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#ifndef QTCONCURRENT_REDUCEKERNEL_H

#define QTCONCURRENT_REDUCEKERNEL_H

#include <QtCore/qglobal.h>

#ifndef QT_NO_CONCURRENT

#include <QtCore/qatomic.h>

#include <QtCore/qlist.h>

#include <QtCore/qmap.h>

#include <QtCore/qmutex.h>

#include <QtCore/qthread.h>

#include <QtCore/qthreadpool.h>

#include <QtCore/qvector.h>

QT_BEGIN_HEADER

QT_BEGIN_NAMESPACE

QT_MODULE(Core)

namespace QtConcurrent {

#ifndef qdoc

/*

    The ReduceQueueStartLimit and ReduceQueueThrottleLimit constants

    limit the reduce queue size for MapReduce. When the number of

    reduce blocks in the queue exceeds ReduceQueueStartLimit,

    MapReduce won't start any new threads, and when it exceeds

    ReduceQueueThrottleLimit running threads will be stopped.

*/

enum {

    ReduceQueueStartLimit = 20,

    ReduceQueueThrottleLimit = 30

};

// IntermediateResults holds a block of intermediate results from a

// map or filter functor. The begin/end offsets indicates the origin

// and range of the block.

template <typename T>

class IntermediateResults

{

public:

    int begin, end;

    QVector<T> vector;

};

#endif // qdoc

enum ReduceOption {

    UnorderedReduce = 0x1,

    OrderedReduce = 0x2,

    SequentialReduce = 0x4

    // ParallelReduce = 0x8

};

Q_DECLARE_FLAGS(ReduceOptions, ReduceOption)

Q_DECLARE_OPERATORS_FOR_FLAGS(ReduceOptions)

#ifndef qdoc

// supports both ordered and out-of-order reduction

template <typename ReduceFunctor, typename ReduceResultType, typename T>

class ReduceKernel

{

    typedef QMap<int, IntermediateResults<T> > ResultsMap;

    const ReduceOptions reduceOptions;

    QMutex mutex;

    int progress, resultsMapSize, threadCount;

    ResultsMap resultsMap;

    bool canReduce(int begin) const

    {

        return (((reduceOptions & UnorderedReduce)

                 && progress == 0)

                || ((reduceOptions & OrderedReduce)

                    && progress == begin));

    }

    void reduceResult(ReduceFunctor &reduce,

                      ReduceResultType &r,

                      const IntermediateResults<T> &result)

    {

        for (int i = 0; i < result.vector.size(); ++i) {

            reduce(r, result.vector.at(i));

        }

    }

    void reduceResults(ReduceFunctor &reduce,

                       ReduceResultType &r,

                       ResultsMap &map)

    {

        typename ResultsMap::iterator it = map.begin();

        while (it != map.end()) {

            reduceResult(reduce, r, it.value());

            ++it;

        }

    }

public:

    ReduceKernel(ReduceOptions _reduceOptions)

        : reduceOptions(_reduceOptions), progress(0), resultsMapSize(0), 

          threadCount(QThreadPool::globalInstance()->maxThreadCount())

    { }

    void runReduce(ReduceFunctor &reduce,

                   ReduceResultType &r,

                   const IntermediateResults<T> &result)

    {

        QMutexLocker locker(&mutex);

        if (!canReduce(result.begin)) {

            ++resultsMapSize;

            resultsMap.insert(result.begin, result);

            return;

        }

        if (reduceOptions & UnorderedReduce) {

            // UnorderedReduce

            progress = -1;

            // reduce this result

            locker.unlock();

            reduceResult(reduce, r, result);

            locker.relock();

            // reduce all stored results as well

            while (!resultsMap.isEmpty()) {

                ResultsMap resultsMapCopy = resultsMap;

                resultsMap.clear();

                locker.unlock();

                reduceResults(reduce, r, resultsMapCopy);

                locker.relock();

                resultsMapSize -= resultsMapCopy.size();

            }

            progress = 0;

        } else {

            // reduce this result

            locker.unlock();

            reduceResult(reduce, r, result);

            locker.relock();

            // OrderedReduce

            progress += result.end - result.begin;

            // reduce as many other results as possible

            typename ResultsMap::iterator it = resultsMap.begin();

            while (it != resultsMap.end()) {

                if (it.value().begin != progress)

                    break;

                locker.unlock();

                reduceResult(reduce, r, it.value());

                locker.relock();

                --resultsMapSize;

                progress += it.value().end - it.value().begin;

                it = resultsMap.erase(it);

            }

        }

    }

    // final reduction

    void finish(ReduceFunctor &reduce, ReduceResultType &r)

    {

        reduceResults(reduce, r, resultsMap);

    }

    inline bool shouldThrottle()

    {

        return (resultsMapSize > (ReduceQueueThrottleLimit * threadCount));

    }

    inline bool shouldStartThread()

    {

        return (resultsMapSize <= (ReduceQueueStartLimit * threadCount));

    }

};

template <typename Sequence, typename Base, typename Functor1, typename Functor2>

struct SequenceHolder2 : public Base

{

    SequenceHolder2(const Sequence &_sequence,

                    Functor1 functor1,

                    Functor2 functor2,

                    ReduceOptions reduceOptions)

        : Base(_sequence.begin(), _sequence.end(), functor1, functor2, reduceOptions),

          sequence(_sequence)

    { }

    Sequence sequence;

    void finish()

    {

        Base::finish();

        // Clear the sequence to make sure all temporaries are destroyed

        // before finished is signaled.

        sequence = Sequence();

    }

};

#endif //qdoc

} // namespace QtConcurrent

QT_END_NAMESPACE

QT_END_HEADER

#endif // QT_NO_CONCURRENT

#endif