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

     /*-
      * Copyright (c) 1997 Berkeley Software Design, Inc. 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.
     * 3. Berkeley Software Design Inc's name may not be used to endorse or
     *    promote products derived from this software without specific prior
     *    written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY BERKELEY SOFTWARE DESIGN INC ``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 BERKELEY SOFTWARE DESIGN INC 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: releng/10.0/sys/sys/_mutex.h 242901 2012-11-11 23:25:47Z attilio $
     */
    
    #ifndef _SYS__MUTEX_H_
    #define _SYS__MUTEX_H_
    
    #include <machine/param.h>
    
    /*
     * Sleep/spin mutex.
     *
     * All mutex implementations must always have a member called mtx_lock.
     * Other locking primitive structures are not allowed to use this name
     * for their members.
     * If this rule needs to change, the bits in the mutex implementation must
     * be modified appropriately.
     */
    struct mtx {
            struct lock_object      lock_object;    /* Common lock properties. */
            volatile uintptr_t      mtx_lock;       /* Owner and flags. */
    };
    
    /*
     * Members of struct mtx_padalign must mirror members of struct mtx.
     * mtx_padalign mutexes can use the mtx(9) API transparently without
     * modification.
     * Pad-aligned mutexes used within structures should generally be the
     * first member of the struct.  Otherwise, the compiler can generate
     * additional padding for the struct to keep a correct alignment for
     * the mutex.
     */
    struct mtx_padalign {
            struct lock_object      lock_object;    /* Common lock properties. */
            volatile uintptr_t      mtx_lock;       /* Owner and flags. */
    } __aligned(CACHE_LINE_SIZE);
    
    #endif /* !_SYS__MUTEX_H_ */

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