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  *
    4  * Redistribution and use in source and binary forms, with or without
    5  * modification, are permitted provided that the following conditions
    6  * are met:
    7  * 1. Redistributions of source code must retain the above copyright
    8  *    notice, this list of conditions and the following disclaimer.
    9  * 2. Redistributions in binary form must reproduce the above copyright
   10  *    notice, this list of conditions and the following disclaimer in the
   11  *    documentation and/or other materials provided with the distribution.
   12  *
   13  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   14  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   15  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   16  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   17  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   18  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   19  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   20  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   21  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   22  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   23  * SUCH DAMAGE.
   24  *
   25  * $FreeBSD$
   26  */
   27 
   28 #ifndef _SYS_TURNSTILE_H_
   29 #define _SYS_TURNSTILE_H_
   30 
   31 /*
   32  * Turnstile interface.  Non-sleepable locks use a turnstile for the
   33  * queue of threads blocked on them when they are contested.  Each
   34  * turnstile contains two sub-queues: one for threads waiting for a
   35  * shared, or read, lock, and one for threads waiting for an
   36  * exclusive, or write, lock.
   37  *
   38  * A thread calls turnstile_chain_lock() to lock the turnstile chain
   39  * associated with a given lock.  A thread calls turnstile_wait() when
   40  * the lock is contested to be put on the queue and block.  If a thread
   41  * calls turnstile_trywait() and decides to retry a lock operation instead
   42  * of blocking, it should call turnstile_cancel() to unlock the associated
   43  * turnstile chain lock.
   44  *
   45  * When a lock is released, the thread calls turnstile_lookup() to look
   46  * up the turnstile associated with the given lock in the hash table.  Then
   47  * it calls either turnstile_signal() or turnstile_broadcast() to mark
   48  * blocked threads for a pending wakeup.  turnstile_signal() marks the
   49  * highest priority blocked thread while turnstile_broadcast() marks all
   50  * blocked threads.  The turnstile_signal() function returns true if the
   51  * turnstile became empty as a result.  After the higher level code finishes
   52  * releasing the lock, turnstile_unpend() must be called to wake up the
   53  * pending thread(s) and give up ownership of the turnstile.
   54  *
   55  * Alternatively, if a thread wishes to relinquish ownership of a lock
   56  * without waking up any waiters, it may call turnstile_disown().
   57  *
   58  * When a lock is acquired that already has at least one thread contested
   59  * on it, the new owner of the lock must claim ownership of the turnstile
   60  * via turnstile_claim().
   61  *
   62  * Each thread allocates a turnstile at thread creation via turnstile_alloc()
   63  * and releases it at thread destruction via turnstile_free().  Note that
   64  * a turnstile is not tied to a specific thread and that the turnstile
   65  * released at thread destruction may not be the same turnstile that the
   66  * thread allocated when it was created.
   67  *
   68  * The highest priority thread blocked on a specified queue of a
   69  * turnstile can be obtained via turnstile_head().  A given queue can
   70  * also be queried to see if it is empty via turnstile_empty().
   71  */
   72 
   73 struct lock_object;
   74 struct thread;
   75 struct turnstile;
   76 
   77 #ifdef _KERNEL
   78 
   79 /* Which queue to block on or which queue to wakeup one or more threads from. */
   80 #define TS_EXCLUSIVE_QUEUE      0
   81 #define TS_SHARED_QUEUE         1
   82 
   83 /* The type of lock currently held. */
   84 #define TS_EXCLUSIVE_LOCK       TS_EXCLUSIVE_QUEUE
   85 #define TS_SHARED_LOCK          TS_SHARED_QUEUE
   86 
   87 void    init_turnstiles(void);
   88 void    turnstile_adjust(struct thread *, u_char);
   89 struct turnstile *turnstile_alloc(void);
   90 void    turnstile_broadcast(struct turnstile *, int);
   91 void    turnstile_cancel(struct turnstile *);
   92 void    turnstile_chain_lock(struct lock_object *);
   93 void    turnstile_chain_unlock(struct lock_object *);
   94 void    turnstile_claim(struct turnstile *);
   95 void    turnstile_disown(struct turnstile *);
   96 int     turnstile_empty(struct turnstile *ts, int queue);
   97 void    turnstile_free(struct turnstile *);
   98 struct thread *turnstile_head(struct turnstile *, int);
   99 struct turnstile *turnstile_lookup(struct lock_object *);
  100 int     turnstile_signal(struct turnstile *, int);
  101 struct turnstile *turnstile_trywait(struct lock_object *);
  102 void    turnstile_unpend(struct turnstile *, int);
  103 void    turnstile_wait(struct turnstile *, struct thread *, int);
  104 
  105 #endif  /* _KERNEL */
  106 #endif  /* _SYS_TURNSTILE_H_ */

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