[lttng-dev] [PATCH] urcu wfcqueue: introduce nonblocking API
Mathieu Desnoyers
mathieu.desnoyers at efficios.com
Sun Oct 21 22:30:49 EDT 2012
Introduce nonblocking API in wfcqueue, allowing RT threads to try to
dequeue, splice, or iterate on spliced queues without blocking: the
caller needs to handle CDS_WFCQ_WOULDBLOCK return value (or nonzero
return value for splice).
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
CC: Paul McKenney <paulmck at linux.vnet.ibm.com>
CC: Lai Jiangshan <laijs at cn.fujitsu.com>
---
diff --git a/urcu/static/wfcqueue.h b/urcu/static/wfcqueue.h
index 4a9003e..120a598 100644
--- a/urcu/static/wfcqueue.h
+++ b/urcu/static/wfcqueue.h
@@ -2,7 +2,7 @@
#define _URCU_WFCQUEUE_STATIC_H
/*
- * wfcqueue-static.h
+ * urcu/static/wfcqueue.h
*
* Userspace RCU library - Concurrent Queue with Wait-Free Enqueue/Blocking Dequeue
*
@@ -171,7 +171,7 @@ static inline void _cds_wfcq_enqueue(struct cds_wfcq_head *head,
* Waiting for enqueuer to complete enqueue and return the next node.
*/
static inline struct cds_wfcq_node *
-___cds_wfcq_node_sync_next(struct cds_wfcq_node *node)
+___cds_wfcq_node_sync_next(struct cds_wfcq_node *node, int blocking)
{
struct cds_wfcq_node *next;
int attempt = 0;
@@ -180,6 +180,8 @@ ___cds_wfcq_node_sync_next(struct cds_wfcq_node *node)
* Adaptative busy-looping waiting for enqueuer to complete enqueue.
*/
while ((next = CMM_LOAD_SHARED(node->next)) == NULL) {
+ if (!blocking)
+ return CDS_WFCQ_WOULDBLOCK;
if (++attempt >= WFCQ_ADAPT_ATTEMPTS) {
poll(NULL, 0, WFCQ_WAIT); /* Wait for 10ms */
attempt = 0;
@@ -191,34 +193,23 @@ ___cds_wfcq_node_sync_next(struct cds_wfcq_node *node)
return next;
}
-/*
- * __cds_wfcq_first_blocking: get first node of a queue, without dequeuing.
- *
- * Content written into the node before enqueue is guaranteed to be
- * consistent, but no other memory ordering is ensured.
- * Dequeue/splice/iteration mutual exclusion should be ensured by the
- * caller.
- *
- * Used by for-like iteration macros in urcu/wfqueue.h:
- * __cds_wfcq_for_each_blocking()
- * __cds_wfcq_for_each_blocking_safe()
- */
static inline struct cds_wfcq_node *
-___cds_wfcq_first_blocking(struct cds_wfcq_head *head,
- struct cds_wfcq_tail *tail)
+___cds_wfcq_first(struct cds_wfcq_head *head,
+ struct cds_wfcq_tail *tail,
+ int blocking)
{
struct cds_wfcq_node *node;
if (_cds_wfcq_empty(head, tail))
return NULL;
- node = ___cds_wfcq_node_sync_next(&head->node);
+ node = ___cds_wfcq_node_sync_next(&head->node, blocking);
/* Load head->node.next before loading node's content */
cmm_smp_read_barrier_depends();
return node;
}
/*
- * __cds_wfcq_next_blocking: get next node of a queue, without dequeuing.
+ * __cds_wfcq_first_blocking: get first node of a queue, without dequeuing.
*
* Content written into the node before enqueue is guaranteed to be
* consistent, but no other memory ordering is ensured.
@@ -230,9 +221,31 @@ ___cds_wfcq_first_blocking(struct cds_wfcq_head *head,
* __cds_wfcq_for_each_blocking_safe()
*/
static inline struct cds_wfcq_node *
-___cds_wfcq_next_blocking(struct cds_wfcq_head *head,
+___cds_wfcq_first_blocking(struct cds_wfcq_head *head,
+ struct cds_wfcq_tail *tail)
+{
+ return ___cds_wfcq_first(head, tail, 1);
+}
+
+
+/*
+ * __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.
+ */
+static inline struct cds_wfcq_node *
+___cds_wfcq_first_nonblocking(struct cds_wfcq_head *head,
+ struct cds_wfcq_tail *tail)
+{
+ return ___cds_wfcq_first(head, tail, 0);
+}
+
+static inline struct cds_wfcq_node *
+___cds_wfcq_next(struct cds_wfcq_head *head,
struct cds_wfcq_tail *tail,
- struct cds_wfcq_node *node)
+ struct cds_wfcq_node *node,
+ int blocking)
{
struct cds_wfcq_node *next;
@@ -247,7 +260,7 @@ ___cds_wfcq_next_blocking(struct cds_wfcq_head *head,
cmm_smp_rmb();
if (CMM_LOAD_SHARED(tail->p) == node)
return NULL;
- next = ___cds_wfcq_node_sync_next(node);
+ next = ___cds_wfcq_node_sync_next(node, blocking);
}
/* Load node->next before loading next's content */
cmm_smp_read_barrier_depends();
@@ -255,24 +268,50 @@ ___cds_wfcq_next_blocking(struct cds_wfcq_head *head,
}
/*
- * __cds_wfcq_dequeue_blocking: dequeue a node from the queue.
+ * __cds_wfcq_next_blocking: get next node of a queue, without dequeuing.
*
* Content written into the node before enqueue is guaranteed to be
* consistent, but no other memory ordering is ensured.
- * It is valid to reuse and free a dequeued node immediately.
* Dequeue/splice/iteration mutual exclusion should be ensured by the
* caller.
+ *
+ * Used by for-like iteration macros in urcu/wfqueue.h:
+ * __cds_wfcq_for_each_blocking()
+ * __cds_wfcq_for_each_blocking_safe()
*/
static inline struct cds_wfcq_node *
-___cds_wfcq_dequeue_blocking(struct cds_wfcq_head *head,
- struct cds_wfcq_tail *tail)
+___cds_wfcq_next_blocking(struct cds_wfcq_head *head,
+ struct cds_wfcq_tail *tail,
+ struct cds_wfcq_node *node)
+{
+ return ___cds_wfcq_next(head, tail, node, 1);
+}
+
+/*
+ * __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.
+ */
+static inline struct cds_wfcq_node *
+___cds_wfcq_next_nonblocking(struct cds_wfcq_head *head,
+ struct cds_wfcq_tail *tail,
+ struct cds_wfcq_node *node)
+{
+ return ___cds_wfcq_next(head, tail, node, 0);
+}
+
+static inline struct cds_wfcq_node *
+___cds_wfcq_dequeue(struct cds_wfcq_head *head,
+ struct cds_wfcq_tail *tail,
+ int blocking)
{
struct cds_wfcq_node *node, *next;
if (_cds_wfcq_empty(head, tail))
return NULL;
- node = ___cds_wfcq_node_sync_next(&head->node);
+ node = ___cds_wfcq_node_sync_next(&head->node, blocking);
if ((next = CMM_LOAD_SHARED(node->next)) == NULL) {
/*
@@ -292,7 +331,7 @@ ___cds_wfcq_dequeue_blocking(struct cds_wfcq_head *head,
_cds_wfcq_node_init(&head->node);
if (uatomic_cmpxchg(&tail->p, node, &head->node) == node)
return node;
- next = ___cds_wfcq_node_sync_next(node);
+ next = ___cds_wfcq_node_sync_next(node, blocking);
}
/*
@@ -306,26 +345,50 @@ ___cds_wfcq_dequeue_blocking(struct cds_wfcq_head *head,
}
/*
- * __cds_wfcq_splice_blocking: enqueue all src_q nodes at the end of dest_q.
+ * __cds_wfcq_dequeue_blocking: dequeue a node from the queue.
*
- * Dequeue all nodes from src_q.
- * dest_q must be already initialized.
- * Dequeue/splice/iteration mutual exclusion for src_q should be ensured
- * by the caller.
+ * Content written into the node before enqueue is guaranteed to be
+ * consistent, but no other memory ordering is ensured.
+ * It is valid to reuse and free a dequeued node immediately.
+ * Dequeue/splice/iteration mutual exclusion should be ensured by the
+ * caller.
*/
-static inline void
-___cds_wfcq_splice_blocking(
+static inline struct cds_wfcq_node *
+___cds_wfcq_dequeue_blocking(struct cds_wfcq_head *head,
+ struct cds_wfcq_tail *tail)
+{
+ return ___cds_wfcq_dequeue(head, tail, 1);
+}
+
+/*
+ * __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.
+ */
+static inline struct cds_wfcq_node *
+___cds_wfcq_dequeue_nonblocking(struct cds_wfcq_head *head,
+ struct cds_wfcq_tail *tail)
+{
+ return ___cds_wfcq_dequeue(head, tail, 0);
+}
+
+static inline int
+___cds_wfcq_splice(
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)
+ struct cds_wfcq_tail *src_q_tail,
+ int blocking)
{
struct cds_wfcq_node *head, *tail;
if (_cds_wfcq_empty(src_q_head, src_q_tail))
- return;
+ return 0;
- head = ___cds_wfcq_node_sync_next(&src_q_head->node);
+ head = ___cds_wfcq_node_sync_next(&src_q_head->node, blocking);
+ if (head == CDS_WFCQ_WOULDBLOCK)
+ return -1;
_cds_wfcq_node_init(&src_q_head->node);
/*
@@ -341,6 +404,44 @@ ___cds_wfcq_splice_blocking(
* require mutual exclusion on dest_q (wait-free).
*/
___cds_wfcq_append(dest_q_head, dest_q_tail, head, tail);
+ return 0;
+}
+
+
+/*
+ * __cds_wfcq_splice_blocking: enqueue all src_q nodes at the end of dest_q.
+ *
+ * Dequeue all nodes from src_q.
+ * dest_q must be already initialized.
+ * Dequeue/splice/iteration mutual exclusion for src_q should be ensured
+ * by the caller.
+ */
+static inline void
+___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,
+ 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.
+ */
+static inline int
+___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,
+ struct cds_wfcq_tail *src_q_tail)
+{
+ return ___cds_wfcq_splice(dest_q_head, dest_q_tail,
+ src_q_head, src_q_tail, 0);
}
/*
diff --git a/urcu/wfcqueue.h b/urcu/wfcqueue.h
index ba2f2ed..fe2862e 100644
--- 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 +43,8 @@ extern "C" {
* McKenney.
*/
+#define CDS_WFCQ_WOULDBLOCK ((void *) -1UL)
+
struct cds_wfcq_node {
struct cds_wfcq_node *next;
};
@@ -86,6 +88,16 @@ 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 */
/*
@@ -179,7 +191,7 @@ extern void cds_wfcq_splice_blocking(
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.
@@ -192,6 +204,16 @@ extern struct cds_wfcq_node *__cds_wfcq_dequeue_blocking(
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.
*
* Dequeue all nodes from src_q.
@@ -208,6 +230,18 @@ extern void __cds_wfcq_splice_blocking(
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 nonzero if it needs to
+ * block.
+ */
+extern int __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,
+ struct cds_wfcq_tail *src_q_tail);
+
+/*
* __cds_wfcq_first_blocking: get first node of a queue, without dequeuing.
*
* Content written into the node before enqueue is guaranteed to be
@@ -224,6 +258,16 @@ extern struct cds_wfcq_node *__cds_wfcq_first_blocking(
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.
*
* Content written into the node before enqueue is guaranteed to be
@@ -240,6 +284,17 @@ 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 */
/*
diff --git a/wfcqueue.c b/wfcqueue.c
index 1fa27ac..3474ee0 100644
--- a/wfcqueue.c
+++ b/wfcqueue.c
@@ -90,6 +90,13 @@ struct cds_wfcq_node *__cds_wfcq_dequeue_blocking(
return ___cds_wfcq_dequeue_blocking(head, tail);
}
+struct cds_wfcq_node *__cds_wfcq_dequeue_nonblocking(
+ struct cds_wfcq_head *head,
+ struct cds_wfcq_tail *tail)
+{
+ return ___cds_wfcq_dequeue_nonblocking(head, tail);
+}
+
void __cds_wfcq_splice_blocking(
struct cds_wfcq_head *dest_q_head,
struct cds_wfcq_tail *dest_q_tail,
@@ -100,6 +107,16 @@ void __cds_wfcq_splice_blocking(
src_q_head, src_q_tail);
}
+int __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,
+ struct cds_wfcq_tail *src_q_tail)
+{
+ return ___cds_wfcq_splice_nonblocking(dest_q_head, dest_q_tail,
+ src_q_head, src_q_tail);
+}
+
struct cds_wfcq_node *__cds_wfcq_first_blocking(
struct cds_wfcq_head *head,
struct cds_wfcq_tail *tail)
@@ -107,6 +124,13 @@ struct cds_wfcq_node *__cds_wfcq_first_blocking(
return ___cds_wfcq_first_blocking(head, tail);
}
+struct cds_wfcq_node *__cds_wfcq_first_nonblocking(
+ struct cds_wfcq_head *head,
+ struct cds_wfcq_tail *tail)
+{
+ return ___cds_wfcq_first_nonblocking(head, tail);
+}
+
struct cds_wfcq_node *__cds_wfcq_next_blocking(
struct cds_wfcq_head *head,
struct cds_wfcq_tail *tail,
@@ -114,3 +138,11 @@ struct cds_wfcq_node *__cds_wfcq_next_blocking(
{
return ___cds_wfcq_next_blocking(head, tail, node);
}
+
+struct cds_wfcq_node *__cds_wfcq_next_nonblocking(
+ struct cds_wfcq_head *head,
+ struct cds_wfcq_tail *tail,
+ struct cds_wfcq_node *node)
+{
+ return ___cds_wfcq_next_nonblocking(head, tail, node);
+}
--
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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