qtdeclarative/src/qml/memory/qv4mm.cpp

// Copyright (C) 2021 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only

#include "qv4engine_p.h"
#include "qv4object_p.h"
#include "qv4mm_p.h"
#include "qv4qobjectwrapper_p.h"
#include "qv4identifiertable_p.h"
#include <QtCore/qalgorithms.h>
#include <QtCore/private/qnumeric_p.h>
#include <QtCore/qloggingcategory.h>
#include <private/qv4alloca_p.h>
#include <qqmlengine.h>
#include "PageReservation.h"
#include "PageAllocation.h"

#include <QElapsedTimer>
#include <QMap>
#include <QScopedValueRollback>

#include <iostream>
#include <cstdlib>
#include <algorithm>
#include "qv4profiling_p.h"
#include "qv4mapobject_p.h"
#include "qv4setobject_p.h"

#include <chrono>

//#define MM_STATS

#if !defined(MM_STATS) && !defined(QT_NO_DEBUG)
#define MM_STATS
#endif

#if MM_DEBUG
#define DEBUG qDebug() << "MM:"
#else
#define DEBUG if (1) ; else qDebug() << "MM:"
#endif

#ifdef V4_USE_VALGRIND
#include <valgrind/valgrind.h>
#include <valgrind/memcheck.h>
#endif

#ifdef V4_USE_HEAPTRACK
#include <heaptrack_api.h>
#endif

#if OS(QNX)
#include <sys/storage.h>   // __tls()
#endif

#if USE(PTHREADS) && HAVE(PTHREAD_NP_H)
#include <pthread_np.h>
#endif

Q_LOGGING_CATEGORY(lcGcStats, "qt.qml.gc.statistics")
Q_DECLARE_LOGGING_CATEGORY(lcGcStats)
Q_LOGGING_CATEGORY(lcGcAllocatorStats, "qt.qml.gc.allocatorStats")
Q_DECLARE_LOGGING_CATEGORY(lcGcAllocatorStats)

using namespace WTF;

QT_BEGIN_NAMESPACE

namespace QV4 {

enum {
    MinSlotsGCLimit = QV4::Chunk::AvailableSlots*16,
    GCOverallocation = 200 /* Max overallocation by the GC in % */
};

struct MemorySegment {
    enum {
#ifdef Q_OS_RTEMS
        NumChunks = sizeof(quint64),
#else
        NumChunks = 8*sizeof(quint64),
#endif
        SegmentSize = NumChunks*Chunk::ChunkSize,
    };

    MemorySegment(size_t size)
    {
        size += Chunk::ChunkSize; // make sure we can get enough 64k alignment memory
        if (size < SegmentSize)
            size = SegmentSize;

        pageReservation = PageReservation::reserve(size, OSAllocator::JSGCHeapPages);
        base = reinterpret_cast<Chunk *>((reinterpret_cast<quintptr>(pageReservation.base()) + Chunk::ChunkSize - 1) & ~(Chunk::ChunkSize - 1));
        nChunks = NumChunks;
        availableBytes = size - (reinterpret_cast<quintptr>(base) - reinterpret_cast<quintptr>(pageReservation.base()));
        if (availableBytes < SegmentSize)
            --nChunks;
    }
    MemorySegment(MemorySegment &&other) {
        qSwap(pageReservation, other.pageReservation);
        qSwap(base, other.base);
        qSwap(allocatedMap, other.allocatedMap);
        qSwap(availableBytes, other.availableBytes);
        qSwap(nChunks, other.nChunks);
    }

    ~MemorySegment() {
        if (base)
            pageReservation.deallocate();
    }

    void setBit(size_t index) {
        Q_ASSERT(index < nChunks);
        quint64 bit = static_cast<quint64>(1) << index;
//        qDebug() << "    setBit" << hex << index << (index & (Bits - 1)) << bit;
        allocatedMap |= bit;
    }
    void clearBit(size_t index) {
        Q_ASSERT(index < nChunks);
        quint64 bit = static_cast<quint64>(1) << index;
//        qDebug() << "    setBit" << hex << index << (index & (Bits - 1)) << bit;
        allocatedMap &= ~bit;
    }
    bool testBit(size_t index) const {
        Q_ASSERT(index < nChunks);
        quint64 bit = static_cast<quint64>(1) << index;
        return (allocatedMap & bit);
    }

    Chunk *allocate(size_t size);
    void free(Chunk *chunk, size_t size) {
        DEBUG << "freeing chunk" << chunk;
        size_t index = static_cast<size_t>(chunk - base);
        size_t end = qMin(static_cast<size_t>(NumChunks), index + (size - 1)/Chunk::ChunkSize + 1);
        while (index < end) {
            Q_ASSERT(testBit(index));
            clearBit(index);
            ++index;
        }

        size_t pageSize = WTF::pageSize();
        size = (size + pageSize - 1) & ~(pageSize - 1);
#if !defined(Q_OS_LINUX) && !defined(Q_OS_WIN)
        // Linux and Windows zero out pages that have been decommitted and get committed again.
        // unfortunately that's not true on other OSes (e.g. BSD based ones), so zero out the
        // memory before decommit, so that we can be sure that all chunks we allocate will be
        // zero initialized.
        memset(chunk, 0, size);
#endif
        pageReservation.decommit(chunk, size);
    }

    bool contains(Chunk *c) const {
        return c >= base && c < base + nChunks;
    }

    PageReservation pageReservation;
    Chunk *base = nullptr;
    quint64 allocatedMap = 0;
    size_t availableBytes = 0;
    uint nChunks = 0;
};

Chunk *MemorySegment::allocate(size_t size)
{
    if (!allocatedMap && size >= SegmentSize) {
        // chunk allocated for one huge allocation
        Q_ASSERT(availableBytes >= size);
        pageReservation.commit(base, size);
        allocatedMap = ~static_cast<quint64>(0);
        return base;
    }
    size_t requiredChunks = (size + sizeof(Chunk) - 1)/sizeof(Chunk);
    uint sequence = 0;
    Chunk *candidate = nullptr;
    for (uint i = 0; i < nChunks; ++i) {
        if (!testBit(i)) {
            if (!candidate)
                candidate = base + i;
            ++sequence;
        } else {
            candidate = nullptr;
            sequence = 0;
        }
        if (sequence == requiredChunks) {
            pageReservation.commit(candidate, size);
            for (uint i = 0; i < requiredChunks; ++i)
                setBit(candidate - base + i);
            DEBUG << "allocated chunk " << candidate << Qt::hex << size;

            return candidate;
        }
    }
    return nullptr;
}

struct ChunkAllocator {
    ChunkAllocator() {}

    size_t requiredChunkSize(size_t size) {
        size += Chunk::HeaderSize; // space required for the Chunk header
        size_t pageSize = WTF::pageSize();
        size = (size + pageSize - 1) & ~(pageSize - 1); // align to page sizes
        if (size < Chunk::ChunkSize)
            size = Chunk::ChunkSize;
        return size;
    }

    Chunk *allocate(size_t size = 0);
    void free(Chunk *chunk, size_t size = 0);

    std::vector<MemorySegment> memorySegments;
};

Chunk *ChunkAllocator::allocate(size_t size)
{
    size = requiredChunkSize(size);
    for (auto &m : memorySegments) {
        if (~m.allocatedMap) {
            Chunk *c = m.allocate(size);
            if (c)
                return c;
        }
    }

    // allocate a new segment
    memorySegments.push_back(MemorySegment(size));
    Chunk *c = memorySegments.back().allocate(size);
    Q_ASSERT(c);
    return c;
}

void ChunkAllocator::free(Chunk *chunk, size_t size)
{
    size = requiredChunkSize(size);
    for (auto &m : memorySegments) {
        if (m.contains(chunk)) {
            m.free(chunk, size);
            return;
        }
    }
    Q_ASSERT(false);
}

#ifdef DUMP_SWEEP
QString binary(quintptr n) {
    QString s = QString::number(n, 2);
    while (s.length() < 64)
        s.prepend(QChar::fromLatin1('0'));
    return s;
}
#define SDUMP qDebug
#else
QString binary(quintptr) { return QString(); }
#define SDUMP if (1) ; else qDebug
#endif

// Stores a classname -> freed count mapping.
typedef QHash<const char*, int> MMStatsHash;
Q_GLOBAL_STATIC(MMStatsHash, freedObjectStatsGlobal)

// This indirection avoids sticking QHash code in each of the call sites, which
// shaves off some instructions in the case that it's unused.
static void increaseFreedCountForClass(const char *className)
{
    (*freedObjectStatsGlobal())[className]++;
}

//bool Chunk::sweep(ClassDestroyStatsCallback classCountPtr)
bool Chunk::sweep(ExecutionEngine *engine)
{
    bool hasUsedSlots = false;
    SDUMP() << "sweeping chunk" << this;
    HeapItem *o = realBase();
    bool lastSlotFree = false;
    for (uint i = 0; i < Chunk::EntriesInBitmap; ++i) {
        quintptr toFree = objectBitmap[i] ^ blackBitmap[i];
        Q_ASSERT((toFree & objectBitmap[i]) == toFree); // check all black objects are marked as being used
        quintptr e = extendsBitmap[i];
        SDUMP() << "   index=" << i;
        SDUMP() << "        toFree      =" << binary(toFree);
        SDUMP() << "        black       =" << binary(blackBitmap[i]);
        SDUMP() << "        object      =" << binary(objectBitmap[i]);
        SDUMP() << "        extends     =" << binary(e);
        if (lastSlotFree)
            e &= (e + 1); // clear all lowest extent bits
        while (toFree) {
            uint index = qCountTrailingZeroBits(toFree);
            quintptr bit = (static_cast<quintptr>(1) << index);

            toFree ^= bit; // mask out freed slot
            //            DEBUG << "       index" << hex << index << toFree;

            // remove all extends slots that have been freed
            // this is a bit of bit trickery.
            quintptr mask = (bit << 1) - 1; // create a mask of 1's to the right of and up to the current bit
            quintptr objmask = e | mask; // or'ing mask with e gives all ones until the end of the current object
            quintptr result = objmask + 1;
            Q_ASSERT(qCountTrailingZeroBits(result) - index != 0); // ensure we freed something
            result |= mask; // ensure we don't clear stuff to the right of the current object
            e &= result;

            HeapItem *itemToFree = o + index;
            Heap::Base *b = *itemToFree;
            const VTable *v = b->internalClass->vtable;
//            if (Q_UNLIKELY(classCountPtr))
//                classCountPtr(v->className);
            if (v->destroy) {
                v->destroy(b);
                b->_checkIsDestroyed();
            }
#ifdef V4_USE_HEAPTRACK
            heaptrack_report_free(itemToFree);
#endif
        }
        Q_V4_PROFILE_DEALLOC(engine, qPopulationCount((objectBitmap[i] | extendsBitmap[i])
                                                      - (blackBitmap[i] | e)) * Chunk::SlotSize,
                             Profiling::SmallItem);
        objectBitmap[i] = blackBitmap[i];
        hasUsedSlots |= (blackBitmap[i] != 0);
        extendsBitmap[i] = e;
        lastSlotFree = !((objectBitmap[i]|extendsBitmap[i]) >> (sizeof(quintptr)*8 - 1));
        SDUMP() << "        new extends =" << binary(e);
        SDUMP() << "        lastSlotFree" << lastSlotFree;
        Q_ASSERT((objectBitmap[i] & extendsBitmap[i]) == 0);
        o += Chunk::Bits;
    }
    //    DEBUG << "swept chunk" << this << "freed" << slotsFreed << "slots.";
    return hasUsedSlots;
}

void Chunk::freeAll(ExecutionEngine *engine)
{
    //    DEBUG << "sweeping chunk" << this << (*freeList);
    HeapItem *o = realBase();
    for (uint i = 0; i < Chunk::EntriesInBitmap; ++i) {
        quintptr toFree = objectBitmap[i];
        quintptr e = extendsBitmap[i];
        //        DEBUG << hex << "   index=" << i << toFree;
        while (toFree) {
            uint index = qCountTrailingZeroBits(toFree);
            quintptr bit = (static_cast<quintptr>(1) << index);

            toFree ^= bit; // mask out freed slot
            //            DEBUG << "       index" << hex << index << toFree;

            // remove all extends slots that have been freed
            // this is a bit of bit trickery.
            quintptr mask = (bit << 1) - 1; // create a mask of 1's to the right of and up to the current bit
            quintptr objmask = e | mask; // or'ing mask with e gives all ones until the end of the current object
            quintptr result = objmask + 1;
            Q_ASSERT(qCountTrailingZeroBits(result) - index != 0); // ensure we freed something
            result |= mask; // ensure we don't clear stuff to the right of the current object
            e &= result;

            HeapItem *itemToFree = o + index;
            Heap::Base *b = *itemToFree;
            if (b->internalClass->vtable->destroy) {
                b->internalClass->vtable->destroy(b);
                b->_checkIsDestroyed();
            }
#ifdef V4_USE_HEAPTRACK
            heaptrack_report_free(itemToFree);
#endif
        }
        Q_V4_PROFILE_DEALLOC(engine, (qPopulationCount(objectBitmap[i]|extendsBitmap[i])
                             - qPopulationCount(e)) * Chunk::SlotSize, Profiling::SmallItem);
        objectBitmap[i] = 0;
        extendsBitmap[i] = e;
        o += Chunk::Bits;
    }
    //    DEBUG << "swept chunk" << this << "freed" << slotsFreed << "slots.";
}

void Chunk::resetBlackBits()
{
    memset(blackBitmap, 0, sizeof(blackBitmap));
}

void Chunk::sortIntoBins(HeapItem **bins, uint nBins)
{
//    qDebug() << "sortIntoBins:";
    HeapItem *base = realBase();
#if QT_POINTER_SIZE == 8
    const int start = 0;
#else
    const int start = 1;
#endif
#ifndef QT_NO_DEBUG
    uint freeSlots = 0;
    uint allocatedSlots = 0;
#endif
    for (int i = start; i < EntriesInBitmap; ++i) {
        quintptr usedSlots = (objectBitmap[i]|extendsBitmap[i]);
#if QT_POINTER_SIZE == 8
        if (!i)
            usedSlots |= (static_cast<quintptr>(1) << (HeaderSize/SlotSize)) - 1;
#endif
#ifndef QT_NO_DEBUG
        allocatedSlots += qPopulationCount(usedSlots);
//        qDebug() << hex << "   i=" << i << "used=" << usedSlots;
#endif
        while (1) {
            uint index = qCountTrailingZeroBits(usedSlots + 1);
            if (index == Bits)
                break;
            uint freeStart = i*Bits + index;
            usedSlots &= ~((static_cast<quintptr>(1) << index) - 1);
            while (!usedSlots) {
                if (++i < EntriesInBitmap) {
                    usedSlots = (objectBitmap[i]|extendsBitmap[i]);
                } else {
                    Q_ASSERT(i == EntriesInBitmap);
                    // Overflows to 0 when counting trailing zeroes above in next iteration.
                    // Then, all the bits are zeroes and we break.
                    usedSlots = std::numeric_limits<quintptr>::max();
                    break;
                }
#ifndef QT_NO_DEBUG
                allocatedSlots += qPopulationCount(usedSlots);
//                qDebug() << hex << "   i=" << i << "used=" << usedSlots;
#endif
            }
            HeapItem *freeItem = base + freeStart;

            index = qCountTrailingZeroBits(usedSlots);
            usedSlots |= (quintptr(1) << index) - 1;
            uint freeEnd = i*Bits + index;
            uint nSlots = freeEnd - freeStart;
#ifndef QT_NO_DEBUG
//            qDebug() << hex << "   got free slots from" << freeStart << "to" << freeEnd << "n=" << nSlots << "usedSlots=" << usedSlots;
            freeSlots += nSlots;
#endif
            Q_ASSERT(freeEnd > freeStart && freeEnd <= NumSlots);
            freeItem->freeData.availableSlots = nSlots;
            uint bin = qMin(nBins - 1, nSlots);
            freeItem->freeData.next = bins[bin];
            bins[bin] = freeItem;
        }
    }
#ifndef QT_NO_DEBUG
    Q_ASSERT(freeSlots + allocatedSlots == (EntriesInBitmap - start) * 8 * sizeof(quintptr));
#endif
}

HeapItem *BlockAllocator::allocate(size_t size, bool forceAllocation) {
    Q_ASSERT((size % Chunk::SlotSize) == 0);
    size_t slotsRequired = size >> Chunk::SlotSizeShift;

    if (allocationStats)
        ++allocationStats[binForSlots(slotsRequired)];

    HeapItem **last;

    HeapItem *m;

    if (slotsRequired < NumBins - 1) {
        m = freeBins[slotsRequired];
        if (m) {
            freeBins[slotsRequired] = m->freeData.next;
            goto done;
        }
    }

    if (nFree >= slotsRequired) {
        // use bump allocation
        Q_ASSERT(nextFree);
        m = nextFree;
        nextFree += slotsRequired;
        nFree -= slotsRequired;
        goto done;
    }

    //        DEBUG << "No matching bin found for item" << size << bin;
    // search last bin for a large enough item
    last = &freeBins[NumBins - 1];
    while ((m = *last)) {
        if (m->freeData.availableSlots >= slotsRequired) {
            *last = m->freeData.next; // take it out of the list

            size_t remainingSlots = m->freeData.availableSlots - slotsRequired;
            //                DEBUG << "found large free slots of size" << m->freeData.availableSlots << m << "remaining" << remainingSlots;
            if (remainingSlots == 0)
                goto done;

            HeapItem *remainder = m + slotsRequired;
            if (remainingSlots > nFree) {
                if (nFree) {
                    size_t bin = binForSlots(nFree);
                    nextFree->freeData.next = freeBins[bin];
                    nextFree->freeData.availableSlots = nFree;
                    freeBins[bin] = nextFree;
                }
                nextFree = remainder;
                nFree = remainingSlots;
            } else {
                remainder->freeData.availableSlots = remainingSlots;
                size_t binForRemainder = binForSlots(remainingSlots);
                remainder->freeData.next = freeBins[binForRemainder];
                freeBins[binForRemainder] = remainder;
            }
            goto done;
        }
        last = &m->freeData.next;
    }

    if (slotsRequired < NumBins - 1) {
        // check if we can split up another slot
        for (size_t i = slotsRequired + 1; i < NumBins - 1; ++i) {
            m = freeBins[i];
            if (m) {
                freeBins[i] = m->freeData.next; // take it out of the list
//                qDebug() << "got item" << slotsRequired << "from slot" << i;
                size_t remainingSlots = i - slotsRequired;
                Q_ASSERT(remainingSlots < NumBins - 1);
                HeapItem *remainder = m + slotsRequired;
                remainder->freeData.availableSlots = remainingSlots;
                remainder->freeData.next = freeBins[remainingSlots];
                freeBins[remainingSlots] = remainder;
                goto done;
            }
        }
    }

    if (!m) {
        if (!forceAllocation)
            return nullptr;
        if (nFree) {
            // Save any remaining slots of the current chunk
            // for later, smaller allocations.
            size_t bin = binForSlots(nFree);
            nextFree->freeData.next = freeBins[bin];
            nextFree->freeData.availableSlots = nFree;
            freeBins[bin] = nextFree;
        }
        Chunk *newChunk = chunkAllocator->allocate();
        Q_V4_PROFILE_ALLOC(engine, Chunk::DataSize, Profiling::HeapPage);
        chunks.push_back(newChunk);
        nextFree = newChunk->first();
        nFree = Chunk::AvailableSlots;
        m = nextFree;
        nextFree += slotsRequired;
        nFree -= slotsRequired;
    }

done:
    m->setAllocatedSlots(slotsRequired);
    Q_V4_PROFILE_ALLOC(engine, slotsRequired * Chunk::SlotSize, Profiling::SmallItem);
#ifdef V4_USE_HEAPTRACK
    heaptrack_report_alloc(m, slotsRequired * Chunk::SlotSize);
#endif
    //        DEBUG << "   " << hex << m->chunk() << m->chunk()->objectBitmap[0] << m->chunk()->extendsBitmap[0] << (m - m->chunk()->realBase());
    return m;
}

void BlockAllocator::sweep()
{
    nextFree = nullptr;
    nFree = 0;
    memset(freeBins, 0, sizeof(freeBins));

//    qDebug() << "BlockAlloc: sweep";
    usedSlotsAfterLastSweep = 0;

    auto firstEmptyChunk = std::partition(chunks.begin(), chunks.end(), [this](Chunk *c) {
        return c->sweep(engine);
    });

    std::for_each(chunks.begin(), firstEmptyChunk, [this](Chunk *c) {
        c->sortIntoBins(freeBins, NumBins);
        usedSlotsAfterLastSweep += c->nUsedSlots();
    });

    // only free the chunks at the end to avoid that the sweep() calls indirectly
    // access freed memory
    std::for_each(firstEmptyChunk, chunks.end(), [this](Chunk *c) {
        Q_V4_PROFILE_DEALLOC(engine, Chunk::DataSize, Profiling::HeapPage);
        chunkAllocator->free(c);
    });

    chunks.erase(firstEmptyChunk, chunks.end());
}

void BlockAllocator::freeAll()
{
    for (auto c : chunks)
        c->freeAll(engine);
    for (auto c : chunks) {
        Q_V4_PROFILE_DEALLOC(engine, Chunk::DataSize, Profiling::HeapPage);
        chunkAllocator->free(c);
    }
}

void BlockAllocator::resetBlackBits()
{
    for (auto c : chunks)
        c->resetBlackBits();
}

HeapItem *HugeItemAllocator::allocate(size_t size) {
    MemorySegment *m = nullptr;
    Chunk *c = nullptr;
    if (size >= MemorySegment::SegmentSize/2) {
        // too large to handle through the ChunkAllocator, let's get our own memory segement
        size += Chunk::HeaderSize; // space required for the Chunk header
        size_t pageSize = WTF::pageSize();
        size = (size + pageSize - 1) & ~(pageSize - 1); // align to page sizes
        m = new MemorySegment(size);
        c = m->allocate(size);
    } else {
        c = chunkAllocator->allocate(size);
    }
    Q_ASSERT(c);
    chunks.push_back(HugeChunk{m, c, size});
    Chunk::setBit(c->objectBitmap, c->first() - c->realBase());
    Q_V4_PROFILE_ALLOC(engine, size, Profiling::LargeItem);
#ifdef V4_USE_HEAPTRACK
    heaptrack_report_alloc(c, size);
#endif
    return c->first();
}

static void freeHugeChunk(ChunkAllocator *chunkAllocator, const HugeItemAllocator::HugeChunk &c, ClassDestroyStatsCallback classCountPtr)
{
    HeapItem *itemToFree = c.chunk->first();
    Heap::Base *b = *itemToFree;
    const VTable *v = b->internalClass->vtable;
    if (Q_UNLIKELY(classCountPtr))
        classCountPtr(v->className);

    if (v->destroy) {
        v->destroy(b);
        b->_checkIsDestroyed();
    }
    if (c.segment) {
        // own memory segment
        c.segment->free(c.chunk, c.size);
        delete c.segment;
    } else {
        chunkAllocator->free(c.chunk, c.size);
    }
#ifdef V4_USE_HEAPTRACK
    heaptrack_report_free(c.chunk);
#endif
}

void HugeItemAllocator::sweep(ClassDestroyStatsCallback classCountPtr)
{
    auto isBlack = [this, classCountPtr] (const HugeChunk &c) {
        bool b = c.chunk->first()->isBlack();
        Chunk::clearBit(c.chunk->blackBitmap, c.chunk->first() - c.chunk->realBase());
        if (!b) {
            Q_V4_PROFILE_DEALLOC(engine, c.size, Profiling::LargeItem);
            freeHugeChunk(chunkAllocator, c, classCountPtr);
        }
        return !b;
    };

    auto newEnd = std::remove_if(chunks.begin(), chunks.end(), isBlack);
    chunks.erase(newEnd, chunks.end());
}

void HugeItemAllocator::resetBlackBits()
{
    for (auto c : chunks)
        Chunk::clearBit(c.chunk->blackBitmap, c.chunk->first() - c.chunk->realBase());
}

void HugeItemAllocator::freeAll()
{
    for (auto &c : chunks) {
        Q_V4_PROFILE_DEALLOC(engine, c.size, Profiling::LargeItem);
        freeHugeChunk(chunkAllocator, c, nullptr);
    }
}

namespace {
using ExtraData = GCStateInfo::ExtraData;
GCState markStart(GCStateMachine *that, ExtraData &)
{
    //Initialize the mark stack
    that->mm->m_markStack = std::make_unique<MarkStack>(that->mm->engine);
    that->mm->engine->isGCOngoing = true;
    return MarkGlobalObject;
}

GCState markGlobalObject(GCStateMachine *that, ExtraData &)
{
    that->mm->engine->markObjects(that->mm->m_markStack.get());
    return MarkJSStack;
}

GCState markJSStack(GCStateMachine *that, ExtraData &)
{
    that->mm->collectFromJSStack(that->mm->markStack());
    return InitMarkPersistentValues;
}

GCState initMarkPersistentValues(GCStateMachine *that, ExtraData &stateData)
{
    if (!that->mm->m_persistentValues)
        return InitMarkWeakValues; // no persistent values to mark
    stateData = GCIteratorStorage { that->mm->m_persistentValues->begin() };
    return MarkPersistentValues;
}

static constexpr int markLoopIterationCount = 1024;

bool wasDrainNecessary(MarkStack *ms, QDeadlineTimer deadline)
{
    if (ms->remainingBeforeSoftLimit() < markLoopIterationCount)
        return false;
    // drain
    ms->drain(deadline);
    return true;
}

GCState markPersistentValues(GCStateMachine *that, ExtraData &stateData) {
    auto markStack = that->mm->markStack();
    if (wasDrainNecessary(markStack, that->deadline) && that->deadline.hasExpired())
        return MarkPersistentValues;
    PersistentValueStorage::Iterator& it = get<GCIteratorStorage>(stateData).it;
    // avoid repeatedly hitting the timer constantly by batching iterations
    for (int i = 0; i < markLoopIterationCount; ++i) {
        if (!it.p)
            return InitMarkWeakValues;
        if (Managed *m = (*it).as<Managed>())
            m->mark(markStack);
        ++it;
    }
    return MarkPersistentValues;
}

GCState initMarkWeakValues(GCStateMachine *that, ExtraData &stateData)
{
    stateData = GCIteratorStorage { that->mm->m_weakValues->begin() };
    return MarkWeakValues;
}

GCState markWeakValues(GCStateMachine *that, ExtraData &stateData)
{
    auto markStack = that->mm->markStack();
    if (wasDrainNecessary(markStack, that->deadline) && that->deadline.hasExpired())
        return MarkWeakValues;
    PersistentValueStorage::Iterator& it = get<GCIteratorStorage>(stateData).it;
    // avoid repeatedly hitting the timer constantly by batching iterations
    for (int i = 0; i < markLoopIterationCount; ++i) {
        if (!it.p)
            return MarkDrain;
        QObjectWrapper *qobjectWrapper = (*it).as<QObjectWrapper>();
        ++it;
        if (!qobjectWrapper)
            continue;
        QObject *qobject = qobjectWrapper->object();
        if (!qobject)
            continue;
        bool keepAlive = QQmlData::keepAliveDuringGarbageCollection(qobject);

        if (!keepAlive) {
            if (QObject *parent = qobject->parent()) {
                while (parent->parent())
                    parent = parent->parent();
                keepAlive = QQmlData::keepAliveDuringGarbageCollection(parent);
            }
        }

        if (keepAlive)
            qobjectWrapper->mark(that->mm->markStack());
    }
    return MarkWeakValues;
}

GCState markDrain(GCStateMachine *that, ExtraData &)
{
    if (that->deadline.isForever()) {
        that->mm->markStack()->drain();
        return MarkReady;
    }
    auto drainState = that->mm->m_markStack->drain(that->deadline);
    return drainState == MarkStack::DrainState::Complete
            ? MarkReady
            : MarkDrain;
}

GCState markReady(GCStateMachine *, ExtraData &)
{
    //Possibility to do some clean up, stat printing, etc...
    return Sweep;
}

GCState sweepPhase(GCStateMachine *that, ExtraData &)
{
    // if we don't have a deletion barrier, then we need to rescan
    that->mm->collectFromJSStack(that->mm->markStack());
    that->mm->m_markStack->drain();
    if (!that->mm->gcCollectorStats) {
        that->mm->sweep();
    } else {
        that->mm->sweep(false, increaseFreedCountForClass);
    }
    that->mm->m_markStack.reset();
    that->mm->engine->isGCOngoing = false;
    return Invalid;
}

}


MemoryManager::MemoryManager(ExecutionEngine *engine)
    : engine(engine)
    , chunkAllocator(new ChunkAllocator)
    , blockAllocator(chunkAllocator, engine)
    , icAllocator(chunkAllocator, engine)
    , hugeItemAllocator(chunkAllocator, engine)
    , m_persistentValues(new PersistentValueStorage(engine))
    , m_weakValues(new PersistentValueStorage(engine))
    , unmanagedHeapSizeGCLimit(MinUnmanagedHeapSizeGCLimit)
    , aggressiveGC(!qEnvironmentVariableIsEmpty("QV4_MM_AGGRESSIVE_GC"))
    , gcStats(lcGcStats().isDebugEnabled())
    , gcCollectorStats(lcGcAllocatorStats().isDebugEnabled())
{
#ifdef V4_USE_VALGRIND
    VALGRIND_CREATE_MEMPOOL(this, 0, true);
#endif
    memset(statistics.allocations, 0, sizeof(statistics.allocations));
    if (gcStats)
        blockAllocator.allocationStats = statistics.allocations;

    gcStateMachine = std::make_unique<GCStateMachine>();
    gcStateMachine->mm = this;

    gcStateMachine->stateInfoMap[GCState::MarkStart] = {
        markStart,
        false,
    };
    gcStateMachine->stateInfoMap[GCState::MarkGlobalObject] = {
        markGlobalObject,
        false,
    };
    gcStateMachine->stateInfoMap[GCState::MarkJSStack] = {
        markJSStack,
        false,
    };
    gcStateMachine->stateInfoMap[GCState::InitMarkPersistentValues] = {
        initMarkPersistentValues,
        false,
    };
    gcStateMachine->stateInfoMap[GCState::MarkPersistentValues] = {
        markPersistentValues,
        false,
    };
    gcStateMachine->stateInfoMap[GCState::InitMarkWeakValues] = {
        initMarkWeakValues,
        false,
    };
    gcStateMachine->stateInfoMap[GCState::MarkWeakValues] = {
        markWeakValues,
        false,
    };
    gcStateMachine->stateInfoMap[GCState::MarkDrain] = {
        markDrain,
        false,
    };
    gcStateMachine->stateInfoMap[GCState::MarkReady] = {
        markReady,
        true, //Break after this step, so that Sweep is only executed the next time GC is allowed
              // as sweep is not concurrent, we want to provide as much time as possible to it
    };
    gcStateMachine->stateInfoMap[GCState::Sweep] = {
        sweepPhase,
        false,
    };
}

Heap::Base *MemoryManager::allocString(std::size_t unmanagedSize)
{
    const size_t stringSize = align(sizeof(Heap::String));
#ifdef MM_STATS
    lastAllocRequestedSlots = stringSize >> Chunk::SlotSizeShift;
    ++allocationCount;
#endif
    unmanagedHeapSize += unmanagedSize;

    HeapItem *m = allocate(&blockAllocator, stringSize);
    memset(m, 0, stringSize);
    if (m_markStack) {
        // If the gc is running right now, it will not have a chance to mark the newly created item
        // and may therefore sweep it right away.
        // Protect the new object from the current GC run to avoid this.
        m->as<Heap::Base>()->setMarkBit();
    }

    return *m;
}

Heap::Base *MemoryManager::allocData(std::size_t size)
{
#ifdef MM_STATS
    lastAllocRequestedSlots = size >> Chunk::SlotSizeShift;
    ++allocationCount;
#endif

    Q_ASSERT(size >= Chunk::SlotSize);
    Q_ASSERT(size % Chunk::SlotSize == 0);

    HeapItem *m = allocate(&blockAllocator, size);
    memset(m, 0, size);
    if (m_markStack) {
        // If the gc is running right now, it will not have a chance to mark the newly created item
        // and may therefore sweep it right away.
        // Protect the new object from the current GC run to avoid this.
        m->as<Heap::Base>()->setMarkBit();
    }

    return *m;
}

Heap::Object *MemoryManager::allocObjectWithMemberData(const QV4::VTable *vtable, uint nMembers)
{
    uint size = (vtable->nInlineProperties + vtable->inlinePropertyOffset)*sizeof(Value);
    Q_ASSERT(!(size % sizeof(HeapItem)));

    Heap::Object *o;
    if (nMembers <= vtable->nInlineProperties) {
        o = static_cast<Heap::Object *>(allocData(size));
    } else {
        // Allocate both in one go through the block allocator
        nMembers -= vtable->nInlineProperties;
        std::size_t memberSize = align(sizeof(Heap::MemberData) + (nMembers - 1)*sizeof(Value));
        size_t totalSize = size + memberSize;
        Heap::MemberData *m;
        if (totalSize > Chunk::DataSize) {
            o = static_cast<Heap::Object *>(allocData(size));
            m = hugeItemAllocator.allocate(memberSize)->as<Heap::MemberData>();
        } else {
            HeapItem *mh = reinterpret_cast<HeapItem *>(allocData(totalSize));
            Heap::Base *b = *mh;
            o = static_cast<Heap::Object *>(b);
            mh += (size >> Chunk::SlotSizeShift);
            m = mh->as<Heap::MemberData>();
            Chunk *c = mh->chunk();
            size_t index = mh - c->realBase();
            Chunk::setBit(c->objectBitmap, index);
            Chunk::clearBit(c->extendsBitmap, index);
        }
        /* If the gc is running, then o will be black,as allocData allocates black during gc
           However, m points to "clear" memory. We must mark it, too, otherwise it might be
           collected. Note that this must happen after (un)setting the object and extends bit
           otherwise we hit an assertion.
           Actually, the write barrier of o->memberData would save us (at leas as long as we
           keep using a Dijkstra style barrier; however, setting the mark bit directly avoids
           some unnecessary work.
         */
        if (m_markStack) // gc running
            m->setMarkBit();
        o->memberData.set(engine, m);
        m->internalClass.set(engine, engine->internalClasses(EngineBase::Class_MemberData));
        Q_ASSERT(o->memberData->internalClass);
        m->values.alloc = static_cast<uint>((memberSize - sizeof(Heap::MemberData) + sizeof(Value))/sizeof(Value));
        m->values.size = o->memberData->values.alloc;
        m->init();
//        qDebug() << "    got" << o->memberData << o->memberData->size;
    }
//    qDebug() << "allocating object with memberData" << o << o->memberData.operator->();
    return o;
}

static uint markStackSize = 0;

MarkStack::MarkStack(ExecutionEngine *engine)
    : m_engine(engine)
{
    m_base = (Heap::Base **)engine->gcStack->base();
    m_top = m_base;
    const size_t size = engine->maxGCStackSize() / sizeof(Heap::Base);
    m_hardLimit = m_base + size;
    m_softLimit = m_base + size * 3 / 4;
}

void MarkStack::drain()
{
    // we're not calling drain(QDeadlineTimer::Forever) as that has higher overhead
    while (m_top > m_base) {
        Heap::Base *h = pop();
        ++markStackSize;
        Q_ASSERT(h); // at this point we should only have Heap::Base objects in this area on the stack. If not, weird things might happen.
        h->internalClass->vtable->markObjects(h, this);
    }
}

MarkStack::DrainState MarkStack::drain(QDeadlineTimer deadline)
{
    do {
        for (int i = 0; i <= markLoopIterationCount * 10; ++i) {
            if (m_top == m_base)
                return DrainState::Complete;
            Heap::Base *h = pop();
            ++markStackSize;
            Q_ASSERT(h); // at this point we should only have Heap::Base objects in this area on the stack. If not, weird things might happen.
            h->internalClass->vtable->markObjects(h, this);
        }
    } while (!deadline.hasExpired());
    return DrainState::Ongoing;
}

void MemoryManager::onEventLoop()
{
    if (engine->inShutdown)
        return;
    gcBlocked = false;
    if (gcStateMachine->inProgress()) {
        runGC();
    }
}


void MemoryManager::setGCTimeLimit(int timeMs)
{
    gcStateMachine->timeLimit = std::chrono::milliseconds(timeMs);
}

void MemoryManager::sweep(bool lastSweep, ClassDestroyStatsCallback classCountPtr)
{

    for (PersistentValueStorage::Iterator it = m_weakValues->begin(); it != m_weakValues->end(); ++it) {
        Managed *m = (*it).managed();
        if (!m || m->markBit())
            continue;
        // we need to call destroyObject on qobjectwrappers now, so that they can emit the destroyed
        // signal before we start sweeping the heap
        if (QObjectWrapper *qobjectWrapper = (*it).as<QObjectWrapper>()) {
            qobjectWrapper->destroyObject(lastSweep);
        }
    }

    for (auto [map, lastMap] = std::tuple {weakMaps, &weakMaps }; map; map = map->nextWeakMap)  {
        if (!map->isMarked())
            continue;
        map->removeUnmarkedKeys();
        *lastMap = map;
        lastMap = &map->nextWeakMap;
    }

    for (auto [set, lastSet] = std::tuple {weakSets, &weakSets}; set; set = set->nextWeakSet) {

        if (!set->isMarked())
            continue;
        set->removeUnmarkedKeys();
        *lastSet = set;
        lastSet = &set->nextWeakSet;
    }

    // onDestruction handlers may have accessed other QObject wrappers and reset their value, so ensure
    // that they are all set to undefined.
    for (PersistentValueStorage::Iterator it = m_weakValues->begin(); it != m_weakValues->end(); ++it) {
        Managed *m = (*it).managed();
        if (!m || m->markBit())
            continue;
        (*it) = Value::undefinedValue();
    }

    // Now it is time to free QV4::QObjectWrapper Value, we must check the Value's tag to make sure its object has been destroyed
    const int pendingCount = m_pendingFreedObjectWrapperValue.size();
    if (pendingCount) {
        QVector<Value *> remainingWeakQObjectWrappers;
        remainingWeakQObjectWrappers.reserve(pendingCount);
        for (int i = 0; i < pendingCount; ++i) {
            Value *v = m_pendingFreedObjectWrapperValue.at(i);
            if (v->isUndefined() || v->isEmpty())
                PersistentValueStorage::free(v);
            else
                remainingWeakQObjectWrappers.append(v);
        }
        m_pendingFreedObjectWrapperValue = remainingWeakQObjectWrappers;
    }

    if (MultiplyWrappedQObjectMap *multiplyWrappedQObjects = engine->m_multiplyWrappedQObjects) {
        for (MultiplyWrappedQObjectMap::Iterator it = multiplyWrappedQObjects->begin(); it != multiplyWrappedQObjects->end();) {
            if (it.value().isNullOrUndefined())
                it = multiplyWrappedQObjects->erase(it);
            else
                ++it;
        }
    }

    if (!lastSweep) {
        engine->identifierTable->sweep();
        blockAllocator.sweep(/*classCountPtr*/);
        hugeItemAllocator.sweep(classCountPtr);
        icAllocator.sweep(/*classCountPtr*/);
    }

    // reset all black bits
    blockAllocator.resetBlackBits();
    hugeItemAllocator.resetBlackBits();
    icAllocator.resetBlackBits();

    usedSlotsAfterLastFullSweep = blockAllocator.usedSlotsAfterLastSweep + icAllocator.usedSlotsAfterLastSweep;
    gcBlocked = false;
}

bool MemoryManager::shouldRunGC() const
{
    size_t total = blockAllocator.totalSlots() + icAllocator.totalSlots();
    if (total > MinSlotsGCLimit && usedSlotsAfterLastFullSweep * GCOverallocation < total * 100)
        return true;
    return false;
}

static size_t dumpBins(BlockAllocator *b, const char *title)
{
    const QLoggingCategory &stats = lcGcAllocatorStats();
    size_t totalSlotMem = 0;
    if (title)
        qDebug(stats) << "Slot map for" << title << "allocator:";
    for (uint i = 0; i < BlockAllocator::NumBins; ++i) {
        uint nEntries = 0;
        HeapItem *h = b->freeBins[i];
        while (h) {
            ++nEntries;
            totalSlotMem += h->freeData.availableSlots;
            h = h->freeData.next;
        }
        if (title)
            qDebug(stats) << "    number of entries in slot" << i << ":" << nEntries;
    }
    SDUMP() << "    large slot map";
    HeapItem *h = b->freeBins[BlockAllocator::NumBins - 1];
    while (h) {
        SDUMP() << "        " << Qt::hex << (quintptr(h)/32) << h->freeData.availableSlots;
        h = h->freeData.next;
    }

    if (title)
        qDebug(stats) << "  total mem in bins" << totalSlotMem*Chunk::SlotSize;
    return totalSlotMem*Chunk::SlotSize;
}

void MemoryManager::runGC()
{
    if (gcBlocked) {
        return;
    }

    gcBlocked = true;

    if (gcStats) {
        statistics.maxReservedMem = qMax(statistics.maxReservedMem, getAllocatedMem());
        statistics.maxAllocatedMem = qMax(statistics.maxAllocatedMem, getUsedMem() + getLargeItemsMem());
    }

    if (!gcCollectorStats) {
        gcStateMachine->step();
    } else {
        bool triggeredByUnmanagedHeap = (unmanagedHeapSize > unmanagedHeapSizeGCLimit);
        size_t oldUnmanagedSize = unmanagedHeapSize;

        const size_t totalMem = getAllocatedMem();
        const size_t usedBefore = getUsedMem();
        const size_t largeItemsBefore = getLargeItemsMem();

        const QLoggingCategory &stats = lcGcAllocatorStats();
        qDebug(stats) << "========== GC ==========";
#ifdef MM_STATS
        qDebug(stats) << "    Triggered by alloc request of" << lastAllocRequestedSlots << "slots.";
        qDebug(stats) << "    Allocations since last GC" << allocationCount;
        allocationCount = 0;
#endif
        size_t oldChunks = blockAllocator.chunks.size();
        qDebug(stats) << "Allocated" << totalMem << "bytes in" << oldChunks << "chunks";
        qDebug(stats) << "Fragmented memory before GC" << (totalMem - usedBefore);
        dumpBins(&blockAllocator, "Block");
        dumpBins(&icAllocator, "InternalClass");

        QElapsedTimer t;
        t.start();
        gcStateMachine->step();
        qint64 markTime = t.nsecsElapsed()/1000;
        t.restart();
        const size_t usedAfter = getUsedMem();
        const size_t largeItemsAfter = getLargeItemsMem();

        if (triggeredByUnmanagedHeap) {
            qDebug(stats) << "triggered by unmanaged heap:";
            qDebug(stats) << "   old unmanaged heap size:" << oldUnmanagedSize;
            qDebug(stats) << "   new unmanaged heap:" << unmanagedHeapSize;
            qDebug(stats) << "   unmanaged heap limit:" << unmanagedHeapSizeGCLimit;
        }
        size_t memInBins = dumpBins(&blockAllocator, "Block")
                + dumpBins(&icAllocator, "InternalClasss");
        qDebug(stats) << "Marked object in" << markTime << "us.";
        qDebug(stats) << "   " << markStackSize << "objects marked";

        // sort our object types by number of freed instances
        MMStatsHash freedObjectStats;
        std::swap(freedObjectStats, *freedObjectStatsGlobal());
        typedef std::pair<const char*, int> ObjectStatInfo;
        std::vector<ObjectStatInfo> freedObjectsSorted;
        freedObjectsSorted.reserve(freedObjectStats.size());
        for (auto it = freedObjectStats.constBegin(); it != freedObjectStats.constEnd(); ++it) {
            freedObjectsSorted.push_back(std::make_pair(it.key(), it.value()));
        }
        std::sort(freedObjectsSorted.begin(), freedObjectsSorted.end(), [](const ObjectStatInfo &a, const ObjectStatInfo &b) {
            return a.second > b.second && strcmp(a.first, b.first) < 0;
        });

        qDebug(stats) << "Used memory before GC:" << usedBefore;
        qDebug(stats) << "Used memory after GC:" << usedAfter;
        qDebug(stats) << "Freed up bytes      :" << (usedBefore - usedAfter);
        qDebug(stats) << "Freed up chunks     :" << (oldChunks - blockAllocator.chunks.size());
        size_t lost = blockAllocator.allocatedMem() + icAllocator.allocatedMem()
                - memInBins - usedAfter;
        if (lost)
            qDebug(stats) << "!!!!!!!!!!!!!!!!!!!!! LOST MEM:" << lost << "!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!";
        if (largeItemsBefore || largeItemsAfter) {
            qDebug(stats) << "Large item memory before GC:" << largeItemsBefore;
            qDebug(stats) << "Large item memory after GC:" << largeItemsAfter;
            qDebug(stats) << "Large item memory freed up:" << (largeItemsBefore - largeItemsAfter);
        }

        for (auto it = freedObjectsSorted.cbegin(); it != freedObjectsSorted.cend(); ++it) {
            qDebug(stats).noquote() << QString::fromLatin1("Freed JS type: %1 (%2 instances)").arg(QString::fromLatin1(it->first), QString::number(it->second));
        }

        qDebug(stats) << "======== End GC ========";
    }

    if (gcStats)
        statistics.maxUsedMem = qMax(statistics.maxUsedMem, getUsedMem() + getLargeItemsMem());

    if (aggressiveGC) {
        // ensure we don't 'loose' any memory
        Q_ASSERT(blockAllocator.allocatedMem()
                 == blockAllocator.usedMem() + dumpBins(&blockAllocator, nullptr));
        Q_ASSERT(icAllocator.allocatedMem()
                 == icAllocator.usedMem() + dumpBins(&icAllocator, nullptr));
    }
}

size_t MemoryManager::getUsedMem() const
{
    return blockAllocator.usedMem() + icAllocator.usedMem();
}

size_t MemoryManager::getAllocatedMem() const
{
    return blockAllocator.allocatedMem() + icAllocator.allocatedMem() + hugeItemAllocator.usedMem();
}

size_t MemoryManager::getLargeItemsMem() const
{
    return hugeItemAllocator.usedMem();
}

void MemoryManager::registerWeakMap(Heap::MapObject *map)
{
    map->nextWeakMap = weakMaps;
    weakMaps = map;
}

void MemoryManager::registerWeakSet(Heap::SetObject *set)
{
    set->nextWeakSet = weakSets;
    weakSets = set;
}

MemoryManager::~MemoryManager()
{
    delete m_persistentValues;
    dumpStats();

    // do one last non-incremental sweep to clean up C++ objects
    // first, abort any on-going incremental gc operation
    setGCTimeLimit(-1);
    if (engine->isGCOngoing) {
        engine->isGCOngoing = false;
        m_markStack.reset();
        gcStateMachine->state = GCState::Invalid;
        blockAllocator.resetBlackBits();
        hugeItemAllocator.resetBlackBits();
        icAllocator.resetBlackBits();
    }
    // then sweep
    sweep(/*lastSweep*/true);

    blockAllocator.freeAll();
    hugeItemAllocator.freeAll();
    icAllocator.freeAll();

    delete m_weakValues;
#ifdef V4_USE_VALGRIND
    VALGRIND_DESTROY_MEMPOOL(this);
#endif
    delete chunkAllocator;
}


void MemoryManager::dumpStats() const
{
    if (!gcStats)
        return;

    const QLoggingCategory &stats = lcGcStats();
    qDebug(stats) << "Qml GC memory allocation statistics:";
    qDebug(stats) << "Total memory allocated:" << statistics.maxReservedMem;
    qDebug(stats) << "Max memory used before a GC run:" << statistics.maxAllocatedMem;
    qDebug(stats) << "Max memory used after a GC run:" << statistics.maxUsedMem;
    qDebug(stats) << "Requests for different item sizes:";
    for (int i = 1; i < BlockAllocator::NumBins - 1; ++i)
        qDebug(stats) << "     <" << (i << Chunk::SlotSizeShift) << " bytes: " << statistics.allocations[i];
    qDebug(stats) << "     >=" << ((BlockAllocator::NumBins - 1) << Chunk::SlotSizeShift) << " bytes: " << statistics.allocations[BlockAllocator::NumBins - 1];
}

void MemoryManager::collectFromJSStack(MarkStack *markStack) const
{
    Value *v = engine->jsStackBase;
    Value *top = engine->jsStackTop;
    while (v < top) {
        Managed *m = v->managed();
        if (m) {
            Q_ASSERT(m->inUse());
            // Skip pointers to already freed objects, they are bogus as well
            m->mark(markStack);
        }
        ++v;
    }
}

GCStateMachine::GCStateMachine()
{
    // base assumption: target 60fps, use at most 1/3 of time for gc
    timeLimit = std::chrono::milliseconds { (1000 / 60) / 3 };
}

void GCStateMachine::transition() {
    if (timeLimit.count() > 0) {
        deadline = QDeadlineTimer(timeLimit);
        bool deadlineExpired = false;
        while (!(deadlineExpired = deadline.hasExpired()) && state != GCState::Invalid) {
            GCStateInfo& stateInfo = stateInfoMap[int(state)];
            state = stateInfo.execute(this, stateData);
            if (stateInfo.breakAfter)
                break;
        }
        if (deadlineExpired)
            handleTimeout(state);
        if (state != GCState::Invalid)
            QMetaObject::invokeMethod(mm->engine->publicEngine, [this]{
                mm->onEventLoop();
            }, Qt::QueuedConnection);
    } else {
        deadline = QDeadlineTimer::Forever;
        while (state != GCState::Invalid) {
            GCStateInfo& stateInfo = stateInfoMap[int(state)];
            state = stateInfo.execute(this, stateData);
        }
    }
}

} // namespace QV4

QT_END_NAMESPACE