Source/JavaScriptCore/heap/IncrementalSweeper.cpp

/*
 * Copyright (C) 2012, 2016 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
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 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
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 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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#include "config.h"
#include "IncrementalSweeper.h"

#include "Heap.h"
#include "JSObject.h"
#include "JSString.h"
#include "MarkedBlock.h"
#include "JSCInlines.h"
#include <wtf/CurrentTime.h>

namespace JSC {

static const double sweepTimeSlice = .01; // seconds
static const double sweepTimeTotal = .10;
static const double sweepTimeMultiplier = 1.0 / sweepTimeTotal;

void IncrementalSweeper::scheduleTimer()
{
    Base::scheduleTimer(sweepTimeSlice * sweepTimeMultiplier);
}

IncrementalSweeper::IncrementalSweeper(Heap* heap)
    : Base(heap->vm())
    , m_currentAllocator(nullptr)
{
}

void IncrementalSweeper::doWork()
{
    doSweep(WTF::monotonicallyIncreasingTime());
}

void IncrementalSweeper::doSweep(double sweepBeginTime)
{
    while (sweepNextBlock()) {
        double elapsedTime = WTF::monotonicallyIncreasingTime() - sweepBeginTime;
        if (elapsedTime < sweepTimeSlice)
            continue;

        scheduleTimer();
        return;
    }

    cancelTimer();
}

bool IncrementalSweeper::sweepNextBlock()
{
    m_vm->heap.stopIfNecessary();

    MarkedBlock::Handle* block = nullptr;
    
    for (; m_currentAllocator; m_currentAllocator = m_currentAllocator->nextAllocator()) {
        block = m_currentAllocator->findBlockToSweep();
        if (block)
            break;
    }
    
    if (block) {
        DeferGCForAWhile deferGC(m_vm->heap);
        block->sweep();
        m_vm->heap.objectSpace().freeOrShrinkBlock(block);
        return true;
    }

    return m_vm->heap.sweepNextLogicallyEmptyWeakBlock();
}

void IncrementalSweeper::startSweeping()
{
    scheduleTimer();
    m_currentAllocator = m_vm->heap.objectSpace().firstAllocator();
}

void IncrementalSweeper::stopSweeping()
{
    m_currentAllocator = nullptr;
    if (m_vm)
        cancelTimer();
}

} // namespace JSC