doc/examples: signal flavor
[urcu.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 #define RCU_SIGNAL /* Signal-based RCU flavor */
26 #include <urcu.h>
27 #include <urcu/rculist.h> /* List example */
28 #include <urcu/compiler.h> /* For CAA_ARRAY_SIZE */
29
30 /*
31 * Example showing how to use the signal-based Userspace RCU flavor.
32 *
33 * This is a mock-up example where updates and RCU traversals are
34 * performed by the same thread to keep things simple on purpose.
35 */
36
37 static CDS_LIST_HEAD(mylist);
38
39 struct mynode {
40 uint64_t value;
41 struct cds_list_head node; /* linked-list chaining */
42 struct rcu_head rcu_head; /* for call_rcu() */
43 };
44
45 static
46 int add_node(uint64_t v)
47 {
48 struct mynode *node;
49
50 node = calloc(sizeof(*node), 1);
51 if (!node)
52 return -1;
53 node->value = v;
54 cds_list_add_rcu(&node->node, &mylist);
55 return 0;
56 }
57
58 static
59 void rcu_free_node(struct rcu_head *rh)
60 {
61 struct mynode *node = caa_container_of(rh, struct mynode, rcu_head);
62
63 free(node);
64 }
65
66 int main(int argc, char **argv)
67 {
68 uint64_t values[] = { 42, 36, 24, };
69 unsigned int i;
70 int ret;
71 struct mynode *node, *n;
72
73 /*
74 * Each thread need using RCU read-side need to be explicitly
75 * registered.
76 */
77 rcu_register_thread();
78
79 /*
80 * Adding nodes to the linked-list. Safe against concurrent
81 * RCU traversals, require mutual exclusion with list updates.
82 */
83 for (i = 0; i < CAA_ARRAY_SIZE(values); i++) {
84 ret = add_node(values[i]);
85 if (ret)
86 goto end;
87 }
88
89 /*
90 * We need to explicitly mark RCU read-side critical sections
91 * with rcu_read_lock() and rcu_read_unlock(). They can be
92 * nested. Those are no-ops for the QSBR flavor.
93 */
94 rcu_read_lock();
95
96 /*
97 * RCU traversal of the linked list.
98 */
99 cds_list_for_each_entry_rcu(node, &mylist, node) {
100 printf("Value: %" PRIu64 "\n", node->value);
101 }
102 rcu_read_unlock();
103
104 /*
105 * Removing nodes from linked list. Safe against concurrent RCU
106 * traversals, require mutual exclusion with list updates.
107 */
108 cds_list_for_each_entry_safe(node, n, &mylist, node) {
109 cds_list_del_rcu(&node->node);
110 call_rcu(&node->rcu_head, rcu_free_node);
111 }
112
113 sleep(1);
114
115 /*
116 * Waiting for previously called call_rcu handlers to complete
117 * before program exits, or in library destructors, is a good
118 * practice.
119 */
120 rcu_barrier();
121
122 end:
123 rcu_unregister_thread();
124 return ret;
125 }
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