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[urcu.git] / urcu-wait.h
1 #ifndef _URCU_WAIT_H
2 #define _URCU_WAIT_H
3
4 /*
5 * urcu-wait.h
6 *
7 * Userspace RCU library wait/wakeup management
8 *
9 * Copyright (c) 2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
10 *
11 * This library is free software; you can redistribute it and/or
12 * modify it under the terms of the GNU Lesser General Public
13 * License as published by the Free Software Foundation; either
14 * version 2.1 of the License, or (at your option) any later version.
15 *
16 * This library is distributed in the hope that it will be useful,
17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
19 * Lesser General Public License for more details.
20 *
21 * You should have received a copy of the GNU Lesser General Public
22 * License along with this library; if not, write to the Free Software
23 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
24 */
25
26 #include <urcu/uatomic.h>
27 #include <urcu/wfstack.h>
28
29 /*
30 * Number of busy-loop attempts before waiting on futex for grace period
31 * batching.
32 */
33 #define URCU_WAIT_ATTEMPTS 1000
34
35 enum urcu_wait_state {
36 /* URCU_WAIT_WAITING is compared directly (futex compares it). */
37 URCU_WAIT_WAITING = 0,
38 /* non-zero are used as masks. */
39 URCU_WAIT_WAKEUP = (1 << 0),
40 URCU_WAIT_RUNNING = (1 << 1),
41 URCU_WAIT_TEARDOWN = (1 << 2),
42 };
43
44 struct urcu_wait_node {
45 struct cds_wfs_node node;
46 int32_t state; /* enum urcu_wait_state */
47 };
48
49 #define URCU_WAIT_NODE_INIT(name, _state) \
50 { .state = _state }
51
52 #define DEFINE_URCU_WAIT_NODE(name, state) \
53 struct urcu_wait_node name = URCU_WAIT_NODE_INIT(name, state)
54
55 #define DECLARE_URCU_WAIT_NODE(name) \
56 struct urcu_wait_node name
57
58 struct urcu_wait_queue {
59 struct cds_wfs_stack stack;
60 };
61
62 #define URCU_WAIT_QUEUE_HEAD_INIT(name) \
63 { .stack.head = CDS_WFS_END, .stack.lock = PTHREAD_MUTEX_INITIALIZER }
64
65 #define DECLARE_URCU_WAIT_QUEUE(name) \
66 struct urcu_wait_queue name
67
68 #define DEFINE_URCU_WAIT_QUEUE(name) \
69 struct urcu_wait_queue name = URCU_WAIT_QUEUE_HEAD_INIT(name)
70
71 struct urcu_waiters {
72 struct cds_wfs_head *head;
73 };
74
75 /*
76 * Add ourself atomically to a wait queue. Return 0 if queue was
77 * previously empty, else return 1.
78 * A full memory barrier is issued before being added to the wait queue.
79 */
80 static inline
81 bool urcu_wait_add(struct urcu_wait_queue *queue,
82 struct urcu_wait_node *node)
83 {
84 return cds_wfs_push(&queue->stack, &node->node);
85 }
86
87 /*
88 * Atomically move all waiters from wait queue into our local struct
89 * urcu_waiters.
90 */
91 static inline
92 void urcu_move_waiters(struct urcu_waiters *waiters,
93 struct urcu_wait_queue *queue)
94 {
95 waiters->head = __cds_wfs_pop_all(&queue->stack);
96 }
97
98 static inline
99 void urcu_wait_set_state(struct urcu_wait_node *node,
100 enum urcu_wait_state state)
101 {
102 node->state = state;
103 }
104
105 static inline
106 void urcu_wait_node_init(struct urcu_wait_node *node,
107 enum urcu_wait_state state)
108 {
109 urcu_wait_set_state(node, state);
110 cds_wfs_node_init(&node->node);
111 }
112
113 /*
114 * Note: urcu_adaptative_wake_up needs "value" to stay allocated
115 * throughout its execution. In this scheme, the waiter owns the node
116 * memory, and we only allow it to free this memory when it receives the
117 * URCU_WAIT_TEARDOWN flag.
118 */
119 static inline
120 void urcu_adaptative_wake_up(struct urcu_wait_node *wait)
121 {
122 cmm_smp_mb();
123 assert(uatomic_read(&wait->state) == URCU_WAIT_WAITING);
124 uatomic_set(&wait->state, URCU_WAIT_WAKEUP);
125 if (!(uatomic_read(&wait->state) & URCU_WAIT_RUNNING))
126 futex_noasync(&wait->state, FUTEX_WAKE, 1, NULL, NULL, 0);
127 /* Allow teardown of struct urcu_wait memory. */
128 uatomic_or(&wait->state, URCU_WAIT_TEARDOWN);
129 }
130
131 /*
132 * Caller must initialize "value" to URCU_WAIT_WAITING before passing its
133 * memory to waker thread.
134 */
135 static inline
136 void urcu_adaptative_busy_wait(struct urcu_wait_node *wait)
137 {
138 unsigned int i;
139
140 /* Load and test condition before read state */
141 cmm_smp_rmb();
142 for (i = 0; i < URCU_WAIT_ATTEMPTS; i++) {
143 if (uatomic_read(&wait->state) != URCU_WAIT_WAITING)
144 goto skip_futex_wait;
145 caa_cpu_relax();
146 }
147 futex_noasync(&wait->state, FUTEX_WAIT,
148 URCU_WAIT_WAITING, NULL, NULL, 0);
149 skip_futex_wait:
150
151 /* Tell waker thread than we are running. */
152 uatomic_or(&wait->state, URCU_WAIT_RUNNING);
153
154 /*
155 * Wait until waker thread lets us know it's ok to tear down
156 * memory allocated for struct urcu_wait.
157 */
158 for (i = 0; i < URCU_WAIT_ATTEMPTS; i++) {
159 if (uatomic_read(&wait->state) & URCU_WAIT_TEARDOWN)
160 break;
161 caa_cpu_relax();
162 }
163 while (!(uatomic_read(&wait->state) & URCU_WAIT_TEARDOWN))
164 poll(NULL, 0, 10);
165 assert(uatomic_read(&wait->state) & URCU_WAIT_TEARDOWN);
166 }
167
168 static inline
169 void urcu_wake_all_waiters(struct urcu_waiters *waiters)
170 {
171 struct cds_wfs_node *iter, *iter_n;
172
173 /* Wake all waiters in our stack head */
174 cds_wfs_for_each_blocking_safe(waiters->head, iter, iter_n) {
175 struct urcu_wait_node *wait_node =
176 caa_container_of(iter, struct urcu_wait_node, node);
177
178 /* Don't wake already running threads */
179 if (wait_node->state & URCU_WAIT_RUNNING)
180 continue;
181 urcu_adaptative_wake_up(wait_node);
182 }
183 }
184
185 #endif /* _URCU_WAIT_H */
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