1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 3 * 4 * Copyright (c) 2002 John Baldwin <jhb@FreeBSD.org> 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26 * SUCH DAMAGE. 27 * 28 * $FreeBSD$ 29 */ 30 31 #ifndef _SYS_TURNSTILE_H_ 32 #define _SYS_TURNSTILE_H_ 33 34 /* 35 * Turnstile interface. Non-sleepable locks use a turnstile for the 36 * queue of threads blocked on them when they are contested. Each 37 * turnstile contains two sub-queues: one for threads waiting for a 38 * shared, or read, lock, and one for threads waiting for an 39 * exclusive, or write, lock. 40 * 41 * A thread calls turnstile_chain_lock() to lock the turnstile chain 42 * associated with a given lock. A thread calls turnstile_wait() when 43 * the lock is contested to be put on the queue and block. If a thread 44 * calls turnstile_trywait() and decides to retry a lock operation instead 45 * of blocking, it should call turnstile_cancel() to unlock the associated 46 * turnstile chain lock. 47 * 48 * When a lock is released, the thread calls turnstile_lookup() to look 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. 57 * 58 * Alternatively, if a thread wishes to relinquish ownership of a lock 59 * without waking up any waiters, it may call turnstile_disown(). 60 * 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(). 64 * 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. 70 * 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(). 74 */ 75 76 struct lock_object; 77 struct thread; 78 struct turnstile; 79 80 #ifdef _KERNEL 81 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 85 86 void init_turnstiles(void); 87 void turnstile_adjust(struct thread *, u_char); 88 struct turnstile *turnstile_alloc(void); 89 void turnstile_broadcast(struct turnstile *, int); 90 void turnstile_cancel(struct turnstile *); 91 void turnstile_chain_lock(struct lock_object *); 92 void turnstile_chain_unlock(struct lock_object *); 93 void turnstile_claim(struct turnstile *); 94 void turnstile_disown(struct turnstile *); 95 int turnstile_empty(struct turnstile *ts, int queue); 96 void turnstile_free(struct turnstile *); 97 struct thread *turnstile_head(struct turnstile *, int); 98 struct turnstile *turnstile_lookup(struct lock_object *); 99 int turnstile_signal(struct turnstile *, int); 100 struct turnstile *turnstile_trywait(struct lock_object *); 101 void turnstile_unpend(struct turnstile *); 102 void turnstile_wait(struct turnstile *, struct thread *, int); 103 struct thread *turnstile_lock(struct turnstile *, struct lock_object **); 104 void turnstile_unlock(struct turnstile *, struct lock_object *); 105 void turnstile_assert(struct turnstile *); 106 #endif /* _KERNEL */ 107 #endif /* _SYS_TURNSTILE_H_ */ 108