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
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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: releng/8.1/sys/sys/turnstile.h 199583 2009-11-20 15:27:52Z jhb $
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. 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.
42 * A thread calls turnstile_lock() to lock the turnstile chain associated
43 * with a given lock. A thread calls turnstile_wait() when the lock is
44 * contested to be put on the queue and block. If a thread needs to retry
45 * a lock operation instead of blocking, it should call turnstile_release()
46 * to unlock the associated turnstile chain lock.
48 * When a lock is released, the thread calls turnstile_lookup() to loop
49 * up the turnstile associated with the given lock in the hash table. Then
50 * it calls either turnstile_signal() or turnstile_broadcast() to mark
51 * blocked threads for a pending wakeup. turnstile_signal() marks the
52 * highest priority blocked thread while turnstile_broadcast() marks all
53 * blocked threads. The turnstile_signal() function returns true if the
54 * turnstile became empty as a result. After the higher level code finishes
55 * releasing the lock, turnstile_unpend() must be called to wake up the
56 * pending thread(s) and give up ownership of the turnstile.
58 * Alternatively, if a thread wishes to relinquish ownership of a thread
59 * without waking up any waiters, it may call turnstile_disown().
61 * When a lock is acquired that already has at least one thread contested
62 * on it, the new owner of the lock must claim ownership of the turnstile
63 * via turnstile_claim().
65 * Each thread allocates a turnstile at thread creation via turnstile_alloc()
66 * and releases it at thread destruction via turnstile_free(). Note that
67 * a turnstile is not tied to a specific thread and that the turnstile
68 * released at thread destruction may not be the same turnstile that the
69 * thread allocated when it was created.
71 * The highest priority thread blocked on a specified queue of a
72 * turnstile can be obtained via turnstile_head(). A given queue can
73 * also be queried to see if it is empty via turnstile_empty().
76 struct lock_object;
77 struct thread;
78 struct turnstile;
80 #ifdef _KERNEL
82 /* Which queue to block on or which queue to wakeup one or more threads from. */
83 #define TS_EXCLUSIVE_QUEUE 0
84 #define TS_SHARED_QUEUE 1
86 /* The type of lock currently held. */
87 #define TS_EXCLUSIVE_LOCK TS_EXCLUSIVE_QUEUE
88 #define TS_SHARED_LOCK TS_SHARED_QUEUE
90 void init_turnstiles(void);
91 void turnstile_adjust(struct thread *, u_char);
92 struct turnstile *turnstile_alloc(void);
93 void turnstile_broadcast(struct turnstile *, int);
94 void turnstile_cancel(struct turnstile *);
95 void turnstile_chain_lock(struct lock_object *);
96 void turnstile_chain_unlock(struct lock_object *);
97 void turnstile_claim(struct turnstile *);
98 void turnstile_disown(struct turnstile *);
99 int turnstile_empty(struct turnstile *ts, int queue);
100 void turnstile_free(struct turnstile *);
101 struct thread *turnstile_head(struct turnstile *, int);
102 struct turnstile *turnstile_lookup(struct lock_object *);
103 int turnstile_signal(struct turnstile *, int);
104 struct turnstile *turnstile_trywait(struct lock_object *);
105 void turnstile_unpend(struct turnstile *, int);
106 void turnstile_wait(struct turnstile *, struct thread *, int);
108 #endif /* _KERNEL */
109 #endif /* _SYS_TURNSTILE_H_ */
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