csce313-mp4pinie64backup/semaphore.h

/* 
    File: semaphore.H

    Author: R. Bettati
            Department of Computer Science
            Texas A&M University
    Date  : 08/02/11

*/

#ifndef _semaphore_H_                   // include file only once
#define _semaphore_H_

/*--------------------------------------------------------------------------*/
/* DEFINES */
/*--------------------------------------------------------------------------*/

/* -- (none) -- */

/*--------------------------------------------------------------------------*/
/* INCLUDES */
/*--------------------------------------------------------------------------*/

#include <pthread.h>
//#include <mutex>

/*--------------------------------------------------------------------------*/
/* DATA STRUCTURES */ 
/*--------------------------------------------------------------------------*/

/* -- (none) -- */

/*--------------------------------------------------------------------------*/
/* FORWARDS */ 
/*--------------------------------------------------------------------------*/

/* -- (none) -- */

/*--------------------------------------------------------------------------*/
/* CLASS   S e m a p h o r e  */
/*--------------------------------------------------------------------------*/

class Semaphore {
private:
  /* -- INTERNAL DATA STRUCTURES
     You may need to change them to fit your implementation. */

  int value;
  pthread_mutex_t m;
  pthread_cond_t  c;

public:

  /* -- CONSTRUCTOR/DESTRUCTOR */

  Semaphore(int _val){
    value = _val;
    pthread_mutex_init(&m, NULL);
    pthread_cond_init(&c, NULL);
  }

  ~Semaphore(){}

  /* -- SEMAPHORE OPERATIONS */

  int P() {
    //This is to lock the Semaphore.
    pthread_mutex_lock( &m );
    
    --value;
    //If counter is negative, wait until condition, basically wait until signaled.
    if(value < 0) {
      pthread_cond_wait( &c, &m );
    }

    //Some code here.

    //Unlock the Semaphore.
    pthread_mutex_unlock( &m );
  }
      //;
  int V() {
    pthread_mutex_lock( &m );
    
    ++value;

    if(value <= 0) {
      pthread_cond_signal( &c );
    }
    
    pthread_mutex_unlock( &m );
  }
};

#endif