1 /* 2 * Copyright 2010-2015 Samy Al Bahra. 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 17 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24 * SUCH DAMAGE. 25 */ 26 27 #ifndef CK_SPINLOCK_MCS_H 28 #define CK_SPINLOCK_MCS_H 29 30 #include <ck_cc.h> 31 #include <ck_pr.h> 32 #include <ck_stdbool.h> 33 #include <ck_stddef.h> 34 35 #ifndef CK_F_SPINLOCK_MCS 36 #define CK_F_SPINLOCK_MCS 37 38 struct ck_spinlock_mcs { 39 unsigned int locked; 40 struct ck_spinlock_mcs *next; 41 }; 42 typedef struct ck_spinlock_mcs * ck_spinlock_mcs_t; 43 typedef struct ck_spinlock_mcs ck_spinlock_mcs_context_t; 44 45 #define CK_SPINLOCK_MCS_INITIALIZER (NULL) 46 47 CK_CC_INLINE static void 48 ck_spinlock_mcs_init(struct ck_spinlock_mcs **queue) 49 { 50 51 *queue = NULL; 52 ck_pr_barrier(); 53 return; 54 } 55 56 CK_CC_INLINE static bool 57 ck_spinlock_mcs_trylock(struct ck_spinlock_mcs **queue, 58 struct ck_spinlock_mcs *node) 59 { 60 bool r; 61 62 node->locked = true; 63 node->next = NULL; 64 ck_pr_fence_store_atomic(); 65 66 r = ck_pr_cas_ptr(queue, NULL, node); 67 ck_pr_fence_lock(); 68 return r; 69 } 70 71 CK_CC_INLINE static bool 72 ck_spinlock_mcs_locked(struct ck_spinlock_mcs **queue) 73 { 74 bool r; 75 76 r = ck_pr_load_ptr(queue) != NULL; 77 ck_pr_fence_acquire(); 78 return r; 79 } 80 81 CK_CC_INLINE static void 82 ck_spinlock_mcs_lock(struct ck_spinlock_mcs **queue, 83 struct ck_spinlock_mcs *node) 84 { 85 struct ck_spinlock_mcs *previous; 86 87 /* 88 * In the case that there is a successor, let them know they must 89 * wait for us to unlock. 90 */ 91 node->locked = true; 92 node->next = NULL; 93 ck_pr_fence_store_atomic(); 94 95 /* 96 * Swap current tail with current lock request. If the swap operation 97 * returns NULL, it means the queue was empty. If the queue was empty, 98 * then the operation is complete. 99 */ 100 previous = ck_pr_fas_ptr(queue, node); 101 if (previous != NULL) { 102 /* 103 * Let the previous lock holder know that we are waiting on 104 * them. 105 */ 106 ck_pr_store_ptr(&previous->next, node); 107 while (ck_pr_load_uint(&node->locked) == true) 108 ck_pr_stall(); 109 } 110 111 ck_pr_fence_lock(); 112 return; 113 } 114 115 CK_CC_INLINE static void 116 ck_spinlock_mcs_unlock(struct ck_spinlock_mcs **queue, 117 struct ck_spinlock_mcs *node) 118 { 119 struct ck_spinlock_mcs *next; 120 121 ck_pr_fence_unlock(); 122 123 next = ck_pr_load_ptr(&node->next); 124 if (next == NULL) { 125 /* 126 * If there is no request following us then it is a possibilty 127 * that we are the current tail. In this case, we may just 128 * mark the spinlock queue as empty. 129 */ 130 if (ck_pr_load_ptr(queue) == node && 131 ck_pr_cas_ptr(queue, node, NULL) == true) { 132 return; 133 } 134 135 /* 136 * If the node is not the current tail then a lock operation 137 * is in-progress. In this case, busy-wait until the queue is 138 * in a consistent state to wake up the incoming lock 139 * request. 140 */ 141 for (;;) { 142 next = ck_pr_load_ptr(&node->next); 143 if (next != NULL) 144 break; 145 146 ck_pr_stall(); 147 } 148 } 149 150 /* Allow the next lock operation to complete. */ 151 ck_pr_store_uint(&next->locked, false); 152 return; 153 } 154 #endif /* CK_F_SPINLOCK_MCS */ 155 #endif /* CK_SPINLOCK_MCS_H */ 156