8176499: Dependence on java.util.Timer freezes screen when OS time re…

…sets backwards

Reviewed-by: jvos

modules/javafx.graphics/src/main/java/com/sun/glass/ui/monocle/MonocleTimer.java

@@ -26,13 +26,16 @@
 package com.sun.glass.ui.monocle;
 
 import com.sun.glass.ui.Timer;
+import java.util.concurrent.ScheduledFuture;
+import java.util.concurrent.ScheduledThreadPoolExecutor;
+import java.util.concurrent.TimeUnit;
 
 /**
  * Monocle implementation class for Timer.
  */
 final class MonocleTimer extends Timer {
-    private static java.util.Timer timer;
-    private java.util.TimerTask task;
+    private static ScheduledThreadPoolExecutor scheduler;
+    private ScheduledFuture<?> task;
 
     MonocleTimer(final Runnable runnable) {
         super(runnable);
@@ -47,19 +50,11 @@ static int getMaxPeriod_impl() {
     }
 
     @Override protected long _start(final Runnable runnable, int period) {
-        if (timer == null) {
-            timer = new java.util.Timer(true);
+        if (scheduler == null) {
+            scheduler = new ScheduledThreadPoolExecutor(1);
         }
 
-        task = new java.util.TimerTask() {
-
-            @Override
-            public void run() {
-                runnable.run();
-            }
-        };
-
-        timer.schedule(task, 0, (long)period);
+        task = scheduler.scheduleAtFixedRate(runnable, 0, period, TimeUnit.MILLISECONDS);
         return 1; // need something non-zero to denote success.
     }
 
@@ -69,7 +64,7 @@ public void run() {
 
     @Override protected void _stop(long timer) {
         if (task != null) {
-            task.cancel();
+            task.cancel(false);
             task = null;
         }
     }