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