[lttng-dev] [PATCH 01/16] Fix: wfcqueue nonblocking dequeue

[Lai Jiangshan]

On 11/21/2012 03:40 AM, Mathieu Desnoyers wrote:
> Failures were not handled in the nonblocking dequeue implementation.
> 
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> ---
>  urcu/static/wfcqueue.h |   11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/urcu/static/wfcqueue.h b/urcu/static/wfcqueue.h
> index 8733771..a284b58 100644
> --- a/urcu/static/wfcqueue.h
> +++ b/urcu/static/wfcqueue.h
> @@ -312,6 +312,8 @@ ___cds_wfcq_dequeue(struct cds_wfcq_head *head,
>  		return NULL;
>  
>  	node = ___cds_wfcq_node_sync_next(&head->node, blocking);
> +	if (!blocking && node == CDS_WFCQ_WOULDBLOCK)
> +		return CDS_WFCQ_WOULDBLOCK;
>  
>  	if ((next = CMM_LOAD_SHARED(node->next)) == NULL) {
>  		/*
> @@ -332,6 +334,15 @@ ___cds_wfcq_dequeue(struct cds_wfcq_head *head,
>  		if (uatomic_cmpxchg(&tail->p, node, &head->node) == node)
>  			return node;

Is it this simpler?
we had just loaded node->next via "if ((next = CMM_LOAD_SHARED(node->next)) == NULL)"


+		if (!blocking)
+			return CDS_WFCQ_WOULDBLOCK

>  		next = ___cds_wfcq_node_sync_next(node, blocking);

and remove the following.

> +		/*
> +		 * In nonblocking mode, if we would need to block to
> +		 * get node's next, set the head next node pointer
> +		 * (currently NULL) back to its original value.
> +		 */
> +		if (!blocking && next == CDS_WFCQ_WOULDBLOCK) {
> +			head->node.next = node;
> +			return CDS_WFCQ_WOULDBLOCK;
> +		}
>  	}
>  
>  	/*