wfstack: return whether pop is popping the last element

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

diff --git a/urcu/static/wfstack.h b/urcu/static/wfstack.h
index 9bc9519f16f43c87a65974ad1697fecfb242d94e..db0d5b8b1abda178f7cf0e14a0530d5bae43f8aa 100644 (file)
--- a/urcu/static/wfstack.h
+++ b/urcu/static/wfstack.h
@@ -161,29 +161,37 @@ ___cds_wfs_node_sync_next(struct cds_wfs_node *node, int blocking)
 
 static inline
 struct cds_wfs_node *
-___cds_wfs_pop(struct cds_wfs_stack *s, int blocking)
+___cds_wfs_pop(struct cds_wfs_stack *s, int *state, int blocking)
 {
        struct cds_wfs_head *head, *new_head;
        struct cds_wfs_node *next;
 
+       if (state)
+               *state = 0;
        for (;;) {
                head = CMM_LOAD_SHARED(s->head);
-               if (___cds_wfs_end(head))
+               if (___cds_wfs_end(head)) {
                        return NULL;
+               }
                next = ___cds_wfs_node_sync_next(&head->node, blocking);
-               if (!blocking && next == CDS_WFS_WOULDBLOCK)
+               if (!blocking && next == CDS_WFS_WOULDBLOCK) {
                        return CDS_WFS_WOULDBLOCK;
+               }
                new_head = caa_container_of(next, struct cds_wfs_head, node);
-               if (uatomic_cmpxchg(&s->head, head, new_head) == head)
+               if (uatomic_cmpxchg(&s->head, head, new_head) == head) {
+                       if (state && ___cds_wfs_end(new_head))
+                               *state |= CDS_WFS_STATE_LAST;
                        return &head->node;
-               if (!blocking)
+               }
+               if (!blocking) {
                        return CDS_WFS_WOULDBLOCK;
+               }
                /* busy-loop if head changed under us */
        }
 }
 
 /*
- * __cds_wfs_pop_blocking: pop a node from the stack.
+ * __cds_wfs_pop_with_state_blocking: pop a node from the stack, with state.
  *
  * Returns NULL if stack is empty.
  *
@@ -197,12 +205,36 @@ ___cds_wfs_pop(struct cds_wfs_stack *s, int blocking)
  *     __cds_wfs_pop_blocking and __cds_wfs_pop_all callers.
  * 3) Ensuring that only ONE thread can call __cds_wfs_pop_blocking()
  *    and __cds_wfs_pop_all(). (multi-provider/single-consumer scheme).
+ *
+ * "state" saves state flags atomically sampled with pop operation.
  */
+static inline
+struct cds_wfs_node *
+___cds_wfs_pop_with_state_blocking(struct cds_wfs_stack *s, int *state)
+{
+       return ___cds_wfs_pop(s, state, 1);
+}
+
 static inline
 struct cds_wfs_node *
 ___cds_wfs_pop_blocking(struct cds_wfs_stack *s)
 {
-       return ___cds_wfs_pop(s, 1);
+       return ___cds_wfs_pop_with_state_blocking(s, NULL);
+}
+
+/*
+ * __cds_wfs_pop_with_state_nonblocking: pop a node from the stack.
+ *
+ * Same as __cds_wfs_pop_with_state_blocking, but returns
+ * CDS_WFS_WOULDBLOCK if it needs to block.
+ *
+ * "state" saves state flags atomically sampled with pop operation.
+ */
+static inline
+struct cds_wfs_node *
+___cds_wfs_pop_with_state_nonblocking(struct cds_wfs_stack *s, int *state)
+{
+       return ___cds_wfs_pop(s, state, 0);
 }
 
 /*
@@ -215,7 +247,7 @@ static inline
 struct cds_wfs_node *
 ___cds_wfs_pop_nonblocking(struct cds_wfs_stack *s)
 {
-       return ___cds_wfs_pop(s, 0);
+       return ___cds_wfs_pop_with_state_nonblocking(s, NULL);
 }
 
 /*
@@ -280,20 +312,30 @@ static inline void _cds_wfs_pop_unlock(struct cds_wfs_stack *s)
 }
 
 /*
- * Call __cds_wfs_pop_blocking with an internal pop mutex held.
+ * Call __cds_wfs_pop_with_state_blocking with an internal pop mutex held.
  */
 static inline
 struct cds_wfs_node *
-_cds_wfs_pop_blocking(struct cds_wfs_stack *s)
+_cds_wfs_pop_with_state_blocking(struct cds_wfs_stack *s, int *state)
 {
        struct cds_wfs_node *retnode;
 
        _cds_wfs_pop_lock(s);
-       retnode = ___cds_wfs_pop_blocking(s);
+       retnode = ___cds_wfs_pop_with_state_blocking(s, state);
        _cds_wfs_pop_unlock(s);
        return retnode;
 }
 
+/*
+ * Call _cds_wfs_pop_with_state_blocking without saving any state.
+ */
+static inline
+struct cds_wfs_node *
+_cds_wfs_pop_blocking(struct cds_wfs_stack *s)
+{
+       return _cds_wfs_pop_with_state_blocking(s, NULL);
+}
+
 /*
  * Call __cds_wfs_pop_all with an internal pop mutex held.
  */