X-Git-Url: https://git.liburcu.org/?a=blobdiff_plain;f=urcu%2Fstatic%2Fwfcqueue.h;h=4a9003e525d0e1ed34ae4fdd9ea6eb3f7a3aea44;hb=6e3319a2481eea847224b53ce8c2bd1571b42bf8;hp=a989984b4030b52f79cc737604aed997f2163d4a;hpb=8ad4ce587f001ae026d5560ac509c2e48986130b;p=urcu.git

diff --git a/urcu/static/wfcqueue.h b/urcu/static/wfcqueue.h
index a989984..4a9003e 100644
--- a/urcu/static/wfcqueue.h
+++ b/urcu/static/wfcqueue.h
@@ -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 */
@@ -189,7 +196,12 @@ ___cds_wfcq_node_sync_next(struct cds_wfcq_node *node)
  *
  * 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_first_blocking(struct cds_wfcq_head *head,
@@ -210,7 +222,12 @@ ___cds_wfcq_first_blocking(struct cds_wfcq_head *head,
  *
  * 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,
@@ -240,15 +257,11 @@ ___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.
- *
  * 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.
  */
 static inline struct cds_wfcq_node *
 ___cds_wfcq_dequeue_blocking(struct cds_wfcq_head *head,
@@ -297,7 +310,8 @@ ___cds_wfcq_dequeue_blocking(struct cds_wfcq_head *head,
  *
  * Dequeue all nodes from src_q.
  * dest_q must be already initialized.
- * Should be called with cds_wfcq_dequeue_lock() held on src_q.
+ * Dequeue/splice/iteration mutual exclusion for src_q should be ensured
+ * by the caller.
  */
 static inline void
 ___cds_wfcq_splice_blocking(
@@ -334,7 +348,7 @@ ___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 +371,7 @@ _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