【学习体会】OpenCV的cv::parallel_for_使用

仅仅只是多线程的话，cv::parallel_for_并不会比openmp快多少，不相上下

#include<opencv2/opencv.hpp>
#include<omp.h>
#include<thread>
#include <stdio.h>
#include <chrono>
#include<iostream>
class LoopBody : public cv::ParallelLoopBody
{
public:
    LoopBody (int*_a,int*_b,int*_c):a(_a),b(_b),c(_c)
    {
    }
    virtual void operator()(const cv::Range& r) const
    {
        for (int i = r.start; i != r.end; i++)  //遍历
        {
            c[i] = a[i]+b[i];
        }
    }

protected:
    int *a;
    int *b;
    int *c;
};

int main(int argc, char** argv)
{
    int num = 10000;

    {
        int* a = new int[num];
        int* b = new int[num];
        int* c = new int[num];

        for(int i=0;i<num;i++){
            a[i]=1;
            b[i]=2;
            c[i]=0;
        }
        if(num<=10){
            for(int i=0;i<num;i++){
                std::cout<<c[i]<<" ";
            }
            std::cout<<std::endl<<std::endl;
        }

        std::chrono::system_clock::time_point start = std::chrono::system_clock::now();

        #pragma omp parallel for num_threads(2 * omp_get_num_procs() - 1)
        for(int i=0;i<num;i++){
            //printf("thread ID %d\n", std::this_thread::get_id());
            c[i] = a[i]+b[i];
        }

        std::chrono::system_clock::time_point end = std::chrono::system_clock::now();
        std::chrono::microseconds duration = std::chrono::duration_cast<std::chrono::microseconds>(end - start);
        std::cout << "openmp Spent " << double(duration.count()) * std::chrono::microseconds::period::num / std::chrono::microseconds::period::den << " seconds." << std::endl;

        if(num<=10){
            for(int i=0;i<num;i++){
                std::cout<<c[i]<<" ";
            }
            std::cout<<std::endl<<std::endl;
        }
        delete[] a;
        delete[] b;
        delete[] c;
    }

    {
        int* a = new int[num];
        int* b = new int[num];
        int* c = new int[num];

        for(int i=0;i<num;i++){
            a[i]=1;
            b[i]=2;
            c[i]=0;
        }
        if(num<=10){
            for(int i=0;i<num;i++){
                std::cout<<c[i]<<" ";
            }
            std::cout<<std::endl<<std::endl;
        }
        std::chrono::system_clock::time_point start = std::chrono::system_clock::now();
        cv::setNumThreads(2 * omp_get_num_procs() - 1);
        LoopBody body(a,b,c);
        cv::parallel_for_(cv::Range(0, num), body);


        std::chrono::system_clock::time_point end = std::chrono::system_clock::now();
        std::chrono::microseconds duration = std::chrono::duration_cast<std::chrono::microseconds>(end - start);
        std::cout << "parallel_for Spent " << double(duration.count()) * std::chrono::microseconds::period::num / std::chrono::microseconds::period::den << " seconds." << std::endl;
        if(num<=10){
            for(int i=0;i<num;i++){
                std::cout<<c[i]<<" ";
            }
            std::cout<<std::endl<<std::endl;
        }
        delete[] a;
        delete[] b;
        delete[] c;
    }

    

    return 0;
}