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1c87adb3 MJ |
1 | // SPDX-FileCopyrightText: 2013 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
2 | // | |
3 | // SPDX-License-Identifier: LGPL-2.1-or-later | |
1fe327be MD |
4 | |
5 | #include <unistd.h> | |
6 | #include <stdlib.h> | |
7 | #include <stdio.h> | |
8 | #include <stdint.h> | |
9 | #include <inttypes.h> | |
10 | ||
b9050d91 | 11 | #include <urcu/urcu-signal.h> /* Signal-based RCU flavor */ |
1fe327be MD |
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 signal-based Userspace RCU flavor. | |
17 | * | |
18 | * This is a mock-up example where updates and RCU traversals are | |
19 | * performed by the same thread to keep things simple on purpose. | |
20 | */ | |
21 | ||
22 | static CDS_LIST_HEAD(mylist); | |
23 | ||
24 | struct mynode { | |
25 | uint64_t value; | |
26 | struct cds_list_head node; /* linked-list chaining */ | |
27 | struct rcu_head rcu_head; /* for call_rcu() */ | |
28 | }; | |
29 | ||
30 | static | |
31 | int add_node(uint64_t v) | |
32 | { | |
33 | struct mynode *node; | |
34 | ||
35 | node = calloc(sizeof(*node), 1); | |
36 | if (!node) | |
37 | return -1; | |
38 | node->value = v; | |
39 | cds_list_add_rcu(&node->node, &mylist); | |
40 | return 0; | |
41 | } | |
42 | ||
43 | static | |
44 | void rcu_free_node(struct rcu_head *rh) | |
45 | { | |
46 | struct mynode *node = caa_container_of(rh, struct mynode, rcu_head); | |
47 | ||
48 | free(node); | |
49 | } | |
50 | ||
70469b43 | 51 | int main(void) |
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52 | { |
53 | uint64_t values[] = { 42, 36, 24, }; | |
54 | unsigned int i; | |
55 | int ret; | |
56 | struct mynode *node, *n; | |
57 | ||
58 | /* | |
59 | * Each thread need using RCU read-side need to be explicitly | |
60 | * registered. | |
61 | */ | |
b9050d91 | 62 | urcu_signal_register_thread(); |
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63 | |
64 | /* | |
65 | * Adding nodes to the linked-list. Safe against concurrent | |
66 | * RCU traversals, require mutual exclusion with list updates. | |
67 | */ | |
68 | for (i = 0; i < CAA_ARRAY_SIZE(values); i++) { | |
69 | ret = add_node(values[i]); | |
70 | if (ret) | |
71 | goto end; | |
72 | } | |
73 | ||
74 | /* | |
75 | * We need to explicitly mark RCU read-side critical sections | |
76 | * with rcu_read_lock() and rcu_read_unlock(). They can be | |
77 | * nested. Those are no-ops for the QSBR flavor. | |
78 | */ | |
b9050d91 | 79 | urcu_signal_read_lock(); |
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80 | |
81 | /* | |
82 | * RCU traversal of the linked list. | |
83 | */ | |
84 | cds_list_for_each_entry_rcu(node, &mylist, node) { | |
85 | printf("Value: %" PRIu64 "\n", node->value); | |
86 | } | |
b9050d91 | 87 | urcu_signal_read_unlock(); |
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88 | |
89 | /* | |
90 | * Removing nodes from linked list. Safe against concurrent RCU | |
91 | * traversals, require mutual exclusion with list updates. | |
92 | */ | |
93 | cds_list_for_each_entry_safe(node, n, &mylist, node) { | |
94 | cds_list_del_rcu(&node->node); | |
238eb13d MD |
95 | /* |
96 | * call_rcu() will ensure that the handler | |
97 | * "rcu_free_node" is executed after a grace period. | |
98 | * call_rcu() can be called from RCU read-side critical | |
99 | * sections. | |
100 | */ | |
b9050d91 | 101 | urcu_signal_call_rcu(&node->rcu_head, rcu_free_node); |
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102 | } |
103 | ||
d7818a6f MD |
104 | /* |
105 | * We can also wait for a quiescent state by calling | |
106 | * synchronize_rcu() rather than using call_rcu(). It is usually | |
107 | * a slower approach than call_rcu(), because the latter can | |
108 | * batch work. Moreover, call_rcu() can be called from a RCU | |
109 | * read-side critical section, but synchronize_rcu() should not. | |
110 | */ | |
b9050d91 | 111 | urcu_signal_synchronize_rcu(); |
d7818a6f | 112 | |
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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 | */ | |
b9050d91 | 120 | urcu_signal_barrier(); |
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121 | |
122 | end: | |
b9050d91 | 123 | urcu_signal_unregister_thread(); |
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124 | return ret; |
125 | } |