Commit | Line | Data |
---|---|---|
3d02c34d MD |
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 | ||
e17d9985 | 29 | #include <urcu-call-rcu.h> |
a2e7bf9c | 30 | #include <urcu/uatomic.h> |
3d02c34d | 31 | #include <assert.h> |
e17d9985 | 32 | #include <errno.h> |
3d02c34d MD |
33 | |
34 | #ifdef __cplusplus | |
35 | extern "C" { | |
36 | #endif | |
37 | ||
e17d9985 MD |
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 | ||
3d02c34d | 44 | /* |
e17d9985 MD |
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. | |
0cca1a2d | 48 | * A dummy node is kept to ensure enqueue and dequeue can always proceed |
e17d9985 MD |
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 | * | |
0cca1a2d MD |
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. | |
e17d9985 | 56 | * |
0cca1a2d MD |
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. | |
3d02c34d MD |
60 | */ |
61 | ||
e17d9985 MD |
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)); | |
8f03ed0d | 69 | assert(dummy); |
e17d9985 | 70 | dummy->parent.next = next; |
fbdb32f6 | 71 | dummy->parent.dummy = 1; |
e17d9985 | 72 | dummy->q = q; |
909292c2 | 73 | return &dummy->parent; |
e17d9985 MD |
74 | } |
75 | ||
76 | static inline | |
f6719811 | 77 | void free_dummy_cb(struct rcu_head *head) |
e17d9985 MD |
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; | |
3d02c34d | 88 | |
fbdb32f6 | 89 | assert(node->dummy); |
909292c2 | 90 | dummy = caa_container_of(node, struct cds_lfq_node_rcu_dummy, parent); |
f6719811 MD |
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 | ||
fbdb32f6 | 99 | assert(node->dummy); |
f6719811 MD |
100 | dummy = caa_container_of(node, struct cds_lfq_node_rcu_dummy, parent); |
101 | free(dummy); | |
e17d9985 MD |
102 | } |
103 | ||
104 | static inline | |
16aa9ee8 | 105 | void _cds_lfq_node_init_rcu(struct cds_lfq_node_rcu *node) |
3d02c34d MD |
106 | { |
107 | node->next = NULL; | |
fbdb32f6 | 108 | node->dummy = 0; |
3d02c34d MD |
109 | } |
110 | ||
e17d9985 | 111 | static inline |
d9b52143 | 112 | void _cds_lfq_init_rcu(struct cds_lfq_queue_rcu *q, |
e17d9985 MD |
113 | void queue_call_rcu(struct rcu_head *head, |
114 | void (*func)(struct rcu_head *head))) | |
115 | { | |
116 | q->tail = make_dummy(q, NULL); | |
0cca1a2d | 117 | q->head = q->tail; |
e17d9985 MD |
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) | |
3d02c34d | 128 | { |
0cca1a2d | 129 | struct cds_lfq_node_rcu *head; |
e17d9985 MD |
130 | |
131 | head = rcu_dereference(q->head); | |
fbdb32f6 | 132 | if (!(head->dummy && head->next == NULL)) |
e17d9985 | 133 | return -EPERM; /* not empty */ |
f6719811 | 134 | free_dummy(head); |
e17d9985 | 135 | return 0; |
3d02c34d MD |
136 | } |
137 | ||
d9b52143 MD |
138 | /* |
139 | * Should be called under rcu read lock critical section. | |
140 | */ | |
e17d9985 | 141 | static inline |
d9b52143 MD |
142 | void _cds_lfq_enqueue_rcu(struct cds_lfq_queue_rcu *q, |
143 | struct cds_lfq_node_rcu *node) | |
3d02c34d | 144 | { |
3d02c34d MD |
145 | /* |
146 | * uatomic_cmpxchg() implicit memory barrier orders earlier stores to | |
147 | * node before publication. | |
148 | */ | |
149 | ||
150 | for (;;) { | |
16aa9ee8 | 151 | struct cds_lfq_node_rcu *tail, *next; |
3d02c34d | 152 | |
3d02c34d | 153 | tail = rcu_dereference(q->tail); |
909292c2 | 154 | next = uatomic_cmpxchg(&tail->next, NULL, node); |
3d02c34d MD |
155 | if (next == NULL) { |
156 | /* | |
157 | * Tail was at the end of queue, we successfully | |
e17d9985 MD |
158 | * appended to it. Now move tail (another |
159 | * enqueue might beat us to it, that's fine). | |
3d02c34d | 160 | */ |
85b57703 | 161 | (void) uatomic_cmpxchg(&q->tail, tail, node); |
3d02c34d MD |
162 | return; |
163 | } else { | |
164 | /* | |
e17d9985 MD |
165 | * Failure to append to current tail. |
166 | * Help moving tail further and retry. | |
3d02c34d | 167 | */ |
85b57703 | 168 | (void) uatomic_cmpxchg(&q->tail, tail, next); |
3d02c34d MD |
169 | continue; |
170 | } | |
171 | } | |
172 | } | |
173 | ||
f6719811 | 174 | static inline |
fbdb32f6 | 175 | void enqueue_dummy(struct cds_lfq_queue_rcu *q) |
f6719811 MD |
176 | { |
177 | struct cds_lfq_node_rcu *node; | |
178 | ||
179 | /* We need to reallocate to protect from ABA. */ | |
180 | node = make_dummy(q, NULL); | |
f6719811 MD |
181 | _cds_lfq_enqueue_rcu(q, node); |
182 | } | |
183 | ||
3d02c34d | 184 | /* |
d9b52143 MD |
185 | * Should be called under rcu read lock critical section. |
186 | * | |
e17d9985 MD |
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. | |
3d02c34d | 190 | */ |
e17d9985 | 191 | static inline |
a34df756 | 192 | struct cds_lfq_node_rcu *_cds_lfq_dequeue_rcu(struct cds_lfq_queue_rcu *q) |
3d02c34d MD |
193 | { |
194 | for (;;) { | |
fbdb32f6 | 195 | struct cds_lfq_node_rcu *head, *next; |
3d02c34d | 196 | |
3d02c34d | 197 | head = rcu_dereference(q->head); |
909292c2 | 198 | next = rcu_dereference(head->next); |
fbdb32f6 | 199 | if (head->dummy && next == NULL) |
e17d9985 MD |
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 | |
fbdb32f6 MD |
205 | * is NULL, which means we need to enqueue a dummy node |
206 | * before we can hope dequeuing anything. | |
e17d9985 | 207 | */ |
f6719811 | 208 | if (!next) { |
fbdb32f6 MD |
209 | enqueue_dummy(q); |
210 | next = rcu_dereference(head->next); | |
f6719811 MD |
211 | } |
212 | if (uatomic_cmpxchg(&q->head, head, next) != head) | |
213 | continue; /* Concurrently pushed. */ | |
fbdb32f6 MD |
214 | if (head->dummy) { |
215 | /* Free dummy after grace period. */ | |
216 | rcu_free_dummy(head); | |
f6719811 | 217 | continue; /* try again */ |
3d02c34d | 218 | } |
f6719811 | 219 | return head; |
3d02c34d MD |
220 | } |
221 | } | |
222 | ||
223 | #ifdef __cplusplus | |
224 | } | |
225 | #endif | |
226 | ||
227 | #endif /* _URCU_RCULFQUEUE_STATIC_H */ |