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

From: Richard Dingwall (rdingwall_at_[hidden])
Date: 2007-06-29 08:43:47

On 6/29/07, Andrej van der Zee <mavdzee_at_[hidden]> wrote:
>
> What do you mean with a long-running read operation?

A read operation that waits indefinitely for any data the server might send.

In my setup, the client only writes data to the
> server. Should I start a thread with a synchronous
> asio::read on the socket?

You could, but...

Or can I do this with an
> asio::asyn_read too?

async_read() is better because you don't have to spawn another thread :)

Is this possible while writing
> over the same socket at the same time?
>

Yes it is.

Thanks,
> Andrej

I recommend you join the asio-users mailing list here:
https://lists.sourceforge.net/lists/listinfo/asio-users

I'm not sure if Chris checks boost-users that often, and he is much better
at answering questions!

Richard

--- 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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>
>
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