FreeBSD/Linux Kernel Cross Reference
sys/sys/refcount.h

     /*-
      * Copyright (c) 2005 John Baldwin <jhb@FreeBSD.org>
      * All rights reserved.
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
      * are met:
      * 1. Redistributions of source code must retain the above copyright
      *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     * $FreeBSD$
     */
    
    #ifndef __SYS_REFCOUNT_H__
    #define __SYS_REFCOUNT_H__
    
    #include <machine/atomic.h>
    
    #ifdef _KERNEL
    #include <sys/systm.h>
    #else
    #define KASSERT(exp, msg)       /* */
    #endif
    
    static __inline void
    refcount_init(volatile u_int *count, u_int value)
    {
    
            *count = value;
    }
    
    static __inline void
    refcount_acquire(volatile u_int *count)
    {
    
            atomic_add_acq_int(count, 1);   
    }
    
    static __inline int
    refcount_release(volatile u_int *count)
    {
            u_int old;
    
            /* XXX: Should this have a rel membar? */
            old = atomic_fetchadd_int(count, -1);
            KASSERT(old > 0, ("negative refcount %p", count));
            return (old == 1);
    }
    
    #endif  /* ! __SYS_REFCOUNT_H__ */

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