From ac8bb107ca7d45115b1877f6ed9d25b16456b4b4 Mon Sep 17 00:00:00 2001
From: drh <drh@sqlite.org>
Date: Sat, 24 May 2003 02:30:47 +0000
Subject: Add tests to detect and avoid division by zero in the windows
 precision timer calibration logic.

---
 ChangeLog        |  5 +++++
 win/tclWinTime.c | 24 ++++++++++++++++++++----
 2 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 5a7543f..71614d4 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2003-05-23  D. Richard Hipp <drh@hwaci.com>
+
+	* win/tclWinTime.c: Add tests to detect and avoid a division by zero
+	in the windows precision timer calibration logic.
+
 2003-05-23  Don Porter  <dgp@users.sourceforge.net>
 
         * generic/tclObj.c (tclCmdNameType):  Converted internal rep
diff --git a/win/tclWinTime.c b/win/tclWinTime.c
index 9953085..593ca55 100644
--- a/win/tclWinTime.c
+++ b/win/tclWinTime.c
@@ -9,7 +9,7 @@
  * See the file "license.terms" for information on usage and redistribution
  * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
  *
- * RCS: @(#) $Id: tclWinTime.c,v 1.18 2003/05/18 19:48:27 kennykb Exp $
+ * RCS: @(#) $Id: tclWinTime.c,v 1.19 2003/05/24 02:30:48 drh Exp $
  */
 
 #include "tclWinInt.h"
@@ -348,7 +348,8 @@ Tcl_GetTime(timePtr)
 	TclpInitUnlock();
     }
 
-    if ( timeInfo.perfCounterAvailable ) {
+    if ( timeInfo.perfCounterAvailable 
+		&& timeInfo.curCounterFreq.QuadPart!=0 ) {
 	
 	/*
 	 * Query the performance counter and use it to calculate the
@@ -449,7 +450,6 @@ StopCalibration( ClientData unused )
  *
  * Results:
  *	Returns a pointer to a static string, or NULL on failure.
- *	Return value is in UTF-8 encoding
  *
  * Side effects:
  *	None.
@@ -785,7 +785,7 @@ CalibrationThread( LPVOID arg )
 
     /* Run the calibration once a second */
 
-    for ( ; ; ) {
+    while (timeInfo.perfCounterAvailable) {
 
 	/* If the exitEvent is set, break out of the loop. */
 
@@ -856,6 +856,22 @@ UpdateTimeEachSecond()
     EnterCriticalSection( &timeInfo.cs );
 
     /*
+     * We devide by timeInfo.curCounterFreq.QuadPart in several places.
+     * That value should always be positive on a correctly functioning
+     * system.  But it is good to be defensive about such matters.
+     * So if something goes wrong and the value does goes to zero, we
+     * clear the timeInfo.perfCounterAvailable in order to cause the
+     * calibration thread to shut itself down, then return without additional
+     * processing.
+     */
+
+    if( timeInfo.curCounterFreq.QuadPart==0 ){
+	LeaveCriticalSection( &timeInfo.cs );
+	timeInfo.perfCounterAvailable = 0;
+	return;
+    }
+
+    /*
      * Several things may have gone wrong here that have to
      * be checked for.
      * (1) The performance counter may have jumped.
-- 
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