Re: [Xenomai-help] uClinux write to pipe returning -ENOMEM

[Philippe Gerum <rpm@xenomai.org>]

Filip Van Rillaer wrote:
> Hello,
> 
> My current test-setup is as follows:
> 1) user-program reads test-samples from a file in non-RT and does a blocking write to the Xenomai-pipe
> 2) a RT-program that implements a V34 modem is listening to the Xenomai-pipe and will send the data over a telephone line.
> ---> so it is the intention that at startup the Xenomai-pipe buffer gets filled up and from than in stationary state the data should stream at the speed of the V34 modem connection.
> 
> The RT-side is using rt_pipe_monitor to be warned when new data from the non-RT write arrives (so no polling).  The RT-side will 'remember' that data from the non-RT side are available and (sometimes a lot) later when enough data have been sent over the telephone line, read new data from the Xenomai pipe.
> 
> Any idea how I can get around this problem?
> 
> Concerning O_SYNC I get the fatal error message:
>  Xenomai: fatal: inserting element twice, holder=00b19cfc, qslot=00b1ab84 at kernel/xenomai/nucleus/pipe.c:96
>   CPU  PID    PRI      TIMEOUT  STAT      NAME
>  >  0  0       -1      0        00400080  ROOT
>     0  112     99      999616310 00300186  RTTask
> I think that this happens around the same time that I get the -ENOMEM when I am not using the O_SYNC flag.
>

Fixed in both the -devel and maintenance branches.

> Best regards,
> Filip
>  
> 
> -----Original Message-----
> From: Philippe Gerum [mailto:rpm@xenomai.org] 
> Sent: 19 August 2008 18:31
> To: Filip Van Rillaer
> Cc: xenomai@xenomai.org
> Subject: Re: [Xenomai-help] uClinux write to pipe returning -ENOMEM
> 
> Filip Van Rillaer wrote:
>> Hello,
>>  
>> I am opening the uClinux side of a Xenomai pipe like (so in blocking mode):
>> FdPipe = open(PipeName, O_RDWR);
>> After some writes to FdPipe I get the returnvalue -ENOMEM.
>> I can understand that the internal buffer gets full as my application 
>> is writing data faster than the Xenomai side is consuming, but I don't 
>> expect to see a returnvalue -ENOMEM : the calling writing-thread 
>> should block, isn't it?  Please comment.
>>
> 
> RT is assumed to consume asap and will preempt the non-RT write() caller immediately upon data receipt, unless the RT code uses some kind of timed polling, which is considered useless and inefficient, since you can ask a RT thread to wait for incoming data in a blocking way.
> 
>> (When adding the O_SYNC flag things get even worse)
>>  
> 
> That is the point that would actually need fixing: what happens with O_SYNC, what is worsening exactly?
> 
>> Why is the code for xnpipe_write saying:
>> if (!mh)
>>   /* Cannot sleep. */   <--- ???????????????????
>>   return -ENOMEM;
>>  
>> I am using svn version 4105.
>>  
>> Best regards,
>> Filip
>>
>>
>> ----------------------------------------------------------------------
>> --
>>
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> 
> 
> --
> Philippe.
> 


-- 
Philippe.