+++ /dev/null
-#ifndef _URCU_RCUWFQUEUE_H
-#define _URCU_RCUWFQUEUE_H
-
-/*
- * rcuwfqueue.h
- *
- * Userspace RCU library - RCU Queue with Wait-Free Enqueue/Blocking Dequeue
- *
- * 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>
-
-#ifdef __cplusplus
-extern "C" {
-#endif
-
-#if (!defined(_GNU_SOURCE) && !defined(_LGPL_SOURCE))
-#error "Dynamic loader LGPL wrappers not implemented yet"
-#endif
-
-/*
- * RCU queue with wait-free enqueue/blocking dequeue 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_WFQ_PERMANENT_REF 128
-
-struct rcu_wfq_node {
- struct rcu_wfq_node *next;
- struct urcu_ref ref;
-};
-
-struct rcu_wfq_queue {
- struct rcu_wfq_node *head, *tail;
- struct rcu_wfq_node init; /* Dummy initialization node */
-};
-
-void rcu_wfq_node_init(struct rcu_wfq_node *node)
-{
- node->next = NULL;
- urcu_ref_init(&node->ref);
-}
-
-void rcu_wfq_init(struct rcu_wfq_queue *q)
-{
- rcu_wfq_node_init(&q->init);
- /* Make sure the initial node is never freed. */
- urcu_ref_set(&q->init.ref, URCU_WFQ_PERMANENT_REF);
- /* Set queue end */
- q->head = q->tail = &q->init;
-}
-
-void rcu_wfq_enqueue(struct rcu_wfq_queue *q, struct rcu_wfq_node *node)
-{
- struct rcu_wfq_node *old_tail;
-
- urcu_ref_get(&node->ref);
- /*
- * uatomic_xchg() implicit memory barrier orders earlier stores to node
- * (setting it to NULL and incrementing the refcount) before
- * publication.
- */
- old_tail = uatomic_xchg(&q->tail, node);
- /*
- * At this point, dequeuers see a NULL old_tail->next, which indicates
- * end of queue. The following store will append "node" to the queue
- * from a dequeuer perspective.
- */
- STORE_SHARED(old_tail->next, node);
-}
-
-/*
- * 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 wfq node returned by dequeue must not be
- * modified/re-used/freed until the reference count reaches zero and a grace
- * period has elapsed (after the refcount reached 0).
- *
- * No need to go on a waitqueue here, as there is no possible state in which the
- * list could cause dequeue to busy-loop needlessly while waiting for another
- * thread to be scheduled. The queue appears empty until tail->next is set by
- * enqueue.
- */
-struct rcu_wfq_node *
-rcu_wfq_dequeue_blocking(struct rcu_wfq_queue *q,
- void (*release)(struct urcu_ref *))
-{
- for (;;) {
- struct rcu_wfq_node *head, *next;
-
- rcu_read_lock();
- head = rcu_dereference(q->head);
- 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 */
- rcu_read_unlock();
- continue;
- }
- } else {
- /* Empty */
- rcu_read_unlock();
- return NULL;
- }
- }
-}
-
-#ifdef __cplusplus
-}
-#endif
-
-#endif /* _URCU_RCUWFQUEUE_H */
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