#define _URCU_WFCQUEUE_H
/*
- * wfcqueue.h
+ * urcu/wfcqueue.h
*
* Userspace RCU library - Concurrent Queue with Wait-Free Enqueue/Blocking Dequeue
*
/*
* Concurrent queue with wait-free enqueue/blocking dequeue.
*
- * Inspired from half-wait-free/half-blocking queue implementation done by
- * Paul E. McKenney.
+ * This queue has been designed and implemented collaboratively by
+ * Mathieu Desnoyers and Lai Jiangshan. Inspired from
+ * half-wait-free/half-blocking queue implementation done by Paul E.
+ * McKenney.
*/
+#define CDS_WFCQ_WOULDBLOCK ((void *) -1UL)
+
+enum cds_wfcq_ret {
+ CDS_WFCQ_RET_WOULDBLOCK = -1,
+ CDS_WFCQ_RET_DEST_EMPTY = 0,
+ CDS_WFCQ_RET_DEST_NON_EMPTY = 1,
+ CDS_WFCQ_RET_SRC_EMPTY = 2,
+};
+
struct cds_wfcq_node {
struct cds_wfcq_node *next;
};
#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 */
/*
*
* For convenience, cds_wfcq_dequeue_blocking() and
* cds_wfcq_splice_blocking() hold the dequeue lock.
+ *
+ * Besides locking, mutual exclusion of dequeue, splice and iteration
+ * can be ensured by performing all of those operations from a single
+ * thread, without requiring any lock.
*/
/*
*
* 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.
*/
-extern void cds_wfcq_enqueue(struct cds_wfcq_head *head,
+extern bool cds_wfcq_enqueue(struct cds_wfcq_head *head,
struct cds_wfcq_tail *tail,
struct cds_wfcq_node *node);
* 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.
- * Mutual exlusion with dequeuers is ensured internally.
+ * Mutual exlusion with cds_wfcq_dequeue_blocking and dequeue lock is
+ * ensured.
*/
extern struct cds_wfcq_node *cds_wfcq_dequeue_blocking(
struct cds_wfcq_head *head,
* dest_q must be already initialized.
* Content written into the node before enqueue is guaranteed to be
* consistent, but no other memory ordering is ensured.
- * Mutual exlusion with dequeuers is ensured internally.
+ * 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. Cannot block.
*/
-extern void cds_wfcq_splice_blocking(
+extern 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);
/*
- * __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.
* It is valid to reuse and free a dequeued node immediately.
- * Should be called with cds_wfcq_dequeue_lock() held.
+ * Dequeue/splice/iteration mutual exclusion should be ensured by the
+ * caller.
*/
extern struct cds_wfcq_node *__cds_wfcq_dequeue_blocking(
struct cds_wfcq_head *head,
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.
*
* dest_q must be already initialized.
* Content written into the node before enqueue is guaranteed to be
* consistent, but no other memory ordering is ensured.
- * Should be called with cds_wfcq_dequeue_lock() held.
+ * 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. Cannot block.
+ */
+extern 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);
+
+/*
+ * __cds_wfcq_splice_nonblocking: enqueue all src_q nodes at the end of dest_q.
+ *
+ * Same as __cds_wfcq_splice_blocking, but returns
+ * CDS_WFCQ_RET_WOULDBLOCK if it needs to block.
*/
-extern void __cds_wfcq_splice_blocking(
+extern enum cds_wfcq_ret __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,
*
* Content written into the node before enqueue is guaranteed to be
* consistent, but no other memory ordering is ensured.
- * Should be called with cds_wfcq_dequeue_lock() held.
+ * Dequeue/splice/iteration mutual exclusion should be ensured by the
+ * caller.
*
* Used by for-like iteration macros:
* __cds_wfcq_for_each_blocking()
struct cds_wfcq_head *head,
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
* consistent, but no other memory ordering is ensured.
- * Should be called with cds_wfcq_dequeue_lock() held.
+ * Dequeue/splice/iteration mutual exclusion should be ensured by the
+ * caller.
*
* Used by for-like iteration macros:
* __cds_wfcq_for_each_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 */
/*
*
* Content written into each node before enqueue is guaranteed to be
* consistent, but no other memory ordering is ensured.
- * Should be called with cds_wfcq_dequeue_lock() held.
+ * Dequeue/splice/iteration mutual exclusion should be ensured by the
+ * caller.
*/
#define __cds_wfcq_for_each_blocking(head, tail, node) \
for (node = __cds_wfcq_first_blocking(head, tail); \
*
* Content written into each node before enqueue is guaranteed to be
* consistent, but no other memory ordering is ensured.
- * Should be called with cds_wfcq_dequeue_lock() held.
+ * Dequeue/splice/iteration mutual exclusion should be ensured by the
+ * caller.
*/
#define __cds_wfcq_for_each_blocking_safe(head, tail, node, n) \
for (node = __cds_wfcq_first_blocking(head, tail), \
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