doc/examples/urcu-flavors/bp.c

   1 /*
   2  * Copyright (C) 2013  Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   3  *
   4  * This library is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU Lesser General Public
   6  * License as published by the Free Software Foundation; either
   7  * version 2.1 of the License, or (at your option) any later version.
   8  *
   9  * This library is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * Lesser General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU Lesser General Public
  15  * License along with this library; if not, write to the Free Software
  16  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  17  */
  18
  19 #include <unistd.h>
  20 #include <stdlib.h>
  21 #include <stdio.h>
  22 #include <stdint.h>
  23 #include <inttypes.h>
  24
  25 #include <urcu/urcu-bp.h>       /* Bulletproof RCU flavor */
  26 #include <urcu/rculist.h>       /* List example */
  27 #include <urcu/compiler.h>      /* For CAA_ARRAY_SIZE */
  28
  29 /*
  30  * Example showing how to use the Bulletproof Userspace RCU flavor.
  31  *
  32  * This is a mock-up example where updates and RCU traversals are
  33  * performed by the same thread to keep things simple on purpose.
  34  */
  35
  36 static CDS_LIST_HEAD(mylist);
  37
  38 struct mynode {
  39         uint64_t value;
  40         struct cds_list_head node;      /* linked-list chaining */
  41         struct rcu_head rcu_head;       /* for call_rcu() */
  42 };
  43
  44 static
  45 int add_node(uint64_t v)
  46 {
  47         struct mynode *node;
  48
  49         node = calloc(sizeof(*node), 1);
  50         if (!node)
  51                 return -1;
  52         node->value = v;
  53         cds_list_add_rcu(&node->node, &mylist);
  54         return 0;
  55 }
  56
  57 int main(void)
  58 {
  59         uint64_t values[] = { 42, 36, 24, };
  60         unsigned int i;
  61         int ret;
  62         struct mynode *node, *n;
  63
  64         /*
  65          * Notice that with the bulletproof flavor, there is no need to
  66          * register/unregister RCU reader threads.
  67          */
  68
  69         /*
  70          * Adding nodes to the linked-list. Safe against concurrent
  71          * RCU traversals, require mutual exclusion with list updates.
  72          */
  73         for (i = 0; i < CAA_ARRAY_SIZE(values); i++) {
  74                 ret = add_node(values[i]);
  75                 if (ret)
  76                         goto end;
  77         }
  78
  79         /*
  80          * We need to explicitly mark RCU read-side critical sections
  81          * with rcu_read_lock() and rcu_read_unlock(). They can be
  82          * nested. Those are no-ops for the QSBR flavor.
  83          */
  84         urcu_bp_read_lock();
  85
  86         /*
  87          * RCU traversal of the linked list.
  88          */
  89         cds_list_for_each_entry_rcu(node, &mylist, node) {
  90                 printf("Value: %" PRIu64 "\n", node->value);
  91         }
  92         urcu_bp_read_unlock();
  93
  94         /*
  95          * Removing nodes from linked list. Safe against concurrent RCU
  96          * traversals, require mutual exclusion with list updates.
  97          */
  98         cds_list_for_each_entry_safe(node, n, &mylist, node) {
  99                 cds_list_del_rcu(&node->node);
 100
 101                 /*
 102                  * Using synchronize_rcu() directly for synchronization
 103                  * so we keep a minimal impact on the system by not
 104                  * spawning any call_rcu() thread. It is slower though,
 105                  * since there is no batching.
 106                  */
 107                 urcu_bp_synchronize_rcu();
 108                 free(node);
 109         }
 110
 111         sleep(1);
 112
 113 end:
 114         return ret;
 115 }