// test1.c  check if openMP available  compile gcc -fopenmp ...
#include <omp.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int main(int argc, char * argv[])
{
  int myid;
  int def_num_threads, num_threads, num_proc;
  double ttime;

  num_proc = omp_get_num_procs();
  printf("test1.c check for openMP, num_proc=%d \n", num_proc);
  fflush(stdout);
  ttime = omp_get_wtime(); // wall time now, in seconds

  #pragma omp parallel // must be at least one "parallel", else no threads
  {
    #pragma omp master // only the master thread will run { to }
    {
      def_num_threads = omp_get_num_threads(); // must be in parallel
      omp_set_num_threads(6);
      num_threads = omp_get_num_threads();
      printf("def_num_threads=%d, try 6, omp_set_num_threads =%d \n",
	     def_num_threads, num_threads);
      fflush(stdout); // needed to get clean output
    }
    #pragma omp barrier // all threads must be doing nothing
    myid = omp_get_thread_num(); // master == 0
    printf("test1.c in pragma omp parallel myid=%d \n", myid);
    fflush(stdout);
    
  }
  // total wall time is difference
  printf("test1.c ends, %f seconds \n", omp_get_wtime()-ttime);
  fflush(stdout);
  return 0;
} // end test1.c