Re: [OT] Interrupting select.

[Olaf Dietsche <olaf.dietsche--list.linux-kernel@exmail.de>]

Hi,

"Peter T. Breuer" <ptb@it.uc3m.es> writes:

> "A month of sundays ago Alan Cox wrote:"
> > > What IS the magic combination that makes select interruptible
> > > by honest-to-goodness non-blocked signals!
> > man
> > 
> > [seriously man sigaction]
> 
> Equally seriously .. all signals are unblocked in my code and always
> have been. The processes receive signals vurrrrry happily. Except when
> they are in a select-with-timeout loop, when they keep going round the
> loop poking their head out of the select every 5s, and taking no notice
> of the murderous hail of die die die die die stuff being slammed at
> them.
[snip]
> Looking at the kernel code in select.c. I see it's implemented by poll
> (I knew that). sys_select calls do_select and I can't for the life of
> me see where anyone sets a signal mask. OTOH if all signals are
> masked by default when syscalls are made (I don't know, but it seems
> possible) then I can't see where interrupts are allowed again.
> 
> The man page for select says nothing about it being interruptible, or
> not. 
> 
> This has been in the back of my mind for months. I'm glad somebody
> asked about it!

I'm not really sure, what you're asking for. Select() is interruptible.

But: if you have multiple threads, the signal may be delivered to any
thread. So, what you may see, is, that the signal is delivered to a
thread, but the signaled thread is not the thread waiting in the
select() call.

Therefore it _seems_, as if select() is not interruptible, but it
surely is.

Regards, Olaf.