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// SPDX-FileCopyrightText: 2013 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
//
// SPDX-License-Identifier: MIT
/*
* 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/urcu-memb.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(void)
{
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.
*/
urcu_memb_register_thread();
cds_lfq_init_rcu(&myqueue, urcu_memb_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.
*/
urcu_memb_read_lock();
cds_lfq_enqueue_rcu(&myqueue, &node->node);
urcu_memb_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.
*/
urcu_memb_read_lock();
qnode = cds_lfq_dequeue_rcu(&myqueue);
urcu_memb_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);
urcu_memb_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:
urcu_memb_unregister_thread();
return ret;
}
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