未在此作用域中声明OMP_LACES

Question

我正在寻找在代码中使用OMP_PLACES和OMP_PROC_BIND=close的正确方法。当我运行这个时，我得到的是：

error: ‘OMP_PLACES’ was not declared in this scope

#include <iostream>
#include <random>
#include <fstream>
#include <iomanip>
#include <cfloat>
#include <omp.h>
#include <stdlib.h>
using namespace std; 
int main()
{
const int N = 100;
unsigned seed = 0;
double sum = 0.0;
double avg;
srand(seed);
default_random_engine g(seed);
uniform_real_distribution<double> distribution(0.0f, nextafter(1.0f, DBL_MAX));
#pragma omp parallel 
{
OMP_PLACES="cores(4)";
OMP_PROC_BIND=close;

#pragma omp for reduction (+: sum) 
for (int i = 0; i < N; i++) {
double x = distribution(g);
sum = sum + x;
}
avg = sum / static_cast<double> (N);


}

}

Answer 1

必须在shell环境中设置OMP_PLACES和OMP_PROC_BIND变量。所以，如果你使用bash，那么你可以这样做：

$ export OMP_PLACES="cores(4)"
$ export OMP_PROC_BIND=close
$ ./your_application

另一种选择是在代码中使用proc_bind()子句：

// header omitted
int main()
{
const int N = 100;
unsigned seed = 0;
double sum = 0.0;
double avg;
srand(seed);
default_random_engine g(seed);
uniform_real_distribution<double> distribution(0.0f, nextafter(1.0f, DBL_MAX));
#pragma omp parallel proc_bind(close)
{
#pragma omp for reduction (+: sum) 
for (int i = 0; i < N; i++) {
double x = distribution(g);
sum = sum + x;
}
// remainder of code to follow
}
...
}

然后你仍然需要

$ export OMP_PLACES="cores(4)"

指定您希望代码运行的位置。

PS：你可能还想查看这个关于随机数生成器的C++线程安全的SO页面：随机数生成器的C++11线程安全