wfstack: return whether pop is popping the last element

Newly introduced "with_state" pop API members return stack state
atomically sampled with the pop operation.

Allow testing behavior of pop with respect to number of push-to-empty
and pop-all-from-non-empty.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

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.
  */

diff --git a/urcu/wfstack.h b/urcu/wfstack.h
index 34ddb3f3e665465aa22b83fff4d7a2cdf8a7d385..fc0b44b791fcf218c56714711e235cc40465296f 100644 (file)
--- a/urcu/wfstack.h
+++ b/urcu/wfstack.h
@@ -60,6 +60,10 @@ extern "C" {
 
 #define CDS_WFS_WOULDBLOCK     ((void *) -1UL)
 
+enum cds_wfs_state {
+       CDS_WFS_STATE_LAST =            (1U << 0),
+};
+
 /*
  * struct cds_wfs_node is returned by __cds_wfs_pop, and also used as
  * iterator on stack. It is not safe to dereference the node next
@@ -95,6 +99,7 @@ struct cds_wfs_stack {
 
 /* Locking performed internally */
 #define cds_wfs_pop_blocking           _cds_wfs_pop_blocking
+#define cds_wfs_pop_with_state_blocking        _cds_wfs_pop_with_state_blocking
 #define cds_wfs_pop_all_blocking       _cds_wfs_pop_all_blocking
 
 /*
@@ -111,7 +116,11 @@ struct cds_wfs_stack {
 
 /* Synchronization ensured by the caller. See synchronization table. */
 #define __cds_wfs_pop_blocking         ___cds_wfs_pop_blocking
+#define __cds_wfs_pop_with_state_blocking      \
+                                       ___cds_wfs_pop_with_state_blocking
 #define __cds_wfs_pop_nonblocking      ___cds_wfs_pop_nonblocking
+#define __cds_wfs_pop_with_state_nonblocking   \
+                                       ___cds_wfs_pop_with_state_nonblocking
 #define __cds_wfs_pop_all              ___cds_wfs_pop_all
 
 #else /* !_LGPL_SOURCE */
@@ -151,6 +160,15 @@ extern int cds_wfs_push(struct cds_wfs_stack *s, struct cds_wfs_node *node);
  */
 extern struct cds_wfs_node *cds_wfs_pop_blocking(struct cds_wfs_stack *s);
 
+/*
+ * cds_wfs_pop_with_state_blocking: pop a node from the stack, with state.
+ *
+ * Same as cds_wfs_pop_blocking, but stores whether the stack was
+ * empty into state (CDS_WFS_STATE_LAST).
+ */
+extern struct cds_wfs_node *
+       cds_wfs_pop_with_state_blocking(struct cds_wfs_stack *s, int *state);
+
 /*
  * cds_wfs_pop_all_blocking: pop all nodes from a stack.
  *
@@ -223,6 +241,15 @@ extern void cds_wfs_pop_unlock(struct cds_wfs_stack *s);
  */
 extern struct cds_wfs_node *__cds_wfs_pop_blocking(struct cds_wfs_stack *s);
 
+/*
+ * __cds_wfs_pop_with_state_blocking: pop a node from the stack, with state.
+ *
+ * Same as __cds_wfs_pop_blocking, but stores whether the stack was
+ * empty into state (CDS_WFS_STATE_LAST).
+ */
+extern struct cds_wfs_node *
+       __cds_wfs_pop_with_state_blocking(struct cds_wfs_stack *s, int *state);
+
 /*
  * __cds_wfs_pop_nonblocking: pop a node from the stack.
  *
@@ -231,6 +258,16 @@ extern struct cds_wfs_node *__cds_wfs_pop_blocking(struct cds_wfs_stack *s);
  */
 extern struct cds_wfs_node *__cds_wfs_pop_nonblocking(struct cds_wfs_stack *s);
 
+/*
+ * __cds_wfs_pop_with_state_nonblocking: pop a node from the stack, with state.
+ *
+ * Same as __cds_wfs_pop_nonblocking, but stores whether the stack was
+ * empty into state (CDS_WFS_STATE_LAST).
+ */
+extern struct cds_wfs_node *
+       __cds_wfs_pop_with_state_nonblocking(struct cds_wfs_stack *s,
+               int *state);
+
 /*
  * __cds_wfs_pop_all: pop all nodes from a stack.
  *

diff --git a/wfstack.c b/wfstack.c
index 4ccb6b93aaaecc0752d4682842fba13aff2512d9..c8bd7e6214211190be827474c301718882daf7c9 100644 (file)
--- a/wfstack.c
+++ b/wfstack.c
@@ -53,6 +53,12 @@ struct cds_wfs_node *cds_wfs_pop_blocking(struct cds_wfs_stack *s)
        return _cds_wfs_pop_blocking(s);
 }
 
+struct cds_wfs_node *
+       cds_wfs_pop_with_state_blocking(struct cds_wfs_stack *s, int *state)
+{
+       return _cds_wfs_pop_with_state_blocking(s, state);
+}
+
 struct cds_wfs_head *cds_wfs_pop_all_blocking(struct cds_wfs_stack *s)
 {
        return _cds_wfs_pop_all_blocking(s);
@@ -88,11 +94,24 @@ struct cds_wfs_node *__cds_wfs_pop_blocking(struct cds_wfs_stack *s)
        return ___cds_wfs_pop_blocking(s);
 }
 
+struct cds_wfs_node *
+       __cds_wfs_pop_with_state_blocking(struct cds_wfs_stack *s, int *state)
+{
+       return ___cds_wfs_pop_with_state_blocking(s, state);
+}
+
 struct cds_wfs_node *__cds_wfs_pop_nonblocking(struct cds_wfs_stack *s)
 {
        return ___cds_wfs_pop_nonblocking(s);
 }
 
+struct cds_wfs_node *
+       __cds_wfs_pop_with_state_nonblocking(struct cds_wfs_stack *s,
+               int *state)
+{
+       return ___cds_wfs_pop_with_state_nonblocking(s, state);
+}
+
 struct cds_wfs_head *__cds_wfs_pop_all(struct cds_wfs_stack *s)
 {
        return ___cds_wfs_pop_all(s);