X-Git-Url: https://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu%2Fstatic%2Fwfcqueue.h;h=120a5989e6a4341c7d2ec8a4fc719812235542ae;hp=a989984b4030b52f79cc737604aed997f2163d4a;hb=47215721095cf47e110f113d26f9e61514405a4c;hpb=8ad4ce587f001ae026d5560ac509c2e48986130b

diff --git a/urcu/static/wfcqueue.h b/urcu/static/wfcqueue.h
index a989984..120a598 100644
--- a/urcu/static/wfcqueue.h
+++ b/urcu/static/wfcqueue.h
@@ -2,7 +2,7 @@
 #define _URCU_WFCQUEUE_STATIC_H
 
 /*
- * wfcqueue-static.h
+ * urcu/static/wfcqueue.h
  *
  * Userspace RCU library - Concurrent Queue with Wait-Free Enqueue/Blocking Dequeue
  *
@@ -41,21 +41,28 @@ extern "C" {
 /*
  * Concurrent queue with wait-free enqueue/blocking dequeue.
  *
- * Inspired from half-wait-free/half-blocking queue implementation done by
- * Paul E. McKenney.
+ * This queue has been designed and implemented collaboratively by
+ * Mathieu Desnoyers and Lai Jiangshan. Inspired from
+ * half-wait-free/half-blocking queue implementation done by Paul E.
+ * McKenney.
  *
  * Mutual exclusion of __cds_wfcq_* API
  *
  * Unless otherwise stated, the caller must ensure mutual exclusion of
  * queue update operations "dequeue" and "splice" (for source queue).
- * Queue read operations "first" and "next" need to be protected against
- * concurrent "dequeue" and "splice" (for source queue) by the caller.
+ * Queue read operations "first" and "next", which are used by
+ * "for_each" iterations, need to be protected against concurrent
+ * "dequeue" and "splice" (for source queue) by the caller.
  * "enqueue", "splice" (for destination queue), and "empty" are the only
  * operations that can be used without any mutual exclusion.
  * Mutual exclusion can be ensured by holding cds_wfcq_dequeue_lock().
  *
  * For convenience, cds_wfcq_dequeue_blocking() and
  * cds_wfcq_splice_blocking() hold the dequeue lock.
+ *
+ * Besides locking, mutual exclusion of dequeue, splice and iteration
+ * can be ensured by performing all of those operations from a single
+ * thread, without requiring any lock.
  */
 
 #define WFCQ_ADAPT_ATTEMPTS		10	/* Retry if being set */
@@ -164,7 +171,7 @@ static inline void _cds_wfcq_enqueue(struct cds_wfcq_head *head,
  * Waiting for enqueuer to complete enqueue and return the next node.
  */
 static inline struct cds_wfcq_node *
-___cds_wfcq_node_sync_next(struct cds_wfcq_node *node)
+___cds_wfcq_node_sync_next(struct cds_wfcq_node *node, int blocking)
 {
 	struct cds_wfcq_node *next;
 	int attempt = 0;
@@ -173,6 +180,8 @@ ___cds_wfcq_node_sync_next(struct cds_wfcq_node *node)
 	 * Adaptative busy-looping waiting for enqueuer to complete enqueue.
 	 */
 	while ((next = CMM_LOAD_SHARED(node->next)) == NULL) {
+		if (!blocking)
+			return CDS_WFCQ_WOULDBLOCK;
 		if (++attempt >= WFCQ_ADAPT_ATTEMPTS) {
 			poll(NULL, 0, WFCQ_WAIT);	/* Wait for 10ms */
 			attempt = 0;
@@ -184,38 +193,59 @@ ___cds_wfcq_node_sync_next(struct cds_wfcq_node *node)
 	return next;
 }
 
-/*
- * __cds_wfcq_first_blocking: get first node of a queue, without dequeuing.
- *
- * Content written into the node before enqueue is guaranteed to be
- * consistent, but no other memory ordering is ensured.
- * Should be called with cds_wfcq_dequeue_lock() held.
- */
 static inline struct cds_wfcq_node *
-___cds_wfcq_first_blocking(struct cds_wfcq_head *head,
-		struct cds_wfcq_tail *tail)
+___cds_wfcq_first(struct cds_wfcq_head *head,
+		struct cds_wfcq_tail *tail,
+		int blocking)
 {
 	struct cds_wfcq_node *node;
 
 	if (_cds_wfcq_empty(head, tail))
 		return NULL;
-	node = ___cds_wfcq_node_sync_next(&head->node);
+	node = ___cds_wfcq_node_sync_next(&head->node, blocking);
 	/* Load head->node.next before loading node's content */
 	cmm_smp_read_barrier_depends();
 	return node;
 }
 
 /*
- * __cds_wfcq_next_blocking: get next node of a queue, without dequeuing.
+ * __cds_wfcq_first_blocking: get first node of a queue, without dequeuing.
  *
  * Content written into the node before enqueue is guaranteed to be
  * consistent, but no other memory ordering is ensured.
- * Should be called with cds_wfcq_dequeue_lock() held.
+ * Dequeue/splice/iteration mutual exclusion should be ensured by the
+ * caller.
+ *
+ * Used by for-like iteration macros in urcu/wfqueue.h:
+ * __cds_wfcq_for_each_blocking()
+ * __cds_wfcq_for_each_blocking_safe()
  */
 static inline struct cds_wfcq_node *
-___cds_wfcq_next_blocking(struct cds_wfcq_head *head,
+___cds_wfcq_first_blocking(struct cds_wfcq_head *head,
+		struct cds_wfcq_tail *tail)
+{
+	return ___cds_wfcq_first(head, tail, 1);
+}
+
+
+/*
+ * __cds_wfcq_first_nonblocking: get first node of a queue, without dequeuing.
+ *
+ * Same as __cds_wfcq_first_blocking, but returns CDS_WFCQ_WOULDBLOCK if
+ * it needs to block.
+ */
+static inline struct cds_wfcq_node *
+___cds_wfcq_first_nonblocking(struct cds_wfcq_head *head,
+		struct cds_wfcq_tail *tail)
+{
+	return ___cds_wfcq_first(head, tail, 0);
+}
+
+static inline struct cds_wfcq_node *
+___cds_wfcq_next(struct cds_wfcq_head *head,
 		struct cds_wfcq_tail *tail,
-		struct cds_wfcq_node *node)
+		struct cds_wfcq_node *node,
+		int blocking)
 {
 	struct cds_wfcq_node *next;
 
@@ -230,7 +260,7 @@ ___cds_wfcq_next_blocking(struct cds_wfcq_head *head,
 		cmm_smp_rmb();
 		if (CMM_LOAD_SHARED(tail->p) == node)
 			return NULL;
-		next = ___cds_wfcq_node_sync_next(node);
+		next = ___cds_wfcq_node_sync_next(node, blocking);
 	}
 	/* Load node->next before loading next's content */
 	cmm_smp_read_barrier_depends();
@@ -238,28 +268,50 @@ ___cds_wfcq_next_blocking(struct cds_wfcq_head *head,
 }
 
 /*
- * __cds_wfcq_dequeue_blocking: dequeue a node from the queue.
- *
- * 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.
+ * __cds_wfcq_next_blocking: get next node of a queue, without dequeuing.
  *
  * Content written into the node before enqueue is guaranteed to be
  * consistent, but no other memory ordering is ensured.
- * It is valid to reuse and free a dequeued node immediately.
- * Should be called with cds_wfcq_dequeue_lock() held.
+ * Dequeue/splice/iteration mutual exclusion should be ensured by the
+ * caller.
+ *
+ * Used by for-like iteration macros in urcu/wfqueue.h:
+ * __cds_wfcq_for_each_blocking()
+ * __cds_wfcq_for_each_blocking_safe()
  */
 static inline struct cds_wfcq_node *
-___cds_wfcq_dequeue_blocking(struct cds_wfcq_head *head,
-		struct cds_wfcq_tail *tail)
+___cds_wfcq_next_blocking(struct cds_wfcq_head *head,
+		struct cds_wfcq_tail *tail,
+		struct cds_wfcq_node *node)
+{
+	return ___cds_wfcq_next(head, tail, node, 1);
+}
+
+/*
+ * __cds_wfcq_next_blocking: get next node of a queue, without dequeuing.
+ *
+ * Same as __cds_wfcq_next_blocking, but returns CDS_WFCQ_WOULDBLOCK if
+ * it needs to block.
+ */
+static inline struct cds_wfcq_node *
+___cds_wfcq_next_nonblocking(struct cds_wfcq_head *head,
+		struct cds_wfcq_tail *tail,
+		struct cds_wfcq_node *node)
+{
+	return ___cds_wfcq_next(head, tail, node, 0);
+}
+
+static inline struct cds_wfcq_node *
+___cds_wfcq_dequeue(struct cds_wfcq_head *head,
+		struct cds_wfcq_tail *tail,
+		int blocking)
 {
 	struct cds_wfcq_node *node, *next;
 
 	if (_cds_wfcq_empty(head, tail))
 		return NULL;
 
-	node = ___cds_wfcq_node_sync_next(&head->node);
+	node = ___cds_wfcq_node_sync_next(&head->node, blocking);
 
 	if ((next = CMM_LOAD_SHARED(node->next)) == NULL) {
 		/*
@@ -279,7 +331,7 @@ ___cds_wfcq_dequeue_blocking(struct cds_wfcq_head *head,
 		_cds_wfcq_node_init(&head->node);
 		if (uatomic_cmpxchg(&tail->p, node, &head->node) == node)
 			return node;
-		next = ___cds_wfcq_node_sync_next(node);
+		next = ___cds_wfcq_node_sync_next(node, blocking);
 	}
 
 	/*
@@ -293,25 +345,50 @@ ___cds_wfcq_dequeue_blocking(struct cds_wfcq_head *head,
 }
 
 /*
- * __cds_wfcq_splice_blocking: enqueue all src_q nodes at the end of dest_q.
+ * __cds_wfcq_dequeue_blocking: dequeue a node from the queue.
  *
- * Dequeue all nodes from src_q.
- * dest_q must be already initialized.
- * Should be called with cds_wfcq_dequeue_lock() held on src_q.
+ * Content written into the node before enqueue is guaranteed to be
+ * consistent, but no other memory ordering is ensured.
+ * It is valid to reuse and free a dequeued node immediately.
+ * Dequeue/splice/iteration mutual exclusion should be ensured by the
+ * caller.
  */
-static inline void
-___cds_wfcq_splice_blocking(
+static inline struct cds_wfcq_node *
+___cds_wfcq_dequeue_blocking(struct cds_wfcq_head *head,
+		struct cds_wfcq_tail *tail)
+{
+	return ___cds_wfcq_dequeue(head, tail, 1);
+}
+
+/*
+ * __cds_wfcq_dequeue_nonblocking: dequeue a node from a wait-free queue.
+ *
+ * Same as __cds_wfcq_dequeue_blocking, but returns CDS_WFCQ_WOULDBLOCK
+ * if it needs to block.
+ */
+static inline struct cds_wfcq_node *
+___cds_wfcq_dequeue_nonblocking(struct cds_wfcq_head *head,
+		struct cds_wfcq_tail *tail)
+{
+	return ___cds_wfcq_dequeue(head, tail, 0);
+}
+
+static inline int
+___cds_wfcq_splice(
 		struct cds_wfcq_head *dest_q_head,
 		struct cds_wfcq_tail *dest_q_tail,
 		struct cds_wfcq_head *src_q_head,
-		struct cds_wfcq_tail *src_q_tail)
+		struct cds_wfcq_tail *src_q_tail,
+		int blocking)
 {
 	struct cds_wfcq_node *head, *tail;
 
 	if (_cds_wfcq_empty(src_q_head, src_q_tail))
-		return;
+		return 0;
 
-	head = ___cds_wfcq_node_sync_next(&src_q_head->node);
+	head = ___cds_wfcq_node_sync_next(&src_q_head->node, blocking);
+	if (head == CDS_WFCQ_WOULDBLOCK)
+		return -1;
 	_cds_wfcq_node_init(&src_q_head->node);
 
 	/*
@@ -327,6 +404,44 @@ ___cds_wfcq_splice_blocking(
 	 * require mutual exclusion on dest_q (wait-free).
 	 */
 	___cds_wfcq_append(dest_q_head, dest_q_tail, head, tail);
+	return 0;
+}
+
+
+/*
+ * __cds_wfcq_splice_blocking: enqueue all src_q nodes at the end of dest_q.
+ *
+ * Dequeue all nodes from src_q.
+ * dest_q must be already initialized.
+ * Dequeue/splice/iteration mutual exclusion for src_q should be ensured
+ * by the caller.
+ */
+static inline void
+___cds_wfcq_splice_blocking(
+		struct cds_wfcq_head *dest_q_head,
+		struct cds_wfcq_tail *dest_q_tail,
+		struct cds_wfcq_head *src_q_head,
+		struct cds_wfcq_tail *src_q_tail)
+{
+	(void) ___cds_wfcq_splice(dest_q_head, dest_q_tail,
+		src_q_head, src_q_tail, 1);
+}
+
+/*
+ * __cds_wfcq_splice_nonblocking: enqueue all src_q nodes at the end of dest_q.
+ *
+ * Same as __cds_wfcq_splice_blocking, but returns nonzero if it needs to
+ * block.
+ */
+static inline int
+___cds_wfcq_splice_nonblocking(
+		struct cds_wfcq_head *dest_q_head,
+		struct cds_wfcq_tail *dest_q_tail,
+		struct cds_wfcq_head *src_q_head,
+		struct cds_wfcq_tail *src_q_tail)
+{
+	return ___cds_wfcq_splice(dest_q_head, dest_q_tail,
+		src_q_head, src_q_tail, 0);
 }
 
 /*
@@ -334,7 +449,7 @@ ___cds_wfcq_splice_blocking(
  *
  * Content written into the node before enqueue is guaranteed to be
  * consistent, but no other memory ordering is ensured.
- * Mutual exlusion with (and only with) cds_wfcq_splice_blocking is
+ * Mutual exlusion with cds_wfcq_splice_blocking and dequeue lock is
  * ensured.
  * It is valid to reuse and free a dequeued node immediately.
  */
@@ -357,7 +472,7 @@ _cds_wfcq_dequeue_blocking(struct cds_wfcq_head *head,
  * dest_q must be already initialized.
  * Content written into the node before enqueue is guaranteed to be
  * consistent, but no other memory ordering is ensured.
- * Mutual exlusion with (and only with) cds_wfcq_dequeue_blocking is
+ * Mutual exlusion with cds_wfcq_dequeue_blocking and dequeue lock is
  * ensured.
  */
 static inline void