+/*
+ * Copyright (C) 2013 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
+ * OR IMPLIED. ANY USE IS AT YOUR OWN RISK.
+ *
+ * Permission is hereby granted to use or copy this program for any
+ * purpose, provided the above notices are retained on all copies.
+ * Permission to modify the code and to distribute modified code is
+ * granted, provided the above notices are retained, and a notice that
+ * the code was modified is included with the above copyright notice.
+ *
+ * This example shows how to dequeue nodes from a RCU lock-free queue.
+ * This queue requires using a RCU scheme.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <urcu.h> /* RCU flavor */
+#include <urcu/rculfqueue.h> /* RCU Lock-free queue */
+#include <urcu/compiler.h> /* For CAA_ARRAY_SIZE */
+
+/*
+ * Nodes populated into the queue.
+ */
+struct mynode {
+ int value; /* Node content */
+ struct cds_lfq_node_rcu node; /* Chaining in queue */
+ struct rcu_head rcu_head; /* For call_rcu() */
+};
+
+static
+void free_node(struct rcu_head *head)
+{
+ struct mynode *node =
+ caa_container_of(head, struct mynode, rcu_head);
+
+ free(node);
+}
+
+int main(int argc, char **argv)
+{
+ int values[] = { -5, 42, 36, 24, };
+ struct cds_lfq_queue_rcu myqueue; /* Queue */
+ unsigned int i;
+ int ret = 0;
+
+ /*
+ * Each thread need using RCU read-side need to be explicitly
+ * registered.
+ */
+ rcu_register_thread();
+
+ cds_lfq_init_rcu(&myqueue, call_rcu);
+
+ /*
+ * Enqueue nodes.
+ */
+ for (i = 0; i < CAA_ARRAY_SIZE(values); i++) {
+ struct mynode *node;
+
+ node = malloc(sizeof(*node));
+ if (!node) {
+ ret = -1;
+ goto end;
+ }
+
+ cds_lfq_node_init_rcu(&node->node);
+ node->value = values[i];
+ /*
+ * Both enqueue and dequeue need to be called within RCU
+ * read-side critical section.
+ */
+ rcu_read_lock();
+ cds_lfq_enqueue_rcu(&myqueue, &node->node);
+ rcu_read_unlock();
+ }
+
+ /*
+ * Dequeue each node from the queue. Those will be dequeued from
+ * the oldest (first enqueued) to the newest (last enqueued).
+ */
+ printf("dequeued content:");
+ for (;;) {
+ struct cds_lfq_node_rcu *qnode;
+ struct mynode *node;
+
+ /*
+ * Both enqueue and dequeue need to be called within RCU
+ * read-side critical section.
+ */
+ rcu_read_lock();
+ qnode = cds_lfq_dequeue_rcu(&myqueue);
+ rcu_read_unlock();
+ if (!qnode) {
+ break; /* Queue is empty. */
+ }
+ /* Getting the container structure from the node */
+ node = caa_container_of(qnode, struct mynode, node);
+ printf(" %d", node->value);
+ call_rcu(&node->rcu_head, free_node);
+ }
+ printf("\n");
+ /*
+ * Release memory used by the queue.
+ */
+ ret = cds_lfq_destroy_rcu(&myqueue);
+ if (ret) {
+ printf("Error destroying queue (non-empty)\n");
+ }
+end:
+ rcu_unregister_thread();
+ return ret;
+}