Re: Desperately missing a working "pselect()" or similar...

Jan Hudec
2001-10-09T13:36:44Z

>
> > > The select system call doesn't return EINTR when the signal is caught
> > > prior to entry into select.
> >
> > Your friend there is siglongjmp/sigsetjmp - the same problem was true
> > with old versions of alarm that did
> >
> > alarm(num)
> > pause()
> >
> > on a heavily loaded box.
> >
> > Using siglongjmp cures that
>
> Hmmm... would you say the "siglongjmp" method is better than the "self-pipe"
> method for a select on both file descriptors and signals too?
>
> As far as I can see the trade-off is (in the non-race-condition case)
> between having to call read() on the pipe (to empty it after receiving the
> signal) for the "self-pipe" method and having to call sigsetjump() every time
> before one enters select/poll.
>
> My assumption would be that the "self-pipe" method is cheaper... right?

Well, but you don't have to call sigsetjmp before every select; just when you
enter the loop. Than just enable volatile flag, that the handler should now
use the siglongjmp... well, you have to care about 2 signals quickly following
one another and similar nasty cases anyway, so the pipe aproach is less
error-prone. When signal arives, select either returns EINTR, or says the pipe
is ready for writing, so you can save yourself the additional select call by
checking for both conditions.

--------------------------------------------------------------------------------
- Jan Hudec `Bulb' <bulb@ucw.cz>