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