Re: [Xenomai-help] Strange pipe behaviour

[Philippe Gerum <rpm@xenomai.org>]

Ignacio García Pérez wrote:
> Hi,
> 
> I have the following piece of code:
> 
> RT_PIPE_MSG *msg;
> 
> while ((r = rt_pipe_receive(&mypipe, &msg, TM_INFINITE)) >= 0) {
>     /* whatever */
>     rt_pipe_free(msg);
> }
> 
> When that thread enters, it blocks, as expected, in the rt_pipe_receive
> call.
> 
> Then, from user space, I do:
> 
> echo -en "\x00" > /dev/rtp0
> 
> What happens is:
> 
> 1- rt_pipe_receive returns with r >= 0.
> 2- /* whatever */
> 3- Message is freed using rt_pipe_free.
> 4- Next call to rt_pipe_receive returns with r = -EINTR.
> 
> The only explanation I could come up with is that when the pipe is
> closed by the user mode process, the rt_pipe_receive tells the rt task
> by returning -EINTR. Is this right?.

Yes.

  According to the docs, -EINTR is
> only returned if rt_task_unblock() has been called...
> 

Actually, this is what happened through the internal interface.
driver::release(pipe) -> nucleus::unblock(sleepers_on_pipe)

> Nacho.
> 
> 
> 
> 
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-- 

Philippe.