| 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-qsbr.h> /* QSBR 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 QSBR 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 | static |
| 58 | void rcu_free_node(struct rcu_head *rh) |
| 59 | { |
| 60 | struct mynode *node = caa_container_of(rh, struct mynode, rcu_head); |
| 61 | |
| 62 | free(node); |
| 63 | } |
| 64 | |
| 65 | int main(int argc, char **argv) |
| 66 | { |
| 67 | uint64_t values[] = { 42, 36, 24, }; |
| 68 | unsigned int i; |
| 69 | int ret; |
| 70 | struct mynode *node, *n; |
| 71 | |
| 72 | /* |
| 73 | * Each thread need using RCU read-side need to be explicitly |
| 74 | * registered. |
| 75 | */ |
| 76 | urcu_qsbr_register_thread(); |
| 77 | |
| 78 | /* |
| 79 | * Adding nodes to the linked-list. Safe against concurrent |
| 80 | * RCU traversals, require mutual exclusion with list updates. |
| 81 | */ |
| 82 | for (i = 0; i < CAA_ARRAY_SIZE(values); i++) { |
| 83 | ret = add_node(values[i]); |
| 84 | if (ret) |
| 85 | goto end; |
| 86 | } |
| 87 | |
| 88 | /* |
| 89 | * RCU traversal of the linked list. |
| 90 | */ |
| 91 | cds_list_for_each_entry_rcu(node, &mylist, node) { |
| 92 | printf("Value: %" PRIu64 "\n", node->value); |
| 93 | } |
| 94 | |
| 95 | /* |
| 96 | * Removing nodes from linked list. Safe against concurrent RCU |
| 97 | * traversals, require mutual exclusion with list updates. |
| 98 | */ |
| 99 | cds_list_for_each_entry_safe(node, n, &mylist, node) { |
| 100 | cds_list_del_rcu(&node->node); |
| 101 | /* |
| 102 | * call_rcu() will ensure that the handler |
| 103 | * "rcu_free_node" is executed after a grace period. |
| 104 | * call_rcu() can be called from RCU read-side critical |
| 105 | * sections. |
| 106 | */ |
| 107 | urcu_qsbr_call_rcu(&node->rcu_head, rcu_free_node); |
| 108 | } |
| 109 | |
| 110 | /* |
| 111 | * For QSBR flavor, we need to explicitly announce quiescent |
| 112 | * states. Here is how it is done. This should be performed by |
| 113 | * every online registered RCU threads in the program |
| 114 | * periodically. |
| 115 | */ |
| 116 | urcu_qsbr_quiescent_state(); |
| 117 | |
| 118 | /* |
| 119 | * For QSBR flavor, when a thread needs to be in a quiescent |
| 120 | * state for a long period of time, we use rcu_thread_offline() |
| 121 | * and rcu_thread_online(). |
| 122 | */ |
| 123 | urcu_qsbr_thread_offline(); |
| 124 | |
| 125 | sleep(1); |
| 126 | |
| 127 | urcu_qsbr_thread_online(); |
| 128 | |
| 129 | /* |
| 130 | * We can also wait for a quiescent state by calling |
| 131 | * synchronize_rcu() rather than using call_rcu(). It is usually |
| 132 | * a slower approach than call_rcu(), because the latter can |
| 133 | * batch work. Moreover, call_rcu() can be called from a RCU |
| 134 | * read-side critical section, but synchronize_rcu() ensures the |
| 135 | * caller thread is offline, thus acting as a quiescent state. |
| 136 | */ |
| 137 | urcu_qsbr_synchronize_rcu(); |
| 138 | |
| 139 | /* |
| 140 | * Waiting for previously called call_rcu handlers to complete |
| 141 | * before program exits, or in library destructors, is a good |
| 142 | * practice. |
| 143 | */ |
| 144 | urcu_qsbr_barrier(); |
| 145 | |
| 146 | end: |
| 147 | urcu_qsbr_unregister_thread(); |
| 148 | return ret; |
| 149 | } |