Test scenario for sysctl kern.maxfiles

[Peter Holm]

On Thu, Mar 06, 2014 at 07:44:58AM -0800, Garrett Cooper wrote:
> On Mar 6, 2014, at 7:32 AM, Peter Holm <peter at holm.cc> wrote:
> 
> > 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.
> 
> ATF forks, doesn?t spawns threads:
> 
> # grep -r pthread contrib/atf/ || echo not threaded
> not threaded
> 

Hmm ... OK.

$ ldd /usr/tests/sys/kern/unix_seqpacket_test 
/usr/tests/sys/kern/unix_seqpacket_test:
        libthr.so.3 => /lib/libthr.so.3 (0x2806f000)
        libatf-c.so.1 => /usr/lib/libatf-c.so.1 (0x28091000)
        libc.so.7 => /lib/libc.so.7 (0x280a5000)
$ 

> I think that the point that others were trying to make here is that it sets a good standard/precedence to program with atomicity in mind instead of it not being involved, because of how signal handlers are designed.
> 

Oh, I absolutely agree.
-- 
Peter