The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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

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    1 /*-
    2  * Copyright (c) 2002 John Baldwin <jhb@FreeBSD.org>
    3  * All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  * 3. Neither the name of the author nor the names of any co-contributors
   14  *    may be used to endorse or promote products derived from this software
   15  *    without specific prior written permission.
   16  *
   17  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   27  * SUCH DAMAGE.
   28  *
   29  * $FreeBSD$
   30  */
   31 
   32 #ifndef _SYS_TURNSTILE_H_
   33 #define _SYS_TURNSTILE_H_
   34 
   35 /*
   36  * Turnstile interface.  Non-sleepable locks use a turnstile for the
   37  * queue of threads blocked on them when they are contested.
   38  *
   39  * A thread calls turnstile_lookup() to look up the proper turnstile in
   40  * the hash table.  This function returns a pointer to the turnstile and
   41  * locks the associated turnstile chain.  A thread calls turnstile_wait()
   42  * when the lock is contested to be put on the queue and block.  If a
   43  * thread needs to retry a lock operation instead of blocking, it should
   44  * call turnstile_release() to unlock the associated turnstile chain lock.
   45  *
   46  * When a lock is released, either turnstile_signal() or turnstile_broadcast()
   47  * is called to mark blocked threads for a pending wakeup.
   48  * turnstile_signal() marks the highest priority blocked thread while
   49  * turnstile_broadcast() marks all blocked threads.  The turnstile_signal()
   50  * function returns true if the turnstile became empty as a result.  After
   51  * the higher level code finishes releasing the lock, turnstile_unpend()
   52  * must be called to wakeup the pending thread(s).
   53  *
   54  * When a lock is acquired that already has at least one thread contested
   55  * on it, the new owner of the lock must claim ownership of the turnstile
   56  * via turnstile_claim().
   57  *
   58  * Each thread allocates a turnstile at thread creation via turnstile_alloc()
   59  * and releases it at thread destruction via turnstile_free().  Note that
   60  * a turnstile is not tied to a specific thread and that the turnstile
   61  * released at thread destruction may not be the same turnstile that the
   62  * thread allocated when it was created.
   63  *
   64  * A function can query a turnstile to see if it is empty via
   65  * turnstile_empty().  The highest priority thread blocked on a turnstile
   66  * can be obtained via turnstile_head().
   67  */
   68 
   69 struct lock_object;
   70 struct thread;
   71 struct turnstile;
   72 
   73 #ifdef _KERNEL
   74 
   75 void    init_turnstiles(void);
   76 struct turnstile *turnstile_alloc(void);
   77 void    turnstile_broadcast(struct turnstile *);
   78 void    turnstile_claim(struct turnstile *);
   79 int     turnstile_empty(struct turnstile *);
   80 void    turnstile_free(struct turnstile *);
   81 struct thread *turnstile_head(struct turnstile *);
   82 struct turnstile *turnstile_lookup(struct lock_object *);
   83 void    turnstile_release(struct lock_object *);
   84 int     turnstile_signal(struct turnstile *);
   85 void    turnstile_unpend(struct turnstile *);
   86 void    turnstile_wait(struct turnstile *, struct lock_object *,
   87             struct thread *);
   88 
   89 #endif  /* _KERNEL */
   90 #endif  /* _SYS_TURNSTILE_H_ */

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