turnstile.h revision 139825 
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: head/sys/sys/turnstile.h 139825 2005-01-07 02:29:27Z imp $
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_lock() to lock the turnstile chain associated
40 * with a given lock.  A thread calls turnstile_wait() when the lock is
41 * contested to be put on the queue and block.  If a thread needs to retry
42 * a lock operation instead of blocking, it should call turnstile_release()
43 * to unlock the associated turnstile chain lock.
44 *
45 * When a lock is released, the thread calls turnstile_lookup() to loop
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).
54 *
55 * When a lock is acquired that already has at least one thread contested
56 * on it, the new owner of the lock must claim ownership of the turnstile
57 * via turnstile_claim().
58 *
59 * Each thread allocates a turnstile at thread creation via turnstile_alloc()
60 * and releases it at thread destruction via turnstile_free().  Note that
61 * a turnstile is not tied to a specific thread and that the turnstile
62 * released at thread destruction may not be the same turnstile that the
63 * thread allocated when it was created.
64 *
65 * A function can query a turnstile to see if it is empty via
66 * turnstile_empty().  The highest priority thread blocked on a turnstile
67 * can be obtained via turnstile_head().
68 */
69
70struct lock_object;
71struct thread;
72struct turnstile;
73
74#ifdef _KERNEL
75
76void	init_turnstiles(void);
77void	turnstile_adjust(struct thread *, u_char);
78struct turnstile *turnstile_alloc(void);
79void	turnstile_broadcast(struct turnstile *);
80void	turnstile_claim(struct lock_object *);
81int	turnstile_empty(struct turnstile *);
82void	turnstile_free(struct turnstile *);
83struct thread *turnstile_head(struct turnstile *);
84void	turnstile_lock(struct lock_object *);
85struct turnstile *turnstile_lookup(struct lock_object *);
86void	turnstile_release(struct lock_object *);
87int	turnstile_signal(struct turnstile *);
88void	turnstile_unpend(struct turnstile *);
89void	turnstile_wait(struct lock_object *, struct thread *);
90
91#endif	/* _KERNEL */
92#endif	/* _SYS_TURNSTILE_H_ */
93