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: releng/8.1/sys/sys/turnstile.h 199583 2009-11-20 15:27:52Z jhb $
   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.  Each
   38  * turnstile contains two sub-queues: one for threads waiting for a
   39  * shared, or eread, lock, and one for threads waiting for an
   40  * exclusive, or write, lock.
   41  *
   42  * A thread calls turnstile_lock() to lock the turnstile chain associated
   43  * with a given lock.  A thread calls turnstile_wait() when the lock is
   44  * contested to be put on the queue and block.  If a thread needs to retry
   45  * a lock operation instead of blocking, it should call turnstile_release()
   46  * to unlock the associated turnstile chain lock.
   47  *
   48  * When a lock is released, the thread calls turnstile_lookup() to loop
   49  * up the turnstile associated with the given lock in the hash table.  Then
   50  * it calls either turnstile_signal() or turnstile_broadcast() to mark
   51  * blocked threads for a pending wakeup.  turnstile_signal() marks the
   52  * highest priority blocked thread while turnstile_broadcast() marks all
   53  * blocked threads.  The turnstile_signal() function returns true if the
   54  * turnstile became empty as a result.  After the higher level code finishes
   55  * releasing the lock, turnstile_unpend() must be called to wake up the
   56  * pending thread(s) and give up ownership of the turnstile.
   57  *
   58  * Alternatively, if a thread wishes to relinquish ownership of a thread
   59  * without waking up any waiters, it may call turnstile_disown().
   60  *
   61  * When a lock is acquired that already has at least one thread contested
   62  * on it, the new owner of the lock must claim ownership of the turnstile
   63  * via turnstile_claim().
   64  *
   65  * Each thread allocates a turnstile at thread creation via turnstile_alloc()
   66  * and releases it at thread destruction via turnstile_free().  Note that
   67  * a turnstile is not tied to a specific thread and that the turnstile
   68  * released at thread destruction may not be the same turnstile that the
   69  * thread allocated when it was created.
   70  *
   71  * The highest priority thread blocked on a specified queue of a
   72  * turnstile can be obtained via turnstile_head().  A given queue can
   73  * also be queried to see if it is empty via turnstile_empty().
   74  */
   75 
   76 struct lock_object;
   77 struct thread;
   78 struct turnstile;
   79 
   80 #ifdef _KERNEL
   81 
   82 /* Which queue to block on or which queue to wakeup one or more threads from. */
   83 #define TS_EXCLUSIVE_QUEUE      0
   84 #define TS_SHARED_QUEUE         1
   85 
   86 /* The type of lock currently held. */
   87 #define TS_EXCLUSIVE_LOCK       TS_EXCLUSIVE_QUEUE
   88 #define TS_SHARED_LOCK          TS_SHARED_QUEUE
   89 
   90 void    init_turnstiles(void);
   91 void    turnstile_adjust(struct thread *, u_char);
   92 struct turnstile *turnstile_alloc(void);
   93 void    turnstile_broadcast(struct turnstile *, int);
   94 void    turnstile_cancel(struct turnstile *);
   95 void    turnstile_chain_lock(struct lock_object *);
   96 void    turnstile_chain_unlock(struct lock_object *);
   97 void    turnstile_claim(struct turnstile *);
   98 void    turnstile_disown(struct turnstile *);
   99 int     turnstile_empty(struct turnstile *ts, int queue);
  100 void    turnstile_free(struct turnstile *);
  101 struct thread *turnstile_head(struct turnstile *, int);
  102 struct turnstile *turnstile_lookup(struct lock_object *);
  103 int     turnstile_signal(struct turnstile *, int);
  104 struct turnstile *turnstile_trywait(struct lock_object *);
  105 void    turnstile_unpend(struct turnstile *, int);
  106 void    turnstile_wait(struct turnstile *, struct thread *, int);
  107 
  108 #endif  /* _KERNEL */
  109 #endif  /* _SYS_TURNSTILE_H_ */

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