doc: update examples to API changes
[userspace-rcu.git] / doc / examples / urcu-flavors / signal.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 <unistd.h>
20 #include <stdlib.h>
21 #include <stdio.h>
22 #include <stdint.h>
23 #include <inttypes.h>
24
25 #include <urcu/urcu-signal.h> /* Signal-based RCU flavor */
26 #include <urcu/rculist.h> /* List example */
27 #include <urcu/compiler.h> /* For CAA_ARRAY_SIZE */
28
29 /*
30 * Example showing how to use the signal-based Userspace RCU flavor.
31 *
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
36 static CDS_LIST_HEAD(mylist);
37
38 struct 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
44 static
45 int 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
57 static
58 void 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
65 int 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 /*
73 * Each thread need using RCU read-side need to be explicitly
74 * registered.
75 */
76 urcu_signal_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
88 /*
89 * We need to explicitly mark RCU read-side critical sections
90 * with rcu_read_lock() and rcu_read_unlock(). They can be
91 * nested. Those are no-ops for the QSBR flavor.
92 */
93 urcu_signal_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 urcu_signal_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 /*
110 * call_rcu() will ensure that the handler
111 * "rcu_free_node" is executed after a grace period.
112 * call_rcu() can be called from RCU read-side critical
113 * sections.
114 */
115 urcu_signal_call_rcu(&node->rcu_head, rcu_free_node);
116 }
117
118 /*
119 * We can also wait for a quiescent state by calling
120 * synchronize_rcu() rather than using call_rcu(). It is usually
121 * a slower approach than call_rcu(), because the latter can
122 * batch work. Moreover, call_rcu() can be called from a RCU
123 * read-side critical section, but synchronize_rcu() should not.
124 */
125 urcu_signal_synchronize_rcu();
126
127 sleep(1);
128
129 /*
130 * Waiting for previously called call_rcu handlers to complete
131 * before program exits, or in library destructors, is a good
132 * practice.
133 */
134 urcu_signal_barrier();
135
136 end:
137 urcu_signal_unregister_thread();
138 return ret;
139 }
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