Re: [Xenomai] Are concurrent writes to XDDP sockets allowed ?

[Philippe Gerum <rpm@xenomai.org>]

On 05/21/2015 05:32 PM, Thierry Bultel wrote:
> 
> 
> Le 21/05/2015 17:23, Philippe Gerum a écrit :
>> On 05/21/2015 05:03 PM, Thierry Bultel wrote:
>>>
>>> Le 21/05/2015 14:07, Philippe Gerum a écrit :
>>>> On 05/21/2015 08:34 AM, Thierry Bultel wrote:
>>>>> Hi,
>>>>> In an application, we have one regular thread listening on an RTP
>>>>> device,
>>>>> and 2 realtime threads that concurrently write data in the XDDP socket
>>>>> backend.
>>>>> We use the POSIX skin.
>>>>>
>>>>> Sometimes, the regular thread gets its blocking read() call just
>>>>> return 0.
>>>>> That never happens with the classic "one reader, one writer" case.
>>>>>
>>>>> Also, we notice that the 'return 0' case occurrence is not the same,
>>>>> depending
>>>>> on the fact that the realtime task uses 'write' instead of 'sendto'
>>>>> (more occurrences with 'sendto')
>>>>>
>>>> There is no restriction with respect to concurrent sending to such
>>>> socket.
>>> Ok, thanks
>>>> Knowing about the Xenomai release number,
>>> This is 2.6.4
>>>> and a simple test code that
>>>> actually illustrates the intended usage and ideally reproduces the
>>>> issue
>>>> would help.
>>> Here is the test code, based on xddp-echo.c . Unfortunalely this does
>>> not reproduce the issue.
>>> Compared to our application, we also have 3 other additional
>>> realtime-regular pairs communicating on 3 dedicated channels.
>>>
>>> What would trigger the 'read' return with zero ?
>> Sending zero len messages from the rt side via sendto(), which is legit
>> with XDDP. Using write() won't send anything.
>>
> This was my first assumption.
> But the way we use it eliminates that possible cause; the sent struct is
> on stack.
> Moreover, we have 'zero' read even when using the 'write' instead of
> 'sendto'
> 'sendto' just seem to increase the number of zero read occurences.
> 
>    RAWFRAME message;
> 
> ...
> 
>         nb = write(channel, &message, sizeof(message));
> 
> 
> 

Any spurious wake up fixed with this?

diff --git a/ksrc/nucleus/pipe.c b/ksrc/nucleus/pipe.c
index 3c4dccf..df587ab 100644
--- a/ksrc/nucleus/pipe.c
+++ b/ksrc/nucleus/pipe.c
@@ -122,13 +122,17 @@ static inline void xnpipe_dequeue_all(struct xnpipe_state *state, int mask)
 	xnpipe_enqueue_wait(__state, __mask);				\
 	xnlock_put_irqrestore(&nklock, __s);				\
 									\
-	prepare_to_wait_exclusive(__waitq, &__wait, TASK_INTERRUPTIBLE);\
-									\
-	if (!(__cond))							\
+	for (;;) {							\
+		__sigpending = signal_pending(current);			\
+		if (__sigpending)					\
+			break;						\
+		prepare_to_wait_exclusive(__waitq, &__wait, TASK_INTERRUPTIBLE); \
+		if (__cond)						\
+			break;						\
 		schedule();						\
+	}								\
 									\
 	finish_wait(__waitq, &__wait);					\
-	__sigpending = signal_pending(current);				\
 									\
 	/* Restore the interrupt state initially set by the caller. */	\
 	xnlock_get_irqsave(&nklock, __s);

-- 
Philippe.