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

From: Andrej van der Zee (mavdzee_at_[hidden])
Date: 2007-06-29 08:49:36

Thanks. I did some tests in the meanwhile and
asio::asyn_read() does detect broken connections very
well, without spanning an extra thread.
Cheers,
Andrej

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

> 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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