/*
 * Condition variables demo: this demo simulates a semaphore using
 * mutex and condition variables
 *
 * Copyright (C) 2002 by Paolo Gai
 * Copyright (C) 2016 by Luca Abeni 
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */


#include <unistd.h>
#include <stdio.h>
#include <pthread.h>

struct mysem {
  pthread_mutex_t mutex;
  pthread_cond_t cond;
  int counter;
};

static struct mysem mysem;

void mysem_init(struct mysem *s, int num)
{
  s->counter = num;

  pthread_mutex_init(&s->mutex, NULL);

  pthread_cond_init(&s->cond, NULL);
}

void mysem_wait(struct mysem *s)
{
  pthread_mutex_lock(&s->mutex);
  while (!s->counter) {
    pthread_cond_wait(&s->cond, &s->mutex);
  }
  
  s->counter--;

  pthread_mutex_unlock(&s->mutex);
}

void mysem_post(struct mysem *s)
{
  pthread_mutex_lock(&s->mutex);

  s->counter++;
  pthread_cond_signal(&s->cond);

  pthread_mutex_unlock(&s->mutex);
}


/**
 * Here is the real program...
 */


void *body(void *arg)
{
  int j;
  
  mysem_wait(&mysem);
  for (j=0; j<40; j++) {
    usleep(200000); 
    fprintf(stderr, "%s", (char *)arg);
  }
  mysem_post(&mysem);

  return NULL;
}

int main(int argc, char *argv[])
{
  pthread_t t1,t2,t3;

  mysem_init(&mysem,1);

  pthread_create(&t1, NULL, body, (void *)".");
  pthread_create(&t2, NULL, body, (void *)"#");
  pthread_create(&t3, NULL, body, (void *)"o");

  pthread_join(t1, NULL);
  pthread_join(t2, NULL);
  pthread_join(t3, NULL);

  printf("\n");

  return 0;
}