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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_MCS_H
#define CK_SPINLOCK_MCS_H
#include <ck_cc.h>
#include <ck_pr.h>
#include <ck_stdbool.h>
#include <ck_stddef.h>
#ifndef CK_F_SPINLOCK_MCS
#define CK_F_SPINLOCK_MCS
struct ck_spinlock_mcs {
unsigned int locked;
struct ck_spinlock_mcs *next;
};
typedef struct ck_spinlock_mcs * ck_spinlock_mcs_t;
typedef struct ck_spinlock_mcs ck_spinlock_mcs_context_t;
#define CK_SPINLOCK_MCS_INITIALIZER (NULL)
CK_CC_INLINE static void
ck_spinlock_mcs_init(struct ck_spinlock_mcs **queue)
{
*queue = NULL;
ck_pr_barrier();
return;
}
CK_CC_INLINE static bool
ck_spinlock_mcs_trylock(struct ck_spinlock_mcs **queue,
struct ck_spinlock_mcs *node)
{
bool r;
node->locked = true;
node->next = NULL;
ck_pr_fence_store_atomic();
r = ck_pr_cas_ptr(queue, NULL, node);
ck_pr_fence_lock();
return r;
}
CK_CC_INLINE static bool
ck_spinlock_mcs_locked(struct ck_spinlock_mcs **queue)
{
bool r;
r = ck_pr_load_ptr(queue) != NULL;
ck_pr_fence_acquire();
return r;
}
CK_CC_INLINE static void
ck_spinlock_mcs_lock(struct ck_spinlock_mcs **queue,
struct ck_spinlock_mcs *node)
{
struct ck_spinlock_mcs *previous;
/*
* In the case that there is a successor, let them know they must
* wait for us to unlock.
*/
node->locked = true;
node->next = NULL;
ck_pr_fence_store_atomic();
/*
* Swap current tail with current lock request. If the swap operation
* returns NULL, it means the queue was empty. If the queue was empty,
* then the operation is complete.
*/
previous = ck_pr_fas_ptr(queue, node);
if (previous != NULL) {
/*
* Let the previous lock holder know that we are waiting on
* them.
*/
ck_pr_store_ptr(&previous->next, node);
while (ck_pr_load_uint(&node->locked) == true)
ck_pr_stall();
}
ck_pr_fence_lock();
return;
}
CK_CC_INLINE static void
ck_spinlock_mcs_unlock(struct ck_spinlock_mcs **queue,
struct ck_spinlock_mcs *node)
{
struct ck_spinlock_mcs *next;
ck_pr_fence_unlock();
next = ck_pr_load_ptr(&node->next);
if (next == NULL) {
/*
* If there is no request following us then it is a possibilty
* that we are the current tail. In this case, we may just
* mark the spinlock queue as empty.
*/
if (ck_pr_load_ptr(queue) == node &&
ck_pr_cas_ptr(queue, node, NULL) == true) {
return;
}
/*
* If the node is not the current tail then a lock operation
* is in-progress. In this case, busy-wait until the queue is
* in a consistent state to wake up the incoming lock
* request.
*/
for (;;) {
next = ck_pr_load_ptr(&node->next);
if (next != NULL)
break;
ck_pr_stall();
}
}
/* Allow the next lock operation to complete. */
ck_pr_store_uint(&next->locked, false);
return;
}
#endif /* CK_F_SPINLOCK_MCS */
#endif /* CK_SPINLOCK_MCS_H */
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