Date: Fri, 14 Mar 2008 18:05:26 +0200 From: "Vlad GALU" <dudu@dudu.ro> To: "Dan Nelson" <dnelson@allantgroup.com> Cc: freebsd-hackers@freebsd.org Subject: Re: A (perhaps silly) kqueue question Message-ID: <ad79ad6b0803140905s1ec8a730u15bc728077c430aa@mail.gmail.com> In-Reply-To: <20080314153801.GB30116@dan.emsphone.com> References: <ad79ad6b0803070847v7464381en958ef73455ed9c89@mail.gmail.com> <20080307223723.X42870@fledge.watson.org> <ad79ad6b0803080009w45fc866euf43ea7e9dbf6b5f5@mail.gmail.com> <ad79ad6b0803140530td3376b8v9307628ed147a89d@mail.gmail.com> <ad79ad6b0803140553j2b509e8alf17696f268eeb350@mail.gmail.com> <20080314153801.GB30116@dan.emsphone.com>
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On 3/14/08, Dan Nelson <dnelson@allantgroup.com> wrote:
> In the last episode (Mar 14), Vlad GALU said:
> > 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)
>
> > > -- 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.
>
>
> Are you sure the event is being removed? I used to have a hack that
> made the kernel return its current eventlist for a kqueue when you
> called kevent() with nchanges set to -1 (handy for placing in a program
> and using truss to print the result), but it has rotted. I'm attaching
> it in case anyone wants to make it work again.
>
Yep, I'm sure, I've just read the app logs again, we close the
descriptor in the connection destructor..
> Since you got EOF status for both the read and write halves of the
> socket, why not just close the fd? From my reading of the manpages,
> unless you specified EV_ONESHOT when you added the event, events will
> fire until you remove them or the condition that triggers them stops.
>
>
> --
> Dan Nelson
> dnelson@allantgroup.com
>
>
--
Mahnahmahnah!
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