doc/examples: update qsbr example
[urcu.git] / doc / examples / urcu-flavors / qsbr.c
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1/*
2 * Copyright (C) 2013 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
3 *
4 * This library is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU Lesser General Public
6 * License as published by the Free Software Foundation; either
7 * version 2.1 of the License, or (at your option) any later version.
8 *
9 * This library is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 * Lesser General Public License for more details.
13 *
14 * You should have received a copy of the GNU Lesser General Public
15 * License along with this library; if not, write to the Free Software
16 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
17 */
18
88c3c5ba 19#include <unistd.h>
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20#include <stdlib.h>
21#include <stdio.h>
22#include <stdint.h>
23#include <inttypes.h>
24
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25#include <urcu-qsbr.h> /* QSBR RCU flavor */
26#include <urcu/rculist.h> /* List example */
27#include <urcu/compiler.h> /* For CAA_ARRAY_SIZE */
28
8bad63a0 29/*
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30 * Example showing how to use the QSBR Userspace RCU flavor.
31 *
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32 * This is a mock-up example where updates and RCU traversals are
33 * performed by the same thread to keep things simple on purpose.
34 */
35
36static CDS_LIST_HEAD(mylist);
37
38struct mynode {
39 uint64_t value;
40 struct cds_list_head node; /* linked-list chaining */
41 struct rcu_head rcu_head; /* for call_rcu() */
42};
43
44static
45int add_node(uint64_t v)
46{
47 struct mynode *node;
48
49 node = calloc(sizeof(*node), 1);
50 if (!node)
51 return -1;
52 node->value = v;
53 cds_list_add_rcu(&node->node, &mylist);
54 return 0;
55}
56
57static
58void rcu_free_node(struct rcu_head *rh)
59{
60 struct mynode *node = caa_container_of(rh, struct mynode, rcu_head);
61
62 free(node);
63}
64
65int main(int argc, char **argv)
66{
67 uint64_t values[] = { 42, 36, 24, };
68 unsigned int i;
69 int ret;
70 struct mynode *node, *n;
71
72 /*
8fd9af4a 73 * Each thread need using RCU read-side need to be explicitly
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74 * registered.
75 */
76 rcu_register_thread();
77
78 /*
79 * Adding nodes to the linked-list. Safe against concurrent
80 * RCU traversals, require mutual exclusion with list updates.
81 */
82 for (i = 0; i < CAA_ARRAY_SIZE(values); i++) {
83 ret = add_node(values[i]);
84 if (ret)
85 goto end;
86 }
87
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88 /*
89 * RCU traversal of the linked list.
90 */
91 cds_list_for_each_entry_rcu(node, &mylist, node) {
92 printf("Value: %" PRIu64 "\n", node->value);
93 }
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94
95 /*
96 * Removing nodes from linked list. Safe against concurrent RCU
97 * traversals, require mutual exclusion with list updates.
98 */
99 cds_list_for_each_entry_safe(node, n, &mylist, node) {
100 cds_list_del_rcu(&node->node);
101 call_rcu(&node->rcu_head, rcu_free_node);
102 }
103
104 /*
105 * For QSBR flavor, we need to explicitly announce quiescent
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106 * states. Here is how it is done. This should be performed by
107 * every online registered RCU threads in the program
108 * periodically.
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109 */
110 rcu_quiescent_state();
111
112 /*
113 * For QSBR flavor, when a thread needs to be in a quiescent
114 * state for a long period of time, we use rcu_thread_offline()
115 * and rcu_thread_online().
116 */
117 rcu_thread_offline();
118
119 sleep(1);
120
121 rcu_thread_online();
122
123 /*
124 * Waiting for previously called call_rcu handlers to complete
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125 * before program exits, or in library destructors, is a good
126 * practice.
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127 */
128 rcu_barrier();
129
130end:
131 rcu_unregister_thread();
132 return ret;
133}
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