+++ /dev/null
-/*
- * rculfqueue.h
- *
- * Userspace RCU library - Lock-Free RCU Queue
- *
- * Copyright 2010 - 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 <urcu/urcu_ref.h>
-#include <assert.h>
-
-#if (!defined(_GNU_SOURCE) && !defined(_LGPL_SOURCE))
-#error "Dynamic loader LGPL wrappers not implemented yet"
-#endif
-
-/*
- * Lock-free RCU queue using reference counting. Enqueue and dequeue operations
- * hold a RCU read lock to deal with cmpxchg ABA problem. This implementation
- * keeps a dummy head node to ensure we can always update the queue locklessly.
- * Given that this is a queue, the dummy head node must always advance as we
- * dequeue entries. Therefore, we keep a reference count on each entry we are
- * dequeueing, so they can be kept as dummy head node until the next dequeue, at
- * which point their reference count will be decremented.
- */
-
-#define URCU_LFQ_PERMANENT_REF 128
-
-struct rcu_lfq_node {
- struct rcu_lfq_node *next;
- struct urcu_ref ref;
-};
-
-struct rcu_lfq_queue {
- struct rcu_lfq_node *head, *tail;
- struct rcu_lfq_node init; /* Dummy initialization node */
-};
-
-void rcu_lfq_node_init(struct rcu_lfq_node *node)
-{
- node->next = NULL;
- urcu_ref_init(&node->ref);
-}
-
-void rcu_lfq_init(struct rcu_lfq_queue *q)
-{
- rcu_lfq_node_init(&q->init);
- /* Make sure the initial node is never freed. */
- urcu_ref_set(&q->init.ref, URCU_LFQ_PERMANENT_REF);
- q->head = q->tail = &q->init;
-}
-
-void rcu_lfq_enqueue(struct rcu_lfq_queue *q, struct rcu_lfq_node *node)
-{
- urcu_ref_get(&node->ref);
-
- /*
- * uatomic_cmpxchg() implicit memory barrier orders earlier stores to
- * node before publication.
- */
-
- rcu_read_lock();
- for (;;) {
- struct rcu_lfq_node *tail = rcu_dereference(q->tail);
- struct rcu_lfq_node *next;
-
- /*
- * Typically expect tail->next to be NULL.
- */
- next = uatomic_cmpxchg(&tail->next, NULL, node);
- if (next == NULL) {
- /*
- * Tail was at the end of queue, we successfully
- * appended to it.
- * Now move tail (another enqueue might beat
- * us to it, that's fine).
- */
- uatomic_cmpxchg(&q->tail, tail, node);
- rcu_read_unlock();
- return;
- } else {
- /*
- * Failure to append to current tail. Help moving tail
- * further and retry.
- */
- uatomic_cmpxchg(&q->tail, tail, next);
- continue;
- }
- }
-}
-
-/*
- * The entry returned by dequeue must be taken care of by doing a urcu_ref_put,
- * which calls the release primitive when the reference count drops to zero. A
- * grace period must be waited before performing the actual memory reclamation
- * in the release primitive.
- * The entry lfq node returned by dequeue must no be re-used before the
- * reference count reaches zero.
- */
-struct rcu_lfq_node *
-rcu_lfq_dequeue(struct rcu_lfq_queue *q, void (*release)(struct urcu_ref *))
-{
- rcu_read_lock();
- for (;;) {
- struct rcu_lfq_node *head = rcu_dereference(q->head);
- struct rcu_lfq_node *next = rcu_dereference(head->next);
-
- if (next) {
- if (uatomic_cmpxchg(&q->head, head, next) == head) {
- rcu_read_unlock();
- urcu_ref_put(&head->ref, release);
- return next;
- } else {
- /* Concurrently pushed, retry */
- continue;
- }
- } else {
- /* Empty */
- rcu_read_unlock();
- return NULL;
- }
- }
-}
projects / urcu.git / blobdiff