cleanup: use an enum for the error states of nr_cpus_mask
[urcu.git] / doc / examples / urcu-flavors / bp.c
1 // SPDX-FileCopyrightText: 2013 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
2 //
3 // SPDX-License-Identifier: LGPL-2.1-or-later
4
5 #include <unistd.h>
6 #include <stdlib.h>
7 #include <stdio.h>
8 #include <stdint.h>
9 #include <inttypes.h>
10
11 #include <urcu/urcu-bp.h> /* Bulletproof RCU flavor */
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 Bulletproof 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 int main(void)
44 {
45 uint64_t values[] = { 42, 36, 24, };
46 unsigned int i;
47 int ret;
48 struct mynode *node, *n;
49
50 /*
51 * Notice that with the bulletproof flavor, there is no need to
52 * register/unregister RCU reader threads.
53 */
54
55 /*
56 * Adding nodes to the linked-list. Safe against concurrent
57 * RCU traversals, require mutual exclusion with list updates.
58 */
59 for (i = 0; i < CAA_ARRAY_SIZE(values); i++) {
60 ret = add_node(values[i]);
61 if (ret)
62 goto end;
63 }
64
65 /*
66 * We need to explicitly mark RCU read-side critical sections
67 * with rcu_read_lock() and rcu_read_unlock(). They can be
68 * nested. Those are no-ops for the QSBR flavor.
69 */
70 urcu_bp_read_lock();
71
72 /*
73 * RCU traversal of the linked list.
74 */
75 cds_list_for_each_entry_rcu(node, &mylist, node) {
76 printf("Value: %" PRIu64 "\n", node->value);
77 }
78 urcu_bp_read_unlock();
79
80 /*
81 * Removing nodes from linked list. Safe against concurrent RCU
82 * traversals, require mutual exclusion with list updates.
83 */
84 cds_list_for_each_entry_safe(node, n, &mylist, node) {
85 cds_list_del_rcu(&node->node);
86
87 /*
88 * Using synchronize_rcu() directly for synchronization
89 * so we keep a minimal impact on the system by not
90 * spawning any call_rcu() thread. It is slower though,
91 * since there is no batching.
92 */
93 urcu_bp_synchronize_rcu();
94 free(node);
95 }
96
97 sleep(1);
98
99 end:
100 return ret;
101 }
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