[lttng-dev] [RFC PATCH urcu 2/2] wfcqueue: add C++ compatibility API

[Paul E. McKenney]

On Tue, Mar 08, 2016 at 05:20:25PM +0000, Mathieu Desnoyers wrote:
> ----- On Mar 8, 2016, at 12:11 PM, Paul E. McKenney paulmck at linux.vnet.ibm.com wrote:
> 
> > On Mon, Mar 07, 2016 at 07:33:44PM -0500, Mathieu Desnoyers wrote:
> >> Introduce __cds_wfcq_head_cast and cds_wfcq_head_cast for compability
> >> of wfcqueue with c++. Those are effect-less in C, where transparent
> >> unions are supported. However, in C++, those transform struct
> >> cds_wfcq_head and struct __cds_wfcq_head pointers to
> >> cds_wfcq_head_ptr_t.
> >> 
> >> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> > 
> > Good stuff!!!
> > 
> > Reviewed-by: Paul E. McKenney <paulmck at linux.vnet.ibm.com>
> > Tested-by: Paul E. McKenney <paulmck at linux.vnet.ibm.com>
> 
> Thanks!
> 
> Will merge into urcu master and stable-0.9.

Very good, thank you!!!

							Thanx, Paul

> Mathieu
> 
> > 
> >> ---
> >>  urcu/static/wfcqueue.h | 16 +++++++++-------
> >>  urcu/wfcqueue.h        | 40 ++++++++++++++++++++++++++++++++++++++++
> >>  2 files changed, 49 insertions(+), 7 deletions(-)
> >> 
> >> diff --git a/urcu/static/wfcqueue.h b/urcu/static/wfcqueue.h
> >> index 7c9d548..4ababbf 100644
> >> --- a/urcu/static/wfcqueue.h
> >> +++ b/urcu/static/wfcqueue.h
> >> @@ -257,7 +257,7 @@ ___cds_wfcq_first(cds_wfcq_head_ptr_t u_head,
> >>  	struct __cds_wfcq_head *head = u_head._h;
> >>  	struct cds_wfcq_node *node;
> >> 
> >> -	if (_cds_wfcq_empty(head, tail))
> >> +	if (_cds_wfcq_empty(__cds_wfcq_head_cast(head), tail))
> >>  		return NULL;
> >>  	node = ___cds_wfcq_node_sync_next(&head->node, blocking);
> >>  	/* Load head->node.next before loading node's content */
> >> @@ -375,7 +375,7 @@ ___cds_wfcq_dequeue_with_state(cds_wfcq_head_ptr_t u_head,
> >>  	if (state)
> >>  		*state = 0;
> >> 
> >> -	if (_cds_wfcq_empty(head, tail)) {
> >> +	if (_cds_wfcq_empty(__cds_wfcq_head_cast(head), tail)) {
> >>  		return NULL;
> >>  	}
> >> 
> >> @@ -509,7 +509,7 @@ ___cds_wfcq_splice(
> >>  	 * Initial emptiness check to speed up cases where queue is
> >>  	 * empty: only require loads to check if queue is empty.
> >>  	 */
> >> -	if (_cds_wfcq_empty(src_q_head, src_q_tail))
> >> +	if (_cds_wfcq_empty(__cds_wfcq_head_cast(src_q_head), src_q_tail))
> >>  		return CDS_WFCQ_RET_SRC_EMPTY;
> >> 
> >>  	for (;;) {
> >> @@ -539,7 +539,8 @@ ___cds_wfcq_splice(
> >>  	 * Append the spliced content of src_q into dest_q. Does not
> >>  	 * require mutual exclusion on dest_q (wait-free).
> >>  	 */
> >> -	if (___cds_wfcq_append(dest_q_head, dest_q_tail, head, tail))
> >> +	if (___cds_wfcq_append(__cds_wfcq_head_cast(dest_q_head), dest_q_tail,
> >> +			head, tail))
> >>  		return CDS_WFCQ_RET_DEST_NON_EMPTY;
> >>  	else
> >>  		return CDS_WFCQ_RET_DEST_EMPTY;
> >> @@ -599,7 +600,8 @@ _cds_wfcq_dequeue_with_state_blocking(struct cds_wfcq_head
> >> *head,
> >>  	struct cds_wfcq_node *retval;
> >> 
> >>  	_cds_wfcq_dequeue_lock(head, tail);
> >> -	retval = ___cds_wfcq_dequeue_with_state_blocking(head, tail, state);
> >> +	retval = ___cds_wfcq_dequeue_with_state_blocking(cds_wfcq_head_cast(head),
> >> +			tail, state);
> >>  	_cds_wfcq_dequeue_unlock(head, tail);
> >>  	return retval;
> >>  }
> >> @@ -638,8 +640,8 @@ _cds_wfcq_splice_blocking(
> >>  	enum cds_wfcq_ret ret;
> >> 
> >>  	_cds_wfcq_dequeue_lock(src_q_head, src_q_tail);
> >> -	ret = ___cds_wfcq_splice_blocking(dest_q_head, dest_q_tail,
> >> -			src_q_head, src_q_tail);
> >> +	ret = ___cds_wfcq_splice_blocking(cds_wfcq_head_cast(dest_q_head),
> >> dest_q_tail,
> >> +			cds_wfcq_head_cast(src_q_head), src_q_tail);
> >>  	_cds_wfcq_dequeue_unlock(src_q_head, src_q_tail);
> >>  	return ret;
> >>  }
> >> diff --git a/urcu/wfcqueue.h b/urcu/wfcqueue.h
> >> index c0bb289..ec86032 100644
> >> --- a/urcu/wfcqueue.h
> >> +++ b/urcu/wfcqueue.h
> >> @@ -74,6 +74,7 @@ struct cds_wfcq_head {
> >>  	pthread_mutex_t lock;
> >>  };
> >> 
> >> +#ifndef __cplusplus
> >>  /*
> >>   * The transparent union allows calling functions that work on both
> >>   * struct cds_wfcq_head and struct __cds_wfcq_head on any of those two
> >> @@ -84,6 +85,45 @@ typedef union {
> >>  	struct cds_wfcq_head *h;
> >>  } __attribute__((__transparent_union__)) cds_wfcq_head_ptr_t;
> >> 
> >> +/*
> >> + * This static inline is only present for compatibility with C++. It is
> >> + * effect-less in C.
> >> + */
> >> +static inline struct __cds_wfcq_head *__cds_wfcq_head_cast(struct
> >> __cds_wfcq_head *head)
> >> +{
> >> +	return head;
> >> +}
> >> +
> >> +/*
> >> + * This static inline is only present for compatibility with C++. It is
> >> + * effect-less in C.
> >> + */
> >> +static inline struct cds_wfcq_head *cds_wfcq_head_cast(struct cds_wfcq_head
> >> *head)
> >> +{
> >> +	return head;
> >> +}
> >> +#else /* #ifndef __cplusplus */
> >> +
> >> +/* C++ ignores transparent union. */
> >> +typedef union {
> >> +	struct __cds_wfcq_head *_h;
> >> +	struct cds_wfcq_head *h;
> >> +} cds_wfcq_head_ptr_t;
> >> +
> >> +/* C++ ignores transparent union. Requires an explicit conversion. */
> >> +static inline cds_wfcq_head_ptr_t __cds_wfcq_head_cast(struct __cds_wfcq_head
> >> *head)
> >> +{
> >> +	cds_wfcq_head_ptr_t ret = { ._h = head };
> >> +	return ret;
> >> +}
> >> +/* C++ ignores transparent union. Requires an explicit conversion. */
> >> +static inline cds_wfcq_head_ptr_t cds_wfcq_head_cast(struct cds_wfcq_head
> >> *head)
> >> +{
> >> +	cds_wfcq_head_ptr_t ret = { .h = head };
> >> +	return ret;
> >> +}
> >> +#endif /* #else #ifndef __cplusplus */
> >> +
> >>  struct cds_wfcq_tail {
> >>  	struct cds_wfcq_node *p;
> >>  };
> >> --
> >> 2.1.4
> 
> -- 
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com
>