doc/examples: introduce urcu-flavors examples directory
[urcu.git] / doc / examples / urcu-flavors / qsbr.c
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
19 #include <stdlib.h>
20 #include <stdio.h>
21 #include <stdint.h>
22 #include <inttypes.h>
23
24 #include <urcu-qsbr.h> /* QSBR RCU flavor */
25 #include <urcu/rculist.h> /* List example */
26 #include <urcu/compiler.h> /* For CAA_ARRAY_SIZE */
27
28 /*
29 * Example showing how to use the QSBR Userspace RCU flavor.
30 *
31 * This is a mock-up example where updates and RCU traversals are
32 * performed by the same thread to keep things simple on purpose.
33 */
34
35 static CDS_LIST_HEAD(mylist);
36
37 struct mynode {
38 uint64_t value;
39 struct cds_list_head node; /* linked-list chaining */
40 struct rcu_head rcu_head; /* for call_rcu() */
41 };
42
43 static
44 int add_node(uint64_t v)
45 {
46 struct mynode *node;
47
48 node = calloc(sizeof(*node), 1);
49 if (!node)
50 return -1;
51 node->value = v;
52 cds_list_add_rcu(&node->node, &mylist);
53 return 0;
54 }
55
56 static
57 void rcu_free_node(struct rcu_head *rh)
58 {
59 struct mynode *node = caa_container_of(rh, struct mynode, rcu_head);
60
61 free(node);
62 }
63
64 int main(int argc, char **argv)
65 {
66 uint64_t values[] = { 42, 36, 24, };
67 unsigned int i;
68 int ret;
69 struct mynode *node, *n;
70
71 /*
72 * Each thread need using RCU read-side need to be explicitly
73 * registered.
74 */
75 rcu_register_thread();
76
77 /*
78 * Adding nodes to the linked-list. Safe against concurrent
79 * RCU traversals, require mutual exclusion with list updates.
80 */
81 for (i = 0; i < CAA_ARRAY_SIZE(values); i++) {
82 ret = add_node(values[i]);
83 if (ret)
84 goto end;
85 }
86
87 /*
88 * For all RCU flavors except QSBR, we need to explicitly mark
89 * RCU read-side critical sections with rcu_read_lock() and
90 * rcu_read_unlock(). They can be nested. Those are no-ops for
91 * the QSBR flavor.
92 */
93 rcu_read_lock();
94
95 /*
96 * RCU traversal of the linked list.
97 */
98 cds_list_for_each_entry_rcu(node, &mylist, node) {
99 printf("Value: %" PRIu64 "\n", node->value);
100 }
101 rcu_read_unlock();
102
103 /*
104 * Removing nodes from linked list. Safe against concurrent RCU
105 * traversals, require mutual exclusion with list updates.
106 */
107 cds_list_for_each_entry_safe(node, n, &mylist, node) {
108 cds_list_del_rcu(&node->node);
109 call_rcu(&node->rcu_head, rcu_free_node);
110 }
111
112 /*
113 * For QSBR flavor, we need to explicitly announce quiescent
114 * states. Here is how it is done. This should be performed by
115 * every online registered RCU threads in the program
116 * periodically.
117 */
118 rcu_quiescent_state();
119
120 /*
121 * For QSBR flavor, when a thread needs to be in a quiescent
122 * state for a long period of time, we use rcu_thread_offline()
123 * and rcu_thread_online().
124 */
125 rcu_thread_offline();
126
127 sleep(1);
128
129 rcu_thread_online();
130
131 /*
132 * Waiting for previously called call_rcu handlers to complete
133 * before program exits, or in library destructors, is a good
134 * practice.
135 */
136 rcu_barrier();
137
138 end:
139 rcu_unregister_thread();
140 return ret;
141 }
This page took 0.043813 seconds and 4 git commands to generate.