FreeBSD/Linux Kernel Cross Reference
sys/sys/turnstile.h
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: releng/5.2/sys/sys/turnstile.h 122516 2003-11-11 23:08:26Z 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_wakeup()
47 * is called to mark blocked threads for a pending wakeup.
48 * turnstile_signal() marks the highest priority blocked thread while
49 * turnstile_wakeup() 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 time via
59 * turnstile_alloc() and frees it at thread destroy time via
60 * turnstile_free().
61 *
62 * A function can query a turnstile to see if it is empty via
63 * turnstile_empty(). The highest priority thread blocked on a turnstile
64 * can be obtained via turnstile_head().
65 */
66
67 struct lock_object;
68 struct thread;
69 struct turnstile;
70
71 #ifdef _KERNEL
72
73 void init_turnstiles(void);
74 struct turnstile *turnstile_alloc(void);
75 void turnstile_claim(struct turnstile *);
76 void turnstile_free(struct turnstile *);
77 struct turnstile *turnstile_lookup(struct lock_object *);
78 void turnstile_release(struct lock_object *);
79 int turnstile_signal(struct turnstile *);
80 void turnstile_unpend(struct turnstile *);
81 void turnstile_wait(struct turnstile *, struct lock_object *,
82 struct thread *);
83 void turnstile_wakeup(struct turnstile *);
84 struct thread *turnstile_head(struct turnstile *);
85 int turnstile_empty(struct turnstile *);
86
87 #endif /* _KERNEL */
88 #endif /* _SYS_TURNSTILE_H_ */
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