/* thread_loop.c  run 4 threads, three stops and start, in loop twice */

#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define n_thread  4
#define np        5
#define nloop     2
static int nb = 0;
static int results[n_thread];
static pthread_cond_t go;
static pthread_mutex_t bar;

void barrier(void)
{
  printf("in barrier \n");
  fflush(stdout);

  pthread_mutex_lock(&bar);
    nb++;
    printf("nb=%d of np=%d \n", nb, np);
    fflush(stdout);

    if(nb == np)
    {
      nb = 0;
      printf("about to broadcast \n");
      fflush(stdout);
      pthread_cond_broadcast(&go);
    }
    else
    {
      printf("about to cond wait \n");
      fflush(stdout);
      pthread_cond_wait(&go, &bar);      
    }
  pthread_mutex_unlock(&bar);
} /* end barrier */

void * thread_compute(void * threadID)
{
  int i, iloop; /* local variables in each thread */

  i = (int)threadID;
  printf("   thread %d at first barrier, iloop %d \n", i, iloop);
  fflush(stdout);
  barrier(); /* B1 */

  for(iloop=0; iloop<nloop; iloop++)
  {
    printf("   thread %d running after first barrier, iloop %d \n", i, iloop);
    fflush(stdout);
    results[i] = 10*(i+1)+iloop;
    /* done this far */
    printf("   thread %d at second barrier, iloop %d \n", i, iloop);
    fflush(stdout);
    barrier(); /* B2 */

    printf("   thread %d running after second barrier, iloop %d \n", i, iloop);
    fflush(stdout);
    results[i] += 100*(i+1);
    /* done this far */
    printf("   thread %d at third barrier, iloop= \n", i, iloop);
    fflush(stdout);
    barrier(); /* B3 */

    printf("   thread %d running after third barrier, iloop %d \n", i, iloop);
    fflush(stdout);
    results[i] += 1000*(i+1);
    /* done */
    printf("   thread %d at fourth barrier, iloop %d \n", i, iloop);
    fflush(stdout);
    barrier(); /* B4 */
  } /* end iloop */
  /* pthread_exit(NULL); */
  return threadID;
}

int main(int argc, char * argv[])
{
  int rc, t;
  int errcode;
  int status;
  int iloop;
  pthread_t threads[n_thread];

  printf("pthread_loop.c running \n");
  fflush(stdout);

  pthread_mutex_init(&bar, NULL);
  pthread_mutex_unlock(&bar);
  pthread_cond_init(&go, NULL);

  for(t=0; t<n_thread; t++)
  {
    printf("creating thread %d \n", t);
    fflush(stdout);
    results[t] = 0;
    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(); /* B1 wait for all threads to run */

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

    printf("wait for all threads to finish second task \n");
    fflush(stdout);
    barrier(); /* B2 */

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

    printf("wait for all threads to finish third task \n");
    fflush(stdout);
    barrier(); /* B3 */

    printf("all threads finished third task \n");
    fflush(stdout);
    barrier(); /* B4 wait for all at "done" */
    for(t=0; t<n_thread; t++)
    {
      printf("final results[%d]=%d \n", t, results[t]);
      fflush(stdout);
    }
  } /* end iloop */

  /* wait for all threads to exit and join*/
  for(t=0; t<n_thread; t++)
  {
    if (errcode=pthread_join(threads[t],(void *)&status)) 
      printf("compute &d failed join: %s\n", t, strerror(errcode));
    /* check thread's exit status and release its resources */
    if (status != t)
      printf("compute %d terminated abnormally, status=%d \n", t, status);
  }

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