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1c87adb3 MJ |
1 | // SPDX-FileCopyrightText: 2013 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
2 | // | |
3 | // SPDX-License-Identifier: MIT | |
4 | ||
650b434b | 5 | /* |
650b434b MD |
6 | * This example shows how to add unique nodes into a RCU lock-free hash |
7 | * table. We use a "seqnum" field to show which node is staying in the | |
8 | * hash table. This hash table requires using a RCU scheme. | |
9 | */ | |
10 | ||
11 | #include <stdio.h> | |
12 | #include <stdlib.h> | |
13 | #include <time.h> | |
14 | ||
b9050d91 | 15 | #include <urcu/urcu-memb.h> /* RCU flavor */ |
650b434b MD |
16 | #include <urcu/rculfhash.h> /* RCU Lock-free hash table */ |
17 | #include <urcu/compiler.h> /* For CAA_ARRAY_SIZE */ | |
18 | #include "jhash.h" /* Example hash function */ | |
19 | ||
20 | /* | |
21 | * Nodes populated into the hash table. | |
22 | */ | |
23 | struct mynode { | |
24 | int value; /* Node content */ | |
25 | int seqnum; /* Our node sequence number */ | |
26 | struct cds_lfht_node node; /* Chaining in hash table */ | |
27 | }; | |
28 | ||
34b3f359 | 29 | static |
650b434b MD |
30 | int match(struct cds_lfht_node *ht_node, const void *_key) |
31 | { | |
32 | struct mynode *node = | |
33 | caa_container_of(ht_node, struct mynode, node); | |
83e334d0 | 34 | const int *key = _key; |
650b434b MD |
35 | |
36 | return *key == node->value; | |
37 | } | |
38 | ||
70469b43 | 39 | int main(void) |
650b434b MD |
40 | { |
41 | int values[] = { -5, 42, 42, 36, 24, }; /* 42 is duplicated */ | |
42 | struct cds_lfht *ht; /* Hash table */ | |
43 | unsigned int i; | |
44 | int ret = 0, seqnum = 0; | |
45 | uint32_t seed; | |
46 | struct cds_lfht_iter iter; /* For iteration on hash table */ | |
47 | struct cds_lfht_node *ht_node; | |
48 | struct mynode *node; | |
49 | ||
50 | /* | |
51 | * Each thread need using RCU read-side need to be explicitly | |
52 | * registered. | |
53 | */ | |
b9050d91 | 54 | urcu_memb_register_thread(); |
650b434b MD |
55 | |
56 | /* Use time as seed for hash table hashing. */ | |
57 | seed = (uint32_t) time(NULL); | |
58 | ||
59 | /* | |
60 | * Allocate hash table. | |
61 | */ | |
b9050d91 | 62 | ht = cds_lfht_new_flavor(1, 1, 0, |
650b434b | 63 | CDS_LFHT_AUTO_RESIZE | CDS_LFHT_ACCOUNTING, |
b9050d91 | 64 | &urcu_memb_flavor, NULL); |
650b434b MD |
65 | if (!ht) { |
66 | printf("Error allocating hash table\n"); | |
67 | ret = -1; | |
68 | goto end; | |
69 | } | |
70 | ||
71 | /* | |
72 | * Add nodes to hash table. | |
73 | */ | |
74 | for (i = 0; i < CAA_ARRAY_SIZE(values); i++) { | |
75 | unsigned long hash; | |
76 | int value; | |
77 | ||
78 | node = malloc(sizeof(*node)); | |
79 | if (!node) { | |
80 | ret = -1; | |
81 | goto end; | |
82 | } | |
83 | ||
84 | cds_lfht_node_init(&node->node); | |
85 | value = values[i]; | |
86 | node->value = value; | |
87 | node->seqnum = seqnum++; | |
88 | hash = jhash(&value, sizeof(value), seed); | |
89 | ||
90 | /* | |
91 | * cds_lfht_add() needs to be called from RCU read-side | |
92 | * critical section. | |
93 | */ | |
b9050d91 | 94 | urcu_memb_read_lock(); |
650b434b MD |
95 | ht_node = cds_lfht_add_unique(ht, hash, match, &value, |
96 | &node->node); | |
97 | /* | |
98 | * cds_lfht_add_unique() returns the added node if not | |
99 | * already present, else returns the node matching the | |
100 | * key. | |
101 | */ | |
102 | if (ht_node != &node->node) { | |
103 | /* | |
104 | * We found a match. Therefore, to ensure we | |
105 | * don't add duplicates, cds_lfht_add_unique() | |
106 | * acted as a RCU lookup, returning the found | |
107 | * match. It did not add the new node to the | |
108 | * hash table, so we can free it on the spot. | |
109 | */ | |
34b3f359 | 110 | printf("Not adding duplicate (key: %d, seqnum: %d)\n", |
650b434b MD |
111 | node->value, node->seqnum); |
112 | free(node); | |
113 | } else { | |
34b3f359 | 114 | printf("Add (key: %d, seqnum: %d)\n", |
650b434b MD |
115 | node->value, node->seqnum); |
116 | } | |
b9050d91 | 117 | urcu_memb_read_unlock(); |
650b434b MD |
118 | } |
119 | ||
120 | /* | |
121 | * Iterate over each hash table node. Those will appear in | |
122 | * random order, depending on the hash seed. Iteration needs to | |
123 | * be performed within RCU read-side critical section. | |
124 | */ | |
125 | printf("hash table content (random order):"); | |
b9050d91 | 126 | urcu_memb_read_lock(); |
650b434b MD |
127 | cds_lfht_for_each_entry(ht, &iter, node, node) { |
128 | printf(" (key: %d, seqnum: %d)", | |
129 | node->value, node->seqnum); | |
130 | } | |
b9050d91 | 131 | urcu_memb_read_unlock(); |
650b434b MD |
132 | printf("\n"); |
133 | ||
134 | end: | |
b9050d91 | 135 | urcu_memb_unregister_thread(); |
650b434b MD |
136 | return ret; |
137 | } |