--- /dev/null
+#ifndef _URCU_RCULFQUEUE_STATIC_H
+#define _URCU_RCULFQUEUE_STATIC_H
+
+/*
+ * rculfqueue-static.h
+ *
+ * Userspace RCU library - Lock-Free RCU Queue
+ *
+ * Copyright 2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See rculfqueue.h for linking
+ * dynamically with the userspace rcu library.
+ *
+ * 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 <urcu/uatomic_arch.h>
+#include <assert.h>
+/* A urcu implementation header should be already included. */
+
+#ifdef __cplusplus
+extern "C" {
+#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
+
+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.
+ */
+
+ for (;;) {
+ struct rcu_lfq_node *tail, *next;
+
+ rcu_read_lock();
+ tail = rcu_dereference(q->tail);
+ /*
+ * 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);
+ rcu_read_unlock();
+ 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 after execution of the release callback before
+ * performing the actual memory reclamation or modifying the rcu_lfq_node
+ * structure.
+ * In other words, the entry lfq 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).
+ */
+struct rcu_lfq_node *
+_rcu_lfq_dequeue(struct rcu_lfq_queue *q, void (*release)(struct urcu_ref *))
+{
+ for (;;) {
+ struct rcu_lfq_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_RCULFQUEUE_STATIC_H */
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