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
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14 * may be used to endorse or promote products derived from this software
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23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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29 * $FreeBSD: releng/9.0/sys/sys/turnstile.h 216421 2010-12-13 23:53:55Z mckusick $
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_chain_lock() to lock the turnstile chain
43 * associated with a given lock. A thread calls turnstile_wait() when
44 * the lock is contested to be put on the queue and block. If a thread
45 * calls turnstile_trywait() and decides to retry a lock operation instead
46 * of blocking, it should call turnstile_cancel() to unlock the associated
47 * turnstile chain lock.
49 * When a lock is released, the thread calls turnstile_lookup() to look
50 * up the turnstile associated with the given lock in the hash table. Then
51 * it calls either turnstile_signal() or turnstile_broadcast() to mark
52 * blocked threads for a pending wakeup. turnstile_signal() marks the
53 * highest priority blocked thread while turnstile_broadcast() marks all
54 * blocked threads. The turnstile_signal() function returns true if the
55 * turnstile became empty as a result. After the higher level code finishes
56 * releasing the lock, turnstile_unpend() must be called to wake up the
57 * pending thread(s) and give up ownership of the turnstile.
59 * Alternatively, if a thread wishes to relinquish ownership of a lock
60 * without waking up any waiters, it may call turnstile_disown().
62 * When a lock is acquired that already has at least one thread contested
63 * on it, the new owner of the lock must claim ownership of the turnstile
64 * via turnstile_claim().
66 * Each thread allocates a turnstile at thread creation via turnstile_alloc()
67 * and releases it at thread destruction via turnstile_free(). Note that
68 * a turnstile is not tied to a specific thread and that the turnstile
69 * released at thread destruction may not be the same turnstile that the
70 * thread allocated when it was created.
72 * The highest priority thread blocked on a specified queue of a
73 * turnstile can be obtained via turnstile_head(). A given queue can
74 * also be queried to see if it is empty via turnstile_empty().
77 struct lock_object;
78 struct thread;
79 struct turnstile;
81 #ifdef _KERNEL
83 /* Which queue to block on or which queue to wakeup one or more threads from. */
84 #define TS_EXCLUSIVE_QUEUE 0
85 #define TS_SHARED_QUEUE 1
87 /* The type of lock currently held. */
88 #define TS_EXCLUSIVE_LOCK TS_EXCLUSIVE_QUEUE
89 #define TS_SHARED_LOCK TS_SHARED_QUEUE
91 void init_turnstiles(void);
92 void turnstile_adjust(struct thread *, u_char);
93 struct turnstile *turnstile_alloc(void);
94 void turnstile_broadcast(struct turnstile *, int);
95 void turnstile_cancel(struct turnstile *);
96 void turnstile_chain_lock(struct lock_object *);
97 void turnstile_chain_unlock(struct lock_object *);
98 void turnstile_claim(struct turnstile *);
99 void turnstile_disown(struct turnstile *);
100 int turnstile_empty(struct turnstile *ts, int queue);
101 void turnstile_free(struct turnstile *);
102 struct thread *turnstile_head(struct turnstile *, int);
103 struct turnstile *turnstile_lookup(struct lock_object *);
104 int turnstile_signal(struct turnstile *, int);
105 struct turnstile *turnstile_trywait(struct lock_object *);
106 void turnstile_unpend(struct turnstile *, int);
107 void turnstile_wait(struct turnstile *, struct thread *, int);
109 #endif /* _KERNEL */
110 #endif /* _SYS_TURNSTILE_H_ */
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