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144 lines
3.7 KiB
144 lines
3.7 KiB
/*
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* Copyright 2010-2015 Samy Al Bahra.
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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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*
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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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#ifndef CK_SPINLOCK_DEC_H
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#define CK_SPINLOCK_DEC_H
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#include <ck_backoff.h>
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#include <ck_cc.h>
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#include <ck_elide.h>
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#include <ck_pr.h>
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#include <ck_stdbool.h>
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#ifndef CK_F_SPINLOCK_DEC
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#define CK_F_SPINLOCK_DEC
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/*
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* This is similar to the CACAS lock but makes use of an atomic decrement
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* operation to check if the lock value was decremented to 0 from 1. The
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* idea is that a decrement operation is cheaper than a compare-and-swap.
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*/
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struct ck_spinlock_dec {
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unsigned int value;
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};
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typedef struct ck_spinlock_dec ck_spinlock_dec_t;
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#define CK_SPINLOCK_DEC_INITIALIZER {1}
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CK_CC_INLINE static void
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ck_spinlock_dec_init(struct ck_spinlock_dec *lock)
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{
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lock->value = 1;
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ck_pr_barrier();
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return;
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}
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CK_CC_INLINE static bool
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ck_spinlock_dec_trylock(struct ck_spinlock_dec *lock)
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{
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unsigned int value;
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value = ck_pr_fas_uint(&lock->value, 0);
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ck_pr_fence_lock();
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return value == 1;
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}
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CK_CC_INLINE static bool
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ck_spinlock_dec_locked(struct ck_spinlock_dec *lock)
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{
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bool r;
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r = ck_pr_load_uint(&lock->value) != 1;
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ck_pr_fence_acquire();
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return r;
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}
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CK_CC_INLINE static void
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ck_spinlock_dec_lock(struct ck_spinlock_dec *lock)
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{
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bool r;
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for (;;) {
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/*
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* Only one thread is guaranteed to decrement lock to 0.
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* Overflow must be protected against. No more than
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* UINT_MAX lock requests can happen while the lock is held.
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*/
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ck_pr_dec_uint_zero(&lock->value, &r);
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if (r == true)
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break;
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/* Load value without generating write cycles. */
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while (ck_pr_load_uint(&lock->value) != 1)
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ck_pr_stall();
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}
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ck_pr_fence_lock();
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return;
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}
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CK_CC_INLINE static void
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ck_spinlock_dec_lock_eb(struct ck_spinlock_dec *lock)
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{
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ck_backoff_t backoff = CK_BACKOFF_INITIALIZER;
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bool r;
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for (;;) {
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ck_pr_dec_uint_zero(&lock->value, &r);
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if (r == true)
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break;
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ck_backoff_eb(&backoff);
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}
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ck_pr_fence_lock();
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return;
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}
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CK_CC_INLINE static void
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ck_spinlock_dec_unlock(struct ck_spinlock_dec *lock)
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{
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ck_pr_fence_unlock();
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/*
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* Unconditionally set lock value to 1 so someone can decrement lock
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* to 0.
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*/
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ck_pr_store_uint(&lock->value, 1);
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return;
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}
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CK_ELIDE_PROTOTYPE(ck_spinlock_dec, ck_spinlock_dec_t,
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ck_spinlock_dec_locked, ck_spinlock_dec_lock,
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ck_spinlock_dec_locked, ck_spinlock_dec_unlock)
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CK_ELIDE_TRYLOCK_PROTOTYPE(ck_spinlock_dec, ck_spinlock_dec_t,
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ck_spinlock_dec_locked, ck_spinlock_dec_trylock)
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#endif /* CK_F_SPINLOCK_DEC */
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#endif /* CK_SPINLOCK_DEC_H */
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