doc/examples/urcu-flavors/bp.c

   1 // SPDX-FileCopyrightText: 2013 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   2 //
   3 // SPDX-License-Identifier: LGPL-2.1-or-later
   4
   5 #include <unistd.h>
   6 #include <stdlib.h>
   7 #include <stdio.h>
   8 #include <stdint.h>
   9 #include <inttypes.h>
  10
  11 #include <urcu/urcu-bp.h>       /* Bulletproof RCU flavor */
  12 #include <urcu/rculist.h>       /* List example */
  13 #include <urcu/compiler.h>      /* For CAA_ARRAY_SIZE */
  14
  15 /*
  16  * Example showing how to use the Bulletproof Userspace RCU flavor.
  17  *
  18  * This is a mock-up example where updates and RCU traversals are
  19  * performed by the same thread to keep things simple on purpose.
  20  */
  21
  22 static CDS_LIST_HEAD(mylist);
  23
  24 struct mynode {
  25         uint64_t value;
  26         struct cds_list_head node;      /* linked-list chaining */
  27         struct rcu_head rcu_head;       /* for call_rcu() */
  28 };
  29
  30 static
  31 int add_node(uint64_t v)
  32 {
  33         struct mynode *node;
  34
  35         node = calloc(1, sizeof(*node));
  36         if (!node)
  37                 return -1;
  38         node->value = v;
  39         cds_list_add_rcu(&node->node, &mylist);
  40         return 0;
  41 }
  42
  43 int main(void)
  44 {
  45         uint64_t values[] = { 42, 36, 24, };
  46         unsigned int i;
  47         int ret;
  48         struct mynode *node, *n;
  49
  50         /*
  51          * Notice that with the bulletproof flavor, there is no need to
  52          * register/unregister RCU reader threads.
  53          */
  54
  55         /*
  56          * Adding nodes to the linked-list. Safe against concurrent
  57          * RCU traversals, require mutual exclusion with list updates.
  58          */
  59         for (i = 0; i < CAA_ARRAY_SIZE(values); i++) {
  60                 ret = add_node(values[i]);
  61                 if (ret)
  62                         goto end;
  63         }
  64
  65         /*
  66          * We need to explicitly mark RCU read-side critical sections
  67          * with rcu_read_lock() and rcu_read_unlock(). They can be
  68          * nested. Those are no-ops for the QSBR flavor.
  69          */
  70         urcu_bp_read_lock();
  71
  72         /*
  73          * RCU traversal of the linked list.
  74          */
  75         cds_list_for_each_entry_rcu(node, &mylist, node) {
  76                 printf("Value: %" PRIu64 "\n", node->value);
  77         }
  78         urcu_bp_read_unlock();
  79
  80         /*
  81          * Removing nodes from linked list. Safe against concurrent RCU
  82          * traversals, require mutual exclusion with list updates.
  83          */
  84         cds_list_for_each_entry_safe(node, n, &mylist, node) {
  85                 cds_list_del_rcu(&node->node);
  86
  87                 /*
  88                  * Using synchronize_rcu() directly for synchronization
  89                  * so we keep a minimal impact on the system by not
  90                  * spawning any call_rcu() thread. It is slower though,
  91                  * since there is no batching.
  92                  */
  93                 urcu_bp_synchronize_rcu();
  94                 free(node);
  95         }
  96
  97         sleep(1);
  98
  99 end:
 100         return ret;
 101 }