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271ce40239
It should fix ck_pr_[load|store]_ptr on mips and riscv, make sure no *fence instructions are used on i386, as older cpus don't support it, and make sure we don't rely on gcc builtins that can lead to calls to libatomic when linked with -O0. MFC after: 1 week
144 lines
3.8 KiB
C
144 lines
3.8 KiB
C
/*
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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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while (ck_pr_load_uint(&lock->value) != 1)
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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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