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.
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
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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
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26 * $FreeBSD: releng/11.1/sys/sys/turnstile.h 299519 2016-05-12 06:20:26Z kib $
29 #ifndef _SYS_TURNSTILE_H_
30 #define _SYS_TURNSTILE_H_
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 read, lock, and one for threads waiting for an
37 * exclusive, or write, lock.
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.
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.
56 * Alternatively, if a thread wishes to relinquish ownership of a lock
57 * without waking up any waiters, it may call turnstile_disown().
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().
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.
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().
74 struct lock_object;
75 struct thread;
76 struct turnstile;
78 #ifdef _KERNEL
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
84 /* The type of lock currently held. */
85 #define TS_EXCLUSIVE_LOCK TS_EXCLUSIVE_QUEUE
86 #define TS_SHARED_LOCK TS_SHARED_QUEUE
88 void init_turnstiles(void);
89 void turnstile_adjust(struct thread *, u_char);
90 struct turnstile *turnstile_alloc(void);
91 void turnstile_broadcast(struct turnstile *, int);
92 void turnstile_cancel(struct turnstile *);
93 void turnstile_chain_lock(struct lock_object *);
94 void turnstile_chain_unlock(struct lock_object *);
95 void turnstile_claim(struct turnstile *);
96 void turnstile_disown(struct turnstile *);
97 int turnstile_empty(struct turnstile *ts, int queue);
98 void turnstile_free(struct turnstile *);
99 struct thread *turnstile_head(struct turnstile *, int);
100 struct turnstile *turnstile_lookup(struct lock_object *);
101 int turnstile_signal(struct turnstile *, int);
102 struct turnstile *turnstile_trywait(struct lock_object *);
103 void turnstile_unpend(struct turnstile *, int);
104 void turnstile_wait(struct turnstile *, struct thread *, int);
106 #endif /* _KERNEL */
107 #endif /* _SYS_TURNSTILE_H_ */
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