openMP一小时初探

参考：

通过 GCC 学习 OpenMP 框架 （详细，我只看到临界区之前）

OpenMP基本概念 （全看，内含并行化控制的三种编程要素：编译制导、API函数集和环境变量）

OpenMP入门教程（一）（也讲了fork-join执行模型、线程概念、数据作用域...）

 

我主要跟着第一篇教程看了部分内容，后面两篇当作补充，这里po一下我打的两个简单例子：

test1.cpp

#include <iostream>
int main()
{
    #pragma omp parallel
    {
        std::cout << "Hello World!\n";
    }
}

我的虚拟机设置的双核

 

test2.cpp

#include <omp.h>
#include <math.h>
#include <time.h>
#include <iostream>
 
int main() 
{
    int i, nthreads;
    clock_t clock_timer;
    double wall_timer;
    double c[1000000]; 
    for (nthreads = 1; nthreads <= 2; ++nthreads) {
        clock_timer = clock();
        wall_timer = omp_get_wtime();
        #pragma omp parallel for private(i) num_threads(nthreads)
        for (i = 0; i < 10; i++)
        {
            c[i] = sqrt(i * 4 + i * 2 + i); 
            std::cout<<" i: "<<i<<"  thread_number: "<<omp_get_thread_num()<< std::endl;
        }
        std::cout << "\nthreads: " << nthreads <<  " time on clock(): " << 
            (double) (clock() - clock_timer) / CLOCKS_PER_SEC
           << " time on wall: " <<  omp_get_wtime() - wall_timer <<"\n\n";
    }
}