1 // SPDX-FileCopyrightText: 2013 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
3 // SPDX-License-Identifier: LGPL-2.1-or-later
11 #include <urcu/urcu-qsbr.h> /* QSBR RCU flavor */
12 #include <urcu/rculist.h> /* List example */
13 #include <urcu/compiler.h> /* For CAA_ARRAY_SIZE */
16 * Example showing how to use the QSBR Userspace RCU flavor.
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.
22 static CDS_LIST_HEAD(mylist
);
26 struct cds_list_head node
; /* linked-list chaining */
27 struct rcu_head rcu_head
; /* for call_rcu() */
31 int add_node(uint64_t v
)
35 node
= calloc(sizeof(*node
), 1);
39 cds_list_add_rcu(&node
->node
, &mylist
);
44 void rcu_free_node(struct rcu_head
*rh
)
46 struct mynode
*node
= caa_container_of(rh
, struct mynode
, rcu_head
);
53 uint64_t values
[] = { 42, 36, 24, };
56 struct mynode
*node
, *n
;
59 * Each thread need using RCU read-side need to be explicitly
62 urcu_qsbr_register_thread();
65 * Adding nodes to the linked-list. Safe against concurrent
66 * RCU traversals, require mutual exclusion with list updates.
68 for (i
= 0; i
< CAA_ARRAY_SIZE(values
); i
++) {
69 ret
= add_node(values
[i
]);
75 * RCU traversal of the linked list.
77 cds_list_for_each_entry_rcu(node
, &mylist
, node
) {
78 printf("Value: %" PRIu64
"\n", node
->value
);
82 * Removing nodes from linked list. Safe against concurrent RCU
83 * traversals, require mutual exclusion with list updates.
85 cds_list_for_each_entry_safe(node
, n
, &mylist
, node
) {
86 cds_list_del_rcu(&node
->node
);
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
93 urcu_qsbr_call_rcu(&node
->rcu_head
, rcu_free_node
);
97 * For QSBR flavor, we need to explicitly announce quiescent
98 * states. Here is how it is done. This should be performed by
99 * every online registered RCU threads in the program
102 urcu_qsbr_quiescent_state();
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().
109 urcu_qsbr_thread_offline();
113 urcu_qsbr_thread_online();
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.
123 urcu_qsbr_synchronize_rcu();
126 * Waiting for previously called call_rcu handlers to complete
127 * before program exits, or in library destructors, is a good
133 urcu_qsbr_unregister_thread();
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