68759713c44c608a19b8c5e48d3fd61c995e5595
[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/urcu-memb.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 static
37 int match(struct cds_lfht_node *ht_node, const void *_key)
38 {
39 struct mynode *node =
40 caa_container_of(ht_node, struct mynode, node);
41 const unsigned int *key = _key;
42
43 return *key == node->value;
44 }
45
46 int main(int argc, char **argv)
47 {
48 int values[] = { -5, 42, 42, 36, 24, }; /* 42 is duplicated */
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 ht_node = cds_lfht_add_unique(ht, hash, match, &value,
103 &node->node);
104 /*
105 * cds_lfht_add_unique() returns the added node if not
106 * already present, else returns the node matching the
107 * key.
108 */
109 if (ht_node != &node->node) {
110 /*
111 * We found a match. Therefore, to ensure we
112 * don't add duplicates, cds_lfht_add_unique()
113 * acted as a RCU lookup, returning the found
114 * match. It did not add the new node to the
115 * hash table, so we can free it on the spot.
116 */
117 printf("Not adding duplicate (key: %d, seqnum: %d)\n",
118 node->value, node->seqnum);
119 free(node);
120 } else {
121 printf("Add (key: %d, seqnum: %d)\n",
122 node->value, node->seqnum);
123 }
124 urcu_memb_read_unlock();
125 }
126
127 /*
128 * Iterate over each hash table node. Those will appear in
129 * random order, depending on the hash seed. Iteration needs to
130 * be performed within RCU read-side critical section.
131 */
132 printf("hash table content (random order):");
133 urcu_memb_read_lock();
134 cds_lfht_for_each_entry(ht, &iter, node, node) {
135 printf(" (key: %d, seqnum: %d)",
136 node->value, node->seqnum);
137 }
138 urcu_memb_read_unlock();
139 printf("\n");
140
141 end:
142 urcu_memb_unregister_thread();
143 return ret;
144 }
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