/*
 * Copyright (c) 1996 Gunther Schadow.  All rights reserved.
 *
 * 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., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#ifndef CXX_SEMAPHORE_H
#define CXX_SEMAPHORE_H

// very simple Semaphore class, does not yet implement everything from
// SYSV ipc's `sem', just the basics, explained in every book about
// operationg systems. Example:
//
// Semaphore mutex;
//
// mutex.p();
//
// ... critical region ...
//
// mutex.v();

#pragma interface

#include <stdlib.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>

#ifdef sun
  extern int semget(key_t key, int nsems, int semflg);
  extern int semctl(int semid, int semnum, int cmd, union semun arg);
  extern int semop(int semid, struct sembuf *sops, int nsops);
#endif

class Semaphore
{
 private:
  int id;
  struct sembuf buf;

 public:
  
  enum op_t {
    P = -1,
    V = +1,
  };

  enum {
    nowait = IPC_NOWAIT,
    undo   = SEM_UNDO,
  };

  Semaphore(int flag = 0);
  virtual ~Semaphore() { semun x; x.val = 0; semctl(id, 0, IPC_RMID, x); }
  int op(op_t o) { buf.sem_op = o; return semop(id, &buf, 1); }
  int p() { return op(P); }
  int v() { return op(V); }  
  short flags(short f) { short o=buf.sem_flg; buf.sem_flg=f; return o; }
  short flags() { return buf.sem_flg; }
  int getval() { semun x; x.val = 0; return semctl(id, 0, GETVAL, x); }
};

#endif