doc/examples/list/cds_list_for_each_rcu.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 do a RCU linked list traversal, safely
   7  * against concurrent RCU updates. cds_list_for_each_rcu() iterates on
   8  * struct cds_list_head, and thus, either caa_container_of() or
   9  * cds_list_entry() are needed to access the container structure.
  10  */
  11
  12 #include <stdio.h>
  13
  14 #include <urcu/urcu-memb.h>     /* Userspace RCU flavor */
  15 #include <urcu/rculist.h>       /* RCU list */
  16 #include <urcu/compiler.h>      /* For CAA_ARRAY_SIZE */
  17
  18 /*
  19  * Nodes populated into the list.
  20  */
  21 struct mynode {
  22         int value;                      /* Node content */
  23         struct cds_list_head node;      /* Linked-list chaining */
  24 };
  25
  26 int main(void)
  27 {
  28         int values[] = { -5, 42, 36, 24, };
  29         CDS_LIST_HEAD(mylist);          /* Defines an empty list head */
  30         unsigned int i;
  31         int ret = 0;
  32         struct cds_list_head *pos;
  33
  34         /*
  35          * Each thread need using RCU read-side need to be explicitly
  36          * registered.
  37          */
  38         urcu_memb_register_thread();
  39
  40         /*
  41          * Adding nodes to the linked-list. Safe against concurrent
  42          * RCU traversals, require mutual exclusion with list updates.
  43          */
  44         for (i = 0; i < CAA_ARRAY_SIZE(values); i++) {
  45                 struct mynode *node;
  46
  47                 node = malloc(sizeof(*node));
  48                 if (!node) {
  49                         ret = -1;
  50                         goto end;
  51                 }
  52                 node->value = values[i];
  53                 cds_list_add_tail_rcu(&node->node, &mylist);
  54         }
  55
  56         /*
  57          * RCU-safe iteration on the list.
  58          */
  59         printf("mylist content:");
  60
  61         /*
  62          * Surround the RCU read-side critical section with urcu_memb_read_lock()
  63          * and urcu_memb_read_unlock().
  64          */
  65         urcu_memb_read_lock();
  66
  67         /*
  68          * This traversal can be performed concurrently with RCU
  69          * updates.
  70          */
  71         cds_list_for_each_rcu(pos, &mylist) {
  72                 struct mynode *node = cds_list_entry(pos, struct mynode, node);
  73
  74                 printf(" %d", node->value);
  75         }
  76
  77         urcu_memb_read_unlock();
  78
  79         printf("\n");
  80 end:
  81         urcu_memb_unregister_thread();
  82         return ret;
  83 }