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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_ANDERSON_H
#define CK_SPINLOCK_ANDERSON_H
#include <ck_cc.h>
#include <ck_limits.h>
#include <ck_md.h>
#include <ck_pr.h>
#include <ck_stdbool.h>
#ifndef CK_F_SPINLOCK_ANDERSON
#define CK_F_SPINLOCK_ANDERSON
/*
* This is an implementation of Anderson's array-based queuing lock.
*/
struct ck_spinlock_anderson_thread {
unsigned int locked;
unsigned int position;
};
typedef struct ck_spinlock_anderson_thread ck_spinlock_anderson_thread_t;
struct ck_spinlock_anderson {
struct ck_spinlock_anderson_thread *slots;
unsigned int count;
unsigned int wrap;
unsigned int mask;
char pad[CK_MD_CACHELINE - sizeof(unsigned int) * 3 - sizeof(void *)];
unsigned int next;
};
typedef struct ck_spinlock_anderson ck_spinlock_anderson_t;
CK_CC_INLINE static void
ck_spinlock_anderson_init(struct ck_spinlock_anderson *lock,
struct ck_spinlock_anderson_thread *slots,
unsigned int count)
{
unsigned int i;
slots[0].locked = false;
slots[0].position = 0;
for (i = 1; i < count; i++) {
slots[i].locked = true;
slots[i].position = i;
}
lock->slots = slots;
lock->count = count;
lock->mask = count - 1;
lock->next = 0;
/*
* If the number of threads is not a power of two then compute
* appropriate wrap-around value in the case of next slot counter
* overflow.
*/
if (count & (count - 1))
lock->wrap = (UINT_MAX % count) + 1;
else
lock->wrap = 0;
ck_pr_barrier();
return;
}
CK_CC_INLINE static bool
ck_spinlock_anderson_locked(struct ck_spinlock_anderson *lock)
{
unsigned int position;
bool r;
position = ck_pr_load_uint(&lock->next) & lock->mask;
r = ck_pr_load_uint(&lock->slots[position].locked);
ck_pr_fence_acquire();
return r;
}
CK_CC_INLINE static void
ck_spinlock_anderson_lock(struct ck_spinlock_anderson *lock,
struct ck_spinlock_anderson_thread **slot)
{
unsigned int position, next;
unsigned int count = lock->count;
/*
* If count is not a power of 2, then it is possible for an overflow
* to reallocate beginning slots to more than one thread. To avoid this
* use a compare-and-swap.
*/
if (lock->wrap != 0) {
position = ck_pr_load_uint(&lock->next);
do {
if (position == UINT_MAX)
next = lock->wrap;
else
next = position + 1;
} while (ck_pr_cas_uint_value(&lock->next, position,
next, &position) == false);
position %= count;
} else {
position = ck_pr_faa_uint(&lock->next, 1);
position &= lock->mask;
}
/* Serialize with respect to previous thread's store. */
ck_pr_fence_load();
/*
* Spin until slot is marked as unlocked. First slot is initialized to
* false.
*/
while (ck_pr_load_uint(&lock->slots[position].locked) == true)
ck_pr_stall();
/* Prepare slot for potential re-use by another thread. */
ck_pr_store_uint(&lock->slots[position].locked, true);
ck_pr_fence_lock();
*slot = lock->slots + position;
return;
}
CK_CC_INLINE static void
ck_spinlock_anderson_unlock(struct ck_spinlock_anderson *lock,
struct ck_spinlock_anderson_thread *slot)
{
unsigned int position;
ck_pr_fence_unlock();
/* Mark next slot as available. */
if (lock->wrap == 0)
position = (slot->position + 1) & lock->mask;
else
position = (slot->position + 1) % lock->count;
ck_pr_store_uint(&lock->slots[position].locked, false);
return;
}
#endif /* CK_F_SPINLOCK_ANDERSON */
#endif /* CK_SPINLOCK_ANDERSON_H */
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