source: trunk/src/corelib/concurrent/qtconcurrentiteratekernel.h@ 813

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#ifndef QTCONCURRENT_ITERATEKERNEL_H
#define QTCONCURRENT_ITERATEKERNEL_H

#include <QtCore/qglobal.h>

#ifndef QT_NO_CONCURRENT

#include <QtCore/qatomic.h>
#include <QtCore/qtconcurrentmedian.h>
#include <QtCore/qtconcurrentthreadengine.h>

#ifndef QT_NO_STL
#  include <iterator>
#endif

QT_BEGIN_HEADER
QT_BEGIN_NAMESPACE

QT_MODULE(Core)

#ifndef qdoc

namespace QtConcurrent {

#ifndef QT_NO_STL
    using std::advance;
#else
    template <typename It, typename T>
    void advance(It &it, T value)
    {
        it+=value;
    }
#endif

/*
    The BlockSizeManager class manages how many iterations a thread should
    reserve and process at a time. This is done by measuring the time spent
    in the user code versus the control part code, and then increasing
    the block size if the ratio between them is to small. The block size
    management is done on the basis of the median of several timing measuremens,
    and it is done induvidualy for each thread.
*/
class Q_CORE_EXPORT BlockSizeManager
{
public:
    BlockSizeManager(int iterationCount);
    void timeBeforeUser();
    void timeAfterUser();
    int blockSize();
private:
    inline bool blockSizeMaxed()
    {
        return (m_blockSize >= maxBlockSize);
    }

    const int maxBlockSize;
    qint64 beforeUser;
    qint64 afterUser;
    Median<double> controlPartElapsed;
    Median<double> userPartElapsed;
    int m_blockSize;
};

template <typename T>
class ResultReporter
{
public:
    ResultReporter(ThreadEngine<T> *_threadEngine)
    :threadEngine(_threadEngine)
    {

    }

    void reserveSpace(int resultCount)
    {
        currentResultCount = resultCount;
        vector.resize(qMax(resultCount, vector.count()));
    }

    void reportResults(int begin)
    {
        const int useVectorThreshold = 4; // Tunable parameter.
        if (currentResultCount > useVectorThreshold) {
            vector.resize(currentResultCount);
            threadEngine->reportResults(vector, begin);
        } else {
            for (int i = 0; i < currentResultCount; ++i)
                threadEngine->reportResult(&vector.at(i), begin + i);
        }
    }

    inline T * getPointer()
    {
        return vector.data();
    }

    int currentResultCount;
    ThreadEngine<T> *threadEngine;
    QVector<T> vector;
};

template <>
class ResultReporter<void>
{
public:
    inline ResultReporter(ThreadEngine<void> *) { }
    inline void reserveSpace(int) { };
    inline void reportResults(int) { };
    inline void * getPointer() { return 0; }
};