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turnstile.h
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turnstile.h
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/*-
* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
*
* Copyright (c) 2002 John Baldwin <jhb@FreeBSD.org>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* $FreeBSD$
*/
#ifndef _SYS_TURNSTILE_H_
#define _SYS_TURNSTILE_H_
/*
* Turnstile interface. Non-sleepable locks use a turnstile for the
* queue of threads blocked on them when they are contested. Each
* turnstile contains two sub-queues: one for threads waiting for a
* shared, or read, lock, and one for threads waiting for an
* exclusive, or write, lock.
*
* A thread calls turnstile_chain_lock() to lock the turnstile chain
* associated with a given lock. A thread calls turnstile_wait() when
* the lock is contested to be put on the queue and block. If a thread
* calls turnstile_trywait() and decides to retry a lock operation instead
* of blocking, it should call turnstile_cancel() to unlock the associated
* turnstile chain lock.
*
* When a lock is released, the thread calls turnstile_lookup() to look
* up the turnstile associated with the given lock in the hash table. Then
* it calls either turnstile_signal() or turnstile_broadcast() to mark
* blocked threads for a pending wakeup. turnstile_signal() marks the
* highest priority blocked thread while turnstile_broadcast() marks all
* blocked threads. The turnstile_signal() function returns true if the
* turnstile became empty as a result. After the higher level code finishes
* releasing the lock, turnstile_unpend() must be called to wake up the
* pending thread(s) and give up ownership of the turnstile.
*
* Alternatively, if a thread wishes to relinquish ownership of a lock
* without waking up any waiters, it may call turnstile_disown().
*
* When a lock is acquired that already has at least one thread contested
* on it, the new owner of the lock must claim ownership of the turnstile
* via turnstile_claim().
*
* Each thread allocates a turnstile at thread creation via turnstile_alloc()
* and releases it at thread destruction via turnstile_free(). Note that
* a turnstile is not tied to a specific thread and that the turnstile
* released at thread destruction may not be the same turnstile that the
* thread allocated when it was created.
*
* The highest priority thread blocked on a specified queue of a
* turnstile can be obtained via turnstile_head(). A given queue can
* also be queried to see if it is empty via turnstile_empty().
*/
struct lock_object;
struct thread;
struct turnstile;
#ifdef _KERNEL
/* Which queue to block on or which queue to wakeup one or more threads from. */
#define TS_EXCLUSIVE_QUEUE 0
#define TS_SHARED_QUEUE 1
void init_turnstiles(void);
void turnstile_adjust(struct thread *, u_char);
struct turnstile *turnstile_alloc(void);
void turnstile_broadcast(struct turnstile *, int);
void turnstile_cancel(struct turnstile *);
void turnstile_chain_lock(struct lock_object *);
void turnstile_chain_unlock(struct lock_object *);
void turnstile_claim(struct turnstile *);
void turnstile_disown(struct turnstile *);
int turnstile_empty(struct turnstile *ts, int queue);
void turnstile_free(struct turnstile *);
struct thread *turnstile_head(struct turnstile *, int);
struct turnstile *turnstile_lookup(struct lock_object *);
int turnstile_signal(struct turnstile *, int);
struct turnstile *turnstile_trywait(struct lock_object *);
void turnstile_unpend(struct turnstile *);
void turnstile_wait(struct turnstile *, struct thread *, int);
bool turnstile_lock(struct turnstile *, struct lock_object **,
struct thread **);
void turnstile_unlock(struct turnstile *, struct lock_object *);
void turnstile_assert(struct turnstile *);
#endif /* _KERNEL */
#endif /* _SYS_TURNSTILE_H_ */