[RFC] add a shutdown event

[Hardening]

On 18/03/2013 13:48, Uli Schlachter wrote:
> Hi,
> 
> On 18.03.2013 00:30, Hardening wrote:
>> On 17/03/2013 23:59, Sylvain BERTRAND wrote:
>>> On Sun, Mar 17, 2013 at 11:32:21PM +0100, Hardening wrote:
>>>> This patch adds a shutdow event so that clients can be notified
>>>> when the compositor is about to exit (and potentially kill its
>>>> child processes). 
>>>> This patch is based on gh next.
>>>
>>> Is the socket disconnect not enough information for the clients?
>>>
>> As most of the time the compositor launched all the wayland clients,
>> they may be killed before they discover the socket has disconnected.
> 
> I might be missing something obvious, but who kills the clients and via which
> mechanism? The only thing that I can imagine would be SIGPIPE (if they try to
> use their socket to weston) and that one can easily be avoided without a
> shutdown event.

I'm very sorry, i've just reread docs on process management. I thought
child process were killed when the father dies, but they aren't. They're
just orphaned.

I still think it's a good thing for clients to know when the compositor
is shutting down cleanly. In the present situation, we have the
following cases:
* the compositor crashes: from the client point of view the socket
disconnect and it's the end of the show (at least with all actions that
involve the compositor)
* the compositor exits cleanly (ctrl+alt+backspace or software request):
the client will receive series of "global_remove" events but without
knowing if it's part of hotplug system, or if it's a clean shutdown

I think explicit is better than implicit and that the clients should be
notified of this very special event: the compositor shutdown.