/*
 * Campeonato entre 4 threads.
 */ 
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

volatile int s = 0;

int vez_final = 0;
int inter_final[2] = { 0, 0 };

int vez_elim [2] = {0, 0};
int inter_elim[4] = { 0, 0, 0, 0};


void* f_thread(void *v) {
  int id, bit0, bit1;
  int pos_elim, adv_elim, pos_final, adv_final;
  int i;
  
  id = *(int *) v;
  bit0 = id & 1;
  bit1 = (id >> 1);

  pos_elim = id;
  adv_elim = bit1 * 2 + ( 1 - bit0);
  pos_final = bit1;
  adv_final = 1 - bit1;

  for (i = 0; i < 20; i++) {

    inter_elim[pos_elim] = 1;
    vez_elim[pos_final] = id;

    while (vez_elim[pos_final] == id && inter_elim[adv_elim]) ; 

    sleep(1);
    inter_final[pos_final] = 1;
    vez_final = id;
    while (vez_final == id && inter_final[adv_final]) ; 

    sleep(1);
    s = id;
    printf("Thread %d, s = %d.\n", id, s); 

    inter_final[pos_final] = 0;    
    inter_elim[pos_elim] = 0;
  }

  return NULL;
}

int main() {

  pthread_t thr[4];
  int id[4];
  int i;
  
  for (i = 0; i < 4; i++) {
    id[i] = i;
    pthread_create(&thr[i], NULL, start_thread, (void*) &id[i]);
  }

  for (i = 0; i < 4; i++) 
    pthread_join(thr[i], NULL); 

  return 0;
}