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d14301c2 MD |
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 use cds_lfht_destroy() to clear memory used | |
14 | * by a a RCU lock-free hash table. This hash table requires using a | |
15 | * RCU scheme. | |
16 | */ | |
17 | ||
18 | #include <stdio.h> | |
19 | #include <stdlib.h> | |
20 | #include <time.h> | |
21 | ||
22 | #include <urcu.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 | struct cds_lfht_node node; /* Chaining in hash table */ | |
33 | struct rcu_head rcu_head; /* For call_rcu() */ | |
34 | }; | |
35 | ||
36 | static | |
37 | void free_node(struct rcu_head *head) | |
38 | { | |
39 | struct mynode *node = caa_container_of(head, struct mynode, rcu_head); | |
40 | ||
41 | free(node); | |
42 | } | |
43 | ||
44 | int main(int argc, char **argv) | |
45 | { | |
46 | int values[] = { -5, 42, 42, 36, 24, }; /* 42 is duplicated */ | |
47 | struct cds_lfht *ht; /* Hash table */ | |
48 | unsigned int i; | |
49 | int ret = 0; | |
50 | uint32_t seed; | |
51 | struct cds_lfht_iter iter; /* For iteration on hash table */ | |
52 | struct cds_lfht_node *ht_node; | |
53 | struct mynode *node; | |
54 | ||
55 | /* | |
56 | * Each thread need using RCU read-side need to be explicitly | |
57 | * registered. | |
58 | */ | |
59 | rcu_register_thread(); | |
60 | ||
61 | /* Use time as seed for hash table hashing. */ | |
62 | seed = (uint32_t) time(NULL); | |
63 | ||
64 | /* | |
65 | * Allocate hash table. | |
66 | */ | |
67 | ht = cds_lfht_new(1, 1, 0, | |
68 | CDS_LFHT_AUTO_RESIZE | CDS_LFHT_ACCOUNTING, | |
69 | NULL); | |
70 | if (!ht) { | |
71 | printf("Error allocating hash table\n"); | |
72 | ret = -1; | |
73 | goto end; | |
74 | } | |
75 | ||
76 | /* | |
77 | * Add nodes to hash table. | |
78 | */ | |
79 | for (i = 0; i < CAA_ARRAY_SIZE(values); i++) { | |
80 | unsigned long hash; | |
81 | int value; | |
82 | ||
83 | node = malloc(sizeof(*node)); | |
84 | if (!node) { | |
85 | ret = -1; | |
86 | goto end; | |
87 | } | |
88 | ||
89 | cds_lfht_node_init(&node->node); | |
90 | value = values[i]; | |
91 | node->value = value; | |
92 | hash = jhash(&value, sizeof(value), seed); | |
93 | ||
94 | /* | |
95 | * cds_lfht_add() needs to be called from RCU read-side | |
96 | * critical section. | |
97 | */ | |
98 | rcu_read_lock(); | |
99 | cds_lfht_add(ht, hash, &node->node); | |
100 | rcu_read_unlock(); | |
101 | } | |
102 | ||
103 | /* | |
104 | * Iterate over each hash table node. Those will appear in | |
105 | * random order, depending on the hash seed. Iteration needs to | |
106 | * be performed within RCU read-side critical section. | |
107 | */ | |
108 | printf("hash table content (random order):"); | |
109 | rcu_read_lock(); | |
110 | cds_lfht_for_each_entry(ht, &iter, node, node) { | |
111 | printf(" %d", node->value); | |
112 | } | |
113 | rcu_read_unlock(); | |
114 | printf("\n"); | |
115 | ||
116 | ||
117 | /* | |
118 | * Make sure all hash table nodes are removed before destroying. | |
119 | */ | |
120 | printf("removing all nodes:"); | |
121 | rcu_read_lock(); | |
122 | cds_lfht_for_each_entry(ht, &iter, node, node) { | |
123 | ht_node = cds_lfht_iter_get_node(&iter); | |
124 | ret = cds_lfht_del(ht, ht_node); | |
125 | printf(" %d", node->value); | |
126 | if (ret) { | |
127 | printf(" (concurrently deleted)"); | |
128 | } else { | |
129 | call_rcu(&node->rcu_head, free_node); | |
130 | } | |
131 | } | |
132 | rcu_read_unlock(); | |
133 | printf("\n"); | |
134 | ||
135 | /* | |
136 | * cds_lfht_destroy() must be called from a very specific | |
137 | * context: it needs to be called from a registered RCU reader | |
138 | * thread. However, this thread should _not_ be within a RCU | |
139 | * read-side critical section. Also, it should _not_ be called | |
140 | * from a call_rcu thread. | |
141 | */ | |
142 | ret = cds_lfht_destroy(ht, NULL); | |
143 | if (ret) { | |
144 | printf("Destroying hash table failed\n"); | |
145 | } | |
146 | end: | |
147 | rcu_unregister_thread(); | |
148 | return ret; | |
149 | } |