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1fe327be MD |
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 | ||
b9050d91 | 25 | #include <urcu/urcu-signal.h> /* Signal-based RCU flavor */ |
1fe327be MD |
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 | */ | |
b9050d91 | 76 | urcu_signal_register_thread(); |
1fe327be MD |
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 | */ | |
b9050d91 | 93 | urcu_signal_read_lock(); |
1fe327be MD |
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 | } | |
b9050d91 | 101 | urcu_signal_read_unlock(); |
1fe327be MD |
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); | |
238eb13d MD |
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 | */ | |
b9050d91 | 115 | urcu_signal_call_rcu(&node->rcu_head, rcu_free_node); |
1fe327be MD |
116 | } |
117 | ||
d7818a6f MD |
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 | */ | |
b9050d91 | 125 | urcu_signal_synchronize_rcu(); |
d7818a6f | 126 | |
1fe327be MD |
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 | */ | |
b9050d91 | 134 | urcu_signal_barrier(); |
1fe327be MD |
135 | |
136 | end: | |
b9050d91 | 137 | urcu_signal_unregister_thread(); |
1fe327be MD |
138 | return ret; |
139 | } |