Re: Connect gnuplot_x11 to exterior application window

[Dave D. <dde...@es...>]

Daniel J Sebald <dan...@ie...> writes:

>> I also disagree with the comments about
>> /* NOTE:  The removing of plots via the ErrorHandler routine is
>> rather
>>    tricky.  The error events can happen at any time during execution of
>>    the program, very similar to an interrupt.
>
> I think it is.  I spent a lot of time on that code trying to dream
> up a safe way of maintaining the list. 
>
>> It's nowhere near as bad as that. The errors can only be delivered to
>> the program when xlib is actually reading from the socket. That can
>> only happen either when it is waiting for a reply to a round-trip
>> request, or when you are reading events.
>
> I'm not sure that implies the problem doesn't exist.  The issue is
> the following.  The ErrorHandler is called in response to the "close
> window" or "destroy window" (whatever it is called) that comes from
> the system by pressing that little box with an x in it at the top
> right corner.

Well, that's true at a high level, but you have missed many important
details.

When you close the window, the window manager may send the app a
request to close the window, or it may just delete the window. That
will trigger some events to the app to tell you it has closed. (It
depends on whether you add a property that tells the window manager
that you want to handle the close yourself.)

eg if I run xprop on my firefox window, I see

WM_PROTOCOLS(ATOM): protocols  WM_DELETE_WINDOW, WM_TAKE_FOCUS


I think that's the one that tells the window manager I want to be told
about closes.

Ah - I see gnuplot sets the WM_DELETE_WINDOW hint too. So that means
that the window shouldn't get closed abruptly by a compliant window
manager.


If the app ignores these events, and continues to send requests which
mention this window (or if there were requests in transit, since the
protocol is asynchronous), that will trigger errors to be sent to the
application.

But the error handler is not invoked until the application reads them
from the socket (from a getnextevent call or similar). And that should
only happen under the control of the app.

if you put a breakpoint on the error handler, and look at the call
stack when it is invoked, it should always be from a fn that reads the
network.


I guess the only time it could be asynchronous is if you are using a
multi-threaded version of xlib.


dd
-- 
Dave Denholm              <dde...@es...>       http://www.esmertec.com