Re: [Xenomai] RT->nonRT communication (Xenomai 2.6.4)

From: C Smith <csmithquestions@gmail.com>
To: xenomai@xenomai.org
Subject: Re: [Xenomai] RT->nonRT communication (Xenomai 2.6.4)
Date: Thu, 28 Sep 2017 13:27:11 -0700	[thread overview]
Message-ID: <CA+K1mPEz7US3SHFwn=j9jLy0pP_3W5y37hhx=dbnBf=Hm=Tw9A@mail.gmail.com> (raw)
In-Reply-To: <CA+K1mPHs7A6GSh281Z6Tb2a3AZQ0vasTMdgX0hsj6Fkb01_Y+A@mail.gmail.com>

Hi all -- I sent this last week but it never showed up in my inbox, so I'm
assuming you haven't seen it...

On Fri, Sep 22, 2017 at 5:54 PM, C Smith <csmithquestions@gmail.com> wrote:

> Hi all --
>
> Thanks to your help, I am now using XDDP sockets for communication between
> non-RT processes and a single RT process.  It is generally working -- I
> start the RT task first, and it opens several sockets.  It starts doing
> non-blocking reads and writes, and since no process is on the other end,
> they return immediately.
>
> Then I start one or more non-RT processes that connect, either O_RDONLY or
> O_WRONLY, to several of the non-RT ends of the sockets (via /dev/rtpXX).
> That works well, now the RT and non-RT processes are exchanging data.
>
> The problem comes if I run one of the non-RT processes in a debugger and
> halt it (after it has connected).  The evidence is ambiguous, but usually
> it seems the RT task just hangs.  Then if I continue the non-RT process,
> everything becomes healthy again and messages flow.  Or, if I kill the
> non-RT process, at least the RT task doesn't hang.
>
> I haven't been able to figure out anything about the RT process when it is
> "hung".  The first time I saw this today, it appeared that a socket
> sendto() operation in the RT process was returning errno = ENOMEM, but I
> wasn't able to reproduce it.  If I attach to the RT process in a debugger
> while it is hung, I'm not able to get it to continue.  And if I start the
> RT process in a debugger, then break when it hangs, I can single step
> through the entire infinite loop of the RT process without problem; but
> then when I continue it goes back to the hang behavior.  (One thing the
> infinite loop does is increment a counter in shared memory -- I can see
> this happen when I'm single stepping, but then when I continue I see from
> non-RT processes that the counter in shared memory stops incrementing.)
>
> Any ideas, either what is expected when the process on one end of an XDDP
> socket is suspended, or how I could figure out what's going on in the RT
> process?
>
> Thanks for all you help so far!
> Bob
>