2 * Copyright (C) 2013 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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.
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.
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
25 #include <urcu/urcu-qsbr.h> /* QSBR RCU flavor */
26 #include <urcu/rculist.h> /* List example */
27 #include <urcu/compiler.h> /* For CAA_ARRAY_SIZE */
30 * Example showing how to use the QSBR Userspace RCU flavor.
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.
36 static CDS_LIST_HEAD(mylist
);
40 struct cds_list_head node
; /* linked-list chaining */
41 struct rcu_head rcu_head
; /* for call_rcu() */
45 int add_node(uint64_t v
)
49 node
= calloc(sizeof(*node
), 1);
53 cds_list_add_rcu(&node
->node
, &mylist
);
58 void rcu_free_node(struct rcu_head
*rh
)
60 struct mynode
*node
= caa_container_of(rh
, struct mynode
, rcu_head
);
65 int main(int argc
, char **argv
)
67 uint64_t values
[] = { 42, 36, 24, };
70 struct mynode
*node
, *n
;
73 * Each thread need using RCU read-side need to be explicitly
76 urcu_qsbr_register_thread();
79 * Adding nodes to the linked-list. Safe against concurrent
80 * RCU traversals, require mutual exclusion with list updates.
82 for (i
= 0; i
< CAA_ARRAY_SIZE(values
); i
++) {
83 ret
= add_node(values
[i
]);
89 * RCU traversal of the linked list.
91 cds_list_for_each_entry_rcu(node
, &mylist
, node
) {
92 printf("Value: %" PRIu64
"\n", node
->value
);
96 * Removing nodes from linked list. Safe against concurrent RCU
97 * traversals, require mutual exclusion with list updates.
99 cds_list_for_each_entry_safe(node
, n
, &mylist
, node
) {
100 cds_list_del_rcu(&node
->node
);
102 * call_rcu() will ensure that the handler
103 * "rcu_free_node" is executed after a grace period.
104 * call_rcu() can be called from RCU read-side critical
107 urcu_qsbr_call_rcu(&node
->rcu_head
, rcu_free_node
);
111 * For QSBR flavor, we need to explicitly announce quiescent
112 * states. Here is how it is done. This should be performed by
113 * every online registered RCU threads in the program
116 urcu_qsbr_quiescent_state();
119 * For QSBR flavor, when a thread needs to be in a quiescent
120 * state for a long period of time, we use rcu_thread_offline()
121 * and rcu_thread_online().
123 urcu_qsbr_thread_offline();
127 urcu_qsbr_thread_online();
130 * We can also wait for a quiescent state by calling
131 * synchronize_rcu() rather than using call_rcu(). It is usually
132 * a slower approach than call_rcu(), because the latter can
133 * batch work. Moreover, call_rcu() can be called from a RCU
134 * read-side critical section, but synchronize_rcu() ensures the
135 * caller thread is offline, thus acting as a quiescent state.
137 urcu_qsbr_synchronize_rcu();
140 * Waiting for previously called call_rcu handlers to complete
141 * before program exits, or in library destructors, is a good
147 urcu_qsbr_unregister_thread();
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