/* File:     omp_hello.c
 *
 * Purpose:  A parallel hello, world program that uses OpenMP
 *
 * Compile:  gcc -g -Wall -fopenmp -o omp_hello omp_hello.c
 * Run:      ./omp_hello <number of threads>
 * 
 * Input:    none
 * Output:   A message from each thread
 *
 * Note:     This version does some basic error checking:  it checks
 *           the command line argument, and it checks the number of
 *           threads started by the parallel directive.  It also
 *           checks for availability of OpenMP by testing for the
 *           _OPENMP macro
 *
 * IPP:      Section 5.1.3 (pp. 215 and ff.)
 */
#include <stdio.h>
#include <stdlib.h>
#ifdef _OPENMP
#  include <omp.h>   
#endif _OPENMP

void Usage(char* prog_name);
void Hello(int thread_count);  /* Thread function */

/*--------------------------------------------------------------------*/
int main(int argc, char* argv[]) {
   int thread_count;

   if (argc != 2) Usage(argv[0]);
   thread_count = strtol(argv[1], NULL, 10); 
   if (thread_count <= 0) Usage(argv[0]);

#  pragma omp parallel num_threads(thread_count) 
   Hello(thread_count);

   return 0; 
}  /* main */

/*--------------------------------------------------------------------
 * Function:  Usage
 * Purpose:   Print a message indicating how program should be started
 *            and terminate.
 */
void Usage(char *prog_name) {
   fprintf(stderr, "usage: %s <thread_count>\n", prog_name);
   fprintf(stderr, "   thread_count should be positive\n");
   exit(0);
}  /* Usage */

/*--------------------------------------------------------------------
 * Function:    Hello
 * Purpose:     Thread function that prints message
 */
void Hello(int thread_count) {
#  ifdef _OPENMP
      int my_rank = omp_get_thread_num();
      int actual_thread_count = omp_get_num_threads();
#  else
      int my_rank = 0;
      int actual_thread_count = 1;
#  endif

   if (my_rank == 0 && thread_count != actual_thread_count)
      fprintf(stderr, "Number of threads started != %d\n", thread_count);
   printf("Hello from thread %d of %d\n", my_rank, actual_thread_count);

}  /* Hello */