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qtconcurrentmapkernel.h：源码内容
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#ifndef QTCONCURRENT_MAPKERNEL_H
#define QTCONCURRENT_MAPKERNEL_H
#include <QtCore/qglobal.h>
#ifndef QT_NO_CONCURRENT
#include <QtCore/qtconcurrentiteratekernel.h>
#include <QtCore/qtconcurrentreducekernel.h>
QT_BEGIN_HEADER
QT_BEGIN_NAMESPACE
QT_MODULE(Core)
#ifndef qdoc
namespace QtConcurrent {
// map kernel, works with both parallel-for and parallel-while
template <typename Iterator, typename MapFunctor>
class MapKernel : public IterateKernel<Iterator, void>
{
    MapFunctor map;
public:
    typedef void ReturnType;
    MapKernel(Iterator begin, Iterator end, MapFunctor _map)
        : IterateKernel<Iterator, void>(begin, end), map(_map)
    { }
    bool runIteration(Iterator it, int, void *)
    {
        map(*it);
        return false;
    }
    bool runIterations(Iterator sequenceBeginIterator, int beginIndex, int endIndex, void *)
    {
        Iterator it = sequenceBeginIterator;
        advance(it, beginIndex);
        for (int i = beginIndex; i < endIndex; ++i) {
            runIteration(it, i, 0);
            advance(it, 1);
        }
       
        return false;
    }
};
template <typename ReducedResultType,
          typename Iterator,
          typename MapFunctor,
          typename ReduceFunctor,
          typename Reducer = ReduceKernel<ReduceFunctor,
                                          ReducedResultType,
                                          typename MapFunctor::result_type> >
class MappedReducedKernel : public IterateKernel<Iterator, ReducedResultType>
{
    ReducedResultType reducedResult;
    MapFunctor map;
    ReduceFunctor reduce;
    Reducer reducer;
public:
    typedef ReducedResultType ReturnType;
    MappedReducedKernel(Iterator begin, Iterator end, MapFunctor _map, ReduceFunctor _reduce, ReduceOptions reduceOptions)
        : IterateKernel<Iterator, ReducedResultType>(begin, end), reducedResult(), map(_map), reduce(_reduce), reducer(reduceOptions)
    { }
    MappedReducedKernel(ReducedResultType initialValue,
                     MapFunctor _map,
                     ReduceFunctor _reduce)
        : reducedResult(initialValue), map(_map), reduce(_reduce)
    { }
    bool runIteration(Iterator it, int index, ReducedResultType *)
    {
        IntermediateResults<typename MapFunctor::result_type> results;
        results.begin = index;
        results.end = index + 1;
        results.vector.append(map(*it));
        reducer.runReduce(reduce, reducedResult, results);
        return false;
    }
    bool runIterations(Iterator sequenceBeginIterator, int begin, int end, ReducedResultType *)
    {
        IntermediateResults<typename MapFunctor::result_type> results;
        results.begin = begin;
        results.end = end;
        results.vector.reserve(end - begin);
        Iterator it = sequenceBeginIterator;
        advance(it, begin);
        for (int i = begin; i < end; ++i) {
            results.vector.append(map(*(it)));
            advance(it, 1);
        }
        reducer.runReduce(reduce, reducedResult, results);
        return false;
    }
    void finish()
    {
        reducer.finish(reduce, reducedResult);
    }
    bool shouldThrottleThread()
    {
        return IterateKernel<Iterator, ReducedResultType>::shouldThrottleThread() || reducer.shouldThrottle();
    }
    bool shouldStartThread()
    {
        return IterateKernel<Iterator, ReducedResultType>::shouldStartThread() && reducer.shouldStartThread();
    }
    typedef ReducedResultType ResultType;
    ReducedResultType *result()
    {
        return &reducedResult;
    }
};
template <typename Iterator, typename MapFunctor>
class MappedEachKernel : public IterateKernel<Iterator, typename MapFunctor::result_type>
{
    MapFunctor map;
    typedef typename MapFunctor::result_type T;
public:
    typedef T ReturnType;
    typedef T ResultType;
    MappedEachKernel(Iterator begin, Iterator end, MapFunctor _map)
        : IterateKernel<Iterator, T>(begin, end), map(_map) { }
    bool runIteration(Iterator it, int,  T *result)
    {
        *result = map(*it);
        return true;
    }
    bool runIterations(Iterator sequenceBeginIterator, int begin, int end, T *results)
    {
        Iterator it = sequenceBeginIterator;
        advance(it, begin);
        for (int i = begin; i < end; ++i) {
            runIteration(it, i, results + (i - begin));
            advance(it, 1);
        }
        return true;
    }
};
template <typename Iterator, typename Functor>
inline ThreadEngineStarter<void> startMap(Iterator begin, Iterator end, Functor functor)
{
    return startThreadEngine(new MapKernel<Iterator, Functor>(begin, end, functor));
}
template <typename T, typename Iterator, typename Functor>
inline ThreadEngineStarter<T> startMapped(Iterator begin, Iterator end, Functor functor)
{
    return startThreadEngine(new MappedEachKernel<Iterator, Functor>(begin, end, functor));
}
/*
    The SequnceHolder class is used to hold a reference to the
    sequence we are working on.
*/
template <typename Sequence, typename Base, typename Functor>
struct SequenceHolder1 : public Base
{
    SequenceHolder1(const Sequence &_sequence, Functor functor)
        : Base(_sequence.begin(), _sequence.end(), functor), sequence(_sequence)
    { }
    Sequence sequence;
    void finish()
    {
        Base::finish();
        // Clear the sequence to make sure all temporaries are destroyed
        // before finished is signaled.
        sequence = Sequence();
    }
};
template <typename T, typename Sequence, typename Functor>
inline ThreadEngineStarter<T> startMapped(const Sequence &sequence, Functor functor)
{
    typedef SequenceHolder1<Sequence,
                            MappedEachKernel<typename Sequence::const_iterator , Functor>, Functor>
                            SequenceHolderType;
    return startThreadEngine(new SequenceHolderType(sequence, functor));
}
template <typename IntermediateType, typename ResultType, typename Sequence, typename MapFunctor, typename ReduceFunctor>
inline ThreadEngineStarter<ResultType> startMappedReduced(const Sequence & sequence,
                                                           MapFunctor mapFunctor, ReduceFunctor reduceFunctor,
                                                           ReduceOptions options)
{
    typedef typename Sequence::const_iterator Iterator;
    typedef ReduceKernel<ReduceFunctor, ResultType, IntermediateType> Reducer;
    typedef MappedReducedKernel<ResultType, Iterator, MapFunctor, ReduceFunctor, Reducer> MappedReduceType;
    typedef SequenceHolder2<Sequence, MappedReduceType, MapFunctor, ReduceFunctor> SequenceHolderType;
    return startThreadEngine(new SequenceHolderType(sequence, mapFunctor, reduceFunctor, options));
}
template <typename IntermediateType, typename ResultType, typename Iterator, typename MapFunctor, typename ReduceFunctor>
inline ThreadEngineStarter<ResultType> startMappedReduced(Iterator begin, Iterator end,
                                                           MapFunctor mapFunctor, ReduceFunctor reduceFunctor,
                                                           ReduceOptions options)
{
    typedef ReduceKernel<ReduceFunctor, ResultType, IntermediateType> Reducer;
    typedef MappedReducedKernel<ResultType, Iterator, MapFunctor, ReduceFunctor, Reducer> MappedReduceType;
    return startThreadEngine(new MappedReduceType(begin, end, mapFunctor, reduceFunctor, options));
}
} // namespace QtConcurrent
#endif //qdoc
QT_END_NAMESPACE
QT_END_HEADER
#endif // QT_NO_CONCURRENT
#endif

						