X-Git-Url: http://git.liburcu.org/?p=userspace-rcu.git;a=blobdiff_plain;f=include%2Furcu%2Fstatic%2Fwfqueue.h;fp=include%2Furcu%2Fstatic%2Fwfqueue.h;h=df9f62f28bafa189a5b2f0d61fcbfce8b978b7b4;hp=0000000000000000000000000000000000000000;hb=6893800a4d1cc14dff0395ddcd660a5138db183d;hpb=a59f39055b5ecb77b68cf78b9839aa9e8e4ec332

diff --git a/include/urcu/static/wfqueue.h b/include/urcu/static/wfqueue.h
new file mode 100644
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+++ b/include/urcu/static/wfqueue.h
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+#ifndef _URCU_WFQUEUE_STATIC_H
+#define _URCU_WFQUEUE_STATIC_H
+
+/*
+ * wfqueue-static.h
+ *
+ * Userspace RCU library - Queue with Wait-Free Enqueue/Blocking Dequeue
+ *
+ * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See wfqueue.h for linking
+ * dynamically with the userspace rcu library.
+ *
+ * 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 <pthread.h>
+#include <assert.h>
+#include <poll.h>
+#include <urcu/compiler.h>
+#include <urcu/uatomic.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/*
+ * Queue with wait-free enqueue/blocking dequeue.
+ * This implementation adds a dummy head node when the queue is empty to ensure
+ * we can always update the queue locklessly.
+ *
+ * Inspired from half-wait-free/half-blocking queue implementation done by
+ * Paul E. McKenney.
+ */
+
+#define WFQ_ADAPT_ATTEMPTS		10	/* Retry if being set */
+#define WFQ_WAIT			10	/* Wait 10 ms if being set */
+
+static inline void _cds_wfq_node_init(struct cds_wfq_node *node)
+{
+	node->next = NULL;
+}
+
+static inline void _cds_wfq_init(struct cds_wfq_queue *q)
+{
+	int ret;
+
+	_cds_wfq_node_init(&q->dummy);
+	/* Set queue head and tail */
+	q->head = &q->dummy;
+	q->tail = &q->dummy.next;
+	ret = pthread_mutex_init(&q->lock, NULL);
+	assert(!ret);
+}
+
+static inline void _cds_wfq_destroy(struct cds_wfq_queue *q)
+{
+	int ret = pthread_mutex_destroy(&q->lock);
+	assert(!ret);
+}
+
+static inline void _cds_wfq_enqueue(struct cds_wfq_queue *q,
+				    struct cds_wfq_node *node)
+{
+	struct cds_wfq_node **old_tail;
+
+	/*
+	 * uatomic_xchg() implicit memory barrier orders earlier stores to data
+	 * structure containing node and setting node->next to NULL before
+	 * publication.
+	 */
+	old_tail = uatomic_xchg(&q->tail, &node->next);
+	/*
+	 * At this point, dequeuers see a NULL old_tail->next, which indicates
+	 * that the queue is being appended to. The following store will append
+	 * "node" to the queue from a dequeuer perspective.
+	 */
+	CMM_STORE_SHARED(*old_tail, node);
+}
+
+/*
+ * Waiting for enqueuer to complete enqueue and return the next node
+ */
+static inline struct cds_wfq_node *
+___cds_wfq_node_sync_next(struct cds_wfq_node *node)
+{
+	struct cds_wfq_node *next;
+	int attempt = 0;
+
+	/*
+	 * Adaptative busy-looping waiting for enqueuer to complete enqueue.
+	 */
+	while ((next = CMM_LOAD_SHARED(node->next)) == NULL) {
+		if (++attempt >= WFQ_ADAPT_ATTEMPTS) {
+			(void) poll(NULL, 0, WFQ_WAIT);	/* Wait for 10ms */
+			attempt = 0;
+		} else
+			caa_cpu_relax();
+	}
+
+	return next;
+}
+
+/*
+ * It is valid to reuse and free a dequeued node immediately.
+ *
+ * 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.
+ */
+static inline struct cds_wfq_node *
+___cds_wfq_dequeue_blocking(struct cds_wfq_queue *q)
+{
+	struct cds_wfq_node *node, *next;
+
+	/*
+	 * Queue is empty if it only contains the dummy node.
+	 */
+	if (q->head == &q->dummy && CMM_LOAD_SHARED(q->tail) == &q->dummy.next)
+		return NULL;
+	node = q->head;
+
+	next = ___cds_wfq_node_sync_next(node);
+
+	/*
+	 * Move queue head forward.
+	 */
+	q->head = next;
+	/*
+	 * Requeue dummy node if we just dequeued it.
+	 */
+	if (node == &q->dummy) {
+		_cds_wfq_node_init(node);
+		_cds_wfq_enqueue(q, node);
+		return ___cds_wfq_dequeue_blocking(q);
+	}
+	return node;
+}
+
+static inline struct cds_wfq_node *
+_cds_wfq_dequeue_blocking(struct cds_wfq_queue *q)
+{
+	struct cds_wfq_node *retnode;
+	int ret;
+
+	ret = pthread_mutex_lock(&q->lock);
+	assert(!ret);
+	retnode = ___cds_wfq_dequeue_blocking(q);
+	ret = pthread_mutex_unlock(&q->lock);
+	assert(!ret);
+	return retnode;
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _URCU_WFQUEUE_STATIC_H */