doc/examples/rcu-flavor-qsbr/rcu-flavor-qsbr.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 #define _LGPL_SOURCE
  20 #include <urcu-qsbr.h>
  21 #include <urcu/rculist.h>
  22 #include <urcu/compiler.h>
  23
  24 #include <stdlib.h>
  25 #include <stdio.h>
  26 #include <stdint.h>
  27 #include <inttypes.h>
  28
  29 /*
  30  * This is a mock-up example where updates and RCU traversals are
  31  * performed by the same thread to keep things simple on purpose.
  32  */
  33
  34 static CDS_LIST_HEAD(mylist);
  35
  36 struct mynode {
  37         uint64_t value;
  38         struct cds_list_head node;      /* linked-list chaining */
  39         struct rcu_head rcu_head;       /* for call_rcu() */
  40 };
  41
  42 static
  43 int add_node(uint64_t v)
  44 {
  45         struct mynode *node;
  46
  47         node = calloc(sizeof(*node), 1);
  48         if (!node)
  49                 return -1;
  50         node->value = v;
  51         cds_list_add_rcu(&node->node, &mylist);
  52         return 0;
  53 }
  54
  55 static
  56 void rcu_free_node(struct rcu_head *rh)
  57 {
  58         struct mynode *node = caa_container_of(rh, struct mynode, rcu_head);
  59
  60         free(node);
  61 }
  62
  63 int main(int argc, char **argv)
  64 {
  65         uint64_t values[] = { 42, 36, 24, };
  66         unsigned int i;
  67         int ret;
  68         struct mynode *node, *n;
  69
  70         /*
  71          * Each thread need using RCU read-side need to be explicitly
  72          * registered.
  73          */
  74         rcu_register_thread();
  75
  76         /*
  77          * Adding nodes to the linked-list. Safe against concurrent
  78          * RCU traversals, require mutual exclusion with list updates.
  79          */
  80         for (i = 0; i < CAA_ARRAY_SIZE(values); i++) {
  81                 ret = add_node(values[i]);
  82                 if (ret)
  83                         goto end;
  84         }
  85
  86         /*
  87          * For all RCU flavors except QSBR, we need to explicitly mark
  88          * RCU read-side critical sections with rcu_read_lock() and
  89          * rcu_read_unlock(). They can be nested. Those are no-ops for
  90          * the QSBR flavor.
  91          */
  92         rcu_read_lock();
  93
  94         /*
  95          * RCU traversal of the linked list.
  96          */
  97         cds_list_for_each_entry_rcu(node, &mylist, node) {
  98                 printf("Value: %" PRIu64 "\n", node->value);
  99         }
 100         rcu_read_unlock();
 101
 102         /*
 103          * Removing nodes from linked list. Safe against concurrent RCU
 104          * traversals, require mutual exclusion with list updates.
 105          */
 106         cds_list_for_each_entry_safe(node, n, &mylist, node) {
 107                 cds_list_del_rcu(&node->node);
 108                 call_rcu(&node->rcu_head, rcu_free_node);
 109         }
 110
 111         /*
 112          * For QSBR flavor, we need to explicitly announce quiescent
 113          * states.
 114          */
 115         rcu_quiescent_state();
 116
 117         /*
 118          * For QSBR flavor, when a thread needs to be in a quiescent
 119          * state for a long period of time, we use rcu_thread_offline()
 120          * and rcu_thread_online().
 121          */
 122         rcu_thread_offline();
 123
 124         sleep(1);
 125
 126         rcu_thread_online();
 127
 128         /*
 129          * Waiting for previously called call_rcu handlers to complete
 130          * before program exits is a good practice.
 131          */
 132         rcu_barrier();
 133
 134 end:
 135         rcu_unregister_thread();
 136         return ret;
 137 }