collector.cpp

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{
    suspendThread(thread->platformThread);

    PlatformThreadRegisters regs;
    size_t regSize = getPlatformThreadRegisters(thread->platformThread, regs);

    // mark the thread's registers
    markConservatively(static_cast<void*>(&regs), static_cast<void*>(reinterpret_cast<char*>(&regs) + regSize));

    void* stackPointer = otherThreadStackPointer(regs);
    markConservatively(stackPointer, thread->stackBase);

    resumeThread(thread->platformThread);
}

#endif

void Heap::markStackObjectsConservatively()
{
    markCurrentThreadConservatively();

#if ENABLE(JSC_MULTIPLE_THREADS)

    if (m_currentThreadRegistrar) {

        MutexLocker lock(m_registeredThreadsMutex);

#ifndef NDEBUG
        // Forbid malloc during the mark phase. Marking a thread suspends it, so 
        // a malloc inside mark() would risk a deadlock with a thread that had been 
        // suspended while holding the malloc lock.
        fastMallocForbid();
#endif
        // It is safe to access the registeredThreads list, because we earlier asserted that locks are being held,
        // and since this is a shared heap, they are real locks.
        for (Thread* thread = m_registeredThreads; thread; thread = thread->next) {
            if (!pthread_equal(thread->posixThread, pthread_self()))
                markOtherThreadConservatively(thread);
        }
#ifndef NDEBUG
        fastMallocAllow();
#endif
    }
#endif
}

void Heap::setGCProtectNeedsLocking()
{
    // Most clients do not need to call this, with the notable exception of WebCore.
    // Clients that use shared heap have JSLock protection, while others are supposed
    // to do explicit locking. WebCore violates this contract in Database code,
    // which calls gcUnprotect from a secondary thread.
    if (!m_protectedValuesMutex)
        m_protectedValuesMutex.set(new Mutex);
}

void Heap::protect(JSValuePtr k)
{
    ASSERT(k);
    ASSERT(JSLock::currentThreadIsHoldingLock() || !m_globalData->isSharedInstance);

    if (!k.isCell())
        return;

    if (m_protectedValuesMutex)
        m_protectedValuesMutex->lock();

    m_protectedValues.add(k.asCell());

    if (m_protectedValuesMutex)
        m_protectedValuesMutex->unlock();
}

void Heap::unprotect(JSValuePtr k)
{
    ASSERT(k);
    ASSERT(JSLock::currentThreadIsHoldingLock() || !m_globalData->isSharedInstance);

    if (!k.isCell())
        return;

    if (m_protectedValuesMutex)
        m_protectedValuesMutex->lock();

    m_protectedValues.remove(k.asCell());

    if (m_protectedValuesMutex)
        m_protectedValuesMutex->unlock();
}

Heap* Heap::heap(JSValuePtr v)
{
    if (!v.isCell())
        return 0;
    return Heap::cellBlock(v.asCell())->heap;
}

void Heap::markProtectedObjects()
{
    if (m_protectedValuesMutex)
        m_protectedValuesMutex->lock();

    ProtectCountSet::iterator end = m_protectedValues.end();
    for (ProtectCountSet::iterator it = m_protectedValues.begin(); it != end; ++it) {
        JSCell* val = it->first;
        if (!val->marked())
            val->mark();
    }

    if (m_protectedValuesMutex)
        m_protectedValuesMutex->unlock();
}

template <HeapType heapType> size_t Heap::sweep()
{
    typedef typename HeapConstants<heapType>::Block Block;
    typedef typename HeapConstants<heapType>::Cell Cell;

    // SWEEP: delete everything with a zero refcount (garbage) and unmark everything else
    CollectorHeap& heap = heapType == PrimaryHeap ? primaryHeap : numberHeap;
    
    size_t emptyBlocks = 0;
    size_t numLiveObjects = heap.numLiveObjects;
    
    for (size_t block = 0; block < heap.usedBlocks; block++) {
        Block* curBlock = reinterpret_cast<Block*>(heap.blocks[block]);
        
        size_t usedCells = curBlock->usedCells;
        Cell* freeList = curBlock->freeList;
        
        if (usedCells == HeapConstants<heapType>::cellsPerBlock) {
            // special case with a block where all cells are used -- testing indicates this happens often
            for (size_t i = 0; i < HeapConstants<heapType>::cellsPerBlock; i++) {
                if (!curBlock->marked.get(i >> HeapConstants<heapType>::bitmapShift)) {
                    Cell* cell = curBlock->cells + i;
                    
                    if (heapType != NumberHeap) {
                        JSCell* imp = reinterpret_cast<JSCell*>(cell);
                        // special case for allocated but uninitialized object
                        // (We don't need this check earlier because nothing prior this point 
                        // assumes the object has a valid vptr.)
                        if (cell->u.freeCell.zeroIfFree == 0)
                            continue;
                        
                        imp->~JSCell();
                    }
                    
                    --usedCells;
                    --numLiveObjects;
                    
                    // put cell on the free list
                    cell->u.freeCell.zeroIfFree = 0;
                    cell->u.freeCell.next = freeList - (cell + 1);
                    freeList = cell;
                }
            }
        } else {
            size_t minimumCellsToProcess = usedCells;
            for (size_t i = 0; (i < minimumCellsToProcess) & (i < HeapConstants<heapType>::cellsPerBlock); i++) {
                Cell* cell = curBlock->cells + i;
                if (cell->u.freeCell.zeroIfFree == 0) {
                    ++minimumCellsToProcess;
                } else {
                    if (!curBlock->marked.get(i >> HeapConstants<heapType>::bitmapShift)) {
                        if (heapType != NumberHeap) {
                            JSCell* imp = reinterpret_cast<JSCell*>(cell);
                            imp->~JSCell();
                        }
                        --usedCells;
                        --numLiveObjects;
                        
                        // put cell on the free list
                        cell->u.freeCell.zeroIfFree = 0;
                        cell->u.freeCell.next = freeList - (cell + 1); 
                        freeList = cell;
                    }
                }
            }
        }
        
        curBlock->usedCells = static_cast<uint32_t>(usedCells);
        curBlock->freeList = freeList;
        curBlock->marked.clearAll();
        
        if (usedCells == 0) {
            emptyBlocks++;
            if (emptyBlocks > SPARE_EMPTY_BLOCKS) {
#if !DEBUG_COLLECTOR
                freeBlock(reinterpret_cast<CollectorBlock*>(curBlock));
#endif
                // swap with the last block so we compact as we go
                heap.blocks[block] = heap.blocks[heap.usedBlocks - 1];
                heap.usedBlocks--;
                block--; // Don't move forward a step in this case
                
                if (heap.numBlocks > MIN_ARRAY_SIZE && heap.usedBlocks < heap.numBlocks / LOW_WATER_FACTOR) {
                    heap.numBlocks = heap.numBlocks / GROWTH_FACTOR; 
                    heap.blocks = static_cast<CollectorBlock**>(fastRealloc(heap.blocks, heap.numBlocks * sizeof(CollectorBlock*)));
                }
            }
        }
    }
    
    if (heap.numLiveObjects != numLiveObjects)
        heap.firstBlockWithPossibleSpace = 0;
        
    heap.numLiveObjects = numLiveObjects;
    heap.numLiveObjectsAtLastCollect = numLiveObjects;
    heap.extraCost = 0;
    return numLiveObjects;
}
    
bool Heap::collect()
{
#ifndef NDEBUG
    if (m_globalData->isSharedInstance) {
        ASSERT(JSLock::lockCount() > 0);
        ASSERT(JSLock::currentThreadIsHoldingLock());
    }
#endif

    ASSERT((primaryHeap.operationInProgress == NoOperation) | (numberHeap.operationInProgress == NoOperation));
    if ((primaryHeap.operationInProgress != NoOperation) | (numberHeap.operationInProgress != NoOperation))
        CRASH();

    JAVASCRIPTCORE_GC_BEGIN();
    primaryHeap.operationInProgress = Collection;
    numberHeap.operationInProgress = Collection;

    // MARK: first mark all referenced objects recursively starting out from the set of root objects

    markStackObjectsConservatively();
    markProtectedObjects();
    if (m_markListSet && m_markListSet->size())
        ArgList::markLists(*m_markListSet);
    if (m_globalData->exception && !m_globalData->exception.marked())
        m_globalData->exception.mark();
    m_globalData->interpreter->registerFile().markCallFrames(this);
    m_globalData->smallStrings.mark();
    if (m_globalData->scopeNodeBeingReparsed)
        m_globalData->scopeNodeBeingReparsed->mark();

    JAVASCRIPTCORE_GC_MARKED();

    size_t originalLiveObjects = primaryHeap.numLiveObjects + numberHeap.numLiveObjects;
    size_t numLiveObjects = sweep<PrimaryHeap>();
    numLiveObjects += sweep<NumberHeap>();

    primaryHeap.operationInProgress = NoOperation;
    numberHeap.operationInProgress = NoOperation;
    JAVASCRIPTCORE_GC_END(originalLiveObjects, numLiveObjects);

    return numLiveObjects < originalLiveObjects;
}

size_t Heap::objectCount() 
{
    return primaryHeap.numLiveObjects + numberHeap.numLiveObjects - m_globalData->smallStrings.count(); 
}

template <HeapType heapType> 
static void addToStatistics(Heap::Statistics& statistics, const CollectorHeap& heap)
{
    typedef HeapConstants<heapType> HC;
    for (size_t i = 0; i < heap.usedBlocks; ++i) {
        if (heap.blocks[i]) {
            statistics.size += BLOCK_SIZE;
            statistics.free += (HC::cellsPerBlock - heap.blocks[i]->usedCells) * HC::cellSize;
        }
    }
}

Heap::Statistics Heap::statistics() const
{
    Statistics statistics = { 0, 0 };
    JSC::addToStatistics<PrimaryHeap>(statistics, primaryHeap);
    JSC::addToStatistics<NumberHeap>(statistics, numberHeap);
    return statistics;
}

size_t Heap::globalObjectCount()
{
    size_t count = 0;
    if (JSGlobalObject* head = m_globalData->head) {
        JSGlobalObject* o = head;
        do {
            ++count;
            o = o->next();
        } while (o != head);
    }
    return count;
}

size_t Heap::protectedGlobalObjectCount()
{
    if (m_protectedValuesMutex)
        m_protectedValuesMutex->lock();

    size_t count = 0;
    if (JSGlobalObject* head = m_globalData->head) {
        JSGlobalObject* o = head;
        do {
            if (m_protectedValues.contains(o))
                ++count;
            o = o->next();
        } while (o != head);
    }

    if (m_protectedValuesMutex)
        m_protectedValuesMutex->unlock();

    return count;
}

size_t Heap::protectedObjectCount()
{
    if (m_protectedValuesMutex)
        m_protectedValuesMutex->lock();

    size_t result = m_protectedValues.size();

    if (m_protectedValuesMutex)
        m_protectedValuesMutex->unlock();

    return result;
}

static const char* typeName(JSCell* cell)
{
    if (cell->isString())
        return "string";
    if (cell->isNumber())
        return "number";
    if (cell->isGetterSetter())
        return "gettersetter";
    ASSERT(cell->isObject());
    const ClassInfo* info = static_cast<JSObject*>(cell)->classInfo();
    return info ? info->className : "Object";
}

HashCountedSet<const char*>* Heap::protectedObjectTypeCounts()
{
    HashCountedSet<const char*>* counts = new HashCountedSet<const char*>;

    if (m_protectedValuesMutex)
        m_protectedValuesMutex->lock();

    ProtectCountSet::iterator end = m_protectedValues.end();
    for (ProtectCountSet::iterator it = m_protectedValues.begin(); it != end; ++it)
        counts->add(typeName(it->first));

    if (m_protectedValuesMutex)
        m_protectedValuesMutex->unlock();

    return counts;
}

bool Heap::isBusy()
{
    return (primaryHeap.operationInProgress != NoOperation) | (numberHeap.operationInProgress != NoOperation);
}

Heap::iterator Heap::primaryHeapBegin()
{
    return iterator(primaryHeap.blocks, primaryHeap.blocks + primaryHeap.usedBlocks);
}

Heap::iterator Heap::primaryHeapEnd()
{
    return iterator(primaryHeap.blocks + primaryHeap.usedBlocks, primaryHeap.blocks + primaryHeap.usedBlocks);
}

} // namespace JSC