* Horrible hack to make C++ link to liburcu
@ 2016-03-04 20:32 Paul E. McKenney
0 siblings, 0 replies; 3+ messages in thread
From: Paul E. McKenney @ 2016-03-04 20:32 UTC (permalink / raw)
To: lttng-dev; +Cc: jiangshanlai
Hello!
Still working with the C++ standards committee to add RCU to C++, and
of course one step on that path is to make C++ programs build against
liburcu. The following hack-patch makes this work by disabling C++ access
to wfcqueue and by making C++ see the rcu_head ->next field as a void *.
This supports prototyping, but what would be the real fix?
Thanx, Paul
------------------------------------------------------------------------
diff --git a/urcu-call-rcu.h b/urcu-call-rcu.h
index 339ebacc3f7c..d37c49e9d958 100644
--- a/urcu-call-rcu.h
+++ b/urcu-call-rcu.h
@@ -32,7 +32,9 @@
#include <stdlib.h>
#include <pthread.h>
+#ifndef __cplusplus
#include <urcu/wfcqueue.h>
+#endif
#ifdef __cplusplus
extern "C" {
@@ -57,7 +59,11 @@ struct call_rcu_data;
*/
struct rcu_head {
+#ifdef __cplusplus
+ void *next;
+#else
struct cds_wfcq_node next;
+#endif
void (*func)(struct rcu_head *head);
};
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: Horrible hack to make C++ link to liburcu
[not found] ` <410832705.17244.1457190630579.JavaMail.zimbra@efficios.com>
@ 2016-03-08 0:31 ` Mathieu Desnoyers
0 siblings, 0 replies; 3+ messages in thread
From: Mathieu Desnoyers @ 2016-03-08 0:31 UTC (permalink / raw)
To: Paul E. McKenney; +Cc: lttng-dev, Lai Jiangshan
----- On Mar 5, 2016, at 10:10 AM, Mathieu Desnoyers mathieu.desnoyers@efficios.com wrote:
> ----- On Mar 4, 2016, at 3:32 PM, Paul E. McKenney paulmck@linux.vnet.ibm.com
> wrote:
>
>> Hello!
>>
>> Still working with the C++ standards committee to add RCU to C++, and
>> of course one step on that path is to make C++ programs build against
>> liburcu. The following hack-patch makes this work by disabling C++ access
>> to wfcqueue and by making C++ see the rcu_head ->next field as a void *.
>>
>> This supports prototyping, but what would be the real fix?
Hi Paul,
Of course you can remove the _LGPL_SOURCE define. It will work, but
without inlining. I have two fixes that should make inlining work
in C++, even when using wfcqueue.h. Those are currently in
https://github.com/compudj/userspace-rcu-dev/tree/urcu-cpp
(top 2 commits)
Feedback is welcome,
Thanks!
Mathieu
>
> One fix would be:
>
> diff --git a/urcu/wfcqueue.h b/urcu/wfcqueue.h
> index 83ec219..c0bb289 100644
> --- a/urcu/wfcqueue.h
> +++ b/urcu/wfcqueue.h
> @@ -43,7 +43,7 @@ extern "C" {
> * McKenney.
> */
>
> -#define CDS_WFCQ_WOULDBLOCK ((void *) -1UL)
> +#define CDS_WFCQ_WOULDBLOCK ((struct cds_wfcq_node *) -1UL)
>
> enum cds_wfcq_ret {
> CDS_WFCQ_RET_WOULDBLOCK = -1,
>
> In addition, g++ does not support the __transparent_union__ gcc attribute
> (it just ignores it). So we might want to rethink our use of this attribute
> within wfcqueue.h. We current use it for
>
> /*
> * Do not put head and tail on the same cache-line if concurrent
> * enqueue/dequeue are expected from many CPUs. This eliminates
> * false-sharing between enqueue and dequeue.
> */
> struct __cds_wfcq_head {
> struct cds_wfcq_node node;
> };
>
> struct cds_wfcq_head {
> struct cds_wfcq_node node;
> pthread_mutex_t lock;
> };
>
> /*
> * The transparent union allows calling functions that work on both
> * struct cds_wfcq_head and struct __cds_wfcq_head on any of those two
> * types.
> */
> typedef union {
> struct __cds_wfcq_head *_h;
> struct cds_wfcq_head *h;
> } __attribute__((__transparent_union__)) cds_wfcq_head_ptr_t;
>
> Thoughts ?
>
> Thanks,
>
> Mathieu
>
>
>>
>> Thanx, Paul
>>
>> ------------------------------------------------------------------------
>>
>> diff --git a/urcu-call-rcu.h b/urcu-call-rcu.h
>> index 339ebacc3f7c..d37c49e9d958 100644
>> --- a/urcu-call-rcu.h
>> +++ b/urcu-call-rcu.h
>> @@ -32,7 +32,9 @@
>> #include <stdlib.h>
>> #include <pthread.h>
>>
>> +#ifndef __cplusplus
>> #include <urcu/wfcqueue.h>
>> +#endif
>>
>> #ifdef __cplusplus
>> extern "C" {
>> @@ -57,7 +59,11 @@ struct call_rcu_data;
>> */
>>
>> struct rcu_head {
>> +#ifdef __cplusplus
>> + void *next;
>> +#else
>> struct cds_wfcq_node next;
>> +#endif
>> void (*func)(struct rcu_head *head);
>> };
>
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com
>
> _______________________________________________
> lttng-dev mailing list
> lttng-dev@lists.lttng.org
> http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Horrible hack to make C++ link to liburcu
[not found] <20160304203254.GA2033@linux.vnet.ibm.com>
@ 2016-03-05 15:10 ` Mathieu Desnoyers
[not found] ` <410832705.17244.1457190630579.JavaMail.zimbra@efficios.com>
1 sibling, 0 replies; 3+ messages in thread
From: Mathieu Desnoyers @ 2016-03-05 15:10 UTC (permalink / raw)
To: Paul E. McKenney; +Cc: lttng-dev, Lai Jiangshan
----- On Mar 4, 2016, at 3:32 PM, Paul E. McKenney paulmck@linux.vnet.ibm.com wrote:
> Hello!
>
> Still working with the C++ standards committee to add RCU to C++, and
> of course one step on that path is to make C++ programs build against
> liburcu. The following hack-patch makes this work by disabling C++ access
> to wfcqueue and by making C++ see the rcu_head ->next field as a void *.
>
> This supports prototyping, but what would be the real fix?
One fix would be:
diff --git a/urcu/wfcqueue.h b/urcu/wfcqueue.h
index 83ec219..c0bb289 100644
--- a/urcu/wfcqueue.h
+++ b/urcu/wfcqueue.h
@@ -43,7 +43,7 @@ extern "C" {
* McKenney.
*/
-#define CDS_WFCQ_WOULDBLOCK ((void *) -1UL)
+#define CDS_WFCQ_WOULDBLOCK ((struct cds_wfcq_node *) -1UL)
enum cds_wfcq_ret {
CDS_WFCQ_RET_WOULDBLOCK = -1,
In addition, g++ does not support the __transparent_union__ gcc attribute
(it just ignores it). So we might want to rethink our use of this attribute
within wfcqueue.h. We current use it for
/*
* Do not put head and tail on the same cache-line if concurrent
* enqueue/dequeue are expected from many CPUs. This eliminates
* false-sharing between enqueue and dequeue.
*/
struct __cds_wfcq_head {
struct cds_wfcq_node node;
};
struct cds_wfcq_head {
struct cds_wfcq_node node;
pthread_mutex_t lock;
};
/*
* The transparent union allows calling functions that work on both
* struct cds_wfcq_head and struct __cds_wfcq_head on any of those two
* types.
*/
typedef union {
struct __cds_wfcq_head *_h;
struct cds_wfcq_head *h;
} __attribute__((__transparent_union__)) cds_wfcq_head_ptr_t;
Thoughts ?
Thanks,
Mathieu
>
> Thanx, Paul
>
> ------------------------------------------------------------------------
>
> diff --git a/urcu-call-rcu.h b/urcu-call-rcu.h
> index 339ebacc3f7c..d37c49e9d958 100644
> --- a/urcu-call-rcu.h
> +++ b/urcu-call-rcu.h
> @@ -32,7 +32,9 @@
> #include <stdlib.h>
> #include <pthread.h>
>
> +#ifndef __cplusplus
> #include <urcu/wfcqueue.h>
> +#endif
>
> #ifdef __cplusplus
> extern "C" {
> @@ -57,7 +59,11 @@ struct call_rcu_data;
> */
>
> struct rcu_head {
> +#ifdef __cplusplus
> + void *next;
> +#else
> struct cds_wfcq_node next;
> +#endif
> void (*func)(struct rcu_head *head);
> };
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
^ permalink raw reply related [flat|nested] 3+ messages in thread
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2016-03-04 20:32 Horrible hack to make C++ link to liburcu Paul E. McKenney
[not found] <20160304203254.GA2033@linux.vnet.ibm.com>
2016-03-05 15:10 ` Mathieu Desnoyers
[not found] ` <410832705.17244.1457190630579.JavaMail.zimbra@efficios.com>
2016-03-08 0:31 ` Mathieu Desnoyers
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