c - OMP 对于并行线程 ID hello world

Question

我正在尝试开始使用 C 中的基本 OpenMP 功能。我对“omp parallel for”的基本理解使我相信以下内容应该在线程之间分配循环的后续迭代并且应该并发执行。我得到的输出如下。下面的代码。我的 hello world 示例中是否遗漏了一些微妙的东西？

来自 omp 线程 0 的 Hello World来自 omp 线程 0 的 Hello World来自 omp 线程 0 的 Hello World来自 omp 线程 0 的 Hello World来自 omp 线程 0 的 Hello World来自 omp 线程 0 的 Hello World等..

 int HelloFunc()
{
    int i;
    int numthreads = 8;
#pragma omp parallel for default(none) num_threads(numthreads) private(i)
    for (i = 0; i < 100; i++)
    {
        int tid = omp_get_thread_num();
        printf("Hello world from omp thread %d\n", tid);
    }
    return -1;
}

int main()
{
    int result = HelloFunc();
}

Answer 1

#include <omp.h>
#include <stdio.h>


 int HelloFunc()
{
    int i;
    int numthreads = 8;
#pragma omp parallel for default(none) num_threads(numthreads) private(i)
    for (i = 0; i < 100; i++)
    {
        int tid = omp_get_thread_num();
        printf("Hello world from omp thread %d\n", tid);
    }
    return -1;
}

int main()
{
    HelloFunc();

  return 0;
}

然后编译:

gcc t.c -fopenmp -Wall

然后运行:

./a.out

输出:

Hello world from omp thread 7
Hello world from omp thread 7
Hello world from omp thread 7
Hello world from omp thread 7
Hello world from omp thread 7
Hello world from omp thread 7
Hello world from omp thread 7
Hello world from omp thread 7
Hello world from omp thread 7
Hello world from omp thread 7
Hello world from omp thread 7
Hello world from omp thread 7
Hello world from omp thread 3
Hello world from omp thread 3
Hello world from omp thread 3
Hello world from omp thread 3
Hello world from omp thread 3
Hello world from omp thread 3
Hello world from omp thread 3
Hello world from omp thread 3
Hello world from omp thread 3
Hello world from omp thread 3
Hello world from omp thread 3
Hello world from omp thread 3
Hello world from omp thread 3
Hello world from omp thread 0
Hello world from omp thread 0
Hello world from omp thread 0
Hello world from omp thread 0
Hello world from omp thread 0
Hello world from omp thread 0
Hello world from omp thread 0
Hello world from omp thread 0
Hello world from omp thread 0
Hello world from omp thread 0
Hello world from omp thread 0
Hello world from omp thread 0
Hello world from omp thread 0
Hello world from omp thread 5
Hello world from omp thread 5
Hello world from omp thread 5
Hello world from omp thread 5
Hello world from omp thread 6
Hello world from omp thread 6
Hello world from omp thread 6
Hello world from omp thread 6
Hello world from omp thread 6
Hello world from omp thread 6
Hello world from omp thread 6
Hello world from omp thread 6
Hello world from omp thread 6
Hello world from omp thread 6
Hello world from omp thread 6
Hello world from omp thread 6
Hello world from omp thread 5
Hello world from omp thread 5
Hello world from omp thread 5
Hello world from omp thread 5
Hello world from omp thread 5
Hello world from omp thread 5
Hello world from omp thread 5
Hello world from omp thread 5
Hello world from omp thread 2
Hello world from omp thread 2
Hello world from omp thread 4
Hello world from omp thread 4
Hello world from omp thread 4
Hello world from omp thread 4
Hello world from omp thread 2
Hello world from omp thread 1
Hello world from omp thread 4
Hello world from omp thread 2
Hello world from omp thread 1
Hello world from omp thread 4
Hello world from omp thread 2
Hello world from omp thread 2
Hello world from omp thread 4
Hello world from omp thread 1
Hello world from omp thread 1
Hello world from omp thread 1
Hello world from omp thread 1
Hello world from omp thread 1
Hello world from omp thread 1
Hello world from omp thread 1
Hello world from omp thread 2
Hello world from omp thread 4
Hello world from omp thread 1
Hello world from omp thread 2
Hello world from omp thread 4
Hello world from omp thread 1
Hello world from omp thread 1
Hello world from omp thread 4
Hello world from omp thread 2
Hello world from omp thread 1
Hello world from omp thread 4
Hello world from omp thread 4
Hello world from omp thread 2
Hello world from omp thread 2
Hello world from omp thread 2
Hello world from omp thread 2