#ifndef SEMAPHORE_HH
#define SEMAPHORE_HH

#include <pthread.h>


struct Semaphore
{
  int value;
  pthread_mutex_t mutex; 
};


void init (Semaphore& s, int value)
{
  s.value = value;
  
  // initialize mutex
  pthread_mutex_init(&(s.mutex), NULL);
}


void P (Semaphore& s)
{
  pthread_mutex_lock(&(s.mutex));
  while (s.value == 0)
  {
    // active wait
    pthread_mutex_unlock(&(s.mutex));
    pthread_mutex_lock(&(s.mutex));
  }
  s.value = s.value - 1;
  pthread_mutex_unlock(&(s.mutex));
}


void V (Semaphore& s)
{
  pthread_mutex_lock(&(s.mutex));
  s.value = s.value + 1;
  pthread_mutex_unlock(&(s.mutex));
}


void destroy (Semaphore& s)
{
  // cleanup mutex
  pthread_mutex_destroy(&(s.mutex));
}


#endif // SEMAPHORE_HH