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