| Re: Concurrent widget program. [message #11913 is a reply to message #11905] |
Tue, 02 June 1998 00:00   |
Andy Loughe
Messages: 174
Registered: November 1995
|
Senior Member |
|
|
David Fanning wrote:
> But that is not the case at all. Consider this example.
> Suppose the event handler code went into a processing loop
> and that the loop took 5 minutes to execute. Then the user
> could be pushing as many buttons on as many widget programs
> as he or she liked, but nothing would be happening. In
> fact, nothing at all would happen until that loop finished
> and then, probably, all hell would beak loose as IDL rushed
> to handle all the events that had queued over the past five
> minutes.
>
> IDL does only one "thing" at a time. It is not a multi-threaded
> or multi-tasking program. This is exactly why you try to
> avoid writing loops in event handler code. In fact, when you
> need a loop, you try to take advantage of the widget program
> itself *acting* like a loop. A widget animation is a perfect
> example of this. If a widget animation was really in a loop,
> there would be no way to interrupt the animation with, for
> example, a Quit button. You can look at the example XMOVIE on
> my web page for an example of how to use the program itself
> to simulate a loop. You will see that each "event" actually
> displays just a single frame of the animation sequence.
> Between one event and the next a Quit button event, for
> example, could be queued up and processed.
I am not a widget genius, but isn't that one reason you
add the hourglass keyword when controlling widgets that
take "awhile" to process the event?
--
Andrew F. Loughe |
afl@cdc.noaa.gov
University of Colorado, CIRES Box 449 |
http://cdc.noaa.gov/~afl
Boulder, CO 80309-0449 | phn:(303)492-0707
fax:(303)497-7013
------------------------------------------------------------ ---------------
"I do not feel obliged to believe that the same God who has endowed us
with
sense, reason, and intellect has intended us to forego their use."
-Galileo
|
|
|
|
comp.lang.idl-pvwave archive
Members
Search
Help
Login
Home
