wfcqueue: enqueue and splice return queue state

[urcu.git] / urcu / static / wfcqueue.h

diff --git a/urcu/static/wfcqueue.h b/urcu/static/wfcqueue.h
index a284b580af7d8777087ba17e6094c40e03abecc9..1200227f4d3f6ade1f118b47ec77d592b3a508b5 100644 (file)
--- a/urcu/static/wfcqueue.h
+++ b/urcu/static/wfcqueue.h
@@ -128,7 +128,7 @@ static inline void _cds_wfcq_dequeue_unlock(struct cds_wfcq_head *head,
        assert(!ret);
 }
 
-static inline void ___cds_wfcq_append(struct cds_wfcq_head *head,
+static inline bool ___cds_wfcq_append(struct cds_wfcq_head *head,
                struct cds_wfcq_tail *tail,
                struct cds_wfcq_node *new_head,
                struct cds_wfcq_node *new_tail)
@@ -152,6 +152,11 @@ static inline void ___cds_wfcq_append(struct cds_wfcq_head *head,
         * perspective.
         */
        CMM_STORE_SHARED(old_tail->next, new_head);
+       /*
+        * Return false if queue was empty prior to adding the node,
+        * else return true.
+        */
+       return old_tail != &head->node;
 }
 
 /*
@@ -159,12 +164,15 @@ static inline void ___cds_wfcq_append(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.
  */
-static inline void _cds_wfcq_enqueue(struct cds_wfcq_head *head,
+static inline bool _cds_wfcq_enqueue(struct cds_wfcq_head *head,
                struct cds_wfcq_tail *tail,
                struct cds_wfcq_node *new_tail)
 {
-       ___cds_wfcq_append(head, tail, new_tail, new_tail);
+       return ___cds_wfcq_append(head, tail, new_tail, new_tail);
 }
 
 /*
@@ -384,7 +392,7 @@ ___cds_wfcq_dequeue_nonblocking(struct cds_wfcq_head *head,
        return ___cds_wfcq_dequeue(head, tail, 0);
 }
 
-static inline int
+static inline enum cds_wfcq_ret
 ___cds_wfcq_splice(
                struct cds_wfcq_head *dest_q_head,
                struct cds_wfcq_tail *dest_q_tail,
@@ -395,11 +403,11 @@ ___cds_wfcq_splice(
        struct cds_wfcq_node *head, *tail;
 
        if (_cds_wfcq_empty(src_q_head, src_q_tail))
-               return 0;
+               return CDS_WFCQ_RET_SRC_EMPTY;
 
        head = ___cds_wfcq_node_sync_next(&src_q_head->node, blocking);
        if (head == CDS_WFCQ_WOULDBLOCK)
-               return -1;
+               return CDS_WFCQ_RET_WOULDBLOCK;
        _cds_wfcq_node_init(&src_q_head->node);
 
        /*
@@ -414,8 +422,10 @@ ___cds_wfcq_splice(
         * Append the spliced content of src_q into dest_q. Does not
         * require mutual exclusion on dest_q (wait-free).
         */
-       ___cds_wfcq_append(dest_q_head, dest_q_tail, head, tail);
-       return 0;
+       if (___cds_wfcq_append(dest_q_head, dest_q_tail, head, tail))
+               return CDS_WFCQ_RET_DEST_NON_EMPTY;
+       else
+               return CDS_WFCQ_RET_DEST_EMPTY;
 }
 
 
@@ -426,25 +436,27 @@ ___cds_wfcq_splice(
  * dest_q must be already initialized.
  * 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. Never returns CDS_WFCQ_RET_WOULDBLOCK.
  */
-static inline void
+static inline 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)
 {
-       (void) ___cds_wfcq_splice(dest_q_head, dest_q_tail,
+       return ___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.
+ * Same as __cds_wfcq_splice_blocking, but returns
+ * CDS_WFCQ_RET_WOULDBLOCK if it needs to block.
  */
-static inline int
+static inline enum cds_wfcq_ret
 ___cds_wfcq_splice_nonblocking(
                struct cds_wfcq_head *dest_q_head,
                struct cds_wfcq_tail *dest_q_tail,
@@ -485,18 +497,23 @@ _cds_wfcq_dequeue_blocking(struct cds_wfcq_head *head,
  * 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. Never returns CDS_WFCQ_RET_WOULDBLOCK.
  */
-static inline void
+static inline 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)
 {
+       enum cds_wfcq_ret ret;
+
        _cds_wfcq_dequeue_lock(src_q_head, src_q_tail);
-       ___cds_wfcq_splice_blocking(dest_q_head, dest_q_tail,
+       ret = ___cds_wfcq_splice_blocking(dest_q_head, dest_q_tail,
                        src_q_head, src_q_tail);
        _cds_wfcq_dequeue_unlock(src_q_head, src_q_tail);
+       return ret;
 }
 
 #ifdef __cplusplus