19c372675706d9ea7c74775480cd1574d5cdbb50
[urcu.git] / doc / examples / rculfhash / cds_lfht_add_replace.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 nodes into a RCU lock-free hash table
14 * with cds_lfht_add_replace(), which replaces existing nodes with the
15 * same key if found.
16 * We use a "seqnum" field to show which node is staying in the hash
17 * table. This hash table requires using a RCU scheme.
18 */
19
20 #include <stdio.h>
21 #include <stdlib.h>
22 #include <time.h>
23
24 #include <urcu/urcu-memb.h> /* RCU flavor */
25 #include <urcu/rculfhash.h> /* RCU Lock-free hash table */
26 #include <urcu/compiler.h> /* For CAA_ARRAY_SIZE */
27 #include "jhash.h" /* Example hash function */
28
29 /*
30 * Nodes populated into the hash table.
31 */
32 struct mynode {
33 int value; /* Node content */
34 int seqnum; /* Our node sequence number */
35 struct cds_lfht_node node; /* Chaining in hash table */
36 struct rcu_head rcu_head; /* For call_rcu() */
37 };
38
39 static
40 int match(struct cds_lfht_node *ht_node, const void *_key)
41 {
42 struct mynode *node =
43 caa_container_of(ht_node, struct mynode, node);
44 const unsigned int *key = _key;
45
46 return *key == node->value;
47 }
48
49 static
50 void free_node(struct rcu_head *head)
51 {
52 struct mynode *node = caa_container_of(head, struct mynode, rcu_head);
53
54 free(node);
55 }
56
57 int main(int argc, char **argv)
58 {
59 int values[] = { -5, 42, 42, 36, 24, }; /* 42 is duplicated */
60 struct cds_lfht *ht; /* Hash table */
61 unsigned int i;
62 int ret = 0, seqnum = 0;
63 uint32_t seed;
64 struct cds_lfht_iter iter; /* For iteration on hash table */
65 struct cds_lfht_node *ht_node;
66 struct mynode *node;
67
68 /*
69 * Each thread need using RCU read-side need to be explicitly
70 * registered.
71 */
72 urcu_memb_register_thread();
73
74 /* Use time as seed for hash table hashing. */
75 seed = (uint32_t) time(NULL);
76
77 /*
78 * Allocate hash table.
79 */
80 ht = cds_lfht_new_flavor(1, 1, 0,
81 CDS_LFHT_AUTO_RESIZE | CDS_LFHT_ACCOUNTING,
82 &urcu_memb_flavor, NULL);
83 if (!ht) {
84 printf("Error allocating hash table\n");
85 ret = -1;
86 goto end;
87 }
88
89 /*
90 * Add nodes to hash table.
91 */
92 for (i = 0; i < CAA_ARRAY_SIZE(values); i++) {
93 unsigned long hash;
94 int value;
95
96 node = malloc(sizeof(*node));
97 if (!node) {
98 ret = -1;
99 goto end;
100 }
101
102 cds_lfht_node_init(&node->node);
103 value = values[i];
104 node->value = value;
105 node->seqnum = seqnum++;
106 hash = jhash(&value, sizeof(value), seed);
107
108 /*
109 * cds_lfht_add() needs to be called from RCU read-side
110 * critical section.
111 */
112 urcu_memb_read_lock();
113 ht_node = cds_lfht_add_replace(ht, hash, match, &value,
114 &node->node);
115 if (ht_node) {
116 struct mynode *ret_node =
117 caa_container_of(ht_node, struct mynode, node);
118
119 printf("Replaced node (key: %d, seqnum: %d) by (key: %d, seqnum: %d)\n",
120 ret_node->value, ret_node->seqnum,
121 node->value, node->seqnum);
122 urcu_memb_call_rcu(&ret_node->rcu_head, free_node);
123 } else {
124 printf("Add (key: %d, seqnum: %d)\n",
125 node->value, node->seqnum);
126 }
127 urcu_memb_read_unlock();
128 }
129
130 /*
131 * Iterate over each hash table node. Those will appear in
132 * random order, depending on the hash seed. Iteration needs to
133 * be performed within RCU read-side critical section.
134 */
135 printf("hash table content (random order):");
136 urcu_memb_read_lock();
137 cds_lfht_for_each_entry(ht, &iter, node, node) {
138 printf(" (key: %d, seqnum: %d)",
139 node->value, node->seqnum);
140 }
141 urcu_memb_read_unlock();
142 printf("\n");
143
144 end:
145 urcu_memb_unregister_thread();
146 return ret;
147 }
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