/* Mecanisme de synchronisation pour les lectures/ecritures */
/* Copyright (C) 2008  Emmanuel Varoquaux

   This file is part of XOS.

   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 3 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, see <http://www.gnu.org/licenses/>. */

/* L'acces en lecture est autorise en concurrence, mais l'acces en ecriture est
 * exclusif.
 * Les demandes d'acces en ecriture sont prioritaires sur les demandes d'acces
 * en lecture. */

#include <rw_lock_struct.h>
#include <condition.h>

void rw_lock_init(struct rw_lock_struct *rw_lock)
{
  rw_lock->count = 0;
  condition_init(&rw_lock->read_condition);
  condition_init(&rw_lock->write_condition);
}

int rw_lock_lock_read(struct rw_lock_struct *rw_lock)
{
  while (rw_lock->count < 0)
    if (!condition_wait_interruptible(&rw_lock->read_condition))
      return 0;
  rw_lock->count++;
  return 1;
}

int rw_lock_lock_write(struct rw_lock_struct *rw_lock)
{
  while (rw_lock->count)
    if (!condition_wait_interruptible(&rw_lock->write_condition))
      return 0;
  rw_lock->count = -1;
  return 1;
}

void rw_lock_unlock_read(struct rw_lock_struct *rw_lock)
{
  rw_lock->count--;
  if (!rw_lock->count)
    condition_signal(&rw_lock->write_condition);
}

void rw_lock_unlock_write(struct rw_lock_struct *rw_lock)
{
  rw_lock->count = 0;
  condition_signal(&rw_lock->write_condition);
  condition_signal_all(&rw_lock->read_condition);
}