1 // SPDX-FileCopyrightText: 2013 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
3 // SPDX-License-Identifier: MIT
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.
15 #include <urcu/urcu-memb.h> /* RCU flavor */
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 */
21 * Nodes populated into the hash table.
24 int value
; /* Node content */
25 int seqnum
; /* Our node sequence number */
26 struct cds_lfht_node node
; /* Chaining in hash table */
30 int match(struct cds_lfht_node
*ht_node
, const void *_key
)
33 caa_container_of(ht_node
, struct mynode
, node
);
34 const int *key
= _key
;
36 return *key
== node
->value
;
41 int values
[] = { -5, 42, 42, 36, 24, }; /* 42 is duplicated */
42 struct cds_lfht
*ht
; /* Hash table */
44 int ret
= 0, seqnum
= 0;
46 struct cds_lfht_iter iter
; /* For iteration on hash table */
47 struct cds_lfht_node
*ht_node
;
51 * Each thread need using RCU read-side need to be explicitly
54 urcu_memb_register_thread();
56 /* Use time as seed for hash table hashing. */
57 seed
= (uint32_t) time(NULL
);
60 * Allocate hash table.
62 ht
= cds_lfht_new_flavor(1, 1, 0,
63 CDS_LFHT_AUTO_RESIZE
| CDS_LFHT_ACCOUNTING
,
64 &urcu_memb_flavor
, NULL
);
66 printf("Error allocating hash table\n");
72 * Add nodes to hash table.
74 for (i
= 0; i
< CAA_ARRAY_SIZE(values
); i
++) {
78 node
= malloc(sizeof(*node
));
84 cds_lfht_node_init(&node
->node
);
87 node
->seqnum
= seqnum
++;
88 hash
= jhash(&value
, sizeof(value
), seed
);
91 * cds_lfht_add() needs to be called from RCU read-side
94 urcu_memb_read_lock();
95 ht_node
= cds_lfht_add_unique(ht
, hash
, match
, &value
,
98 * cds_lfht_add_unique() returns the added node if not
99 * already present, else returns the node matching the
102 if (ht_node
!= &node
->node
) {
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.
110 printf("Not adding duplicate (key: %d, seqnum: %d)\n",
111 node
->value
, node
->seqnum
);
114 printf("Add (key: %d, seqnum: %d)\n",
115 node
->value
, node
->seqnum
);
117 urcu_memb_read_unlock();
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.
125 printf("hash table content (random order):");
126 urcu_memb_read_lock();
127 cds_lfht_for_each_entry(ht
, &iter
, node
, node
) {
128 printf(" (key: %d, seqnum: %d)",
129 node
->value
, node
->seqnum
);
131 urcu_memb_read_unlock();
135 urcu_memb_unregister_thread();
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