我正在尝试编写一个可以快速计算随机数并可应用于多个线程的程序。我的当前代码如下:
/* Approximating PI using a Monte-Carlo method. */
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>
#include <omp.h>
#define N 1000000000 /* As lareg as possible for increased accuracy */
double random_function(void);
int main(void)
{
int i = 0;
double X, Y;
double count_inside_temp = 0.0, count_inside = 0.0;
unsigned int th_id = omp_get_thread_num();
#pragma omp parallel private(i, X, Y) firstprivate(count_inside_temp)
{
srand(th_id);
#pragma omp for schedule(static)
for (i = 0; i <= N; i++) {
X = 2.0 * random_function() - 1.0;
Y = 2.0 * random_function() - 1.0;
if ((X * X) + (Y * Y) < 1.0) {
count_inside_temp += 1.0;
}
}
#pragma omp atomic
count_inside += count_inside_temp;
}
printf("Approximation to PI is = %.10lf\n", (count_inside * 4.0)/ N);
return 0;
}
double random_function(void)
{
return ((double) rand() / (double) RAND_MAX);
}
这段代码可以运行,但是从资源管理器的观察来看,我知道它没有使用所有的线程。rand()函数在多线程代码中能正常工作吗?如果不能,有没有好的替代方案?非常感谢。Jack