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 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24 * SUCH DAMAGE.
25 *
26 * $FreeBSD$
27 */
28
29#ifndef _SYS_TURNSTILE_H_
30#define _SYS_TURNSTILE_H_
31
32/*
33 * Turnstile interface.  Non-sleepable locks use a turnstile for the
34 * queue of threads blocked on them when they are contested.  Each
35 * turnstile contains two sub-queues: one for threads waiting for a
36 * shared, or eread, lock, and one for threads waiting for an
37 * exclusive, or write, lock.
38 *
39 * A thread calls turnstile_chain_lock() to lock the turnstile chain
40 * associated with a given lock.  A thread calls turnstile_wait() when
41 * the lock is contested to be put on the queue and block.  If a thread
42 * calls turnstile_trywait() and decides to retry a lock operation instead
43 * of blocking, it should call turnstile_cancel() to unlock the associated
44 * turnstile chain lock.
45 *
46 * When a lock is released, the thread calls turnstile_lookup() to look
47 * up the turnstile associated with the given lock in the hash table.  Then
48 * it calls either turnstile_signal() or turnstile_broadcast() to mark
49 * blocked threads for a pending wakeup.  turnstile_signal() marks the
50 * highest priority blocked thread while turnstile_broadcast() marks all
51 * blocked threads.  The turnstile_signal() function returns true if the
52 * turnstile became empty as a result.  After the higher level code finishes
53 * releasing the lock, turnstile_unpend() must be called to wake up the
54 * pending thread(s) and give up ownership of the turnstile.
55 *
56 * Alternatively, if a thread wishes to relinquish ownership of a lock
57 * without waking up any waiters, it may call turnstile_disown().
58 *
59 * When a lock is acquired that already has at least one thread contested
60 * on it, the new owner of the lock must claim ownership of the turnstile
61 * via turnstile_claim().
62 *
63 * Each thread allocates a turnstile at thread creation via turnstile_alloc()
64 * and releases it at thread destruction via turnstile_free().  Note that
65 * a turnstile is not tied to a specific thread and that the turnstile
66 * released at thread destruction may not be the same turnstile that the
67 * thread allocated when it was created.
68 *
69 * The highest priority thread blocked on a specified queue of a
70 * turnstile can be obtained via turnstile_head().  A given queue can
71 * also be queried to see if it is empty via turnstile_empty().
72 */
73
74struct lock_object;
75struct thread;
76struct turnstile;
77
78#ifdef _KERNEL
79
80/* Which queue to block on or which queue to wakeup one or more threads from. */
81#define	TS_EXCLUSIVE_QUEUE	0
82#define	TS_SHARED_QUEUE		1
83
84/* The type of lock currently held. */
85#define	TS_EXCLUSIVE_LOCK	TS_EXCLUSIVE_QUEUE
86#define	TS_SHARED_LOCK		TS_SHARED_QUEUE
87
88void	init_turnstiles(void);
89void	turnstile_adjust(struct thread *, u_char);
90struct turnstile *turnstile_alloc(void);
91void	turnstile_broadcast(struct turnstile *, int);
92void	turnstile_cancel(struct turnstile *);
93void	turnstile_chain_lock(struct lock_object *);
94void	turnstile_chain_unlock(struct lock_object *);
95void	turnstile_claim(struct turnstile *);
96void	turnstile_disown(struct turnstile *);
97int	turnstile_empty(struct turnstile *ts, int queue);
98void	turnstile_free(struct turnstile *);
99struct thread *turnstile_head(struct turnstile *, int);
100struct turnstile *turnstile_lookup(struct lock_object *);
101int	turnstile_signal(struct turnstile *, int);
102struct turnstile *turnstile_trywait(struct lock_object *);
103void	turnstile_unpend(struct turnstile *, int);
104void	turnstile_wait(struct turnstile *, struct thread *, int);
105
106#endif	/* _KERNEL */
107#endif	/* _SYS_TURNSTILE_H_ */
108