spinlock.h

/*
 * Spinlock operations.  These were hand-coded specially for this
 * effort without reference to GPL code.
 *
 * 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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 * Copyright (c) 2003 IBM Corporation.
 */

#ifndef __SPINLOCK_H
#define __SPINLOCK_H

#include "arch/atomic.h"
#include <stdlib.h>
#include "backoff.h"

typedef atomic_t spinlock_t;

#define SPIN_LOCK_UNLOCKED 0

/*
 * Acquire a spinlock.
 */

static inline void
spin_lock(spinlock_t *slp)
{
    unsigned long result;

    backoff_reset();

    for (;; ) {
        result = atomic_cmpxchg4(slp, 0, 1);
        if (result == 0) {
            spin_lock_barrier();
            return;
        }
        while (*slp != 0) {
            backoff_delay();
            memory_barrier();
        }
    }
}

/*
 * Conditionally acquire a spinlock.
 */

static inline int
spin_trylock(spinlock_t *slp)
{
    unsigned long result;

    result = atomic_cmpxchg4(slp, 0, 1);
    spin_lock_barrier();
    return (!result);
}

/*
 * Release a spinlock.
 */

static inline void
spin_unlock(spinlock_t *slp)
{
    unsigned long result;

    spin_unlock_barrier();
    if ((result = atomic_xchg4(slp, SPIN_LOCK_UNLOCKED)) != 1) {
        abort();
    }
}

#endif /* #ifndef __SPINLOCK_H */