListHead.load(atomics::memory_order_acquire);
 173
 174             while ( pNode ) {
 175                 for ( size_t i = 0; i < m_nHazardPointerCount; ++i ) {
 176                     void * hptr = pNode->m_hzp[i];
 177                     if ( hptr )
 178                         plist.push_back( hptr );
 179                 }
 180                 pNode = pNode->m_pNextNode;
 181             }
 182
 183             // Sort plist to simplify search in
 184             std::sort( plist.begin(), plist.end() );
 185
 186             // Stage 2: Search plist
 187             details::retired_vector& arrRetired = pRec->m_arrRetired;
 188
 189             details::retired_vector::iterator itRetired     = arrRetired.begin();
 190             details::retired_vector::iterator itRetiredEnd  = arrRetired.end();
 191             // arrRetired is not a std::vector!
 192             // clear() is just set up item counter to 0, the items is not destroyed
 193             arrRetired.clear();
 194
 195             std::vector< void * >::iterator itBegin = plist.begin();
 196             std::vector< void * >::iterator itEnd = plist.end();
 197             while ( itRetired != itRetiredEnd ) {
 198                 if ( std::binary_search( itBegin, itEnd, itRetired->m_p) ) {
 199                     CDS_HAZARDPTR_STATISTIC( ++m_Stat.m_DeferredNode );
 200                     arrRetired.push( *itRetired );
 201                 }
 202                 else
 203                     DeletePtr( *itRetired );
 204                 ++itRetired;
 205             }
 206         }
 207
 208         void GarbageCollector::inplace_scan( details::hp_record * pRec )
 209         {
 210             CDS_HAZARDPTR_STATISTIC( ++m_Stat.m_ScanCallCount );
 211
 212             // In-place scan algo uses LSB of retired ptr as a mark for internal purposes.
 213             // It is correct if all retired pointers are ar least 2-byte aligned (LSB is zero).
 214             // If it is wrong, we use classic scan algorithm
 215
 216             // Check if all retired pointers has zero LSB
 217             // LSB is used for marking pointers that cannot be deleted yet
 218             details::retired_vector::iterator itRetired     = pRec->m_arrRetired.begin();
 219             details::retired_vector::iterator itRetiredEnd  = pRec->m_arrRetired.end();
 220             for ( auto it = itRetired; it != itRetiredEnd; ++it ) {
 221                 if ( it->m_n & 1 ) {
 222                     // found a pointer with LSB bit set - use classic_scan
 223                     classic_scan( pRec );
 224                     return;
 225                 }
 226             }
 227
 228             // Sort retired pointer array
 229             std::sort( itRetired, itRetiredEnd, cds::gc::details::retired_ptr::less );
 230
 231             // Search guarded pointers in retired array
 232             hplist_node * pNode = m_pListHead.load( atomics::memory_order_acquire );
 233
 234             {
 235                 details::retired_ptr dummyRetired;
 236                 while ( pNode ) {
 237                     for ( size_t i = 0; i < m_nHazardPointerCount; ++i ) {
 238                         void * hptr = pNode->m_hzp[i];
 239                         if ( hptr ) {
 240                             dummyRetired.m_p = hptr;
 241                             details::retired_vector::iterator it = std::lower_bound( itRetired, itRetiredEnd, dummyRetired, cds::gc::details::retired_ptr::less );
 242                             if ( it != itRetiredEnd && it->m_p == hptr ) {
 243                                 // Mark retired pointer as guarded
 244                                 it->m_n |= 1;
 245                             }
 246                         }
 247                     }
 248                     pNode = pNode->m_pNextNode;
 249                 }
 250             }
 251
 252             // Move all marked pointers to head of array
 253             {
 254                 auto itInsert = itRetired;
 255                 for ( auto it = itRetired; it != itRetiredEnd; ++it ) {
 256                     if ( it->m_n & 1 ) {
 257                         it->m_n &= ~1;
 258                         if ( itInsert != it )
 259                             *itInsert = *it;
 260                         ++itInsert;
 261                         CDS_HAZARDPTR_STATISTIC( ++m_Stat.m_DeferredNode );
 262                     }
 263                     else {
 264                         // Retired pointer may be freed
 265                         DeletePtr( *it );
 266                     }
 267                 }
 268                 pRec->m_arrRetired.size( itInsert - itRetired );
 269             }
 270         }
 271
 272         void GarbageCollector::HelpScan( details::hp_record * pThis )
 273         {
 274             CDS_HAZARDPTR_STATISTIC( ++m_Stat.m_HelpScanCallCount );
 275
 276             assert( static_cast<hplist_node *>(pThis)->m_idOwner.load(atomics::memory_order_relaxed) == cds::OS::getCurrentThreadId() );
 277
 278             const cds::OS::ThreadId nullThreadId = cds::OS::c_NullThreadId;
 279             const cds::OS::ThreadId curThreadId = cds::OS::getCurrentThreadId();
 280             for ( hplist_node * hprec = m_pListHead.load(atomics::memory_order_acquire); hprec; hprec = hprec->m_pNextNode ) {
 281
 282                 // If m_bFree == true then hprec->m_arrRetired is empty - we don't need to see it
 283                 if ( hprec->m_bFree.load(atomics::memory_order_acquire) )
 284                     continue;
 285
 286                 // Owns hprec if it is empty.
 287                 // Several threads may work concurrently so we use atomic technique only.
 288                 {
 289                     cds::OS::ThreadId curOwner = hprec->m_idOwner.load(atomics::memory_order_acquire);
 290                     if ( curOwner == nullThreadId || !cds::OS::isThreadAlive( curOwner )) {
 291                         if ( !hprec->m_idOwner.compare_exchange_strong( curOwner, curThreadId, atomics::memory_order_release, atomics::memory_order_relaxed ))
 292                             continue;
 293                     }
 294                     else {
 295                         curOwner = nullThreadId;
 296                         if ( !hprec->m_idOwner.compare_exchange_strong( curOwner, curThreadId, atomics::memory_order_release, atomics::memory_order_relaxed ))
 297                             continue;
 298                     }
 299                 }
 300
 301                 // We own the thread successfully. Now, we can see whether hp_record has retired pointers.
 302                 // If it has ones then we move to pThis that is private for current thread.
 303                 details::retired_vector& src = hprec->m_arrRetired;
 304                 details::retired_vector& dest = pThis->m_arrRetired;
 305                 assert( !dest.isFull());
 306                 details::retired_vector::iterator itRetired = src.begin();
 307                 details::retired_vector::iterator itRetiredEnd = src.end();
 308                 while ( itRetired != itRetiredEnd ) {
 309                     dest.push( *itRetired );
 310                     if ( dest.isFull()) {
 311                         CDS_HAZARDPTR_STATISTIC( ++m_Stat.m_CallScanFromHelpScan );
 312                         Scan( pThis );
 313                     }
 314                     ++itRetired;
 315                 }
 316                 src.clear();
 317
 318                 hprec->m_bFree.store(true, atomics::memory_order_release);
 319                 hprec->m_idOwner.store( nullThreadId, atomics::memory_order_release );
 320             }
 321         }
 322
 323         GarbageCollector::InternalState& GarbageCollector::getInternalState( GarbageCollector::InternalState& stat) const
 324         {
 325             stat.nHPCount                = m_nHazardPointerCount;
 326             stat.nMaxThreadCount         = m_nMaxThreadCount;
 327             stat.nMaxRetiredPtrCount     = m_nMaxRetiredPtrCount;
 328             stat.nHPRecSize              = sizeof( hplist_node )
 329                                             + sizeof(details::retired_ptr) * m_nMaxRetiredPtrCount;
 330
 331             stat.nHPRecAllocated         =
 332                 stat.nHPRecUsed              =
 333                 stat.nTotalRetiredPtrCount   =
 334                 stat.nRetiredPtrInFreeHPRecs = 0;
 335
 336             for ( hplist_node * hprec = m_pListHead.load(atomics::memory_order_acquire); hprec; hprec = hprec->m_pNextNode ) {
 337                 ++stat.nHPRecAllocated;
 338                 stat.nTotalRetiredPtrCount += hprec->m_arrRetired.size();
 339
 340                 if ( hprec->m_bFree.load(atomics::memory_order_relaxed) ) {
 341                     // Free HP record
 342                     stat.nRetiredPtrInFreeHPRecs += hprec->m_arrRetired.size();
 343                 }
 344                 else {
 345                     // Used HP record
 346                     ++stat.nHPRecUsed;
 347                 }
 348             }
 349
 350             // Events
 351             stat.evcAllocHPRec   = m_Stat.m_AllocHPRec;
 352             stat.evcRetireHPRec  = m_Stat.m_RetireHPRec;
 353             stat.evcAllocNewHPRec= m_Stat.m_AllocNewHPRec;
 354             stat.evcDeleteHPRec  = m_Stat.m_DeleteHPRec;
 355
 356             stat.evcScanCall     = m_Stat.m_ScanCallCount;
 357             stat.evcHelpScanCall = m_Stat.m_HelpScanCallCount;
 358             stat.evcScanFromHelpScan= m_Stat.m_CallScanFromHelpScan;
 359
 360             stat.evcDeletedNode  = m_Stat.m_DeletedNode;
 361             stat.evcDeferredNode = m_Stat.m_DeferredNode;
 362
 363             return stat;
 364         }
 365
 366
 367     } //namespace hp
 368 }} // namespace cds::gc