OpenMP学习之--数据环境（代码示例）

这是里把OpenMP常用的数据环境construct用代码示例的方法写出来了，主要包括private，firstprivate，lastprivate和copyin。注释部分对这几种construct作用和区别描述已经很详细了，这里就补多说，相信演示代码会有更好的效果。

 

// Data Environment.cpp : 定义控制台应用程序的入口点。//#include "stdafx.h"#include "omp.h"int cpx = 100; // threadprivate只对全局或静态数据项有效#pragma omp threadprivate(cpx) // 必须在main外int _tmain(int argc, _TCHAR* argv[]){int i, px, fpx, lpx;px=fpx=lpx= 100;cpx = 100;printf("/n--------------------------------private--------------------------------/n");#pragma omp parallel for private(px) // threadprivate和private的区别是private只在并行区中有效，而threadprivate属性是全局范围内有效的。for (i=0; i<5; i++){px = 1000; // private构造px之后,包括主线程在内的所有变量px都是线程私有的，且需要从新初始化，否则运行出错。px += i;printf("threadnum = %d, px = %d/n",omp_get_thread_num(), px);}printf("串行 threadnum = %d, px = %d/n",omp_get_thread_num(), px); // private构造的变量是线程局部的，退出并行去后线程变量自动销毁。这里是原来的串行区对应变量px，并且和下次进入并行区的变量无关。printf("/n--------------------------------firstprivate--------------------------------/n");#pragma omp parallel for firstprivate(fpx) // 设变量属性为private，同时每个线程的这个变量的初始值为串行区对应变量的值，这样就不需要我们再次初始化。for (i=0; i<9; i++){fpx += i; // 这之前没有再次初始化fpxprintf("threadnum = %d, fpx = %d/n",omp_get_thread_num(), fpx);}printf("串行 threadnum = %d, fpx = %d/n",omp_get_thread_num(), fpx); //同样，因为变量属性为private，是局部的，这里的fpx还是以前的（串行区对应变量），值并没有改变。printf("/n--------------------------------lastprivate--------------------------------/n");#pragma omp parallel for lastprivate(lpx) // 最后一次迭代内的lastprivate变量的值将被带出并行区赋给串行区对应的同名变量，当然这个必须和for循环一起用，否则会出错。for (i=0; i<9; i++){lpx = 1000; // lastprivate构造lpx之后,变量lpx变成线程私有的局部变量，因此需要从新初始化，否则运行出错。lpx += i;printf("threadnum = %d, lpx = %d/n",omp_get_thread_num(), lpx);}printf("串行 threadnum = %d, lpx = %d/n",omp_get_thread_num(), lpx); // lastprivate将最后一次迭代的变量值赋给了对应的全局变量，所以这里的lpx值变化了printf("--------------------------------copyin parallel first--------------------------------/n");cpx = 1000;#pragma omp parallel{printf("threadnum = %d, cpx = %d/n", omp_get_thread_num(), cpx); //threadprivate，主线程继承原来串行区的值，其他线程继承对应的全局变量的值。（串行区是由主线程执行的，就是说主线程中的cpx值之前已被更改，而其他的未变）}printf("串行 cpx=%d/n",cpx);printf("--------------------------------copyin parallel second--------------------------------/n");#pragma omp parallel copyin(cpx) // copyin: 把主线程（串行区）全局变量的值拷贝到各线程中同名的threadprivate变量中去。 {printf("copyin，threadnum = %d, original cpx = %d/n", omp_get_thread_num(), cpx);cpx = omp_get_thread_num();printf("after change,threadnum = %d, copyin: cpx = %d/n",omp_get_thread_num(), cpx);}printf("串行 cpx=%d/n",cpx);printf("--------------------------------copyin parallel third--------------------------------/n");#pragma omp parallel //threadprivate不同于private的是前者是全局有效的，再次进入并行区，使用的还是上次退出前赋予的值printf("threadnum = %d, cpx = %d/n", omp_get_thread_num(), cpx);printf("串行 cpx=%d/n",cpx);return 0;}

 

下面是程序的输出结果：

 

--------------------------------private--------------------------------threadnum = 0, px = 1000threadnum = 2, px = 1003threadnum = 0, px = 1001threadnum = 3, px = 1004threadnum = 1, px = 1002串行 threadnum = 0, px = 100--------------------------------firstprivate--------------------------------threadnum = 0, fpx = 100threadnum = 0, fpx = 101threadnum = 2, fpx = 105threadnum = 0, fpx = 103threadnum = 2, fpx = 111threadnum = 3, fpx = 107threadnum = 3, fpx = 115threadnum = 1, fpx = 103threadnum = 1, fpx = 107串行 threadnum = 0, fpx = 100--------------------------------lastprivate--------------------------------threadnum = 0, lpx = 1000threadnum = 1, lpx = 1003threadnum = 0, lpx = 1001threadnum = 1, lpx = 1004threadnum = 0, lpx = 1002threadnum = 3, lpx = 1007threadnum = 3, lpx = 1008threadnum = 2, lpx = 1005threadnum = 2, lpx = 1006串行 threadnum = 0, lpx = 1008--------------------------------copyin parallel first--------------------------------threadnum = 0, cpx = 1000threadnum = 1, cpx = 100threadnum = 3, cpx = 100threadnum = 2, cpx = 100串行 cpx=1000--------------------------------copyin parallel second--------------------------------copyin，threadnum = 1, original cpx = 1000after change,threadnum = 1, copyin: cpx = 1copyin，threadnum = 3, original cpx = 1000after change,threadnum = 3, copyin: cpx = 3copyin，threadnum = 2, original cpx = 1000copyin，threadnum = 0, original cpx = 1000after change,threadnum = 2, copyin: cpx = 2after change,threadnum = 0, copyin: cpx = 0串行 cpx=0--------------------------------copyin parallel third--------------------------------threadnum = 0, cpx = 0threadnum = 1, cpx = 1threadnum = 3, cpx = 3threadnum = 2, cpx = 2串行 cpx=0