/* run_thread.c  run 4 threads plus master */
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <unistd.h>
#include <time.h>

#define n_thread  4
#define np        5
static int nb = 0;
static double results[n_thread];
static pthread_cond_t go;
static pthread_mutex_t bar;
static int cfctr = 10000000; /* iteration count */

void barrier(void)
{
  pthread_mutex_lock(&bar);
    nb++;
    if(nb == np)
    {
      nb = 0;
      pthread_cond_broadcast(&go);
    }
    else
    {
      pthread_cond_wait(&go, &bar);      
    }
  pthread_mutex_unlock(&bar);
} /* end barrier */

void * thread_compute(void * threadID)
{
  int i, j, k;
  double x, y, z;

  i = (int)threadID;
  barrier();   /* wait for all to start together */

  z = 0.001+(double)i/100.0;
  for(j=0; j<10; j++)
  {
    for(k=0; k<cfctr; k++)
    {
      y = exp(sin(z)-cos(z));
      x = sqrt(sqrt(y));
      z = z + x/(double)cfctr;
    }
    printf("   thread %d step %d z=%g \n", i, j, z);
    fflush(stdout);
  }
  results[i] = z;
  /* done this far */

  barrier();

  z = 0.002+(double)i/200.0;
  for(j=0; j<10; j++)
  {
    for(k=0; k<cfctr; k++)
    {
      y = exp(sin(z)-cos(z));
      x = sqrt(sqrt(y));
      z = z + x/(double)cfctr;
    }
    printf("   thread %d again step %d z=%g \n", i, j, z);
    fflush(stdout);
  }
  results[i] = z;
  /* done */

  barrier(); /* let master know we are finished */

  pthread_exit(NULL);
}

int main(int argc, char * argv[])
{
  int rc, t;
  pthread_t threads[n_thread];
  double t_start, t_now;

  printf("run_thread.c running \n");
  fflush(stdout);
  t_now = (double)clock()/(double)CLOCKS_PER_SEC; /* process time */
  t_start = (double)time(NULL);                   /* wall time */

  pthread_mutex_init(&bar, NULL); /* initialization */
  pthread_mutex_unlock(&bar);
  pthread_cond_init(&go, NULL);

  for(t=0; t<n_thread; t++)
  {
    printf("creating thread %d \n", t);
    fflush(stdout);
    rc = pthread_create(&threads[t], NULL, thread_compute, (void *)t);
    if(rc)
    {
      printf("error, thread not created, code=%d, at t=%d \n", rc, t);
      fflush(stdout);
      exit(-1);
    }
  }
  printf("waiting for threads to reach first barrier \n");
  fflush(stdout);
  barrier(); /* wait for all threads to start togrther */

  /* could do something */

  barrier(); /* wait for all threads to finish first task */

  printf("all threads finished first task \n");
  for(t=0; t<n_thread; t++)
  {
    printf("results[%d]=%g \n", t, results[t]);
  }
  fflush(stdout);


  printf("wait for all threads to finish second task \n");
  fflush(stdout);
  barrier();

  printf("all threads finished second task \n");
  for(t=0; t<n_thread; t++)
  {
    printf("final results[%d]=%g \n", t, results[t]);
  }
  printf("CPU time %f sec \n", (double)clock()/(double)CLOCKS_PER_SEC-t_now);
  printf("wall time %f sec \n", (double)time(NULL)-t_start);

  printf("master exiting, run_thread finished \n");
  fflush(stdout);
  return 0;
} /* end run_thread.c */