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

[Mathieu Desnoyers]

----- 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.

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