FreeBSD/Linux Kernel Cross Reference
2 * Copyright (c) 2002 John Baldwin <jhb@FreeBSD.org>
3 * All rights reserved.
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.
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.
29 * $FreeBSD$
32 #ifndef _SYS_TURNSTILE_H_
33 #define _SYS_TURNSTILE_H_
36 * Turnstile interface. Non-sleepable locks use a turnstile for the
37 * queue of threads blocked on them when they are contested.
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.
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).
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().
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.
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().
69 struct lock_object;
70 struct thread;
71 struct turnstile;
73 #ifdef _KERNEL
75 void init_turnstiles(void);
76 struct turnstile *turnstile_alloc(void);
77 void turnstile_broadcast(struct turnstile *);
78 void turnstile_claim(struct turnstile *);
79 int turnstile_empty(struct turnstile *);
80 void turnstile_free(struct turnstile *);
81 struct thread *turnstile_head(struct turnstile *);
82 struct turnstile *turnstile_lookup(struct lock_object *);
83 void turnstile_release(struct lock_object *);
84 int turnstile_signal(struct turnstile *);
85 void turnstile_unpend(struct turnstile *);
86 void turnstile_wait(struct turnstile *, struct lock_object *,
87 struct thread *);
89 #endif /* _KERNEL */
90 #endif /* _SYS_TURNSTILE_H_ */
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