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 * 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 18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 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 24 * SUCH DAMAGE. 25 * 26 * $FreeBSD$ 27 */ 28 29#ifndef _SYS_TURNSTILE_H_ 30#define _SYS_TURNSTILE_H_ 31 32/* 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 eread, lock, and one for threads waiting for an 37 * exclusive, or write, lock. 38 * 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. 45 * 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. 55 * 56 * Alternatively, if a thread wishes to relinquish ownership of a lock 57 * without waking up any waiters, it may call turnstile_disown(). 58 * 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(). 62 * 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. 68 * 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(). 72 */ 73 74struct lock_object; 75struct thread; 76struct turnstile; 77 78#ifdef _KERNEL 79 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 83 84/* The type of lock currently held. */ 85#define TS_EXCLUSIVE_LOCK TS_EXCLUSIVE_QUEUE 86#define TS_SHARED_LOCK TS_SHARED_QUEUE 87 88void init_turnstiles(void); 89void turnstile_adjust(struct thread *, u_char); 90struct turnstile *turnstile_alloc(void); 91void turnstile_broadcast(struct turnstile *, int); 92void turnstile_cancel(struct turnstile *); 93void turnstile_chain_lock(struct lock_object *); 94void turnstile_chain_unlock(struct lock_object *); 95void turnstile_claim(struct turnstile *); 96void turnstile_disown(struct turnstile *); 97int turnstile_empty(struct turnstile *ts, int queue); 98void turnstile_free(struct turnstile *); 99struct thread *turnstile_head(struct turnstile *, int); 100struct turnstile *turnstile_lookup(struct lock_object *); 101int turnstile_signal(struct turnstile *, int); 102struct turnstile *turnstile_trywait(struct lock_object *); 103void turnstile_unpend(struct turnstile *, int); 104void turnstile_wait(struct turnstile *, struct thread *, int); 105 106#endif /* _KERNEL */ 107#endif /* _SYS_TURNSTILE_H_ */ 108