On Sun, 21 Apr 2002 18:50:10 +0200
"Alexander Maryanovsky" <[EMAIL PROTECTED]> wrote:
> So I guess I have two questions:
> 1. What is the technical reason processes crash when the
> X server they're running under crashes?
They loose the connection (Stream Socket -- TCP or Local).
For most, there isn't any sane thing to do without
a display other than (maybe save some critical info and) quit.
> 2. What (if any) is the high-level (design-level) reason
> that such a thing is allowed?
If the process is interactive and lost its display, what
other sane choice exists?
If the process has important functionality other than GUI,
than the programmer should:
1. Either check return values on each call to xlib and
develop his own strategy (tedious and error prone).
2. Acknowledge that his design is flawed. It should be:
A. Separate functional process for the non-interactive
job.
B. Separate display oriented process
C. Some IPC and glue logic between the two.
You should note that I've just advertized the ancient but
solid Model-View-Controler design.
> Why can't one put up a proxy between the processes and the
> X server which would delegate everything to it, make X server
> crashes transparent to the processes and allow restarting
> the X server (again transparently to the processes) when it
> goes down? It seems like a fairly simple thing to do...
You could put a proxy between them (there are proxies like
that for other purposes -- like sending to multiple displays).
However, there is a lot of "state" stored in the X-server
(Graphics-Context etc.), so your proxy should store a copy
of everything, and upon reconnection to the freshly born
X-server, it should "replay" all the state creating commands.
So it isn't simple, and the "replay" time is proportional
to the "history" of the X-server.... not so good.
My advice -- there is no substitute for good design of the
application. A major bad example in this respect is
web-browsers: All of them (the whole concept of them) is
big-bloated-application that does multitude of tasks in
a single application (and normally on a single TCP port -- 80).
So, if you have gazillion browser windows open on different
URLS, many of them in the middle of a session (forms + cookies
+ javascript), some with hidden state (Flash, sound, some other
behemoth) and all of a sudden: KABBBOOOOOMMM.....
Sorry, all your state is lost...
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