Fix -Walloc-size
[userspace-rcu.git] / doc / examples / urcu-flavors / mb.c
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1// SPDX-FileCopyrightText: 2013 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
2//
3// SPDX-License-Identifier: LGPL-2.1-or-later
4
5#include <unistd.h>
6#include <stdlib.h>
7#include <stdio.h>
8#include <stdint.h>
9#include <inttypes.h>
10
11#include <urcu/urcu-mb.h> /* Memory barrier RCU flavor */
12#include <urcu/rculist.h> /* List example */
13#include <urcu/compiler.h> /* For CAA_ARRAY_SIZE */
14
15/*
16 * Example showing how to use the memory-barrier-based Userspace RCU
17 * flavor.
18 *
19 * This is a mock-up example where updates and RCU traversals are
20 * performed by the same thread to keep things simple on purpose.
21 */
22
23static CDS_LIST_HEAD(mylist);
24
25struct mynode {
26 uint64_t value;
27 struct cds_list_head node; /* linked-list chaining */
28 struct rcu_head rcu_head; /* for call_rcu() */
29};
30
31static
32int add_node(uint64_t v)
33{
34 struct mynode *node;
35
36 node = calloc(1, sizeof(*node));
37 if (!node)
38 return -1;
39 node->value = v;
40 cds_list_add_rcu(&node->node, &mylist);
41 return 0;
42}
43
44static
45void rcu_free_node(struct rcu_head *rh)
46{
47 struct mynode *node = caa_container_of(rh, struct mynode, rcu_head);
48
49 free(node);
50}
51
52int main(void)
53{
54 uint64_t values[] = { 42, 36, 24, };
55 unsigned int i;
56 int ret;
57 struct mynode *node, *n;
58
59 /*
60 * Each thread need using RCU read-side need to be explicitly
61 * registered.
62 */
63 urcu_mb_register_thread();
64
65 /*
66 * Adding nodes to the linked-list. Safe against concurrent
67 * RCU traversals, require mutual exclusion with list updates.
68 */
69 for (i = 0; i < CAA_ARRAY_SIZE(values); i++) {
70 ret = add_node(values[i]);
71 if (ret)
72 goto end;
73 }
74
75 /*
76 * We need to explicitly mark RCU read-side critical sections
77 * with rcu_read_lock() and rcu_read_unlock(). They can be
78 * nested. Those are no-ops for the QSBR flavor.
79 */
80 urcu_mb_read_lock();
81
82 /*
83 * RCU traversal of the linked list.
84 */
85 cds_list_for_each_entry_rcu(node, &mylist, node) {
86 printf("Value: %" PRIu64 "\n", node->value);
87 }
88 urcu_mb_read_unlock();
89
90 /*
91 * Removing nodes from linked list. Safe against concurrent RCU
92 * traversals, require mutual exclusion with list updates.
93 */
94 cds_list_for_each_entry_safe(node, n, &mylist, node) {
95 cds_list_del_rcu(&node->node);
96 /*
97 * call_rcu() will ensure that the handler
98 * "rcu_free_node" is executed after a grace period.
99 * call_rcu() can be called from RCU read-side critical
100 * sections.
101 */
102 urcu_mb_call_rcu(&node->rcu_head, rcu_free_node);
103 }
104
105 /*
106 * We can also wait for a quiescent state by calling
107 * synchronize_rcu() rather than using call_rcu(). It is usually
108 * a slower approach than call_rcu(), because the latter can
109 * batch work. Moreover, call_rcu() can be called from a RCU
110 * read-side critical section, but synchronize_rcu() should not.
111 */
112 urcu_mb_synchronize_rcu();
113
114 sleep(1);
115
116 /*
117 * Waiting for previously called call_rcu handlers to complete
118 * before program exits, or in library destructors, is a good
119 * practice.
120 */
121 urcu_mb_barrier();
122
123end:
124 urcu_mb_unregister_thread();
125 return ret;
126}
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