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1c87adb3 MJ |
1 | // SPDX-FileCopyrightText: 2013 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
2 | // | |
3 | // SPDX-License-Identifier: MIT | |
4 | ||
d14301c2 | 5 | /* |
d14301c2 MD |
6 | * This example shows how to use cds_lfht_destroy() to clear memory used |
7 | * by a a RCU lock-free hash table. This hash table requires using a | |
8 | * 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 */ |
d14301c2 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 | struct cds_lfht_node node; /* Chaining in hash table */ | |
26 | struct rcu_head rcu_head; /* For call_rcu() */ | |
27 | }; | |
28 | ||
29 | static | |
30 | void free_node(struct rcu_head *head) | |
31 | { | |
32 | struct mynode *node = caa_container_of(head, struct mynode, rcu_head); | |
33 | ||
34 | free(node); | |
35 | } | |
36 | ||
70469b43 | 37 | int main(void) |
d14301c2 MD |
38 | { |
39 | int values[] = { -5, 42, 42, 36, 24, }; /* 42 is duplicated */ | |
40 | struct cds_lfht *ht; /* Hash table */ | |
41 | unsigned int i; | |
42 | int ret = 0; | |
43 | uint32_t seed; | |
44 | struct cds_lfht_iter iter; /* For iteration on hash table */ | |
45 | struct cds_lfht_node *ht_node; | |
46 | struct mynode *node; | |
47 | ||
48 | /* | |
49 | * Each thread need using RCU read-side need to be explicitly | |
50 | * registered. | |
51 | */ | |
b9050d91 | 52 | urcu_memb_register_thread(); |
d14301c2 MD |
53 | |
54 | /* Use time as seed for hash table hashing. */ | |
55 | seed = (uint32_t) time(NULL); | |
56 | ||
57 | /* | |
58 | * Allocate hash table. | |
59 | */ | |
b9050d91 | 60 | ht = cds_lfht_new_flavor(1, 1, 0, |
d14301c2 | 61 | CDS_LFHT_AUTO_RESIZE | CDS_LFHT_ACCOUNTING, |
b9050d91 | 62 | &urcu_memb_flavor, NULL); |
d14301c2 MD |
63 | if (!ht) { |
64 | printf("Error allocating hash table\n"); | |
65 | ret = -1; | |
66 | goto end; | |
67 | } | |
68 | ||
69 | /* | |
70 | * Add nodes to hash table. | |
71 | */ | |
72 | for (i = 0; i < CAA_ARRAY_SIZE(values); i++) { | |
73 | unsigned long hash; | |
74 | int value; | |
75 | ||
76 | node = malloc(sizeof(*node)); | |
77 | if (!node) { | |
78 | ret = -1; | |
79 | goto end; | |
80 | } | |
81 | ||
82 | cds_lfht_node_init(&node->node); | |
83 | value = values[i]; | |
84 | node->value = value; | |
85 | hash = jhash(&value, sizeof(value), seed); | |
86 | ||
87 | /* | |
88 | * cds_lfht_add() needs to be called from RCU read-side | |
89 | * critical section. | |
90 | */ | |
b9050d91 | 91 | urcu_memb_read_lock(); |
d14301c2 | 92 | cds_lfht_add(ht, hash, &node->node); |
b9050d91 | 93 | urcu_memb_read_unlock(); |
d14301c2 MD |
94 | } |
95 | ||
96 | /* | |
97 | * Iterate over each hash table node. Those will appear in | |
98 | * random order, depending on the hash seed. Iteration needs to | |
99 | * be performed within RCU read-side critical section. | |
100 | */ | |
101 | printf("hash table content (random order):"); | |
b9050d91 | 102 | urcu_memb_read_lock(); |
d14301c2 MD |
103 | cds_lfht_for_each_entry(ht, &iter, node, node) { |
104 | printf(" %d", node->value); | |
105 | } | |
b9050d91 | 106 | urcu_memb_read_unlock(); |
d14301c2 MD |
107 | printf("\n"); |
108 | ||
109 | ||
110 | /* | |
111 | * Make sure all hash table nodes are removed before destroying. | |
112 | */ | |
113 | printf("removing all nodes:"); | |
b9050d91 | 114 | urcu_memb_read_lock(); |
d14301c2 MD |
115 | cds_lfht_for_each_entry(ht, &iter, node, node) { |
116 | ht_node = cds_lfht_iter_get_node(&iter); | |
117 | ret = cds_lfht_del(ht, ht_node); | |
118 | printf(" %d", node->value); | |
119 | if (ret) { | |
120 | printf(" (concurrently deleted)"); | |
121 | } else { | |
b9050d91 | 122 | urcu_memb_call_rcu(&node->rcu_head, free_node); |
d14301c2 MD |
123 | } |
124 | } | |
b9050d91 | 125 | urcu_memb_read_unlock(); |
d14301c2 MD |
126 | printf("\n"); |
127 | ||
128 | /* | |
129 | * cds_lfht_destroy() must be called from a very specific | |
130 | * context: it needs to be called from a registered RCU reader | |
131 | * thread. However, this thread should _not_ be within a RCU | |
132 | * read-side critical section. Also, it should _not_ be called | |
133 | * from a call_rcu thread. | |
134 | */ | |
135 | ret = cds_lfht_destroy(ht, NULL); | |
136 | if (ret) { | |
137 | printf("Destroying hash table failed\n"); | |
138 | } | |
139 | end: | |
b9050d91 | 140 | urcu_memb_unregister_thread(); |
d14301c2 MD |
141 | return ret; |
142 | } |