X-Git-Url: https://git.lttng.org/?p=urcu.git;a=blobdiff_plain;f=urcu%2Fstatic%2Frculfqueue.h;fp=urcu%2Fstatic%2Frculfqueue.h;h=410a4cf8d820714dbc88673db078ef89b1545c45;hp=0000000000000000000000000000000000000000;hb=af7c2dbeac32c663b64ad05e4eca70e18784463b;hpb=acfd099eae9026369f558e73b2a7e35860962d9d

diff --git a/urcu/static/rculfqueue.h b/urcu/static/rculfqueue.h
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+#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 _cds_lfq_node_init_rcu(struct cds_lfq_node_rcu *node)
+{
+	node->next = NULL;
+	urcu_ref_init(&node->ref);
+}
+
+void _cds_lfq_init_rcu(struct cds_lfq_queue_rcu *q,
+		       void (*release)(struct urcu_ref *ref))
+{
+	_cds_lfq_node_init_rcu(&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;
+	q->release = release;
+}
+
+/*
+ * Should be called under rcu read lock critical section.
+ */
+void _cds_lfq_enqueue_rcu(struct cds_lfq_queue_rcu *q,
+			  struct cds_lfq_node_rcu *node)
+{
+	urcu_ref_get(&node->ref);
+	node->queue = q;
+
+	/*
+	 * uatomic_cmpxchg() implicit memory barrier orders earlier stores to
+	 * node before publication.
+	 */
+
+	for (;;) {
+		struct cds_lfq_node_rcu *tail, *next;
+
+		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).
+			 */
+			(void) uatomic_cmpxchg(&q->tail, tail, node);
+			return;
+		} else {
+			/*
+			 * Failure to append to current tail. Help moving tail
+			 * further and retry.
+			 */
+			(void) uatomic_cmpxchg(&q->tail, tail, next);
+			continue;
+		}
+	}
+}
+
+/*
+ * Should be called under rcu read lock critical section.
+ *
+ * The entry returned by dequeue must be taken care of by doing a
+ * sequence of urcu_ref_put which release handler should do a call_rcu.
+ *
+ * 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.
+ */
+struct cds_lfq_node_rcu *_cds_lfq_dequeue_rcu(struct cds_lfq_queue_rcu *q)
+{
+	for (;;) {
+		struct cds_lfq_node_rcu *head, *next;
+
+		head = rcu_dereference(q->head);
+		next = rcu_dereference(head->next);
+		if (next) {
+			if (uatomic_cmpxchg(&q->head, head, next) == head) {
+				urcu_ref_put(&head->ref, q->release);
+				return next;
+			} else {
+				/* Concurrently pushed, retry */
+				continue;
+			}
+		} else {
+			/* Empty */
+			return NULL;
+		}
+	}
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _URCU_RCULFQUEUE_STATIC_H */