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-signal.h> /* Signal-based 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 signal-based 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_signal_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 * 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.
93 urcu_signal_read_lock();
96 * RCU traversal of the linked list.
98 cds_list_for_each_entry_rcu(node
, &mylist
, node
) {
99 printf("Value: %" PRIu64
"\n", node
->value
);
101 urcu_signal_read_unlock();
104 * Removing nodes from linked list. Safe against concurrent RCU
105 * traversals, require mutual exclusion with list updates.
107 cds_list_for_each_entry_safe(node
, n
, &mylist
, node
) {
108 cds_list_del_rcu(&node
->node
);
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
115 urcu_signal_call_rcu(&node
->rcu_head
, rcu_free_node
);
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.
125 urcu_signal_synchronize_rcu();
130 * Waiting for previously called call_rcu handlers to complete
131 * before program exits, or in library destructors, is a good
134 urcu_signal_barrier();
137 urcu_signal_unregister_thread();
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