Master and single construct

In OpenMP, Master construct identifies only master thread (who's thread ID is 0) executes the region. For example:

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

int main(void)
{    
    #pragma omp parallel
    {
        #pragma omp master
        {
            printf("Thread %d is executing master construct\n", omp_get_thread_num());
        }
        printf("Thread %d is executing non-master construct\n", omp_get_thread_num());
    }

    return 0;
}

Build and run it on my 24-core machine:

# gcc -fopenmp parallel.c
# ./a.out
Thread 23 is executing non-master construct
Thread 3 is executing non-master construct
Thread 14 is executing non-master construct
Thread 11 is executing non-master construct
Thread 10 is executing non-master construct
Thread 16 is executing non-master construct
Thread 9 is executing non-master construct
Thread 15 is executing non-master construct
Thread 12 is executing non-master construct
Thread 6 is executing non-master construct
Thread 7 is executing non-master construct
Thread 17 is executing non-master construct
Thread 13 is executing non-master construct
Thread 19 is executing non-master construct
Thread 5 is executing non-master construct
Thread 21 is executing non-master construct
Thread 4 is executing non-master construct
Thread 18 is executing non-master construct
Thread 22 is executing non-master construct
Thread 20 is executing non-master construct
Thread 0 is executing master construct
Thread 0 is executing non-master construct
Thread 1 is executing non-master construct
Thread 8 is executing non-master construct
Thread 2 is executing non-master construct

Only master thread outputs "executing master construct" message.

There is another single construct which guarantees only one thread (no need to be the master thread) runs the region. Modify the above code:

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

int main(void)
{    
    #pragma omp parallel
    {
        #pragma omp single
        {
            printf("Thread %d is executing single construct\n", omp_get_thread_num());
        }
        printf("Thread %d is executing non-single construct\n", omp_get_thread_num());
    }

    return 0;
}

Build and run it again:

# gcc -fopenmp parallel.c
# ./a.out
Thread 22 is executing single construct
Thread 14 is executing non-single construct
Thread 23 is executing non-single construct
Thread 4 is executing non-single construct
Thread 16 is executing non-single construct
Thread 18 is executing non-single construct
Thread 5 is executing non-single construct
Thread 9 is executing non-single construct
Thread 12 is executing non-single construct
Thread 3 is executing non-single construct
Thread 15 is executing non-single construct
Thread 7 is executing non-single construct
Thread 2 is executing non-single construct
Thread 10 is executing non-single construct
Thread 21 is executing non-single construct
Thread 8 is executing non-single construct
Thread 13 is executing non-single construct
Thread 6 is executing non-single construct
Thread 20 is executing non-single construct
Thread 1 is executing non-single construct
Thread 17 is executing non-single construct
Thread 11 is executing non-single construct
Thread 0 is executing non-single construct
Thread 19 is executing non-single construct
Thread 22 is executing non-single construct

A random selected thread (whose ID is 22) outputs "executing single construct".