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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 | /* A urcu implementation header should be already included. */ |
34 | ||
35 | #ifdef __cplusplus | |
36 | extern "C" { | |
37 | #endif | |
38 | ||
e17d9985 MD |
39 | struct cds_lfq_node_rcu_dummy { |
40 | struct cds_lfq_node_rcu parent; | |
41 | struct rcu_head head; | |
42 | struct cds_lfq_queue_rcu *q; | |
43 | }; | |
44 | ||
3d02c34d | 45 | /* |
e17d9985 MD |
46 | * Lock-free RCU queue. Enqueue and dequeue operations hold a RCU read |
47 | * lock to deal with cmpxchg ABA problem. This queue is *not* circular: | |
48 | * head points to the oldest node, tail points to the newest node. | |
49 | * Dummy nodes are kept to ensure enqueue and dequeue can always proceed | |
50 | * concurrently. Keeping a separate head and tail helps with large | |
51 | * queues: enqueue and dequeue can proceed concurrently without | |
52 | * wrestling for exclusive access to the same variables. | |
53 | * | |
54 | * We keep two dummy nodes in the queue to distinguish between empty queue | |
55 | * state and intermediate state while a dummy node dequeue/requeue is | |
56 | * being performed. Dequeue retry if it detects that it would be | |
57 | * dequeueing the last node (it means a dummy node dequeue-requeue is in | |
58 | * progress). This ensures that there is always at least one node in | |
59 | * the queue. In a situation where the two dummy nodes are being | |
60 | * requeued (they therefore don't appear in the queue at a given | |
61 | * moment), we are certain that there is at least one non-dummy node in | |
62 | * the queue (ensured by the test for NULL next node upon dequeue). | |
63 | * | |
64 | * In the dequeue operation, we internally reallocate the dummy nodes | |
65 | * upon dequeue/requeue and use call_rcu to free them after a grace | |
66 | * period. | |
3d02c34d MD |
67 | */ |
68 | ||
e17d9985 MD |
69 | static inline |
70 | int is_dummy(struct cds_lfq_node_rcu *node) | |
71 | { | |
72 | return ((unsigned long) node) & 0x1UL; | |
73 | } | |
74 | ||
75 | static inline | |
76 | struct cds_lfq_node_rcu *make_dummy(struct cds_lfq_queue_rcu *q, | |
77 | struct cds_lfq_node_rcu *next) | |
78 | { | |
79 | struct cds_lfq_node_rcu_dummy *dummy; | |
80 | ||
81 | dummy = malloc(sizeof(struct cds_lfq_node_rcu_dummy)); | |
82 | dummy->parent.next = next; | |
83 | dummy->q = q; | |
84 | return (struct cds_lfq_node_rcu *) (((unsigned long) &dummy->parent) | 0x1UL); | |
85 | } | |
86 | ||
87 | static inline | |
88 | struct cds_lfq_node_rcu *get_node(struct cds_lfq_node_rcu *node) | |
89 | { | |
90 | return (struct cds_lfq_node_rcu *) (((unsigned long )node) & ~0x1UL); | |
91 | } | |
92 | ||
93 | static inline | |
94 | void free_dummy(struct rcu_head *head) | |
95 | { | |
96 | struct cds_lfq_node_rcu_dummy *dummy = | |
97 | caa_container_of(head, struct cds_lfq_node_rcu_dummy, head); | |
98 | free(dummy); | |
99 | } | |
100 | ||
101 | static inline | |
102 | void rcu_free_dummy(struct cds_lfq_node_rcu *node) | |
103 | { | |
104 | struct cds_lfq_node_rcu_dummy *dummy; | |
3d02c34d | 105 | |
e17d9985 MD |
106 | dummy = caa_container_of(get_node(node), struct cds_lfq_node_rcu_dummy, |
107 | parent); | |
108 | dummy->q->queue_call_rcu(&dummy->head, free_dummy); | |
109 | } | |
110 | ||
111 | static inline | |
16aa9ee8 | 112 | void _cds_lfq_node_init_rcu(struct cds_lfq_node_rcu *node) |
3d02c34d MD |
113 | { |
114 | node->next = NULL; | |
3d02c34d MD |
115 | } |
116 | ||
e17d9985 | 117 | static inline |
d9b52143 | 118 | void _cds_lfq_init_rcu(struct cds_lfq_queue_rcu *q, |
e17d9985 MD |
119 | void queue_call_rcu(struct rcu_head *head, |
120 | void (*func)(struct rcu_head *head))) | |
121 | { | |
122 | q->tail = make_dummy(q, NULL); | |
123 | q->head = make_dummy(q, q->tail); | |
124 | q->queue_call_rcu = queue_call_rcu; | |
125 | } | |
126 | ||
127 | /* | |
128 | * The queue should be emptied before calling destroy. | |
129 | * | |
130 | * Return 0 on success, -EPERM if queue is not empty. | |
131 | */ | |
132 | static inline | |
133 | int _cds_lfq_destroy_rcu(struct cds_lfq_queue_rcu *q) | |
3d02c34d | 134 | { |
e17d9985 MD |
135 | struct cds_lfq_node_rcu *head, *next; |
136 | ||
137 | head = rcu_dereference(q->head); | |
138 | next = rcu_dereference(get_node(head)->next); | |
139 | if (!(is_dummy(head) && is_dummy(next) && get_node(next)->next == NULL)) | |
140 | return -EPERM; /* not empty */ | |
141 | rcu_free_dummy(head); | |
142 | rcu_free_dummy(next); | |
143 | return 0; | |
3d02c34d MD |
144 | } |
145 | ||
d9b52143 MD |
146 | /* |
147 | * Should be called under rcu read lock critical section. | |
148 | */ | |
e17d9985 | 149 | static inline |
d9b52143 MD |
150 | void _cds_lfq_enqueue_rcu(struct cds_lfq_queue_rcu *q, |
151 | struct cds_lfq_node_rcu *node) | |
3d02c34d | 152 | { |
3d02c34d MD |
153 | /* |
154 | * uatomic_cmpxchg() implicit memory barrier orders earlier stores to | |
155 | * node before publication. | |
156 | */ | |
157 | ||
158 | for (;;) { | |
16aa9ee8 | 159 | struct cds_lfq_node_rcu *tail, *next; |
3d02c34d | 160 | |
3d02c34d | 161 | tail = rcu_dereference(q->tail); |
e17d9985 | 162 | next = uatomic_cmpxchg(&get_node(tail)->next, NULL, node); |
3d02c34d MD |
163 | if (next == NULL) { |
164 | /* | |
165 | * Tail was at the end of queue, we successfully | |
e17d9985 MD |
166 | * appended to it. Now move tail (another |
167 | * enqueue might beat us to it, that's fine). | |
3d02c34d | 168 | */ |
85b57703 | 169 | (void) uatomic_cmpxchg(&q->tail, tail, node); |
3d02c34d MD |
170 | return; |
171 | } else { | |
172 | /* | |
e17d9985 MD |
173 | * Failure to append to current tail. |
174 | * Help moving tail further and retry. | |
3d02c34d | 175 | */ |
85b57703 | 176 | (void) uatomic_cmpxchg(&q->tail, tail, next); |
3d02c34d MD |
177 | continue; |
178 | } | |
179 | } | |
180 | } | |
181 | ||
182 | /* | |
d9b52143 MD |
183 | * Should be called under rcu read lock critical section. |
184 | * | |
e17d9985 MD |
185 | * The caller must wait for a grace period to pass before freeing the returned |
186 | * node or modifying the cds_lfq_node_rcu structure. | |
187 | * Returns NULL if queue is empty. | |
3d02c34d | 188 | */ |
e17d9985 | 189 | static inline |
a34df756 | 190 | struct cds_lfq_node_rcu *_cds_lfq_dequeue_rcu(struct cds_lfq_queue_rcu *q) |
3d02c34d MD |
191 | { |
192 | for (;;) { | |
16aa9ee8 | 193 | struct cds_lfq_node_rcu *head, *next; |
3d02c34d | 194 | |
3d02c34d | 195 | head = rcu_dereference(q->head); |
e17d9985 MD |
196 | next = rcu_dereference(get_node(head)->next); |
197 | if (is_dummy(head) && is_dummy(next) && get_node(next)->next == NULL) | |
198 | return NULL; /* empty */ | |
199 | /* | |
200 | * We never, ever allow dequeue to get to a state where | |
201 | * the queue is empty (we need at least one node in the | |
202 | * queue). This is ensured by checking if the head next | |
203 | * is NULL and retry in that case (this means a | |
204 | * concurrent dummy node re-enqueue is in progress). | |
205 | */ | |
3d02c34d MD |
206 | if (next) { |
207 | if (uatomic_cmpxchg(&q->head, head, next) == head) { | |
e17d9985 MD |
208 | if (is_dummy(head)) { |
209 | struct cds_lfq_node_rcu *node; | |
210 | /* | |
211 | * Requeue dummy. We need to | |
212 | * reallocate to protect from | |
213 | * ABA. | |
214 | */ | |
215 | rcu_free_dummy(head); | |
216 | node = make_dummy(q, NULL); | |
217 | _cds_lfq_enqueue_rcu(q, node); | |
218 | continue; /* try again */ | |
219 | } | |
220 | return head; | |
3d02c34d MD |
221 | } else { |
222 | /* Concurrently pushed, retry */ | |
3d02c34d MD |
223 | continue; |
224 | } | |
225 | } else { | |
e17d9985 MD |
226 | /* Dummy node re-enqueue is in progress, retry. */ |
227 | continue; | |
3d02c34d MD |
228 | } |
229 | } | |
230 | } | |
231 | ||
232 | #ifdef __cplusplus | |
233 | } | |
234 | #endif | |
235 | ||
236 | #endif /* _URCU_RCULFQUEUE_STATIC_H */ |