doc/examples/rculfhash/cds_lfht_add_unique.c

   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 add unique nodes into a RCU lock-free hash
  14  * table. We use a "seqnum" field to show which node is staying in the
  15  * hash table. This hash table requires using a RCU scheme.
  16  */
  17
  18 #include <stdio.h>
  19 #include <stdlib.h>
  20 #include <time.h>
  21
  22 #include <urcu/urcu-memb.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         int seqnum;                     /* Our node sequence number */
  33         struct cds_lfht_node node;      /* Chaining in hash table */
  34 };
  35
  36 static
  37 int match(struct cds_lfht_node *ht_node, const void *_key)
  38 {
  39         struct mynode *node =
  40                 caa_container_of(ht_node, struct mynode, node);
  41         const unsigned int *key = _key;
  42
  43         return *key == node->value;
  44 }
  45
  46 int main(int argc, char **argv)
  47 {
  48         int values[] = { -5, 42, 42, 36, 24, }; /* 42 is duplicated */
  49         struct cds_lfht *ht;    /* Hash table */
  50         unsigned int i;
  51         int ret = 0, seqnum = 0;
  52         uint32_t seed;
  53         struct cds_lfht_iter iter;      /* For iteration on hash table */
  54         struct cds_lfht_node *ht_node;
  55         struct mynode *node;
  56
  57         /*
  58          * Each thread need using RCU read-side need to be explicitly
  59          * registered.
  60          */
  61         urcu_memb_register_thread();
  62
  63         /* Use time as seed for hash table hashing. */
  64         seed = (uint32_t) time(NULL);
  65
  66         /*
  67          * Allocate hash table.
  68          */
  69         ht = cds_lfht_new_flavor(1, 1, 0,
  70                 CDS_LFHT_AUTO_RESIZE | CDS_LFHT_ACCOUNTING,
  71                 &urcu_memb_flavor, NULL);
  72         if (!ht) {
  73                 printf("Error allocating hash table\n");
  74                 ret = -1;
  75                 goto end;
  76         }
  77
  78         /*
  79          * Add nodes to hash table.
  80          */
  81         for (i = 0; i < CAA_ARRAY_SIZE(values); i++) {
  82                 unsigned long hash;
  83                 int value;
  84
  85                 node = malloc(sizeof(*node));
  86                 if (!node) {
  87                         ret = -1;
  88                         goto end;
  89                 }
  90
  91                 cds_lfht_node_init(&node->node);
  92                 value = values[i];
  93                 node->value = value;
  94                 node->seqnum = seqnum++;
  95                 hash = jhash(&value, sizeof(value), seed);
  96
  97                 /*
  98                  * cds_lfht_add() needs to be called from RCU read-side
  99                  * critical section.
 100                  */
 101                 urcu_memb_read_lock();
 102                 ht_node = cds_lfht_add_unique(ht, hash, match, &value,
 103                         &node->node);
 104                 /*
 105                  * cds_lfht_add_unique() returns the added node if not
 106                  * already present, else returns the node matching the
 107                  * key.
 108                  */
 109                 if (ht_node != &node->node) {
 110                         /*
 111                          * We found a match. Therefore, to ensure we
 112                          * don't add duplicates, cds_lfht_add_unique()
 113                          * acted as a RCU lookup, returning the found
 114                          * match. It did not add the new node to the
 115                          * hash table, so we can free it on the spot.
 116                          */
 117                         printf("Not adding duplicate (key: %d, seqnum: %d)\n",
 118                                 node->value, node->seqnum);
 119                         free(node);
 120                 } else {
 121                         printf("Add (key: %d, seqnum: %d)\n",
 122                                 node->value, node->seqnum);
 123                 }
 124                 urcu_memb_read_unlock();
 125         }
 126
 127         /*
 128          * Iterate over each hash table node. Those will appear in
 129          * random order, depending on the hash seed. Iteration needs to
 130          * be performed within RCU read-side critical section.
 131          */
 132         printf("hash table content (random order):");
 133         urcu_memb_read_lock();
 134         cds_lfht_for_each_entry(ht, &iter, node, node) {
 135                 printf(" (key: %d, seqnum: %d)",
 136                         node->value, node->seqnum);
 137         }
 138         urcu_memb_read_unlock();
 139         printf("\n");
 140
 141 end:
 142         urcu_memb_unregister_thread();
 143         return ret;
 144 }