wfstack: implement nonblocking pop and next

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

diff --git a/urcu/static/wfstack.h b/urcu/static/wfstack.h
index 018a1213b525d2266c6187da7b8fffd03dc94e43..9bc9519f16f43c87a65974ad1697fecfb242d94e 100644 (file)
--- a/urcu/static/wfstack.h
+++ b/urcu/static/wfstack.h
@@ -137,7 +137,7 @@ int _cds_wfs_push(struct cds_wfs_stack *s, struct cds_wfs_node *node)
  * Waiting for push to complete enqueue and return the next node.
  */
 static inline struct cds_wfs_node *
-___cds_wfs_node_sync_next(struct cds_wfs_node *node)
+___cds_wfs_node_sync_next(struct cds_wfs_node *node, int blocking)
 {
        struct cds_wfs_node *next;
        int attempt = 0;
@@ -146,6 +146,8 @@ ___cds_wfs_node_sync_next(struct cds_wfs_node *node)
         * Adaptative busy-looping waiting for push to complete.
         */
        while ((next = CMM_LOAD_SHARED(node->next)) == NULL) {
+               if (!blocking)
+                       return CDS_WFS_WOULDBLOCK;
                if (++attempt >= CDS_WFS_ADAPT_ATTEMPTS) {
                        poll(NULL, 0, CDS_WFS_WAIT);    /* Wait for 10ms */
                        attempt = 0;
@@ -157,6 +159,29 @@ ___cds_wfs_node_sync_next(struct cds_wfs_node *node)
        return next;
 }
 
+static inline
+struct cds_wfs_node *
+___cds_wfs_pop(struct cds_wfs_stack *s, int blocking)
+{
+       struct cds_wfs_head *head, *new_head;
+       struct cds_wfs_node *next;
+
+       for (;;) {
+               head = CMM_LOAD_SHARED(s->head);
+               if (___cds_wfs_end(head))
+                       return NULL;
+               next = ___cds_wfs_node_sync_next(&head->node, blocking);
+               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)
+                       return &head->node;
+               if (!blocking)
+                       return CDS_WFS_WOULDBLOCK;
+               /* busy-loop if head changed under us */
+       }
+}
+
 /*
  * __cds_wfs_pop_blocking: pop a node from the stack.
  *
@@ -177,19 +202,20 @@ static inline
 struct cds_wfs_node *
 ___cds_wfs_pop_blocking(struct cds_wfs_stack *s)
 {
-       struct cds_wfs_head *head, *new_head;
-       struct cds_wfs_node *next;
+       return ___cds_wfs_pop(s, 1);
+}
 
-       for (;;) {
-               head = CMM_LOAD_SHARED(s->head);
-               if (___cds_wfs_end(head))
-                       return NULL;
-               next = ___cds_wfs_node_sync_next(&head->node);
-               new_head = caa_container_of(next, struct cds_wfs_head, node);
-               if (uatomic_cmpxchg(&s->head, head, new_head) == head)
-                       return &head->node;
-               /* busy-loop if head changed under us */
-       }
+/*
+ * __cds_wfs_pop_nonblocking: pop a node from the stack.
+ *
+ * Same as __cds_wfs_pop_blocking, but returns CDS_WFS_WOULDBLOCK if
+ * it needs to block.
+ */
+static inline
+struct cds_wfs_node *
+___cds_wfs_pop_nonblocking(struct cds_wfs_stack *s)
+{
+       return ___cds_wfs_pop(s, 0);
 }
 
 /*
@@ -303,6 +329,22 @@ _cds_wfs_first(struct cds_wfs_head *head)
        return &head->node;
 }
 
+static inline struct cds_wfs_node *
+___cds_wfs_next(struct cds_wfs_node *node, int blocking)
+{
+       struct cds_wfs_node *next;
+
+       next = ___cds_wfs_node_sync_next(node, blocking);
+       /*
+        * CDS_WFS_WOULDBLOCK != CSD_WFS_END, so we can check for end
+        * even if ___cds_wfs_node_sync_next returns CDS_WFS_WOULDBLOCK,
+        * and still return CDS_WFS_WOULDBLOCK.
+        */
+       if (___cds_wfs_end(next))
+               return NULL;
+       return next;
+}
+
 /*
  * cds_wfs_next_blocking: get next node of a popped stack.
  *
@@ -319,12 +361,20 @@ _cds_wfs_first(struct cds_wfs_head *head)
 static inline struct cds_wfs_node *
 _cds_wfs_next_blocking(struct cds_wfs_node *node)
 {
-       struct cds_wfs_node *next;
+       return ___cds_wfs_next(node, 1);
+}
 
-       next = ___cds_wfs_node_sync_next(node);
-       if (___cds_wfs_end(next))
-               return NULL;
-       return next;
+
+/*
+ * cds_wfs_next_nonblocking: get next node of a popped stack.
+ *
+ * Same as cds_wfs_next_blocking, but returns CDS_WFS_WOULDBLOCK if it
+ * needs to block.
+ */
+static inline struct cds_wfs_node *
+_cds_wfs_next_nonblocking(struct cds_wfs_node *node)
+{
+       return ___cds_wfs_next(node, 0);
 }
 
 #ifdef __cplusplus

diff --git a/urcu/wfstack.h b/urcu/wfstack.h
index 0e435ba6d8e899ede731739e0fb8cc41db2deaf1..03fee8fb63f74bb3ca8a110e0c8eb971e5ba6937 100644 (file)
--- a/urcu/wfstack.h
+++ b/urcu/wfstack.h
@@ -58,6 +58,8 @@ extern "C" {
  * synchronization.
  */
 
+#define CDS_WFS_WOULDBLOCK     ((void *) -1UL)
+
 /*
  * 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
@@ -183,6 +185,14 @@ extern struct cds_wfs_node *cds_wfs_first(struct cds_wfs_head *head);
  */
 extern struct cds_wfs_node *cds_wfs_next_blocking(struct cds_wfs_node *node);
 
+/*
+ * cds_wfs_next_nonblocking: get next node of a popped stack.
+ *
+ * Same as cds_wfs_next_blocking, but returns CDS_WFS_WOULDBLOCK if it
+ * needs to block.
+ */
+extern struct cds_wfs_node *cds_wfs_next_nonblocking(struct cds_wfs_node *node);
+
 /*
  * cds_wfs_pop_lock: lock stack pop-protection mutex.
  */
@@ -211,6 +221,14 @@ 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_nonblocking: pop a node from the stack.
+ *
+ * Same as __cds_wfs_pop_blocking, but returns CDS_WFS_WOULDBLOCK if
+ * it needs to block.
+ */
+extern struct cds_wfs_node *__cds_wfs_pop_nonblocking(struct cds_wfs_stack *s);
+
 /*
  * __cds_wfs_pop_all: pop all nodes from a stack.
  *

diff --git a/wfstack.c b/wfstack.c
index f0bae57fe5982d77f1047f91b766464bfdaa6768..4ccb6b93aaaecc0752d4682842fba13aff2512d9 100644 (file)
--- a/wfstack.c
+++ b/wfstack.c
@@ -68,6 +68,11 @@ struct cds_wfs_node *cds_wfs_next_blocking(struct cds_wfs_node *node)
        return _cds_wfs_next_blocking(node);
 }
 
+struct cds_wfs_node *cds_wfs_next_nonblocking(struct cds_wfs_node *node)
+{
+       return _cds_wfs_next_nonblocking(node);
+}
+
 void cds_wfs_pop_lock(struct cds_wfs_stack *s)
 {
        _cds_wfs_pop_lock(s);
@@ -83,6 +88,11 @@ 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_nonblocking(struct cds_wfs_stack *s)
+{
+       return ___cds_wfs_pop_nonblocking(s);
+}
+
 struct cds_wfs_head *__cds_wfs_pop_all(struct cds_wfs_stack *s)
 {
        return ___cds_wfs_pop_all(s);