perf_tbb_merge.cpp

#include <algorithm>
#include <iostream>
#include <vector>

#include <tbb/parallel_for.h>

#include "perf.hpp"

// example from: http://www.threadingbuildingblocks.org/docs/help/reference/algorithms/parallel_for_func.htm
using namespace tbb;

template<typename Iterator>
struct ParallelMergeRange {
    static size_t grainsize;
    Iterator begin1, end1; // [begin1,end1) is 1st sequence to be merged
    Iterator begin2, end2; // [begin2,end2) is 2nd sequence to be merged
    Iterator out;               // where to put merged sequence
    bool empty()   const {return (end1-begin1)+(end2-begin2)==0;}
    bool is_divisible() const {
        return std::min( end1-begin1, end2-begin2 ) > grainsize;
    }
    ParallelMergeRange( ParallelMergeRange& r, split ) {
        if( r.end1-r.begin1 < r.end2-r.begin2 ) {
            std::swap(r.begin1,r.begin2);
            std::swap(r.end1,r.end2);
        }
        Iterator m1 = r.begin1 + (r.end1-r.begin1)/2;
        Iterator m2 = std::lower_bound( r.begin2, r.end2, *m1 );
        begin1 = m1;
        begin2 = m2;
        end1 = r.end1;
        end2 = r.end2;
        out = r.out + (m1-r.begin1) + (m2-r.begin2);
        r.end1 = m1;
        r.end2 = m2;
    }
    ParallelMergeRange( Iterator begin1_, Iterator end1_,
                        Iterator begin2_, Iterator end2_,
                        Iterator out_ ) :
        begin1(begin1_), end1(end1_),
        begin2(begin2_), end2(end2_), out(out_)
    {}
};

template<typename Iterator>
size_t ParallelMergeRange<Iterator>::grainsize = 1000;

template<typename Iterator>
struct ParallelMergeBody {
    void operator()( ParallelMergeRange<Iterator>& r ) const {
        std::merge( r.begin1, r.end1, r.begin2, r.end2, r.out );
    }
};

template<typename Iterator>
void ParallelMerge( Iterator begin1, Iterator end1, Iterator begin2, Iterator end2, Iterator out ) {
    parallel_for(
       ParallelMergeRange<Iterator>(begin1,end1,begin2,end2,out),
       ParallelMergeBody<Iterator>(),
       simple_partitioner()
    );
}

int main(int argc, char *argv[])
{
    perf_parse_args(argc, argv);

    std::cout << "size: " << PERF_N << std::endl;
    std::vector<int> v1 = generate_random_vector<int>(PERF_N / 2);
    std::vector<int> v2 = generate_random_vector<int>(PERF_N / 2);
    std::vector<int> v3(PERF_N);

    std::sort(v1.begin(), v1.end());
    std::sort(v2.begin(), v2.end());

    perf_timer t;
    for(size_t trial = 0; trial < PERF_TRIALS; trial++){
        t.start();
        ParallelMerge(v1.begin(), v1.end(), v2.begin(), v2.end(), v3.begin());
        t.stop();
    }
    std::cout << "time: " << t.min_time() / 1e6 << " ms" << std::endl;

    return 0;
}