Test scenario for sysctl kern.maxfiles

[Peter Holm]

On Thu, Mar 06, 2014 at 09:15:58AM -0500, Eitan Adler wrote:
> On 6 March 2014 06:23, Peter Holm <peter at holm.cc> wrote:
> > On Wed, Mar 05, 2014 at 10:08:49AM -0700, Alan Somers wrote:
> >> On Wed, Mar 5, 2014 at 1:58 AM, Peter Holm <peter at holm.cc> wrote:
> >> > Here's an attempt to verify that increasing kern.maxfiles works as
> >> > expected.
> >> >
> >> > http://people.freebsd.org/~pho/kern_descrip_test-v3.diff
> >> > --
> >> > Peter
> >>
> >> 1) done should be of type "static volatile sig_atomic_t", not int,
> >> because it's set by signal handlers.
> >>
> >
> > Yes, that is nicer (I learned something new today :-). But the use
> > here works because there is a call to usleep(3) after each test,
> > forcing the compiler to reload the "done" variable.
> 
> That isn't what sig_atomic_t is trying to prevent.  It is an ""integer
> type of an object that can be accessed as an atomic entity, even in
> the presence of asynchronous interrupts."". In particular, on some
> machines it would be possible for the signal handler to observe a
> half-updated "int" type variable.
> 
> On i386 sig_atomic_t happens to be an "int".  On amd64 it happens to
> be a long.  This is not contractual.
> 

I only just realize that the ATF test programs are threaded.
Anyway it seems to be a good practice to always use "static volatile
sig_atomic_t" for signal handler variables.

-- 
Peter