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Oh dear, forgot this file in the turnstile commit. This header defines

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the turnstile API and includes several comments.

Reminded by:	peter
This commit is contained in:
John Baldwin 2003-11-11 23:08:26 +00:00
parent 94ed763dee
commit efd21294ab
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=122516
1 changed files with 88 additions and 0 deletions
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sys/sys/turnstile.h Normal file
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/*
* Copyright (c) 2002 John Baldwin <jhb@FreeBSD.org>
* All rights reserved.
*
* 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.
* 3. Neither the name of the author nor the names of any co-contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* 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.
*
* A thread calls turnstile_lookup() to look up the proper turnstile in
* the hash table. This function returns a pointer to the turnstile and
* locks the associated turnstile chain. A thread calls turnstile_wait()
* when the lock is contested to be put on the queue and block. If a
* thread needs to retry a lock operation instead of blocking, it should
* call turnstile_release() to unlock the associated turnstile chain lock.
*
* When a lock is released, either turnstile_signal() or turnstile_wakeup()
* is called to mark blocked threads for a pending wakeup.
* turnstile_signal() marks the highest priority blocked thread while
* turnstile_wakeup() 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 wakeup the pending thread(s).
*
* 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 time via
* turnstile_alloc() and frees it at thread destroy time via
* turnstile_free().
*
* A function can query a turnstile to see if it is empty via
* turnstile_empty(). The highest priority thread blocked on a turnstile
* can be obtained via turnstile_head().
*/
struct lock_object;
struct thread;
struct turnstile;
#ifdef _KERNEL
void init_turnstiles(void);
struct turnstile *turnstile_alloc(void);
void turnstile_claim(struct turnstile *);
void turnstile_free(struct turnstile *);
struct turnstile *turnstile_lookup(struct lock_object *);
void turnstile_release(struct lock_object *);
int turnstile_signal(struct turnstile *);
void turnstile_unpend(struct turnstile *);
void turnstile_wait(struct turnstile *, struct lock_object *,
struct thread *);
void turnstile_wakeup(struct turnstile *);
struct thread *turnstile_head(struct turnstile *);
int turnstile_empty(struct turnstile *);
#endif /* _KERNEL */
#endif /* _SYS_TURNSTILE_H_ */