Date: Thu, 6 Mar 2014 17:29:34 +0100 From: Peter Holm <peter@holm.cc> To: Garrett Cooper <yanegomi@gmail.com> Cc: "freebsd-testing@freebsd.org" <freebsd-testing@freebsd.org> Subject: Re: Test scenario for sysctl kern.maxfiles Message-ID: <20140306162934.GB25614@x2.osted.lan> In-Reply-To: <6A23D2B5-4EAA-46EF-A582-8C55FE0ED46B@gmail.com> References: <20140305085806.GA70478@x2.osted.lan> <CAOtMX2hUJ2Hc62bG1jitbQbiHtb8b8Jm8iWaP4VaJPuADXR=Kw@mail.gmail.com> <20140306112322.GA10664@x2.osted.lan> <CAF6rxgmDWg3G9td3sXFTouwG_nxc2cP8SjEy81gr1e_Md-HeGA@mail.gmail.com> <20140306153247.GA22830@x2.osted.lan> <6A23D2B5-4EAA-46EF-A582-8C55FE0ED46B@gmail.com>
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On Thu, Mar 06, 2014 at 07:44:58AM -0800, Garrett Cooper wrote: > On Mar 6, 2014, at 7:32 AM, Peter Holm <peter@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@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@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
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