[fxruby-users] FXDataTarget & widget value update delay

Jeroen van der Zijp jeroen at fox-toolkit.org
Tue Oct 3 14:24:07 EDT 2006

On Tuesday 03 October 2006 10:34, Philippe Lang wrote:
> Hi,
> When assigning a new value to an FXDataTarget programmatically, it takes a certain time for the widget linked to this FXDataTarget to be updated, just as if there was some sort of "polling" inside the framework. Delay can be as long as 1 second sometimes. Why aren't the widgets updated straight away?

The GUI gets updated when the event loop is about to block for events;
as long as there are events [keyboard, mouse, repaints, etc], the event
loop processes those with priority.

When all queued-up events have been processed, one would normally go
to a blocking state [i.e. yield the CPU in some system call waiting on
the event queue].  In FOX we don't yield YET; we instead iterate over
the widget tree, and send a SEL_UPDATE to the target of each widget.

Once we've gone through the entire widget tree, THEN we block and
yield the CPU.  Of course, each time we update one widget, we check
for events again, to ensure that the application reacts instantly
when something happens.

The updating process is therefore mostly invisible in the sense that
interactive performance is not affected by it:- the only time we 
do updates is when there's nothing else we would be doing anyway.

However, this does have a few repercussions on the frequency of updates;
in a very busy system with a large number of widgets it may take some
time before an entire cycle through the widget tree is completed.

For this reason, its important to keep the update-handlers small and
to avoid unnecessary work in then whenever possible.

The code in getNextEvent() is finely tuned to get great performance,
but of course I'm not the one writing the update handlers!  That is
up to the software developer himself;  it helps to know what to do
and what to avoid.  Hence this mail.


		- Jeroen

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