runtime/Collector.h

   1 /*
   2  *  Copyright (C) 1999-2000 Harri Porten (porten@kde.org)
   3  *  Copyright (C) 2001 Peter Kelly (pmk@post.com)
   4  *  Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
   5  *
   6  *  This library is free software; you can redistribute it and/or
   7  *  modify it under the terms of the GNU Lesser General Public
   8  *  License as published by the Free Software Foundation; either
   9  *  version 2 of the License, or (at your option) any later version.
  10  *
  11  *  This library is distributed in the hope that it will be useful,
  12  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14  *  Lesser General Public License for more details.
  15  *
  16  *  You should have received a copy of the GNU Lesser General Public
  17  *  License along with this library; if not, write to the Free Software
  18  *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  19  *
  20  */
  21
  22 #ifndef Collector_h
  23 #define Collector_h
  24
  25 #include <stddef.h>
  26 #include <string.h>
  27 #include <wtf/HashCountedSet.h>
  28 #include <wtf/HashSet.h>
  29 #include <wtf/Noncopyable.h>
  30 #include <wtf/OwnPtr.h>
  31 #include <wtf/StdLibExtras.h>
  32 #include <wtf/Threading.h>
  33
  34 #if ENABLE(JSC_MULTIPLE_THREADS)
  35 #include <pthread.h>
  36 #endif
  37
  38 #define ASSERT_CLASS_FITS_IN_CELL(class) COMPILE_ASSERT(sizeof(class) <= CELL_SIZE, class_fits_in_cell)
  39
  40 namespace JSC {
  41
  42     class CollectorBlock;
  43     class JSCell;
  44     class JSGlobalData;
  45     class JSValue;
  46     class MarkedArgumentBuffer;
  47     class MarkStack;
  48
  49     enum OperationInProgress { NoOperation, Allocation, Collection };
  50
  51     class LiveObjectIterator;
  52
  53     struct CollectorHeap {
  54         size_t nextBlock;
  55         size_t nextCell;
  56         CollectorBlock** blocks;
  57
  58         void* nextNumber;
  59
  60         size_t numBlocks;
  61         size_t usedBlocks;
  62
  63         size_t extraCost;
  64         bool didShrink;
  65
  66         OperationInProgress operationInProgress;
  67     };
  68
  69     class Heap : public Noncopyable {
  70     public:
  71         class Thread;
  72
  73         void destroy();
  74
  75         void* allocateNumber(size_t);
  76         void* allocate(size_t);
  77
  78         bool isBusy(); // true if an allocation or collection is in progress
  79         void collectAllGarbage();
  80
  81         static const size_t minExtraCost = 256;
  82         static const size_t maxExtraCost = 1024 * 1024;
  83
  84         void reportExtraMemoryCost(size_t cost);
  85
  86         size_t objectCount() const;
  87         struct Statistics {
  88             size_t size;
  89             size_t free;
  90         };
  91         Statistics statistics() const;
  92
  93         void protect(JSValue);
  94         void unprotect(JSValue);
  95
  96         static Heap* heap(JSValue); // 0 for immediate values
  97         static Heap* heap(JSCell*);
  98
  99         size_t globalObjectCount();
 100         size_t protectedObjectCount();
 101         size_t protectedGlobalObjectCount();
 102         HashCountedSet<const char*>* protectedObjectTypeCounts();
 103
 104         void registerThread(); // Only needs to be called by clients that can use the same heap from multiple threads.
 105
 106         static bool isCellMarked(const JSCell*);
 107         static void markCell(JSCell*);
 108
 109         void markConservatively(MarkStack&, void* start, void* end);
 110
 111         HashSet<MarkedArgumentBuffer*>& markListSet() { if (!m_markListSet) m_markListSet = new HashSet<MarkedArgumentBuffer*>; return *m_markListSet; }
 112
 113         JSGlobalData* globalData() const { return m_globalData; }
 114         static bool isNumber(JSCell*);
 115
 116         LiveObjectIterator primaryHeapBegin();
 117         LiveObjectIterator primaryHeapEnd();
 118
 119     private:
 120         void reset();
 121         void sweep();
 122         static CollectorBlock* cellBlock(const JSCell*);
 123         static size_t cellOffset(const JSCell*);
 124
 125         friend class JSGlobalData;
 126         Heap(JSGlobalData*);
 127         ~Heap();
 128
 129         NEVER_INLINE CollectorBlock* allocateBlock();
 130         NEVER_INLINE void freeBlock(size_t);
 131         NEVER_INLINE void freeBlockPtr(CollectorBlock*);
 132         void freeBlocks();
 133         void resizeBlocks();
 134         void growBlocks(size_t neededBlocks);
 135         void shrinkBlocks(size_t neededBlocks);
 136         void clearMarkBits();
 137         void clearMarkBits(CollectorBlock*);
 138         size_t markedCells(size_t startBlock = 0, size_t startCell = 0) const;
 139
 140         void recordExtraCost(size_t);
 141
 142         void addToStatistics(Statistics&) const;
 143
 144         void markRoots();
 145         void markProtectedObjects(MarkStack&);
 146         void markCurrentThreadConservatively(MarkStack&);
 147         void markCurrentThreadConservativelyInternal(MarkStack&);
 148         void markOtherThreadConservatively(MarkStack&, Thread*);
 149         void markStackObjectsConservatively(MarkStack&);
 150
 151         typedef HashCountedSet<JSCell*> ProtectCountSet;
 152
 153         CollectorHeap m_heap;
 154
 155         ProtectCountSet m_protectedValues;
 156
 157         HashSet<MarkedArgumentBuffer*>* m_markListSet;
 158
 159 #if ENABLE(JSC_MULTIPLE_THREADS)
 160         void makeUsableFromMultipleThreads();
 161
 162         static void unregisterThread(void*);
 163         void unregisterThread();
 164
 165         Mutex m_registeredThreadsMutex;
 166         Thread* m_registeredThreads;
 167         pthread_key_t m_currentThreadRegistrar;
 168 #endif
 169
 170         JSGlobalData* m_globalData;
 171     };
 172
 173     // tunable parameters
 174     template<size_t bytesPerWord> struct CellSize;
 175
 176     // cell size needs to be a power of two for certain optimizations in collector.cpp
 177 #if USE(JSVALUE32)
 178     template<> struct CellSize<sizeof(uint32_t)> { static const size_t m_value = 32; };
 179 #else
 180     template<> struct CellSize<sizeof(uint32_t)> { static const size_t m_value = 64; };
 181 #endif
 182     template<> struct CellSize<sizeof(uint64_t)> { static const size_t m_value = 64; };
 183
 184     const size_t BLOCK_SIZE = 64 * 1024; // 64k
 185
 186     // derived constants
 187     const size_t BLOCK_OFFSET_MASK = BLOCK_SIZE - 1;
 188     const size_t BLOCK_MASK = ~BLOCK_OFFSET_MASK;
 189     const size_t MINIMUM_CELL_SIZE = CellSize<sizeof(void*)>::m_value;
 190     const size_t CELL_ARRAY_LENGTH = (MINIMUM_CELL_SIZE / sizeof(double)) + (MINIMUM_CELL_SIZE % sizeof(double) != 0 ? sizeof(double) : 0);
 191     const size_t CELL_SIZE = CELL_ARRAY_LENGTH * sizeof(double);
 192     const size_t SMALL_CELL_SIZE = CELL_SIZE / 2;
 193     const size_t CELL_MASK = CELL_SIZE - 1;
 194     const size_t CELL_ALIGN_MASK = ~CELL_MASK;
 195     const size_t CELLS_PER_BLOCK = (BLOCK_SIZE - sizeof(Heap*)) * 8 * CELL_SIZE / (8 * CELL_SIZE + 1) / CELL_SIZE; // one bitmap byte can represent 8 cells.
 196
 197     const size_t BITMAP_SIZE = (CELLS_PER_BLOCK + 7) / 8;
 198     const size_t BITMAP_WORDS = (BITMAP_SIZE + 3) / sizeof(uint32_t);
 199
 200     struct CollectorBitmap {
 201         uint32_t bits[BITMAP_WORDS];
 202         bool get(size_t n) const { return !!(bits[n >> 5] & (1 << (n & 0x1F))); }
 203         void set(size_t n) { bits[n >> 5] |= (1 << (n & 0x1F)); }
 204         void clear(size_t n) { bits[n >> 5] &= ~(1 << (n & 0x1F)); }
 205         void clearAll() { memset(bits, 0, sizeof(bits)); }
 206         size_t count(size_t startCell = 0)
 207         {
 208             size_t result = 0;
 209             for ( ; (startCell & 0x1F) != 0; ++startCell) {
 210                 if (get(startCell))
 211                     ++result;
 212             }
 213             for (size_t i = startCell >> 5; i < BITMAP_WORDS; ++i)
 214                 result += WTF::bitCount(bits[i]);
 215             return result;
 216         }
 217         size_t isEmpty() // Much more efficient than testing count() == 0.
 218         {
 219             for (size_t i = 0; i < BITMAP_WORDS; ++i)
 220                 if (bits[i] != 0)
 221                     return false;
 222             return true;
 223         }
 224     };
 225
 226     struct CollectorCell {
 227         double memory[CELL_ARRAY_LENGTH];
 228     };
 229
 230     class CollectorBlock {
 231     public:
 232         CollectorCell cells[CELLS_PER_BLOCK];
 233         CollectorBitmap marked;
 234         Heap* heap;
 235     };
 236
 237     struct HeapConstants {
 238         static const size_t cellSize = CELL_SIZE;
 239         static const size_t cellsPerBlock = CELLS_PER_BLOCK;
 240         typedef CollectorCell Cell;
 241         typedef CollectorBlock Block;
 242     };
 243
 244     inline CollectorBlock* Heap::cellBlock(const JSCell* cell)
 245     {
 246         return reinterpret_cast<CollectorBlock*>(reinterpret_cast<uintptr_t>(cell) & BLOCK_MASK);
 247     }
 248
 249     inline size_t Heap::cellOffset(const JSCell* cell)
 250     {
 251         return (reinterpret_cast<uintptr_t>(cell) & BLOCK_OFFSET_MASK) / CELL_SIZE;
 252     }
 253
 254     inline bool Heap::isCellMarked(const JSCell* cell)
 255     {
 256         return cellBlock(cell)->marked.get(cellOffset(cell));
 257     }
 258
 259     inline void Heap::markCell(JSCell* cell)
 260     {
 261         cellBlock(cell)->marked.set(cellOffset(cell));
 262     }
 263
 264     inline void Heap::reportExtraMemoryCost(size_t cost)
 265     {
 266         if (cost > minExtraCost)
 267             recordExtraCost(cost);
 268     }
 269
 270     inline void* Heap::allocateNumber(size_t s)
 271     {
 272         if (void* result = m_heap.nextNumber) {
 273             m_heap.nextNumber = 0;
 274             return result;
 275         }
 276
 277         void* result = allocate(s);
 278         m_heap.nextNumber = static_cast<char*>(result) + (CELL_SIZE / 2);
 279         return result;
 280     }
 281
 282 } // namespace JSC
 283
 284 #endif /* Collector_h */