X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu%2Fstatic%2Frculfqueue.h;h=99335c41ec41d33078279e2f843431111cf307e8;hp=f3df7c01f2563bd3d5c7a29314d21ca1333d8a0a;hb=7618919ae496bda84a2efa4f2ad0abe569892a9e;hpb=f671981162a0a84135797ba01661c5c832c5e430

diff --git a/urcu/static/rculfqueue.h b/urcu/static/rculfqueue.h
index f3df7c0..99335c4 100644
--- a/urcu/static/rculfqueue.h
+++ b/urcu/static/rculfqueue.h
@@ -68,6 +68,7 @@ struct cds_lfq_node_rcu *make_dummy(struct cds_lfq_queue_rcu *q,
 	dummy = malloc(sizeof(struct cds_lfq_node_rcu_dummy));
 	assert(dummy);
 	dummy->parent.next = next;
+	dummy->parent.dummy = 1;
 	dummy->q = q;
 	return &dummy->parent;
 }
@@ -85,8 +86,9 @@ void rcu_free_dummy(struct cds_lfq_node_rcu *node)
 {
 	struct cds_lfq_node_rcu_dummy *dummy;
 
+	assert(node->dummy);
 	dummy = caa_container_of(node, struct cds_lfq_node_rcu_dummy, parent);
-	dummy->q->queue_call_rcu(&dummy->head, free_dummy_cb);
+	call_rcu(&dummy->head, free_dummy_cb);
 }
 
 static inline
@@ -94,6 +96,7 @@ void free_dummy(struct cds_lfq_node_rcu *node)
 {
 	struct cds_lfq_node_rcu_dummy *dummy;
 
+	assert(node->dummy);
 	dummy = caa_container_of(node, struct cds_lfq_node_rcu_dummy, parent);
 	free(dummy);
 }
@@ -102,17 +105,14 @@ static inline
 void _cds_lfq_node_init_rcu(struct cds_lfq_node_rcu *node)
 {
 	node->next = NULL;
+	node->dummy = 0;
 }
 
 static inline
-void _cds_lfq_init_rcu(struct cds_lfq_queue_rcu *q,
-		       void queue_call_rcu(struct rcu_head *head,
-				void (*func)(struct rcu_head *head)))
+void _cds_lfq_init_rcu(struct cds_lfq_queue_rcu *q)
 {
 	q->tail = make_dummy(q, NULL);
-	q->dummy = q->tail;
 	q->head = q->tail;
-	q->queue_call_rcu = queue_call_rcu;
 }
 
 /*
@@ -126,14 +126,14 @@ int _cds_lfq_destroy_rcu(struct cds_lfq_queue_rcu *q)
 	struct cds_lfq_node_rcu *head;
 
 	head = rcu_dereference(q->head);
-	if (!(head == q->dummy && head->next == NULL))
+	if (!(head->dummy && head->next == NULL))
 		return -EPERM;	/* not empty */
 	free_dummy(head);
 	return 0;
 }
 
 /*
- * Should be called under rcu read lock critical section.
+ * Acts as a RCU reader.
  */
 static inline
 void _cds_lfq_enqueue_rcu(struct cds_lfq_queue_rcu *q,
@@ -147,6 +147,7 @@ void _cds_lfq_enqueue_rcu(struct cds_lfq_queue_rcu *q,
 	for (;;) {
 		struct cds_lfq_node_rcu *tail, *next;
 
+		rcu_read_lock();
 		tail = rcu_dereference(q->tail);
 		next = uatomic_cmpxchg(&tail->next, NULL, node);
 		if (next == NULL) {
@@ -156,6 +157,7 @@ void _cds_lfq_enqueue_rcu(struct cds_lfq_queue_rcu *q,
 			 * enqueue might beat us to it, that's fine).
 			 */
 			(void) uatomic_cmpxchg(&q->tail, tail, node);
+			rcu_read_unlock();
 			return;
 		} else {
 			/*
@@ -163,28 +165,24 @@ void _cds_lfq_enqueue_rcu(struct cds_lfq_queue_rcu *q,
 			 * Help moving tail further and retry.
 			 */
 			(void) uatomic_cmpxchg(&q->tail, tail, next);
+			rcu_read_unlock();
 			continue;
 		}
 	}
 }
 
 static inline
-void reenqueue_dummy(struct cds_lfq_queue_rcu *q)
+void enqueue_dummy(struct cds_lfq_queue_rcu *q)
 {
 	struct cds_lfq_node_rcu *node;
 
 	/* We need to reallocate to protect from ABA. */
 	node = make_dummy(q, NULL);
-	if (uatomic_cmpxchg(&q->dummy, NULL, node) != NULL) {
-		/* other dequeue populated its new dummy */
-		free_dummy(node);
-		return;
-	}
 	_cds_lfq_enqueue_rcu(q, node);
 }
 
 /*
- * Should be called under rcu read lock critical section.
+ * Acts as a RCU reader.
  *
  * The caller must wait for a grace period to pass before freeing the returned
  * node or modifying the cds_lfq_node_rcu structure.
@@ -194,38 +192,37 @@ static inline
 struct cds_lfq_node_rcu *_cds_lfq_dequeue_rcu(struct cds_lfq_queue_rcu *q)
 {
 	for (;;) {
-		struct cds_lfq_node_rcu *head, *next, *dummy;
+		struct cds_lfq_node_rcu *head, *next;
 
+		rcu_read_lock();
 		head = rcu_dereference(q->head);
 		next = rcu_dereference(head->next);
-		dummy = rcu_dereference(q->dummy);
-		if (head == dummy && next == NULL)
+		if (head->dummy && next == NULL) {
+			rcu_read_unlock();
 			return NULL;	/* empty */
+		}
 		/*
 		 * We never, ever allow dequeue to get to a state where
 		 * the queue is empty (we need at least one node in the
 		 * queue). This is ensured by checking if the head next
-		 * is NULL. This means a concurrent dummy node
-		 * re-enqueue is in progress. We help it reach
-		 * completion, and retry.
+		 * is NULL, which means we need to enqueue a dummy node
+		 * before we can hope dequeuing anything.
 		 */
 		if (!next) {
-			/*
-			 * Dummy node re-enqueue is in progress. Try to
-			 * help.
-			 */
-			reenqueue_dummy(q);
-			continue;	/* try again */
+			enqueue_dummy(q);
+			next = rcu_dereference(head->next);
 		}
-		if (uatomic_cmpxchg(&q->head, head, next) != head)
+		if (uatomic_cmpxchg(&q->head, head, next) != head) {
+			rcu_read_unlock();
 			continue;	/* Concurrently pushed. */
-		if (head == dummy) {
-			/* Free old and requeue new dummy. */
-			rcu_set_pointer(&q->dummy, NULL);
-			rcu_free_dummy(dummy);
-			reenqueue_dummy(q);
+		}
+		if (head->dummy) {
+			/* Free dummy after grace period. */
+			rcu_free_dummy(head);
+			rcu_read_unlock();
 			continue;	/* try again */
 		}
+		rcu_read_unlock();
 		return head;
 	}
 }