Re: [Xenomai-help] rtdm_event_timedwait returns -EINTR

[Philippe Gerum <rpm@xenomai.org>]

On Thu, 2009-04-30 at 07:09 -0700, Thomas Lockhart wrote:
> > Hello, I have a problem with rtdm_event_timedwait() function. It
> > sometimes ends prematurely with -EINTR error code. It depends on
> > special circumstances (CPU load, resizing console window in X, ...).
> 
> In other areas of Xenomai when one sees a EINTR return one should
> reenter the original call. Like this (?):
> 
> do {
>   err = rt_task_wait_period(...)
> } while (err != -EINTR);
> 

Just to clarify a few points more:

Xenomai always tells the kernel that blocking (Xenomai) syscalls
_should_ be restarted when interrupted by a Linux signal (i.e.
-ERESTARTSYS is passed down to the kernel by the Xenomai core in that
case), and the kernel will actually restart that (Xenomai) syscall if no
handler was installed for such signal, or if SA_RESTART is set in the
sigaction() flags for the signal.

In all other cases, the syscall will not be restarted despite the
"should restart" hint passed to the Linux kernel, and -EINTR will be
eventually returned by the native API syscall (or errno == EINTR for the
POSIX skin). The way other skins (e.g. VxWorks) will propagate the
-EINTR condition on interrupted syscalls to the user program depends on
their respective API conventions, but they will propagate that
information in a way or another as well, if the syscall was not
restarted.

Additionally, syscalls may be forcibly unblocked via rt_task_unblock(),
which will cause -EINTR to be returned to the caller as well. This is
totally unrelated to Linux signal management though.

> hth
> 
>                                - Tom
> 
> -- 
> Thomas Lockhart
> Supervisor, Distributed and Real-time Group
> Instrument Software and Science Data Systems
> Caltech/JPL
> 
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-- 
Philippe.