Re: [Libevent-users] Q: Exception callbacks and events that should run immediately

[Mark Ellzey <mthomas@xxxxxxxxxx>]

On Wed, Dec 05, 2012 at 07:28:25PM +0000, Alexander Kolbasov wrote:
> On Dec 5, 2012, at 7:32 AM, Mark Ellzey wrote:
> 
> > On Wed, Dec 05, 2012 at 11:10:04AM +0200, Nir Soffer wrote:
> >> On Wed, Dec 5, 2012 at 10:54 AM, Sashan Govender <sashang@xxxxxxxxx> wrote:
> >> 
> >>> Hi!
> >>> 
> >>> 
> >>>> 1) I don't see any notion of event notification on FD exception - e.g.
> >>>> socket close.
> >>>>    There are some words for buffer events, but nothing for regular file
> >>>>    descriptor based callbacks. So what is a good way to get a callback
> >>>> when specific
> >>>>    FD is closed/disconnected?
> >>>> 
> >>> 
> >>> If the fd is a socket and the peer closes then you'll get a read callback.
> >>> When you read from the fd 'read' will return 0 indicating that the peer
> >>> closed.
> >>> 
> >> 
> >> But if the peer die without closing the socket, you will never get a read
> >> event. In this case you will fail when writing to the socket.
> >> 
> >> You can simulate this by disconnecting the peer from the network.
> > 
> > Writing to the socket, in most cases, not something you want to do just
> > to determine if the socket is alive.
> > 
> > If a peer is disconnected, e.g., it shuts down, the OS *should* 
> > eventually time-out the session which will result in your eventcb being
> > executed. 
> > 
> > Another option is to set your own read timeout on the socket.
> 
> Does it mean that peer close is not triggering EV_READ callback and the user should
> periodically timeout and attempt reads and check for read errors?
> 

Depends on what you mean by peer-closed. I think in this thread we were
speaking about the situation where a client never sends a RST/FIN, i.e.,
the client host is shut down during transmission.

If you set a read timeout via libevent or the OS times the connection
out, the event callback, not the read callback is executed.

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