#include <stdlib.h>    /* for NULL     */
#include "semaphore.h"

semaphore_p newSemaphore(int value){
  semaphore_p retval = (semaphore_p)calloc(1, sizeof(semaphore_t));
  if(retval == NULL) return NULL;
  pthread_mutex_init(&retval->mutex, NULL);
  pthread_cond_init(&retval->cond, NULL);
  retval->value = (value >= 0) ? value : 0;
  return retval;
}
int postSemaphore(semaphore_p sem){
  pthread_mutex_lock(&sem->mutex);
  /* illustrative example: don't worry about overflow */
  sem->value++;
  pthread_cond_signal(&sem->cond);
  pthread_mutex_unlock(&sem->mutex);
  return 0;
}
int waitSemaphore(semaphore_p sem){
  pthread_mutex_lock(&sem->mutex);
  while(sem->value == 0)
    pthread_cond_wait(&sem->cond, &sem->mutex);
  sem->value--;
  pthread_mutex_unlock(&sem->mutex);
  return 0;
}
void freeSemaphore(semaphore_p sem){
  pthread_cond_destroy(&sem->cond);
  pthread_mutex_destroy(&sem->mutex);
  free(sem);
}