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Diffstat (limited to 'sys/contrib/ck/include/spinlock/mcs.h')
| -rw-r--r-- | sys/contrib/ck/include/spinlock/mcs.h | 155 |
1 files changed, 155 insertions, 0 deletions
diff --git a/sys/contrib/ck/include/spinlock/mcs.h b/sys/contrib/ck/include/spinlock/mcs.h new file mode 100644 index 000000000000..262c7205c6ed --- /dev/null +++ b/sys/contrib/ck/include/spinlock/mcs.h @@ -0,0 +1,155 @@ +/* + * 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 */ |