Commit | Line | Data |
---|---|---|
1c87adb3 MJ |
1 | // SPDX-FileCopyrightText: 2013 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
2 | // | |
3 | // SPDX-License-Identifier: LGPL-2.1-or-later | |
8bad63a0 | 4 | |
88c3c5ba | 5 | #include <unistd.h> |
8bad63a0 MD |
6 | #include <stdlib.h> |
7 | #include <stdio.h> | |
8 | #include <stdint.h> | |
9 | #include <inttypes.h> | |
10 | ||
b9050d91 | 11 | #include <urcu/urcu-qsbr.h> /* QSBR RCU flavor */ |
71ea53b1 MD |
12 | #include <urcu/rculist.h> /* List example */ |
13 | #include <urcu/compiler.h> /* For CAA_ARRAY_SIZE */ | |
14 | ||
8bad63a0 | 15 | /* |
6df9f02d MD |
16 | * Example showing how to use the QSBR Userspace RCU flavor. |
17 | * | |
8bad63a0 MD |
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 | ||
81270292 | 35 | node = calloc(1, sizeof(*node)); |
8bad63a0 MD |
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) |
8bad63a0 MD |
52 | { |
53 | uint64_t values[] = { 42, 36, 24, }; | |
54 | unsigned int i; | |
55 | int ret; | |
56 | struct mynode *node, *n; | |
57 | ||
58 | /* | |
8fd9af4a | 59 | * Each thread need using RCU read-side need to be explicitly |
8bad63a0 MD |
60 | * registered. |
61 | */ | |
b9050d91 | 62 | urcu_qsbr_register_thread(); |
8bad63a0 MD |
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 | ||
8bad63a0 MD |
74 | /* |
75 | * RCU traversal of the linked list. | |
76 | */ | |
77 | cds_list_for_each_entry_rcu(node, &mylist, node) { | |
78 | printf("Value: %" PRIu64 "\n", node->value); | |
79 | } | |
8bad63a0 MD |
80 | |
81 | /* | |
82 | * Removing nodes from linked list. Safe against concurrent RCU | |
83 | * traversals, require mutual exclusion with list updates. | |
84 | */ | |
85 | cds_list_for_each_entry_safe(node, n, &mylist, node) { | |
86 | cds_list_del_rcu(&node->node); | |
238eb13d MD |
87 | /* |
88 | * call_rcu() will ensure that the handler | |
89 | * "rcu_free_node" is executed after a grace period. | |
90 | * call_rcu() can be called from RCU read-side critical | |
91 | * sections. | |
92 | */ | |
b9050d91 | 93 | urcu_qsbr_call_rcu(&node->rcu_head, rcu_free_node); |
8bad63a0 MD |
94 | } |
95 | ||
96 | /* | |
97 | * For QSBR flavor, we need to explicitly announce quiescent | |
71ea53b1 MD |
98 | * states. Here is how it is done. This should be performed by |
99 | * every online registered RCU threads in the program | |
100 | * periodically. | |
8bad63a0 | 101 | */ |
b9050d91 | 102 | urcu_qsbr_quiescent_state(); |
8bad63a0 MD |
103 | |
104 | /* | |
105 | * For QSBR flavor, when a thread needs to be in a quiescent | |
106 | * state for a long period of time, we use rcu_thread_offline() | |
107 | * and rcu_thread_online(). | |
108 | */ | |
b9050d91 | 109 | urcu_qsbr_thread_offline(); |
8bad63a0 MD |
110 | |
111 | sleep(1); | |
112 | ||
b9050d91 | 113 | urcu_qsbr_thread_online(); |
8bad63a0 | 114 | |
d7818a6f MD |
115 | /* |
116 | * We can also wait for a quiescent state by calling | |
117 | * synchronize_rcu() rather than using call_rcu(). It is usually | |
118 | * a slower approach than call_rcu(), because the latter can | |
119 | * batch work. Moreover, call_rcu() can be called from a RCU | |
120 | * read-side critical section, but synchronize_rcu() ensures the | |
121 | * caller thread is offline, thus acting as a quiescent state. | |
122 | */ | |
b9050d91 | 123 | urcu_qsbr_synchronize_rcu(); |
d7818a6f | 124 | |
8bad63a0 MD |
125 | /* |
126 | * Waiting for previously called call_rcu handlers to complete | |
71ea53b1 MD |
127 | * before program exits, or in library destructors, is a good |
128 | * practice. | |
8bad63a0 | 129 | */ |
b9050d91 | 130 | urcu_qsbr_barrier(); |
8bad63a0 MD |
131 | |
132 | end: | |
b9050d91 | 133 | urcu_qsbr_unregister_thread(); |
8bad63a0 MD |
134 | return ret; |
135 | } |