1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause 3 * 4 * Copyright (c) 2002 John Baldwin <jhb@FreeBSD.org> 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 16 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 18 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 19 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 20 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 21 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 22 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 23 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 24 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 25 * SUCH DAMAGE. 26 */ 27 28 #ifndef _SYS_TURNSTILE_H_ 29 #define _SYS_TURNSTILE_H_ 30 31 /* 32 * Turnstile interface. Non-sleepable locks use a turnstile for the 33 * queue of threads blocked on them when they are contested. Each 34 * turnstile contains two sub-queues: one for threads waiting for a 35 * shared, or read, lock, and one for threads waiting for an 36 * exclusive, or write, lock. 37 * 38 * A thread calls turnstile_chain_lock() to lock the turnstile chain 39 * associated with a given lock. A thread calls turnstile_wait() when 40 * the lock is contested to be put on the queue and block. If a thread 41 * calls turnstile_trywait() and decides to retry a lock operation instead 42 * of blocking, it should call turnstile_cancel() to unlock the associated 43 * turnstile chain lock. 44 * 45 * When a lock is released, the thread calls turnstile_lookup() to look 46 * up the turnstile associated with the given lock in the hash table. Then 47 * it calls either turnstile_signal() or turnstile_broadcast() to mark 48 * blocked threads for a pending wakeup. turnstile_signal() marks the 49 * highest priority blocked thread while turnstile_broadcast() marks all 50 * blocked threads. The turnstile_signal() function returns true if the 51 * turnstile became empty as a result. After the higher level code finishes 52 * releasing the lock, turnstile_unpend() must be called to wake up the 53 * pending thread(s) and give up ownership of the turnstile. 54 * 55 * Alternatively, if a thread wishes to relinquish ownership of a lock 56 * without waking up any waiters, it may call turnstile_disown(). 57 * 58 * When a lock is acquired that already has at least one thread contested 59 * on it, the new owner of the lock must claim ownership of the turnstile 60 * via turnstile_claim(). 61 * 62 * Each thread allocates a turnstile at thread creation via turnstile_alloc() 63 * and releases it at thread destruction via turnstile_free(). Note that 64 * a turnstile is not tied to a specific thread and that the turnstile 65 * released at thread destruction may not be the same turnstile that the 66 * thread allocated when it was created. 67 * 68 * The highest priority thread blocked on a specified queue of a 69 * turnstile can be obtained via turnstile_head(). A given queue can 70 * also be queried to see if it is empty via turnstile_empty(). 71 */ 72 73 struct lock_object; 74 struct thread; 75 struct turnstile; 76 77 #ifdef _KERNEL 78 79 /* Which queue to block on or which queue to wakeup one or more threads from. */ 80 #define TS_EXCLUSIVE_QUEUE 0 81 #define TS_SHARED_QUEUE 1 82 83 void init_turnstiles(void); 84 void turnstile_adjust(struct thread *, u_char); 85 struct turnstile *turnstile_alloc(void); 86 void turnstile_broadcast(struct turnstile *, int); 87 void turnstile_cancel(struct turnstile *); 88 void turnstile_chain_lock(struct lock_object *); 89 void turnstile_chain_unlock(struct lock_object *); 90 void turnstile_claim(struct turnstile *); 91 void turnstile_disown(struct turnstile *); 92 int turnstile_empty(struct turnstile *ts, int queue); 93 void turnstile_free(struct turnstile *); 94 struct thread *turnstile_head(struct turnstile *, int); 95 struct turnstile *turnstile_lookup(struct lock_object *); 96 int turnstile_signal(struct turnstile *, int); 97 struct turnstile *turnstile_trywait(struct lock_object *); 98 void turnstile_unpend(struct turnstile *); 99 void turnstile_wait(struct turnstile *, struct thread *, int); 100 bool turnstile_lock(struct turnstile *, struct lock_object **, 101 struct thread **); 102 void turnstile_unlock(struct turnstile *, struct lock_object *); 103 void turnstile_assert(struct turnstile *); 104 #endif /* _KERNEL */ 105 #endif /* _SYS_TURNSTILE_H_ */ 106