doc/examples/list/cds_list_for_each_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 to a RCU linked list traversal, safely
  14  * against concurrent RCU updates. cds_list_for_each_rcu() iterates on
  15  * struct cds_list_head, and thus, either caa_container_of() or
  16  * cds_list_entry() are needed to access the container structure.
  17  */
  18
  19 #include <stdio.h>
  20
  21 #include <urcu.h>               /* Userspace RCU flavor */
  22 #include <urcu/rculist.h>       /* RCU list */
  23 #include <urcu/compiler.h>      /* For CAA_ARRAY_SIZE */
  24
  25 /*
  26  * Nodes populated into the list.
  27  */
  28 struct mynode {
  29         int value;                      /* Node content */
  30         struct cds_list_head node;      /* Linked-list chaining */
  31 };
  32
  33 int main(int argc, char **argv)
  34 {
  35         int values[] = { -5, 42, 36, 24, };
  36         CDS_LIST_HEAD(mylist);          /* Defines an empty list head */
  37         unsigned int i;
  38         int ret = 0;
  39         struct cds_list_head *pos;
  40
  41         /*
  42          * Each thread need using RCU read-side need to be explicitely
  43          * registered.
  44          */
  45         rcu_register_thread();
  46
  47         /*
  48          * Adding nodes to the linked-list. Safe against concurrent
  49          * RCU traversals, require mutual exclusion with list updates.
  50          */
  51         for (i = 0; i < CAA_ARRAY_SIZE(values); i++) {
  52                 struct mynode *node;
  53
  54                 node = malloc(sizeof(*node));
  55                 if (!node) {
  56                         ret = -1;
  57                         goto end;
  58                 }
  59                 node->value = values[i];
  60                 cds_list_add_tail_rcu(&node->node, &mylist);
  61         }
  62
  63         /*
  64          * RCU-safe iteration on the list.
  65          */
  66         printf("mylist content:");
  67
  68         /*
  69          * Surround the RCU read-side critical section with rcu_read_lock()
  70          * and rcu_read_unlock().
  71          */
  72         rcu_read_lock();
  73
  74         /*
  75          * This traversal can be performed concurrently with RCU
  76          * updates.
  77          */
  78         cds_list_for_each_rcu(pos, &mylist) {
  79                 struct mynode *node = cds_list_entry(pos, struct mynode, node);
  80
  81                 printf(" %d", node->value);
  82         }
  83
  84         rcu_read_unlock();
  85
  86         printf("\n");
  87 end:
  88         rcu_unregister_thread();
  89         return ret;
  90 }