parallel_sort.h

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/*
    Copyright (c) 2005-2020 Intel Corporation

    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
    You may obtain a copy of the License at

        http://www.apache.org/licenses/LICENSE-2.0

    Unless required by applicable law or agreed to in writing, software
    distributed under the License is distributed on an "AS IS" BASIS,
    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    See the License for the specific language governing permissions and
    limitations under the License.
*/

#ifndef __TBB_parallel_sort_H
#define __TBB_parallel_sort_H

#define __TBB_parallel_sort_H_include_area
#include "internal/_warning_suppress_enable_notice.h"

#include "parallel_for.h"
#include "blocked_range.h"
#include "internal/_range_iterator.h"
#include <algorithm>
#include <iterator>
#include <functional>
#if __TBB_TASK_GROUP_CONTEXT
    #include "tbb_profiling.h"
#endif

namespace tbb {

namespace interface9 {
namespace internal {

using tbb::internal::no_assign;


template<typename RandomAccessIterator, typename Compare>
class quick_sort_range: private no_assign {

    inline size_t median_of_three(const RandomAccessIterator &array, size_t l, size_t m, size_t r) const {
        return comp(array[l], array[m]) ? ( comp(array[m], array[r]) ? m : ( comp( array[l], array[r]) ? r : l ) )
                                        : ( comp(array[r], array[m]) ? m : ( comp( array[r], array[l] ) ? r : l ) );
    }

    inline size_t pseudo_median_of_nine( const RandomAccessIterator &array, const quick_sort_range &range ) const {
        size_t offset = range.size/8u;
        return median_of_three(array,
                               median_of_three(array, 0, offset, offset*2),
                               median_of_three(array, offset*3, offset*4, offset*5),
                               median_of_three(array, offset*6, offset*7, range.size - 1) );

    }

    size_t split_range( quick_sort_range& range ) {
        using std::iter_swap;
        RandomAccessIterator array = range.begin;
        RandomAccessIterator key0 = range.begin;
        size_t m = pseudo_median_of_nine(array, range);
        if (m) iter_swap ( array, array+m );

        size_t i=0;
        size_t j=range.size;
        // Partition interval [i+1,j-1] with key *key0.
        for(;;) {
            __TBB_ASSERT( i<j, NULL );
            // Loop must terminate since array[l]==*key0.
            do {
                --j;
                __TBB_ASSERT( i<=j, "bad ordering relation?" );
            } while( comp( *key0, array[j] ));
            do {
                __TBB_ASSERT( i<=j, NULL );
                if( i==j ) goto partition;
                ++i;
            } while( comp( array[i],*key0 ));
            if( i==j ) goto partition;
            iter_swap( array+i, array+j );
        }
partition:
        // Put the partition key were it belongs
        iter_swap( array+j, key0 );
        // array[l..j) is less or equal to key.
        // array(j..r) is greater or equal to key.
        // array[j] is equal to key
        i=j+1;
        size_t new_range_size = range.size-i;
        range.size = j;
        return new_range_size;
    }

public:

    static const size_t grainsize = 500;
    const Compare &comp;
    size_t size;
    RandomAccessIterator begin;

    quick_sort_range( RandomAccessIterator begin_, size_t size_, const Compare &comp_ ) :
        comp(comp_), size(size_), begin(begin_) {}

    bool empty() const {return size==0;}
    bool is_divisible() const {return size>=grainsize;}

    quick_sort_range( quick_sort_range& range, split )
        : comp(range.comp)
        , size(split_range(range))
          // +1 accounts for the pivot element, which is at its correct place
          // already and, therefore, is not included into subranges.
        , begin(range.begin+range.size+1) {}
};

#if __TBB_TASK_GROUP_CONTEXT

template<typename RandomAccessIterator, typename Compare>
class quick_sort_pretest_body : no_assign {
    const Compare &comp;

public:
    quick_sort_pretest_body(const Compare &_comp) : comp(_comp) {}

    void operator()( const blocked_range<RandomAccessIterator>& range ) const {
        task &my_task = task::self();
        RandomAccessIterator my_end = range.end();

        int i = 0;
        for (RandomAccessIterator k = range.begin(); k != my_end; ++k, ++i) {
            if ( i%64 == 0 && my_task.is_cancelled() ) break;

            // The k-1 is never out-of-range because the first chunk starts at begin+serial_cutoff+1
            if ( comp( *(k), *(k-1) ) ) {
                my_task.cancel_group_execution();
                break;
            }
        }
    }

};
#endif /* __TBB_TASK_GROUP_CONTEXT */


template<typename RandomAccessIterator, typename Compare>
struct quick_sort_body {
    void operator()( const quick_sort_range<RandomAccessIterator,Compare>& range ) const {
        //SerialQuickSort( range.begin, range.size, range.comp );
        std::sort( range.begin, range.begin + range.size, range.comp );
    }
};


template<typename RandomAccessIterator, typename Compare>
void parallel_quick_sort( RandomAccessIterator begin, RandomAccessIterator end, const Compare& comp ) {
#if __TBB_TASK_GROUP_CONTEXT
    task_group_context my_context(PARALLEL_SORT);
    const int serial_cutoff = 9;

    __TBB_ASSERT( begin + serial_cutoff < end, "min_parallel_size is smaller than serial cutoff?" );
    RandomAccessIterator k = begin;
    for ( ; k != begin + serial_cutoff; ++k ) {
        if ( comp( *(k+1), *k ) ) {
            goto do_parallel_quick_sort;
        }
    }

    parallel_for( blocked_range<RandomAccessIterator>(k+1, end),
                  quick_sort_pretest_body<RandomAccessIterator,Compare>(comp),
                  auto_partitioner(),
                  my_context);

    if (my_context.is_group_execution_cancelled())
do_parallel_quick_sort:
#endif /* __TBB_TASK_GROUP_CONTEXT */
        parallel_for( quick_sort_range<RandomAccessIterator,Compare>(begin, end-begin, comp ),
                      quick_sort_body<RandomAccessIterator,Compare>(),
                      auto_partitioner() );
}

} // namespace internal
} // namespace interfaceX



template<typename RandomAccessIterator, typename Compare>
void parallel_sort( RandomAccessIterator begin, RandomAccessIterator end, const Compare& comp) {
    const int min_parallel_size = 500;
    if( end > begin ) {
        if (end - begin < min_parallel_size) {
            std::sort(begin, end, comp);
        } else {
            interface9::internal::parallel_quick_sort(begin, end, comp);
        }
    }
}


template<typename RandomAccessIterator>
inline void parallel_sort( RandomAccessIterator begin, RandomAccessIterator end ) {
    parallel_sort( begin, end, std::less< typename std::iterator_traits<RandomAccessIterator>::value_type >() );
}


template<typename Range, typename Compare>
void parallel_sort(Range& rng, const Compare& comp) {
    parallel_sort(tbb::internal::first(rng), tbb::internal::last(rng), comp);
}


template<typename Range>
void parallel_sort(Range& rng) {
    parallel_sort(tbb::internal::first(rng), tbb::internal::last(rng));
}


template<typename T>
inline void parallel_sort( T * begin, T * end ) {
    parallel_sort( begin, end, std::less< T >() );
}


} // namespace tbb

#include "internal/_warning_suppress_disable_notice.h"
#undef __TBB_parallel_sort_H_include_area

#endif