src/dhp_gc.cpp

   1 //$$CDS-header$$
   2
   3 // Dynamic Hazard Pointer memory manager implementation
   4
   5 #include <algorithm>   // std::fill
   6 #include <functional>  // std::hash
   7
   8 #include <cds/gc/details/dhp.h>
   9 #include <cds/algo/int_algo.h>
  10
  11 namespace cds { namespace gc { namespace dhp {
  12
  13     namespace details {
  14
  15         class liberate_set {
  16             typedef retired_ptr_node *  item_type;
  17             typedef cds::details::Allocator<item_type, CDS_DEFAULT_ALLOCATOR>   allocator_type;
  18
  19             size_t const m_nBucketCount;
  20             item_type *  m_Buckets;
  21
  22             item_type&  bucket( retired_ptr_node& node ) const
  23             {
  24                 return bucket( node.m_ptr.m_p );
  25             }
  26             item_type&  bucket( guard_data::guarded_ptr p ) const
  27             {
  28                 return m_Buckets[ std::hash<guard_data::guarded_ptr>()( p ) & (m_nBucketCount - 1)  ];
  29             }
  30
  31         public:
  32             liberate_set( size_t nBucketCount )
  33                 : m_nBucketCount( nBucketCount )
  34             {
  35                 assert( nBucketCount > 0 );
  36                 assert( (nBucketCount & (nBucketCount - 1)) == 0 );
  37
  38                 m_Buckets = allocator_type().NewArray( nBucketCount );
  39                 std::fill( m_Buckets, m_Buckets + nBucketCount, nullptr );
  40             }
  41
  42             ~liberate_set()
  43             {
  44                 allocator_type().Delete( m_Buckets, m_nBucketCount );
  45             }
  46
  47             void insert( retired_ptr_node& node )
  48             {
  49                 node.m_pNext.store( nullptr, atomics::memory_order_relaxed );
  50
  51                 item_type& refBucket = bucket( node );
  52                 if ( refBucket ) {
  53                     item_type p = refBucket;
  54                     do {
  55                         if ( p->m_ptr.m_p == node.m_ptr.m_p ) {
  56                             assert( node.m_pNextFree.load( atomics::memory_order_relaxed ) == nullptr );
  57
  58                             node.m_pNextFree.store( p->m_pNextFree.load( atomics::memory_order_relaxed ), atomics::memory_order_relaxed );
  59                             p->m_pNextFree.store( &node, atomics::memory_order_relaxed );
  60                             return;
  61                         }
  62                         p = p->m_pNext.load(atomics::memory_order_relaxed);
  63                     } while ( p );
  64
  65                     node.m_pNext.store( refBucket, atomics::memory_order_relaxed );
  66                 }
  67                 refBucket = &node;
  68             }
  69
  70             item_type erase( guard_data::guarded_ptr ptr )
  71             {
  72                 item_type& refBucket = bucket( ptr );
  73                 item_type p = refBucket;
  74                 item_type pPrev = nullptr;
  75
  76                 while ( p ) {
  77                     if ( p->m_ptr.m_p == ptr ) {
  78                         if ( pPrev )
  79                             pPrev->m_pNext.store( p->m_pNext.load(atomics::memory_order_relaxed ), atomics::memory_order_relaxed );
  80                         else
  81                             refBucket = p->m_pNext.load(atomics::memory_order_relaxed);
  82                         p->m_pNext.store( nullptr, atomics::memory_order_relaxed );
  83                         return p;
  84                     }
  85                     pPrev = p;
  86                     p = p->m_pNext.load( atomics::memory_order_relaxed );
  87                 }
  88
  89                 return nullptr;
  90             }
  91
  92             typedef std::pair<item_type, item_type>     list_range;
  93
  94             list_range free_all()
  95             {
  96                 item_type pTail = nullptr;
  97                 list_range ret = std::make_pair( pTail, pTail );
  98
  99                 item_type const * pEndBucket = m_Buckets + m_nBucketCount;
 100                 for ( item_type * ppBucket = m_Buckets; ppBucket < pEndBucket; ++ppBucket ) {
 101                     item_type pBucket = *ppBucket;
 102                     if ( pBucket ) {
 103                         if ( !ret.first )
 104                             ret.first = pBucket;
 105                         else
 106                             pTail->m_pNextFree.store( pBucket, atomics::memory_order_relaxed );
 107
 108                         pTail = pBucket;
 109                         for (;;) {
 110                             item_type pNext = pTail->m_pNext.load( atomics::memory_order_relaxed );
 111                             pTail->m_ptr.free();
 112                             pTail->m_pNext.store( nullptr, atomics::memory_order_relaxed );
 113
 114                             while ( pTail->m_pNextFree.load( atomics::memory_order_relaxed )) {
 115                                 pTail = pTail->m_pNextFree.load( atomics::memory_order_relaxed );
 116                                 pTail->m_ptr.free();
 117                                 pTail->m_pNext.store( nullptr, atomics::memory_order_relaxed );
 118                             }
 119
 120                             if ( pNext ) {
 121                                 pTail->m_pNextFree.store( pNext, atomics::memory_order_relaxed );
 122                                 pTail = pNext;
 123                             }
 124                             else
 125                                 break;
 126                         }
 127                     }
 128                 }
 129
 130                 if ( pTail )
 131                     pTail->m_pNextFree.store( nullptr, atomics::memory_order_relaxed );
 132                 ret.second = pTail;
 133                 return ret;
 134             }
 135         };
 136     }
 137
 138     GarbageCollector * GarbageCollector::m_pManager = nullptr;
 139
 140     void CDS_STDCALL GarbageCollector::Construct(
 141         size_t nLiberateThreshold
 142         , size_t nInitialThreadGuardCount
 143         , size_t nEpochCount
 144     )
 145     {
 146         if ( !m_pManager ) {
 147             m_pManager = new GarbageCollector( nLiberateThreshold, nInitialThreadGuardCount, nEpochCount );
 148         }
 149     }
 150
 151     void CDS_STDCALL GarbageCollector::Destruct()
 152     {
 153         delete m_pManager;
 154         m_pManager = nullptr;
 155     }
 156
 157     GarbageCollector::GarbageCollector( size_t nLiberateThreshold, size_t nInitialThreadGuardCount, size_t nEpochCount )
 158         : m_nLiberateThreshold( nLiberateThreshold ? nLiberateThreshold : 1024 )
 159         , m_nInitialThreadGuardCount( nInitialThreadGuardCount ? nInitialThreadGuardCount : 8 )
 160         , m_RetiredAllocator( static_cast<unsigned int>(nEpochCount))
 161         , m_bStatEnabled( false )
 162     {}
 163
 164     GarbageCollector::~GarbageCollector()
 165     {
 166         scan();
 167     }
 168
 169     void GarbageCollector::scan()
 170     {
 171         details::retired_ptr_buffer::privatize_result retiredList = m_RetiredBuffer.privatize();
 172         if ( retiredList.first ) {
 173
 174             size_t nLiberateThreshold = m_nLiberateThreshold.load(atomics::memory_order_relaxed);
 175             details::liberate_set set( beans::ceil2( retiredList.second > nLiberateThreshold ? retiredList.second : nLiberateThreshold ));
 176
 177             // Get list of retired pointers
 178             size_t nRetiredCount = 0;
 179             details::retired_ptr_node * pHead = retiredList.first;
 180             while ( pHead ) {
 181                 details::retired_ptr_node * pNext = pHead->m_pNext.load( atomics::memory_order_relaxed );
 182                 pHead->m_pNextFree.store( nullptr, atomics::memory_order_relaxed );
 183                 set.insert( *pHead );
 184                 pHead = pNext;
 185                 ++nRetiredCount;
 186             }
 187
 188             // Liberate cycle
 189
 190             details::retired_ptr_node * pBusyFirst = nullptr;
 191             details::retired_ptr_node * pBusyLast = nullptr;
 192             size_t nBusyCount = 0;
 193
 194             for ( details::guard_data * pGuard = m_GuardPool.begin(); pGuard; pGuard = pGuard->pGlobalNext.load(atomics::memory_order_acquire) )
 195             {
 196                 // get guarded pointer
 197                 details::guard_data::guarded_ptr valGuarded = pGuard->pPost.load(atomics::memory_order_acquire);
 198
 199                 if ( valGuarded ) {
 200                     details::retired_ptr_node * pRetired = set.erase( valGuarded );
 201                     if ( pRetired ) {
 202                         // Retired pointer is being guarded
 203                         // pRetired is the head of retired pointers list for which the m_ptr.m_p field is equal
 204                         // List is linked on m_pNextFree field
 205
 206                         if ( pBusyLast )
 207                             pBusyLast->m_pNext.store( pRetired, atomics::memory_order_relaxed );
 208                         else
 209                             pBusyFirst = pRetired;
 210                         pBusyLast = pRetired;
 211                         ++nBusyCount;
 212                         details::retired_ptr_node * p = pBusyLast->m_pNextFree.load(atomics::memory_order_relaxed);
 213                         while ( p != nullptr ) {
 214                             pBusyLast->m_pNext.store( p, atomics::memory_order_relaxed );
 215                             pBusyLast = p;
 216                             ++nBusyCount;
 217                         }
 218                     }
 219                 }
 220             }
 221
 222             // Place [pBusyList, pBusyLast] back to m_RetiredBuffer
 223             if ( pBusyFirst )
 224                 m_RetiredBuffer.push_list( pBusyFirst, pBusyLast, nBusyCount );
 225
 226             // Free all retired pointers
 227             details::liberate_set::list_range range = set.free_all();
 228
 229             m_RetiredAllocator.inc_epoch();
 230
 231             if ( range.first ) {
 232                 assert( range.second != nullptr );
 233                 m_RetiredAllocator.free_range( range.first, range.second );
 234             }
 235             else if ( nRetiredCount >= nLiberateThreshold ) {
 236                 // scan() cycle did not free any retired pointer - double scan() threshold
 237                 m_nLiberateThreshold.compare_exchange_strong( nLiberateThreshold, nLiberateThreshold * 2, atomics::memory_order_release, atomics::memory_order_relaxed );
 238             }
 239         }
 240     }
 241 }}} // namespace cds::gc::dhp