Date: Fri, 14 Mar 2008 14:53:39 +0200 From: "Vlad GALU" <dudu@dudu.ro> To: freebsd-hackers@freebsd.org Subject: Re: A (perhaps silly) kqueue question Message-ID: <ad79ad6b0803140553j2b509e8alf17696f268eeb350@mail.gmail.com> In-Reply-To: <ad79ad6b0803140530td3376b8v9307628ed147a89d@mail.gmail.com> References: <ad79ad6b0803070847v7464381en958ef73455ed9c89@mail.gmail.com> <20080307223723.X42870@fledge.watson.org> <ad79ad6b0803080009w45fc866euf43ea7e9dbf6b5f5@mail.gmail.com> <ad79ad6b0803140530td3376b8v9307628ed147a89d@mail.gmail.com>
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On 3/14/08, Vlad GALU <dudu@dudu.ro> wrote:
> On 3/8/08, Vlad GALU <dudu@dudu.ro> wrote:
> > On 3/8/08, Robert Watson <rwatson@freebsd.org> wrote:
> > > On Fri, 7 Mar 2008, Vlad GALU wrote:
> > >
> > >
> > > > I see an unusual symptom with one of our in-house applications. The main I/O
> > > > loop calls kevent(), which in turn returns two events with EV_EOF error set,
> > > > always for the same descriptors (they're both socket descriptors). As the
> > > > man page is not pretty clear about it and I don't have my UNP copy at hand,
> > > > I would like to ask the list whether the error events are supposed to be
> > > > one-shot or not.
> > >
> > >
> > > I wonder if it's returning one event for the read socket buffer, and one event
> > > for the write socket buffer, since there are really two event sources for each
> > > socket? Not that this is desirable behavior, but it might explain it. If you
> > > shutdown() only read, do you get back one EOF kevent and one writable kevent?
> >
> >
> > I'll try that and see. The only issue being the low frequency this
> > symptom appears at. I'll get back to the list once I have more info.
>
>
> Haven't gotten to the point of testing shutdown() behavior, but
> here's a truss excerpt of the symptom:
>
> -- cut here --
> kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
> 0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
> kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
> 0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
> kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
> 0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
> kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
> 0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
> kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
> 0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
> kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
> 0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
> kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
> 0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
> kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
> 0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
> kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
> 0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
> kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
> 0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
> kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
> 0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
> kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
> 0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
> kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
> 0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
> kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
> 0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
> -- and here --
>
> So two EOF are returrned for descriptor 7, and errno would be
> ECONNRESET. The question is now, why isn't it oneshot?
Ah one more thing. When EOF is caught, a handler which forcibly
removes the event is called, but it keeps poping up again and again.
>
>
> >
> >
> > >
> > > Robert N M Watson
> > > Computer Laboratory
> > > University of Cambridge
> > >
> >
> >
> >
> > --
> > Mahnahmahnah!
> >
>
>
>
> --
> Mahnahmahnah!
>
--
Mahnahmahnah!
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