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Q297826: FIX: CHRSAW() Function Can Hang When AutoYield = .F.

Article: Q297826
Product(s): Microsoft FoxPro
Version(s): 5.0,5.0a,6.0
Operating System(s): 
Keyword(s): kbvfp500 kbvfp500a kbvfp500aBUG kbvfp500bug kbvfp600 kbvfp600bug kbGrpDSFox kbDSupport
Last Modified: 29-AUG-2001

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The information in this article applies to:

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

If the Visual FoxPro AutoYield property is set to .F., the CHRSAW() function may
not be able to check the keyboard buffer properly, and may cause the system to
stop responding (hang).

CAUSE
=====

The AutoYield property prevents Windows event messages from interrupting program
flow. Therefore, when CHRSAW() checks to see whether any keyboard events have
come in, it can get into a state in which it continues to look for an event, but
can't find one.

STATUS
======

This problem was corrected in Microsoft Visual FoxPro version 7.0 for Windows.

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

Steps to Reproduce Behavior
---------------------------

The following code will eventually reproduce the behavior, although perhaps not
on the first run. If you open the Task Manager, you will see that Visual FoxPro
is taking all available CPU time.

  *!* Q297826 FIX: CHRSAW() Function Can Hang System When AutoYield = .F.
  CLEAR

  _VFP.AutoYield = .F.
  lnCount = 1000
  lnStart = SECONDS()

  FOR lnI = 1 TO lnCount
  	@ 1,1 SAY lnI
  	llTest = CHRSAW()
  ENDFOR

  ? SECONDS() - lnStart

Additional query words:

======================================================================
Keywords          : kbvfp500 kbvfp500a kbvfp500aBUG kbvfp500bug kbvfp600 kbvfp600bug kbGrpDSFox kbDSupport kbCodeSnippet kbvfp700fix kbvfp700 
Technology        : kbVFPsearch kbAudDeveloper kbVFP500 kbVFP600 kbVFP500a
Version           : :5.0,5.0a,6.0
Issue type        : kbbug
Solution Type     : kbfix

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