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

[Alexander Kolbasov <akolb@xxxxxxxxxxx>]

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?

- Alex

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