Date: Thu, 6 Mar 2014 16:32:47 +0100 From: Peter Holm <peter@holm.cc> To: Eitan Adler <lists@eitanadler.com> Cc: "freebsd-testing@freebsd.org" <freebsd-testing@freebsd.org> Subject: Re: Test scenario for sysctl kern.maxfiles Message-ID: <20140306153247.GA22830@x2.osted.lan> In-Reply-To: <CAF6rxgmDWg3G9td3sXFTouwG_nxc2cP8SjEy81gr1e_Md-HeGA@mail.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>
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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. -- Peter
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