| 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.h> /* Default: sys_membarrier() 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 sys_membarrier()-based Userspace RCU |
| 31 | * flavor. |
| 32 | * |
| 33 | * This is a mock-up example where updates and RCU traversals are |
| 34 | * performed by the same thread to keep things simple on purpose. |
| 35 | */ |
| 36 | |
| 37 | static CDS_LIST_HEAD(mylist); |
| 38 | |
| 39 | struct mynode { |
| 40 | uint64_t value; |
| 41 | struct cds_list_head node; /* linked-list chaining */ |
| 42 | struct rcu_head rcu_head; /* for call_rcu() */ |
| 43 | }; |
| 44 | |
| 45 | static |
| 46 | int add_node(uint64_t v) |
| 47 | { |
| 48 | struct mynode *node; |
| 49 | |
| 50 | node = calloc(sizeof(*node), 1); |
| 51 | if (!node) |
| 52 | return -1; |
| 53 | node->value = v; |
| 54 | cds_list_add_rcu(&node->node, &mylist); |
| 55 | return 0; |
| 56 | } |
| 57 | |
| 58 | static |
| 59 | void rcu_free_node(struct rcu_head *rh) |
| 60 | { |
| 61 | struct mynode *node = caa_container_of(rh, struct mynode, rcu_head); |
| 62 | |
| 63 | free(node); |
| 64 | } |
| 65 | |
| 66 | int main(int argc, char **argv) |
| 67 | { |
| 68 | uint64_t values[] = { 42, 36, 24, }; |
| 69 | unsigned int i; |
| 70 | int ret; |
| 71 | struct mynode *node, *n; |
| 72 | |
| 73 | /* |
| 74 | * Each thread need using RCU read-side need to be explicitly |
| 75 | * registered. |
| 76 | */ |
| 77 | rcu_register_thread(); |
| 78 | |
| 79 | /* |
| 80 | * Adding nodes to the linked-list. Safe against concurrent |
| 81 | * RCU traversals, require mutual exclusion with list updates. |
| 82 | */ |
| 83 | for (i = 0; i < CAA_ARRAY_SIZE(values); i++) { |
| 84 | ret = add_node(values[i]); |
| 85 | if (ret) |
| 86 | goto end; |
| 87 | } |
| 88 | |
| 89 | /* |
| 90 | * We need to explicitly mark RCU read-side critical sections |
| 91 | * with rcu_read_lock() and rcu_read_unlock(). They can be |
| 92 | * nested. Those are no-ops for the QSBR flavor. |
| 93 | */ |
| 94 | rcu_read_lock(); |
| 95 | |
| 96 | /* |
| 97 | * RCU traversal of the linked list. |
| 98 | */ |
| 99 | cds_list_for_each_entry_rcu(node, &mylist, node) { |
| 100 | printf("Value: %" PRIu64 "\n", node->value); |
| 101 | } |
| 102 | rcu_read_unlock(); |
| 103 | |
| 104 | /* |
| 105 | * Removing nodes from linked list. Safe against concurrent RCU |
| 106 | * traversals, require mutual exclusion with list updates. |
| 107 | */ |
| 108 | cds_list_for_each_entry_safe(node, n, &mylist, node) { |
| 109 | cds_list_del_rcu(&node->node); |
| 110 | /* |
| 111 | * call_rcu() will ensure that the handler |
| 112 | * "rcu_free_node" is executed after a grace period. |
| 113 | * call_rcu() can be called from RCU read-side critical |
| 114 | * sections. |
| 115 | */ |
| 116 | call_rcu(&node->rcu_head, rcu_free_node); |
| 117 | } |
| 118 | |
| 119 | /* |
| 120 | * We can also wait for a quiescent state by calling |
| 121 | * synchronize_rcu() rather than using call_rcu(). It is usually |
| 122 | * a slower approach than call_rcu(), because the latter can |
| 123 | * batch work. Moreover, call_rcu() can be called from a RCU |
| 124 | * read-side critical section, but synchronize_rcu() should not. |
| 125 | */ |
| 126 | synchronize_rcu(); |
| 127 | |
| 128 | sleep(1); |
| 129 | |
| 130 | /* |
| 131 | * Waiting for previously called call_rcu handlers to complete |
| 132 | * before program exits, or in library destructors, is a good |
| 133 | * practice. |
| 134 | */ |
| 135 | rcu_barrier(); |
| 136 | |
| 137 | end: |
| 138 | rcu_unregister_thread(); |
| 139 | return ret; |
| 140 | } |