ec594c803961b8b12ff5c328a33d50192d96ede6
[urcu.git] / doc / examples / rculfhash / cds_lfht_add_unique.c
1 /*
2 * Copyright (C) 2013 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
3 *
4 * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
5 * OR IMPLIED. ANY USE IS AT YOUR OWN RISK.
6 *
7 * Permission is hereby granted to use or copy this program for any
8 * purpose, provided the above notices are retained on all copies.
9 * Permission to modify the code and to distribute modified code is
10 * granted, provided the above notices are retained, and a notice that
11 * the code was modified is included with the above copyright notice.
12 *
13 * This example shows how to add unique nodes into a RCU lock-free hash
14 * table. We use a "seqnum" field to show which node is staying in the
15 * hash table. This hash table requires using a RCU scheme.
16 */
17
18 #include <stdio.h>
19 #include <stdlib.h>
20 #include <time.h>
21
22 #include <urcu.h> /* RCU flavor */
23 #include <urcu/rculfhash.h> /* RCU Lock-free hash table */
24 #include <urcu/compiler.h> /* For CAA_ARRAY_SIZE */
25 #include "jhash.h" /* Example hash function */
26
27 /*
28 * Nodes populated into the hash table.
29 */
30 struct mynode {
31 int value; /* Node content */
32 int seqnum; /* Our node sequence number */
33 struct cds_lfht_node node; /* Chaining in hash table */
34 };
35
36 int match(struct cds_lfht_node *ht_node, const void *_key)
37 {
38 struct mynode *node =
39 caa_container_of(ht_node, struct mynode, node);
40 const unsigned int *key = _key;
41
42 return *key == node->value;
43 }
44
45 int main(int argc, char **argv)
46 {
47 int values[] = { -5, 42, 42, 36, 24, }; /* 42 is duplicated */
48 struct cds_lfht *ht; /* Hash table */
49 unsigned int i;
50 int ret = 0, seqnum = 0;
51 uint32_t seed;
52 struct cds_lfht_iter iter; /* For iteration on hash table */
53 struct cds_lfht_node *ht_node;
54 struct mynode *node;
55
56 /*
57 * Each thread need using RCU read-side need to be explicitly
58 * registered.
59 */
60 rcu_register_thread();
61
62 /* Use time as seed for hash table hashing. */
63 seed = (uint32_t) time(NULL);
64
65 /*
66 * Allocate hash table.
67 */
68 ht = cds_lfht_new(1, 1, 0,
69 CDS_LFHT_AUTO_RESIZE | CDS_LFHT_ACCOUNTING,
70 NULL);
71 if (!ht) {
72 printf("Error allocating hash table\n");
73 ret = -1;
74 goto end;
75 }
76
77 /*
78 * Add nodes to hash table.
79 */
80 for (i = 0; i < CAA_ARRAY_SIZE(values); i++) {
81 unsigned long hash;
82 int value;
83
84 node = malloc(sizeof(*node));
85 if (!node) {
86 ret = -1;
87 goto end;
88 }
89
90 cds_lfht_node_init(&node->node);
91 value = values[i];
92 node->value = value;
93 node->seqnum = seqnum++;
94 hash = jhash(&value, sizeof(value), seed);
95
96 /*
97 * cds_lfht_add() needs to be called from RCU read-side
98 * critical section.
99 */
100 rcu_read_lock();
101 ht_node = cds_lfht_add_unique(ht, hash, match, &value,
102 &node->node);
103 /*
104 * cds_lfht_add_unique() returns the added node if not
105 * already present, else returns the node matching the
106 * key.
107 */
108 if (ht_node != &node->node) {
109 /*
110 * We found a match. Therefore, to ensure we
111 * don't add duplicates, cds_lfht_add_unique()
112 * acted as a RCU lookup, returning the found
113 * match. It did not add the new node to the
114 * hash table, so we can free it on the spot.
115 */
116 printf("Not adding duplicate key: %d, seqnum: %d\n",
117 node->value, node->seqnum);
118 free(node);
119 } else {
120 printf("Add key: %d, seqnum: %d\n",
121 node->value, node->seqnum);
122 }
123 rcu_read_unlock();
124 }
125
126 /*
127 * Iterate over each hash table node. Those will appear in
128 * random order, depending on the hash seed. Iteration needs to
129 * be performed within RCU read-side critical section.
130 */
131 printf("hash table content (random order):");
132 rcu_read_lock();
133 cds_lfht_for_each_entry(ht, &iter, node, node) {
134 printf(" (key: %d, seqnum: %d)",
135 node->value, node->seqnum);
136 }
137 rcu_read_unlock();
138 printf("\n");
139
140 end:
141 rcu_unregister_thread();
142 return ret;
143 }
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