| /* |
| * 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 */ |