doc/examples: introduce urcu-flavors examples directory

[urcu.git] / doc / examples / urcu-flavors / qsbr.c

diff --git a/doc/examples/urcu-flavors/qsbr.c b/doc/examples/urcu-flavors/qsbr.c
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+/*
+ * Copyright (C) 2013  Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <inttypes.h>
+
+#include <urcu-qsbr.h>         /* QSBR RCU flavor */
+#include <urcu/rculist.h>      /* List example */
+#include <urcu/compiler.h>     /* For CAA_ARRAY_SIZE */
+
+/*
+ * Example showing how to use the QSBR Userspace RCU flavor.
+ *
+ * This is a mock-up example where updates and RCU traversals are
+ * performed by the same thread to keep things simple on purpose.
+ */
+
+static CDS_LIST_HEAD(mylist);
+
+struct mynode {
+       uint64_t value;
+       struct cds_list_head node;      /* linked-list chaining */
+       struct rcu_head rcu_head;       /* for call_rcu() */
+};
+
+static
+int add_node(uint64_t v)
+{
+       struct mynode *node;
+
+       node = calloc(sizeof(*node), 1);
+       if (!node)
+               return -1;
+       node->value = v;
+       cds_list_add_rcu(&node->node, &mylist);
+       return 0;
+}
+
+static
+void rcu_free_node(struct rcu_head *rh)
+{
+       struct mynode *node = caa_container_of(rh, struct mynode, rcu_head);
+
+       free(node);
+}
+
+int main(int argc, char **argv)
+{
+       uint64_t values[] = { 42, 36, 24, };
+       unsigned int i;
+       int ret;
+       struct mynode *node, *n;
+
+       /*
+        * Each thread need using RCU read-side need to be explicitly
+        * registered.
+        */
+       rcu_register_thread();
+
+       /*
+        * Adding nodes to the linked-list. Safe against concurrent
+        * RCU traversals, require mutual exclusion with list updates.
+        */
+       for (i = 0; i < CAA_ARRAY_SIZE(values); i++) {
+               ret = add_node(values[i]);
+               if (ret)
+                       goto end;
+       }
+
+       /*
+        * For all RCU flavors except QSBR, we need to explicitly mark
+        * RCU read-side critical sections with rcu_read_lock() and
+        * rcu_read_unlock(). They can be nested. Those are no-ops for
+        * the QSBR flavor.
+        */
+       rcu_read_lock();
+
+       /*
+        * RCU traversal of the linked list.
+        */
+       cds_list_for_each_entry_rcu(node, &mylist, node) {
+               printf("Value: %" PRIu64 "\n", node->value);
+       }
+       rcu_read_unlock();
+
+       /*
+        * Removing nodes from linked list. Safe against concurrent RCU
+        * traversals, require mutual exclusion with list updates.
+        */
+       cds_list_for_each_entry_safe(node, n, &mylist, node) {
+               cds_list_del_rcu(&node->node);
+               call_rcu(&node->rcu_head, rcu_free_node);
+       }
+
+       /*
+        * For QSBR flavor, we need to explicitly announce quiescent
+        * states. Here is how it is done. This should be performed by
+        * every online registered RCU threads in the program
+        * periodically.
+        */
+       rcu_quiescent_state();
+
+       /*
+        * For QSBR flavor, when a thread needs to be in a quiescent
+        * state for a long period of time, we use rcu_thread_offline()
+        * and rcu_thread_online().
+        */
+       rcu_thread_offline();
+
+       sleep(1);
+
+       rcu_thread_online();
+
+       /*
+        * Waiting for previously called call_rcu handlers to complete
+        * before program exits, or in library destructors, is a good
+        * practice.
+        */
+       rcu_barrier();
+
+end:
+       rcu_unregister_thread();
+       return ret;
+}