wfcqueue: enqueue and splice return queue state

[urcu.git] / urcu / wfcqueue.h

diff --git a/urcu/wfcqueue.h b/urcu/wfcqueue.h
index ba2f2edd93276f4f257d4a9c8498f616f3940a03..ddf6b87c478eb808d72fbeb8242fb294726933c5 100644 (file)
--- a/urcu/wfcqueue.h
+++ b/urcu/wfcqueue.h
@@ -2,7 +2,7 @@
 #define _URCU_WFCQUEUE_H
 
 /*
- * wfcqueue.h
+ * urcu/wfcqueue.h
  *
  * Userspace RCU library - Concurrent Queue with Wait-Free Enqueue/Blocking Dequeue
  *
@@ -43,6 +43,15 @@ extern "C" {
  * McKenney.
  */
 
+#define CDS_WFCQ_WOULDBLOCK    ((void *) -1UL)
+
+enum cds_wfcq_ret {
+       CDS_WFCQ_RET_WOULDBLOCK =       -1,
+       CDS_WFCQ_RET_DEST_EMPTY =       0,
+       CDS_WFCQ_RET_DEST_NON_EMPTY =   1,
+       CDS_WFCQ_RET_SRC_EMPTY =        2,
+};
+
 struct cds_wfcq_node {
        struct cds_wfcq_node *next;
 };
@@ -86,6 +95,16 @@ struct cds_wfcq_tail {
 #define __cds_wfcq_first_blocking      ___cds_wfcq_first_blocking
 #define __cds_wfcq_next_blocking       ___cds_wfcq_next_blocking
 
+/*
+ * Locking ensured by caller by holding cds_wfcq_dequeue_lock().
+ * Non-blocking: deque, first, next return CDS_WFCQ_WOULDBLOCK if they
+ * need to block. splice returns nonzero if it needs to block.
+ */
+#define __cds_wfcq_dequeue_nonblocking ___cds_wfcq_dequeue_nonblocking
+#define __cds_wfcq_splice_nonblocking  ___cds_wfcq_splice_nonblocking
+#define __cds_wfcq_first_nonblocking   ___cds_wfcq_first_nonblocking
+#define __cds_wfcq_next_nonblocking    ___cds_wfcq_next_nonblocking
+
 #else /* !_LGPL_SOURCE */
 
 /*
@@ -144,8 +163,11 @@ extern void cds_wfcq_dequeue_unlock(struct cds_wfcq_head *head,
  *
  * Issues a full memory barrier before enqueue. No mutual exclusion is
  * required.
+ *
+ * Returns false if the queue was empty prior to adding the node.
+ * Returns true otherwise.
  */
-extern void cds_wfcq_enqueue(struct cds_wfcq_head *head,
+extern bool cds_wfcq_enqueue(struct cds_wfcq_head *head,
                struct cds_wfcq_tail *tail,
                struct cds_wfcq_node *node);
 
@@ -171,15 +193,18 @@ extern struct cds_wfcq_node *cds_wfcq_dequeue_blocking(
  * consistent, but no other memory ordering is ensured.
  * Mutual exlusion with cds_wfcq_dequeue_blocking and dequeue lock is
  * ensured.
+ *
+ * Returns enum cds_wfcq_ret which indicates the state of the src or
+ * dest queue. Cannot block.
  */
-extern void cds_wfcq_splice_blocking(
+extern enum cds_wfcq_ret 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);
 
 /*
- * __cds_wfcq_dequeue_blocking:
+ * __cds_wfcq_dequeue_blocking: dequeue a node from a wait-free queue.
  *
  * Content written into the node before enqueue is guaranteed to be
  * consistent, but no other memory ordering is ensured.
@@ -191,6 +216,16 @@ extern struct cds_wfcq_node *__cds_wfcq_dequeue_blocking(
                struct cds_wfcq_head *head,
                struct cds_wfcq_tail *tail);
 
+/*
+ * __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.
+ */
+extern struct cds_wfcq_node *__cds_wfcq_dequeue_nonblocking(
+               struct cds_wfcq_head *head,
+               struct cds_wfcq_tail *tail);
+
 /*
  * __cds_wfcq_splice_blocking: enqueue all src_q nodes at the end of dest_q.
  *
@@ -200,8 +235,23 @@ extern struct cds_wfcq_node *__cds_wfcq_dequeue_blocking(
  * consistent, but no other memory ordering is ensured.
  * Dequeue/splice/iteration mutual exclusion for src_q should be ensured
  * by the caller.
+ *
+ * Returns enum cds_wfcq_ret which indicates the state of the src or
+ * dest queue. Cannot block.
  */
-extern void __cds_wfcq_splice_blocking(
+extern enum cds_wfcq_ret __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);
+
+/*
+ * __cds_wfcq_splice_nonblocking: enqueue all src_q nodes at the end of dest_q.
+ *
+ * Same as __cds_wfcq_splice_blocking, but returns
+ * CDS_WFCQ_RET_WOULDBLOCK if it needs to block.
+ */
+extern enum cds_wfcq_ret __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,
@@ -223,6 +273,16 @@ extern struct cds_wfcq_node *__cds_wfcq_first_blocking(
                struct cds_wfcq_head *head,
                struct cds_wfcq_tail *tail);
 
+/*
+ * __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.
+ */
+extern struct cds_wfcq_node *__cds_wfcq_first_nonblocking(
+               struct cds_wfcq_head *head,
+               struct cds_wfcq_tail *tail);
+
 /*
  * __cds_wfcq_next_blocking: get next node of a queue, without dequeuing.
  *
@@ -240,6 +300,17 @@ extern struct cds_wfcq_node *__cds_wfcq_next_blocking(
                struct cds_wfcq_tail *tail,
                struct cds_wfcq_node *node);
 
+/*
+ * __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.
+ */
+extern struct cds_wfcq_node *__cds_wfcq_next_nonblocking(
+               struct cds_wfcq_head *head,
+               struct cds_wfcq_tail *tail,
+               struct cds_wfcq_node *node);
+
 #endif /* !_LGPL_SOURCE */
 
 /*