turnstile.h revision 216421 
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 216421 2010-12-13 23:53:55Z mckusick $
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_chain_lock() to lock the turnstile chain
43 * associated with a given lock.  A thread calls turnstile_wait() when
44 * the lock is contested to be put on the queue and block.  If a thread
45 * calls turnstile_trywait() and decides to retry a lock operation instead
46 * of blocking, it should call turnstile_cancel() to unlock the associated
47 * turnstile chain lock.
48 *
49 * When a lock is released, the thread calls turnstile_lookup() to look
50 * up the turnstile associated with the given lock in the hash table.  Then
51 * it calls either turnstile_signal() or turnstile_broadcast() to mark
52 * blocked threads for a pending wakeup.  turnstile_signal() marks the
53 * highest priority blocked thread while turnstile_broadcast() marks all
54 * blocked threads.  The turnstile_signal() function returns true if the
55 * turnstile became empty as a result.  After the higher level code finishes
56 * releasing the lock, turnstile_unpend() must be called to wake up the
57 * pending thread(s) and give up ownership of the turnstile.
58 *
59 * Alternatively, if a thread wishes to relinquish ownership of a lock
60 * without waking up any waiters, it may call turnstile_disown().
61 *
62 * When a lock is acquired that already has at least one thread contested
63 * on it, the new owner of the lock must claim ownership of the turnstile
64 * via turnstile_claim().
65 *
66 * Each thread allocates a turnstile at thread creation via turnstile_alloc()
67 * and releases it at thread destruction via turnstile_free().  Note that
68 * a turnstile is not tied to a specific thread and that the turnstile
69 * released at thread destruction may not be the same turnstile that the
70 * thread allocated when it was created.
71 *
72 * The highest priority thread blocked on a specified queue of a
73 * turnstile can be obtained via turnstile_head().  A given queue can
74 * also be queried to see if it is empty via turnstile_empty().
75 */
76
77struct lock_object;
78struct thread;
79struct turnstile;
80
81#ifdef _KERNEL
82
83/* Which queue to block on or which queue to wakeup one or more threads from. */
84#define	TS_EXCLUSIVE_QUEUE	0
85#define	TS_SHARED_QUEUE		1
86
87/* The type of lock currently held. */
88#define	TS_EXCLUSIVE_LOCK	TS_EXCLUSIVE_QUEUE
89#define	TS_SHARED_LOCK		TS_SHARED_QUEUE
90
91void	init_turnstiles(void);
92void	turnstile_adjust(struct thread *, u_char);
93struct turnstile *turnstile_alloc(void);
94void	turnstile_broadcast(struct turnstile *, int);
95void	turnstile_cancel(struct turnstile *);
96void	turnstile_chain_lock(struct lock_object *);
97void	turnstile_chain_unlock(struct lock_object *);
98void	turnstile_claim(struct turnstile *);
99void	turnstile_disown(struct turnstile *);
100int	turnstile_empty(struct turnstile *ts, int queue);
101void	turnstile_free(struct turnstile *);
102struct thread *turnstile_head(struct turnstile *, int);
103struct turnstile *turnstile_lookup(struct lock_object *);
104int	turnstile_signal(struct turnstile *, int);
105struct turnstile *turnstile_trywait(struct lock_object *);
106void	turnstile_unpend(struct turnstile *, int);
107void	turnstile_wait(struct turnstile *, struct thread *, int);
108
109#endif	/* _KERNEL */
110#endif	/* _SYS_TURNSTILE_H_ */
111