053e6dd9079a0fd090a8c25704d79e58b82bd72b
[urcu.git] / doc / examples / rculfhash / cds_lfht_lookup.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 lookup keys within a RCU lock-free hash
14 * table. This hash table requires using a RCU scheme.
15 */
16
17 #include <stdio.h>
18 #include <stdlib.h>
19 #include <time.h>
20
21 #include <urcu/urcu-memb.h> /* RCU flavor */
22 #include <urcu/rculfhash.h> /* RCU Lock-free hash table */
23 #include <urcu/compiler.h> /* For CAA_ARRAY_SIZE */
24 #include "jhash.h" /* Example hash function */
25
26 /*
27 * Nodes populated into the hash table.
28 */
29 struct mynode {
30 int value; /* Node content */
31 int seqnum; /* Our node sequence number */
32 struct cds_lfht_node node; /* Chaining in hash table */
33 };
34
35 static
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 int lookup_values[] = { 42, 200, 36, };
49 struct cds_lfht *ht; /* Hash table */
50 unsigned int i;
51 int ret = 0, seqnum = 0;
52 uint32_t seed;
53 struct cds_lfht_iter iter; /* For iteration on hash table */
54 struct cds_lfht_node *ht_node;
55 struct mynode *node;
56
57 /*
58 * Each thread need using RCU read-side need to be explicitly
59 * registered.
60 */
61 urcu_memb_register_thread();
62
63 /* Use time as seed for hash table hashing. */
64 seed = (uint32_t) time(NULL);
65
66 /*
67 * Allocate hash table.
68 */
69 ht = cds_lfht_new_flavor(1, 1, 0,
70 CDS_LFHT_AUTO_RESIZE | CDS_LFHT_ACCOUNTING,
71 &urcu_memb_flavor, NULL);
72 if (!ht) {
73 printf("Error allocating hash table\n");
74 ret = -1;
75 goto end;
76 }
77
78 /*
79 * Add nodes to hash table.
80 */
81 for (i = 0; i < CAA_ARRAY_SIZE(values); i++) {
82 unsigned long hash;
83 int value;
84
85 node = malloc(sizeof(*node));
86 if (!node) {
87 ret = -1;
88 goto end;
89 }
90
91 cds_lfht_node_init(&node->node);
92 value = values[i];
93 node->value = value;
94 node->seqnum = seqnum++;
95 hash = jhash(&value, sizeof(value), seed);
96
97 /*
98 * cds_lfht_add() needs to be called from RCU read-side
99 * critical section.
100 */
101 urcu_memb_read_lock();
102 cds_lfht_add(ht, hash, &node->node);
103 printf("Add (key: %d, seqnum: %d)\n",
104 node->value, node->seqnum);
105 urcu_memb_read_unlock();
106 }
107
108 /*
109 * Iterate over each hash table node. Those will appear in
110 * random order, depending on the hash seed. Iteration needs to
111 * be performed within RCU read-side critical section.
112 */
113 printf("hash table content (random order):");
114 urcu_memb_read_lock();
115 cds_lfht_for_each_entry(ht, &iter, node, node) {
116 printf(" (key: %d, seqnum: %d)",
117 node->value, node->seqnum);
118 }
119 urcu_memb_read_unlock();
120 printf("\n");
121
122 /*
123 * Lookup queries. Note that which node (seqnum) within
124 * duplicates will be found by lookup is random.
125 */
126 printf("Lookups:\n");
127 for (i = 0; i < CAA_ARRAY_SIZE(lookup_values); i++) {
128 int value = lookup_values[i];
129 unsigned long hash = jhash(&value, sizeof(value), seed);
130
131 urcu_memb_read_lock();
132 cds_lfht_lookup(ht, hash, match, &value, &iter);
133 ht_node = cds_lfht_iter_get_node(&iter);
134 if (!ht_node) {
135 printf("Key %d not found\n", value);
136 } else {
137 node = caa_container_of(ht_node, struct mynode, node);
138 printf("(key %d, seqnum %d) found\n",
139 node->value, node->seqnum);
140 }
141 urcu_memb_read_unlock();
142 }
143
144 end:
145 urcu_memb_unregister_thread();
146 return ret;
147 }
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