turnstile.h revision 127951 
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 127951 2004-04-06 19:07:21Z 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.
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
69struct lock_object;
70struct thread;
71struct turnstile;
72
73#ifdef _KERNEL
74
75void	init_turnstiles(void);
76struct turnstile *turnstile_alloc(void);
77void	turnstile_claim(struct turnstile *);
78void	turnstile_free(struct turnstile *);
79struct turnstile *turnstile_lookup(struct lock_object *);
80void	turnstile_release(struct lock_object *);
81int	turnstile_signal(struct turnstile *);
82void	turnstile_unpend(struct turnstile *);
83void	turnstile_wait(struct turnstile *, struct lock_object *,
84	    struct thread *);
85void	turnstile_broadcast(struct turnstile *);
86struct thread *turnstile_head(struct turnstile *);
87int	turnstile_empty(struct turnstile *);
88
89#endif	/* _KERNEL */
90#endif	/* _SYS_TURNSTILE_H_ */
91