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91 lines
4.0 KiB
C
91 lines
4.0 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.
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*
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* A thread calls turnstile_lookup() to look up the proper turnstile in
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* the hash table. This function returns a pointer to the turnstile and
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* locks the associated turnstile chain. A thread calls turnstile_wait()
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* when the lock is contested to be put on the queue and block. If a
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* thread needs to retry a lock operation instead of blocking, it should
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* call turnstile_release() to unlock the associated turnstile chain lock.
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*
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* When a lock is released, either turnstile_signal() or turnstile_broadcast()
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* is called to mark blocked threads for a pending wakeup.
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* turnstile_signal() marks the highest priority blocked thread while
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* turnstile_broadcast() marks all blocked threads. The turnstile_signal()
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* function returns true if the turnstile became empty as a result. After
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* the higher level code finishes releasing the lock, turnstile_unpend()
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* must be called to wakeup the pending thread(s).
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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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* A function can query a turnstile to see if it is empty via
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* turnstile_empty(). The highest priority thread blocked on a turnstile
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* can be obtained via turnstile_head().
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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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void init_turnstiles(void);
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struct turnstile *turnstile_alloc(void);
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void turnstile_broadcast(struct turnstile *);
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void turnstile_claim(struct turnstile *);
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int turnstile_empty(struct turnstile *);
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void turnstile_free(struct turnstile *);
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struct thread *turnstile_head(struct turnstile *);
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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 *);
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void turnstile_unpend(struct turnstile *);
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void turnstile_wait(struct turnstile *, struct lock_object *,
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struct thread *);
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#endif /* _KERNEL */
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#endif /* _SYS_TURNSTILE_H_ */
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