MarkedBlock.cpp

/*
 * Copyright (C) 2011 Apple Inc. All rights reserved.
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#include "config.h"
#include "MarkedBlock.h"

#include "IncrementalSweeper.h"
#include "JSCell.h"
#include "JSDestructibleObject.h"


namespace JSC {

MarkedBlock* MarkedBlock::create(DeadBlock* block, MarkedAllocator* allocator, size_t cellSize, DestructorType destructorType)
{
    Region* region = block->region();
    return new (NotNull, block) MarkedBlock(region, allocator, cellSize, destructorType);
}

MarkedBlock::MarkedBlock(Region* region, MarkedAllocator* allocator, size_t cellSize, DestructorType destructorType)
    : HeapBlock<MarkedBlock>(region)
    , m_atomsPerCell((cellSize + atomSize - 1) / atomSize)
    , m_endAtom(atomsPerBlock - m_atomsPerCell + 1)
    , m_destructorType(destructorType)
    , m_allocator(allocator)
    , m_state(New) // All cells start out unmarked.
    , m_weakSet(allocator->heap()->globalData())
{
    ASSERT(allocator);
    HEAP_LOG_BLOCK_STATE_TRANSITION(this);
}

inline void MarkedBlock::callDestructor(JSCell* cell)
{
    // A previous eager sweep may already have run cell's destructor.
    if (cell->isZapped())
        return;

#if ENABLE(SIMPLE_HEAP_PROFILING)
    m_heap->m_destroyedTypeCounts.countVPtr(vptr);
#endif

    cell->methodTable()->destroy(cell);
    cell->zap();
}

template<MarkedBlock::BlockState blockState, MarkedBlock::SweepMode sweepMode, MarkedBlock::DestructorType dtorType>
MarkedBlock::FreeList MarkedBlock::specializedSweep()
{
    ASSERT(blockState != Allocated && blockState != FreeListed);
    ASSERT(!(dtorType == MarkedBlock::None && sweepMode == SweepOnly));

    // This produces a free list that is ordered in reverse through the block.
    // This is fine, since the allocation code makes no assumptions about the
    // order of the free list.
    FreeCell* head = 0;
    size_t count = 0;
    for (size_t i = firstAtom(); i < m_endAtom; i += m_atomsPerCell) {
        if (blockState == Marked && m_marks.get(i))
            continue;

        JSCell* cell = reinterpret_cast_ptr<JSCell*>(&atoms()[i]);

        if (dtorType != MarkedBlock::None && blockState != New)
            callDestructor(cell);

        if (sweepMode == SweepToFreeList) {
            FreeCell* freeCell = reinterpret_cast<FreeCell*>(cell);
            freeCell->next = head;
            head = freeCell;
            ++count;
        }
    }

    m_state = ((sweepMode == SweepToFreeList) ? FreeListed : Marked);
    return FreeList(head, count * cellSize());
}

MarkedBlock::FreeList MarkedBlock::sweep(SweepMode sweepMode)
{
    HEAP_LOG_BLOCK_STATE_TRANSITION(this);

    m_weakSet.sweep();

    if (sweepMode == SweepOnly && m_destructorType == MarkedBlock::None)
        return FreeList();

    if (m_destructorType == MarkedBlock::ImmortalStructure)
        return sweepHelper<MarkedBlock::ImmortalStructure>(sweepMode);
    if (m_destructorType == MarkedBlock::Normal)
        return sweepHelper<MarkedBlock::Normal>(sweepMode);
    return sweepHelper<MarkedBlock::None>(sweepMode);
}

template<MarkedBlock::DestructorType dtorType>
MarkedBlock::FreeList MarkedBlock::sweepHelper(SweepMode sweepMode)
{
    switch (m_state) {
    case New:
        ASSERT(sweepMode == SweepToFreeList);
        return specializedSweep<New, SweepToFreeList, dtorType>();
    case FreeListed:
        // Happens when a block transitions to fully allocated.
        ASSERT(sweepMode == SweepToFreeList);
        return FreeList();
    case Allocated:
        ASSERT_NOT_REACHED();
        return FreeList();
    case Marked:
        return sweepMode == SweepToFreeList
            ? specializedSweep<Marked, SweepToFreeList, dtorType>()
            : specializedSweep<Marked, SweepOnly, dtorType>();
    }

    ASSERT_NOT_REACHED();
    return FreeList();
}

class SetAllMarksFunctor : public MarkedBlock::VoidFunctor {
public:
    void operator()(JSCell* cell)
    {
        MarkedBlock::blockFor(cell)->setMarked(cell);
    }
};

void MarkedBlock::canonicalizeCellLivenessData(const FreeList& freeList)
{
    HEAP_LOG_BLOCK_STATE_TRANSITION(this);
    FreeCell* head = freeList.head;

    if (m_state == Marked) {
        // If the block is in the Marked state then we know that:
        // 1) It was not used for allocation during the previous allocation cycle.
        // 2) It may have dead objects, and we only know them to be dead by the
        //    fact that their mark bits are unset.
        // Hence if the block is Marked we need to leave it Marked.
        
        ASSERT(!head);
        return;
    }
   
    ASSERT(m_state == FreeListed);
    
    // Roll back to a coherent state for Heap introspection. Cells newly
    // allocated from our free list are not currently marked, so we need another
    // way to tell what's live vs dead. 
    
    SetAllMarksFunctor functor;
    forEachCell(functor);

    FreeCell* next;
    for (FreeCell* current = head; current; current = next) {
        next = current->next;
        reinterpret_cast<JSCell*>(current)->zap();
        clearMarked(current);
    }
    
    m_state = Marked;
}

} // namespace JSC