doc/examples/rculfhash/cds_lfht_destroy.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 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
  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         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
  37 int main(void)
  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          */
  52         urcu_memb_register_thread();
  53
  54         /* Use time as seed for hash table hashing. */
  55         seed = (uint32_t) time(NULL);
  56
  57         /*
  58          * Allocate hash table.
  59          */
  60         ht = cds_lfht_new_flavor(1, 1, 0,
  61                 CDS_LFHT_AUTO_RESIZE | CDS_LFHT_ACCOUNTING,
  62                 &urcu_memb_flavor, NULL);
  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                  */
  91                 urcu_memb_read_lock();
  92                 cds_lfht_add(ht, hash, &node->node);
  93                 urcu_memb_read_unlock();
  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):");
 102         urcu_memb_read_lock();
 103         cds_lfht_for_each_entry(ht, &iter, node, node) {
 104                 printf(" %d", node->value);
 105         }
 106         urcu_memb_read_unlock();
 107         printf("\n");
 108
 109
 110         /*
 111          * Make sure all hash table nodes are removed before destroying.
 112          */
 113         printf("removing all nodes:");
 114         urcu_memb_read_lock();
 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 {
 122                         urcu_memb_call_rcu(&node->rcu_head, free_node);
 123                 }
 124         }
 125         urcu_memb_read_unlock();
 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:
 140         urcu_memb_unregister_thread();
 141         return ret;
 142 }