Conference bulova::decw_jan-89_to_nov-90

1465.0. "DW Programming Performance Rules-Of-Thumb" by VMSDEV::BUFORD (It's a boy!) Wed Sep 20 1989 10:33

    From time-to-time, I am asked whether my group has a Guide to
    DECWindows Performance which advises programmers on how to write fast
    DECWindows applications.  To my chagrin, the answer is "no".  
    But there are a few Rules Of Thumb which may or may not be obvious.
    
    Please feel free to add more ROTs and/or correct the ones listed
    below...
    

	- nothing is obvious; experiment with different algorithms

	- when you study memory and CPU use, remember that you need to consider 
	  not just the application, but the server also

	- windows, widgets, and GCs are NOT cheap; use them sparingly
	  (counter to the MIT design philosophy)

	- use gadgets instead of widgets if at all possible

	- generally, a complex widget is an expensive widget; 
    	  for example, dialog boxes

	- be aware of operations that require the window manager to get 
    	  involved; for example, creating and mapping a window that can be 
    	  resized or iconified has to go through the window manager

	- toolkit widgets pay a performance price for being general purpose;
	  consider writing your own special-purpose widget if necessary

	- if you write your own widget, use the translation manager sparingly

	- process your incoming events and replies ASAP; don't let them pile up
	  and possibly overflow your transport buffers

	- avoid XFlush and XSync; that just means you have to pay more to 
	  transport less

	- remember that there are going to be other applications executing; 
	  handle Focus properly and avoid Grabs if possible

	- watch for flickers or sparkles on your screen; you many be drawing 
    	  the same thing several times

                      
    
    John B.

I'd also add a admonition to free memory wherever needed.  There are just too
many places in the toolkit that make it easy to leak memory.  The compound
string routines are a primary example, but one that some might not think
about are the VAX binding argument list building routines (DWT$VMS_SET_ARG,
etc.)  Unfortunately, the documentation is silent on this - only by
stumbling across the description of the routines that do the freeing might
you start to have a clue that it is necessary.

				Steve

 -  Fonts and large pixmaps are expensive; use them sparingly...

 -  Don't create widgets until you need them.  For example, at start-up
    only create the widgets needed by your "main" window.

 -  Call XtSetValues and XtGetValues sparingly.  For example, create a
    widget with all of its resources set properly, rather than create
    it and then immediately call XtSetValues.  Also, use "convienence"
    routines like DwtToggleButtonGetState instead of XtGetValues, when
    possible.

Leo