doc/examples/list/cds_list_del_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 remove from a linked-list safely against
  14  * concurrent RCU traversals.
  15  */
  16
  17 #include <stdio.h>
  18
  19 #include <urcu.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_rcu(&node->node, &mylist);
  60         }
  61
  62         /*
  63          * Removing all positive values. Safe against concurrent RCU
  64          * traversals, require mutual exclusion with list updates.
  65          * Notice the "safe" iteration: it is safe against removal of
  66          * nodes as we iterate on the list.
  67          */
  68         cds_list_for_each_entry_safe(node, n, &mylist, node) {
  69                 if (node->value > 0) {
  70                         cds_list_del_rcu(&node->node);
  71                         /*
  72                          * We can only reclaim memory after a grace
  73                          * period has passed after cds_list_del_rcu().
  74                          */
  75                         call_rcu(&node->rcu_head, free_node_rcu);
  76                 }
  77         }
  78
  79         /*
  80          * Just show the list content. This is _not_ an RCU-safe
  81          * iteration on the list.
  82          */
  83         printf("mylist content:");
  84         cds_list_for_each_entry(node, &mylist, node) {
  85                 printf(" %d", node->value);
  86         }
  87         printf("\n");
  88 end:
  89         return ret;
  90 }