doc/examples/list/cds_list_replace_rcu.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 replace a node within a linked-list safely
  14  * against concurrent RCU traversals.
  15  */
  16
  17 #include <stdio.h>
  18
  19 #include <urcu/urcu-memb.h>     /* Userspace RCU flavor */
  20 #include <urcu/rculist.h>       /* RCU list */
  21 #include <urcu/compiler.h>      /* For CAA_ARRAY_SIZE */
  22
  23 /*
  24  * Nodes populated into the list.
  25  */
  26 struct mynode {
  27         int value;                      /* Node content */
  28         struct cds_list_head node;      /* Linked-list chaining */
  29         struct rcu_head rcu_head;       /* For call_rcu() */
  30 };
  31
  32 static
  33 void free_node_rcu(struct rcu_head *head)
  34 {
  35         struct mynode *node = caa_container_of(head, struct mynode, rcu_head);
  36
  37         free(node);
  38 }
  39
  40 int main(int argc, char **argv)
  41 {
  42         int values[] = { -5, 42, 36, 24, };
  43         CDS_LIST_HEAD(mylist);          /* Defines an empty list head */
  44         unsigned int i;
  45         int ret = 0;
  46         struct mynode *node, *n;
  47
  48         /*
  49          * Adding nodes to the linked-list. Safe against concurrent
  50          * RCU traversals, require mutual exclusion with list updates.
  51          */
  52         for (i = 0; i < CAA_ARRAY_SIZE(values); i++) {
  53                 node = malloc(sizeof(*node));
  54                 if (!node) {
  55                         ret = -1;
  56                         goto end;
  57                 }
  58                 node->value = values[i];
  59                 cds_list_add_tail_rcu(&node->node, &mylist);
  60         }
  61
  62         /*
  63          * Replacing all values by their negated value. Safe against
  64          * concurrent RCU traversals, require mutual exclusion with list
  65          * updates. Notice the "safe" iteration: it is safe against
  66          * removal (and thus replacement) of nodes as we iterate on the
  67          * list.
  68          */
  69         cds_list_for_each_entry_safe(node, n, &mylist, node) {
  70                 struct mynode *new_node;
  71
  72                 new_node = malloc(sizeof(*node));
  73                 if (!new_node) {
  74                         ret = -1;
  75                         goto end;
  76                 }
  77                 /* Replacement node value is negated original value. */
  78                 new_node->value = -node->value;
  79                 cds_list_replace_rcu(&node->node, &new_node->node);
  80                 urcu_memb_call_rcu(&node->rcu_head, free_node_rcu);
  81         }
  82
  83         /*
  84          * Just show the list content. This is _not_ an RCU-safe
  85          * iteration on the list.
  86          */
  87         printf("mylist content:");
  88         cds_list_for_each_entry(node, &mylist, node) {
  89                 printf(" %d", node->value);
  90         }
  91         printf("\n");
  92 end:
  93         return ret;
  94 }