Added a workaround to the time fluctuation WinXP bug.

git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@2735 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/java/com/threerings/media/timer/SystemMediaTimer.java

@@ -1,8 +1,10 @@
 //
-// $Id: SystemMediaTimer.java,v 1.1 2002/11/20 02:17:38 mdb Exp $
+// $Id: SystemMediaTimer.java,v 1.2 2003/07/29 00:27:32 mdb Exp $
 
 package com.threerings.media.timer;
 
+import com.threerings.media.Log;
+
 /**
  * Implements the {@link MediaTimer} interface using {@link
  * System#currentTimeMillis} to obtain timing information.
@@ -23,7 +25,23 @@ public class SystemMediaTimer implements MediaTimer
     // documentation inherited from interface
     public long getElapsedMillis ()
     {
-        return System.currentTimeMillis() - _resetStamp;
+        long stamp = System.currentTimeMillis() - _resetStamp;
+
+        // on WinXP the time sometimes seems to leap into the
+        // past; here we do our best to work around this insanity
+        if (stamp < _lastStamp) {
+            // only warn once per time anomaly
+            if (stamp > _lastWarning) {
+                Log.warning("Someone call Einstein! The clock is " +
+                            "running backwards [dt=" +
+                            (stamp - _lastStamp) + "].");
+                _lastWarning = _lastStamp;
+            }
+            stamp = _lastStamp;
+        }
+        _lastStamp = stamp;
+
+        return stamp;
     }
 
     // documentation inherited from interface
@@ -34,4 +52,7 @@ public class SystemMediaTimer implements MediaTimer
 
     /** The time at which this timer was last reset. */
     protected long _resetStamp = System.currentTimeMillis();
+
+    /** Used to ensure that the timer is sane. */
+    protected long _lastStamp, _lastWarning;
 }