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94450481 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 | ||
25 | #define RCU_MB /* Memory barrier 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 memory-barrier-based Userspace RCU | |
32 | * flavor. | |
33 | * | |
34 | * This is a mock-up example where updates and RCU traversals are | |
35 | * performed by the same thread to keep things simple on purpose. | |
36 | */ | |
37 | ||
38 | static CDS_LIST_HEAD(mylist); | |
39 | ||
40 | struct mynode { | |
41 | uint64_t value; | |
42 | struct cds_list_head node; /* linked-list chaining */ | |
43 | struct rcu_head rcu_head; /* for call_rcu() */ | |
44 | }; | |
45 | ||
46 | static | |
47 | int add_node(uint64_t v) | |
48 | { | |
49 | struct mynode *node; | |
50 | ||
51 | node = calloc(sizeof(*node), 1); | |
52 | if (!node) | |
53 | return -1; | |
54 | node->value = v; | |
55 | cds_list_add_rcu(&node->node, &mylist); | |
56 | return 0; | |
57 | } | |
58 | ||
59 | static | |
60 | void rcu_free_node(struct rcu_head *rh) | |
61 | { | |
62 | struct mynode *node = caa_container_of(rh, struct mynode, rcu_head); | |
63 | ||
64 | free(node); | |
65 | } | |
66 | ||
67 | int main(int argc, char **argv) | |
68 | { | |
69 | uint64_t values[] = { 42, 36, 24, }; | |
70 | unsigned int i; | |
71 | int ret; | |
72 | struct mynode *node, *n; | |
73 | ||
74 | /* | |
75 | * Each thread need using RCU read-side need to be explicitly | |
76 | * registered. | |
77 | */ | |
78 | rcu_register_thread(); | |
79 | ||
80 | /* | |
81 | * Adding nodes to the linked-list. Safe against concurrent | |
82 | * RCU traversals, require mutual exclusion with list updates. | |
83 | */ | |
84 | for (i = 0; i < CAA_ARRAY_SIZE(values); i++) { | |
85 | ret = add_node(values[i]); | |
86 | if (ret) | |
87 | goto end; | |
88 | } | |
89 | ||
90 | /* | |
91 | * We need to explicitly mark RCU read-side critical sections | |
92 | * with rcu_read_lock() and rcu_read_unlock(). They can be | |
93 | * nested. Those are no-ops for the QSBR flavor. | |
94 | */ | |
95 | rcu_read_lock(); | |
96 | ||
97 | /* | |
98 | * RCU traversal of the linked list. | |
99 | */ | |
100 | cds_list_for_each_entry_rcu(node, &mylist, node) { | |
101 | printf("Value: %" PRIu64 "\n", node->value); | |
102 | } | |
103 | rcu_read_unlock(); | |
104 | ||
105 | /* | |
106 | * Removing nodes from linked list. Safe against concurrent RCU | |
107 | * traversals, require mutual exclusion with list updates. | |
108 | */ | |
109 | cds_list_for_each_entry_safe(node, n, &mylist, node) { | |
110 | cds_list_del_rcu(&node->node); | |
238eb13d MD |
111 | /* |
112 | * call_rcu() will ensure that the handler | |
113 | * "rcu_free_node" is executed after a grace period. | |
114 | * call_rcu() can be called from RCU read-side critical | |
115 | * sections. | |
116 | */ | |
94450481 MD |
117 | call_rcu(&node->rcu_head, rcu_free_node); |
118 | } | |
119 | ||
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120 | /* |
121 | * We can also wait for a quiescent state by calling | |
122 | * synchronize_rcu() rather than using call_rcu(). It is usually | |
123 | * a slower approach than call_rcu(), because the latter can | |
124 | * batch work. Moreover, call_rcu() can be called from a RCU | |
125 | * read-side critical section, but synchronize_rcu() should not. | |
126 | */ | |
127 | synchronize_rcu(); | |
128 | ||
94450481 MD |
129 | sleep(1); |
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 | } |