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

typedef struct semstruct semaphore;

struct semstruct
{
  int max;
  int val;  // semaphore value
  pthread_mutex_t smutex;  // proctects access to semaphore
  pthread_cond_t scond;    // semaphore condition  (val > 0)
};

void semaphore_init(semaphore *sem, int max)// must do before given to threads!
{
  sem->max = max;
  sem->val = sem->max;
  pthread_mutex_init(&(sem->smutex),NULL);
  pthread_cond_init(&(sem->scond),NULL);
}

// wait for semaphore  (decrement)
void proberen(semaphore *sem)
{
   pthread_mutex_lock(&(sem->smutex));
   while (sem->val < 1)  
     pthread_cond_wait(&(sem->scond), &(sem->smutex));
   sem->val -= 1;
   pthread_mutex_unlock(&(sem->smutex));
} // proberen

// signal semaphore  (increment)
void verhogen(semaphore *sem)
{
   pthread_mutex_lock(&(sem->smutex));
   if (sem->val < sem->max) 
     { sem->val += 1;
       pthread_cond_signal(&(sem->scond));  // wake someone up
     }                          // put it in ready state
   pthread_mutex_unlock(&(sem->smutex));
} // verhogen