doc/examples/rculfhash/cds_lfht_add.c

   1 // SPDX-FileCopyrightText: 2013 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   2 //
   3 // SPDX-License-Identifier: MIT
   4
   5 /*
   6  * This example shows how to add nodes (allowing duplicate keys) into a
   7  * RCU lock-free hash table.
   8  * This hash table requires using a RCU scheme.
   9  */
  10
  11 #include <stdio.h>
  12 #include <stdlib.h>
  13 #include <time.h>
  14
  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 */
  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 };
  27
  28 int main(void)
  29 {
  30         int values[] = { -5, 42, 42, 36, 24, }; /* 42 is duplicated */
  31         struct cds_lfht *ht;    /* Hash table */
  32         unsigned int i;
  33         int ret = 0;
  34         uint32_t seed;
  35         struct cds_lfht_iter iter;      /* For iteration on hash table */
  36         struct mynode *node;
  37
  38         /*
  39          * Each thread need using RCU read-side need to be explicitly
  40          * registered.
  41          */
  42         urcu_memb_register_thread();
  43
  44         /* Use time as seed for hash table hashing. */
  45         seed = (uint32_t) time(NULL);
  46
  47         /*
  48          * Allocate hash table.
  49          */
  50         ht = cds_lfht_new_flavor(1, 1, 0,
  51                 CDS_LFHT_AUTO_RESIZE | CDS_LFHT_ACCOUNTING,
  52                 &urcu_memb_flavor, NULL);
  53         if (!ht) {
  54                 printf("Error allocating hash table\n");
  55                 ret = -1;
  56                 goto end;
  57         }
  58
  59         /*
  60          * Add nodes to hash table.
  61          */
  62         for (i = 0; i < CAA_ARRAY_SIZE(values); i++) {
  63                 unsigned long hash;
  64
  65                 node = malloc(sizeof(*node));
  66                 if (!node) {
  67                         ret = -1;
  68                         goto end;
  69                 }
  70
  71                 cds_lfht_node_init(&node->node);
  72                 node->value = values[i];
  73                 hash = jhash(&values[i], sizeof(values[i]), seed);
  74
  75                 /*
  76                  * cds_lfht_add() needs to be called from RCU read-side
  77                  * critical section.
  78                  */
  79                 urcu_memb_read_lock();
  80                 cds_lfht_add(ht, hash, &node->node);
  81                 urcu_memb_read_unlock();
  82         }
  83
  84         /*
  85          * Iterate over each hash table node. Those will appear in
  86          * random order, depending on the hash seed. Iteration needs to
  87          * be performed within RCU read-side critical section.
  88          */
  89         printf("hash table content (random order):");
  90         urcu_memb_read_lock();
  91         cds_lfht_for_each_entry(ht, &iter, node, node) {
  92                 printf(" %d", node->value);
  93         }
  94         urcu_memb_read_unlock();
  95         printf("\n");
  96 end:
  97         urcu_memb_unregister_thread();
  98         return ret;
  99 }