| 1 | #ifndef _URCU_RCULFQUEUE_STATIC_H |
| 2 | #define _URCU_RCULFQUEUE_STATIC_H |
| 3 | |
| 4 | /* |
| 5 | * rculfqueue-static.h |
| 6 | * |
| 7 | * Userspace RCU library - Lock-Free RCU Queue |
| 8 | * |
| 9 | * Copyright 2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
| 10 | * |
| 11 | * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See rculfqueue.h for linking |
| 12 | * dynamically with the userspace rcu library. |
| 13 | * |
| 14 | * This library is free software; you can redistribute it and/or |
| 15 | * modify it under the terms of the GNU Lesser General Public |
| 16 | * License as published by the Free Software Foundation; either |
| 17 | * version 2.1 of the License, or (at your option) any later version. |
| 18 | * |
| 19 | * This library is distributed in the hope that it will be useful, |
| 20 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 21 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| 22 | * Lesser General Public License for more details. |
| 23 | * |
| 24 | * You should have received a copy of the GNU Lesser General Public |
| 25 | * License along with this library; if not, write to the Free Software |
| 26 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA |
| 27 | */ |
| 28 | |
| 29 | #include <urcu-call-rcu.h> |
| 30 | #include <urcu/uatomic.h> |
| 31 | #include <assert.h> |
| 32 | #include <errno.h> |
| 33 | |
| 34 | #ifdef __cplusplus |
| 35 | extern "C" { |
| 36 | #endif |
| 37 | |
| 38 | struct cds_lfq_node_rcu_dummy { |
| 39 | struct cds_lfq_node_rcu parent; |
| 40 | struct rcu_head head; |
| 41 | struct cds_lfq_queue_rcu *q; |
| 42 | }; |
| 43 | |
| 44 | /* |
| 45 | * Lock-free RCU queue. Enqueue and dequeue operations hold a RCU read |
| 46 | * lock to deal with cmpxchg ABA problem. This queue is *not* circular: |
| 47 | * head points to the oldest node, tail points to the newest node. |
| 48 | * A dummy node is kept to ensure enqueue and dequeue can always proceed |
| 49 | * concurrently. Keeping a separate head and tail helps with large |
| 50 | * queues: enqueue and dequeue can proceed concurrently without |
| 51 | * wrestling for exclusive access to the same variables. |
| 52 | * |
| 53 | * Dequeue retry if it detects that it would be dequeueing the last node |
| 54 | * (it means a dummy node dequeue-requeue is in progress). This ensures |
| 55 | * that there is always at least one node in the queue. |
| 56 | * |
| 57 | * In the dequeue operation, we internally reallocate the dummy node |
| 58 | * upon dequeue/requeue and use call_rcu to free the old one after a |
| 59 | * grace period. |
| 60 | */ |
| 61 | |
| 62 | static inline |
| 63 | struct cds_lfq_node_rcu *make_dummy(struct cds_lfq_queue_rcu *q, |
| 64 | struct cds_lfq_node_rcu *next) |
| 65 | { |
| 66 | struct cds_lfq_node_rcu_dummy *dummy; |
| 67 | |
| 68 | dummy = malloc(sizeof(struct cds_lfq_node_rcu_dummy)); |
| 69 | assert(dummy); |
| 70 | dummy->parent.next = next; |
| 71 | dummy->parent.dummy = 1; |
| 72 | dummy->q = q; |
| 73 | return &dummy->parent; |
| 74 | } |
| 75 | |
| 76 | static inline |
| 77 | void free_dummy_cb(struct rcu_head *head) |
| 78 | { |
| 79 | struct cds_lfq_node_rcu_dummy *dummy = |
| 80 | caa_container_of(head, struct cds_lfq_node_rcu_dummy, head); |
| 81 | free(dummy); |
| 82 | } |
| 83 | |
| 84 | static inline |
| 85 | void rcu_free_dummy(struct cds_lfq_node_rcu *node) |
| 86 | { |
| 87 | struct cds_lfq_node_rcu_dummy *dummy; |
| 88 | |
| 89 | assert(node->dummy); |
| 90 | dummy = caa_container_of(node, struct cds_lfq_node_rcu_dummy, parent); |
| 91 | dummy->q->queue_call_rcu(&dummy->head, free_dummy_cb); |
| 92 | } |
| 93 | |
| 94 | static inline |
| 95 | void free_dummy(struct cds_lfq_node_rcu *node) |
| 96 | { |
| 97 | struct cds_lfq_node_rcu_dummy *dummy; |
| 98 | |
| 99 | assert(node->dummy); |
| 100 | dummy = caa_container_of(node, struct cds_lfq_node_rcu_dummy, parent); |
| 101 | free(dummy); |
| 102 | } |
| 103 | |
| 104 | static inline |
| 105 | void _cds_lfq_node_init_rcu(struct cds_lfq_node_rcu *node) |
| 106 | { |
| 107 | node->next = NULL; |
| 108 | node->dummy = 0; |
| 109 | } |
| 110 | |
| 111 | static inline |
| 112 | void _cds_lfq_init_rcu(struct cds_lfq_queue_rcu *q, |
| 113 | void queue_call_rcu(struct rcu_head *head, |
| 114 | void (*func)(struct rcu_head *head))) |
| 115 | { |
| 116 | q->tail = make_dummy(q, NULL); |
| 117 | q->head = q->tail; |
| 118 | q->queue_call_rcu = queue_call_rcu; |
| 119 | } |
| 120 | |
| 121 | /* |
| 122 | * The queue should be emptied before calling destroy. |
| 123 | * |
| 124 | * Return 0 on success, -EPERM if queue is not empty. |
| 125 | */ |
| 126 | static inline |
| 127 | int _cds_lfq_destroy_rcu(struct cds_lfq_queue_rcu *q) |
| 128 | { |
| 129 | struct cds_lfq_node_rcu *head; |
| 130 | |
| 131 | head = rcu_dereference(q->head); |
| 132 | if (!(head->dummy && head->next == NULL)) |
| 133 | return -EPERM; /* not empty */ |
| 134 | free_dummy(head); |
| 135 | return 0; |
| 136 | } |
| 137 | |
| 138 | /* |
| 139 | * Should be called under rcu read lock critical section. |
| 140 | */ |
| 141 | static inline |
| 142 | void _cds_lfq_enqueue_rcu(struct cds_lfq_queue_rcu *q, |
| 143 | struct cds_lfq_node_rcu *node) |
| 144 | { |
| 145 | /* |
| 146 | * uatomic_cmpxchg() implicit memory barrier orders earlier stores to |
| 147 | * node before publication. |
| 148 | */ |
| 149 | |
| 150 | for (;;) { |
| 151 | struct cds_lfq_node_rcu *tail, *next; |
| 152 | |
| 153 | tail = rcu_dereference(q->tail); |
| 154 | next = uatomic_cmpxchg(&tail->next, NULL, node); |
| 155 | if (next == NULL) { |
| 156 | /* |
| 157 | * Tail was at the end of queue, we successfully |
| 158 | * appended to it. Now move tail (another |
| 159 | * enqueue might beat us to it, that's fine). |
| 160 | */ |
| 161 | (void) uatomic_cmpxchg(&q->tail, tail, node); |
| 162 | return; |
| 163 | } else { |
| 164 | /* |
| 165 | * Failure to append to current tail. |
| 166 | * Help moving tail further and retry. |
| 167 | */ |
| 168 | (void) uatomic_cmpxchg(&q->tail, tail, next); |
| 169 | continue; |
| 170 | } |
| 171 | } |
| 172 | } |
| 173 | |
| 174 | static inline |
| 175 | void enqueue_dummy(struct cds_lfq_queue_rcu *q) |
| 176 | { |
| 177 | struct cds_lfq_node_rcu *node; |
| 178 | |
| 179 | /* We need to reallocate to protect from ABA. */ |
| 180 | node = make_dummy(q, NULL); |
| 181 | _cds_lfq_enqueue_rcu(q, node); |
| 182 | } |
| 183 | |
| 184 | /* |
| 185 | * Should be called under rcu read lock critical section. |
| 186 | * |
| 187 | * The caller must wait for a grace period to pass before freeing the returned |
| 188 | * node or modifying the cds_lfq_node_rcu structure. |
| 189 | * Returns NULL if queue is empty. |
| 190 | */ |
| 191 | static inline |
| 192 | struct cds_lfq_node_rcu *_cds_lfq_dequeue_rcu(struct cds_lfq_queue_rcu *q) |
| 193 | { |
| 194 | for (;;) { |
| 195 | struct cds_lfq_node_rcu *head, *next; |
| 196 | |
| 197 | head = rcu_dereference(q->head); |
| 198 | next = rcu_dereference(head->next); |
| 199 | if (head->dummy && next == NULL) |
| 200 | return NULL; /* empty */ |
| 201 | /* |
| 202 | * We never, ever allow dequeue to get to a state where |
| 203 | * the queue is empty (we need at least one node in the |
| 204 | * queue). This is ensured by checking if the head next |
| 205 | * is NULL, which means we need to enqueue a dummy node |
| 206 | * before we can hope dequeuing anything. |
| 207 | */ |
| 208 | if (!next) { |
| 209 | enqueue_dummy(q); |
| 210 | next = rcu_dereference(head->next); |
| 211 | } |
| 212 | if (uatomic_cmpxchg(&q->head, head, next) != head) |
| 213 | continue; /* Concurrently pushed. */ |
| 214 | if (head->dummy) { |
| 215 | /* Free dummy after grace period. */ |
| 216 | rcu_free_dummy(head); |
| 217 | continue; /* try again */ |
| 218 | } |
| 219 | return head; |
| 220 | } |
| 221 | } |
| 222 | |
| 223 | #ifdef __cplusplus |
| 224 | } |
| 225 | #endif |
| 226 | |
| 227 | #endif /* _URCU_RCULFQUEUE_STATIC_H */ |