Q268771: FIX: DOEVENTS Command Runs Slowly

Article: Q268771
Product(s): Microsoft FoxPro
Version(s): 5.0,5.0a,6.0
Operating System(s): 
Keyword(s): kbOOP kbvfp500 kbvfp500a kbvfp600 kbGrpDSFox kbDSupport kbCodeSnippet
Last Modified: 03-APR-2002

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft Visual FoxPro for Windows, versions 5.0, 5.0a, 6.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

The DOEVENTS command allows your program to yield time to process Windows
events. However, in tight loops, DOEVENTS waits for an excessive amount of time
for an event.

WORKAROUND
----------

Use the MOUSE command as shown in "More Information" to give DOEVENTS something
to read.

STATUS
======

Microsoft has confirmed this to be a problem in the Microsoft products that are
listed at the beginning of this article.

This problem was corrected in Microsoft Visual FoxPro version 7.0.

MORE INFORMATION
================

In order to reduce the previously described waiting time, following these
steps:

1. Move the mouse while you're waiting. (This is not considered to be an optimum
  solution.)

2. Programmatically feed the app events for DOEVENTS to process.

The following code shows calling DOEVENTS in a tight loop, programmatically
feeding the app events for DOEVENTS to process, and displaying the resulting
times to perform the loops:

1. Copy the following code into a program file, and note the speed difference
  between the call to DOEVENTS and the call to FastDoEvents.

NOTE: This code works better if there is actually a window open. If there is no
window open, DOEVENTS and FastDoEvents have similar execution times, which fall
between the times recorded with a window open.

  lnSeconds = SECONDS()
  FOR i = 1 to 50
     DOEVENTS
  ENDfor
  ? "Total time: " + STR(SECONDS() - lnSeconds, 7, 4)

  lnSeconds = SECONDS()
  FOR i = 1 to 50
     FastDoEvents()
  ENDfor
  ? "Total time: " + STR(SECONDS() - lnSeconds, 7, 4)

  FUNCTION FastDoEvents
     LOCAL lnRow, lnCol, lcWindow

     lcWindow = WONTOP()

     lnRow = MROW(lcWindow)
     lnCol = MCOL(lcWindow)

     IF ( lnRow > 0 ) AND ( lnCol > 0 )
        IF NOT EMPTY(lcWindow)
           MOUSE AT lnRow, lnCol WINDOW (lcWindow)
        ELSE
           MOUSE AT lnRow, lnCol 
        ENDif
     ELSE
        KEYBOARD " "
        =INKEY()
     ENDif

     DOEVENTS
  RETURN

REFERENCES
==========

For more information on the DOEVENTS and MOUSE commands, please see the Visual
FoxPro Language Reference.

Additional query words:

======================================================================
Keywords          : kbOOP kbvfp500 kbvfp500a kbvfp600 kbGrpDSFox kbDSupport kbCodeSnippet 
Technology        : kbVFPsearch kbAudDeveloper kbVFP500 kbVFP600 kbVFP500a
Version           : :5.0,5.0a,6.0
Issue type        : kbbug
Solution Type     : kbfix

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.