Re: [Boost-users] ASIO: Detecting broken connections

From: Andrej van der Zee (mavdzee_at_[hidden])
Date: 2007-06-29 05:36:10

What do you mean with a long-running read operation?
In my setup, the client only writes data to the
server. Should I start a thread with a synchronous
asio::read on the socket? Or can I do this with an
asio::asyn_read too? Is this possible while writing
over the same socket at the same time? 
Thanks,
Andrej

--- Richard Dingwall <rdingwall_at_[hidden]> wrote:

> On 6/29/07, Cliff Green <cliffg_at_[hidden]>
> wrote:
> >
> >   Andrej van der Zee <mavdzee_at_[hidden]> wrote:
> > > I was wondering how I can find out with ASIO
> whether a
> > > connection is broken. I have a client connected
> to the
> > > server that continuously streams data.
> >
> > The canonical way to consistently detect broken
> TCP
> > connections is to always have a read on the socket
> - it
> > will return 0 on broken connection (in usual BSD
> sockets
> > type reads - I would expect an appropriate error
> parameter
> > set in ASIO). Since you're doing async operations
> this is
> > pretty easy.
> >
> > Many times a write will only buffer the data (at
> the OS /
> > TCP driver level), and an error is not detected
> until a
> > later write (and if the client socket is in a
> "half
> > shutdown" mode, it might be quite a while before
> the TCP
> > keepalive timer pops and the socket is fully
> destroyed).
> >
> > This is absent special ASIO capabilities - if ASIO
> is
> > doing a read "on your behalf", then the problem is
> the
> > "not completely destroyed connection", which is an
> OS /
> > TCP "feature" and nothing that ASIO can help with.
> I
> > haven't found specific details relating to this in
> ASIO,
> > but that may only be because I haven't read enough
> of the
> > ASIO documentation.
> >
> > Chris K (or others), clarifications, corrections,
> or
> > comments?
> 
> 
> You test for a disconnection with Asio the same way
> you would with BSD
> sockets - you need to leave a long-running read
> operating going.
> 
> Check out this post from the Asio-users mailing
> list:
>
http://osdir.com/ml/lib.boost.asio.user/2006-11/msg00035.html
> 
> Richard
> 
> Cliff
> >
> > _______________________________________________
> > Boost-users mailing list
> > Boost-users_at_[hidden]
> >
>
http://lists.boost.org/mailman/listinfo.cgi/boost-users
> >
> > _______________________________________________
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>
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