Sections construct

The sections construct defines some sections which run in parallel:

#pragma omp sections [clause[ [,] clause] ... ] new-line
{[
    #pragma omp section new-line]
        structured-block
    [#pragma omp section new-line
        structured-block]
    ...
}

Check the following code:

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

int main(void)
{        
    #pragma omp parallel
    {
        #pragma omp sections
        {
            printf("Thread %d is running\n", omp_get_thread_num());
            #pragma omp section
            printf("Thread %d is running\n", omp_get_thread_num());
            #pragma omp section
            printf("Thread %d is running\n", omp_get_thread_num());
            #pragma omp section
            printf("Thread %d is running\n", omp_get_thread_num());
        }
    }

    return 0;
}

Build and run it on my 24-core machine:

# gcc -fopenmp parallel.c
# ./a.out
Thread 0 is running
Thread 21 is running
Thread 22 is running
Thread 8 is running

We can see 4 sections (for the first section, #pragma omp section is optional) are dispatched to different threads to run. Like for-loop construct, the following shortcut

#pragma omp parallel sections
{
    ......
}  

if often used instead of:

#pragma omp parallel
{
    #pragma omp sections
    {
        ......
    }
}

Furthermore, some clauses, like private and firstprivate, can also be used for sections construct.