introduced MillisecondsTimePoint.approximateNow() and used where now() is too expensive; re-typed now() to TimePoint

java/com.sap.sse.common/src/com/sap/sse/common/impl/MillisecondsTimePoint.java

@@ -1,6 +1,10 @@
 package com.sap.sse.common.impl;
 
 import java.util.Date;
+import java.util.Timer;
+import java.util.TimerTask;
+
+import com.sap.sse.common.TimePoint;
 
 
 public class MillisecondsTimePoint extends AbstractTimePoint {
@@ -8,7 +12,33 @@ public class MillisecondsTimePoint extends AbstractTimePoint {
     private long millis;
     private Date date;
     
-    public static MillisecondsTimePoint now() {
+    private static TimePoint timePointNoOlderThanOneSecond;
+    
+    static {
+        timePointNoOlderThanOneSecond = MillisecondsTimePoint.now();
+        new Timer("LockUtil timestamp generator", /* isDaemon */ true).schedule(
+            new TimerTask() {
+                @Override
+                public void run() {
+                    timePointNoOlderThanOneSecond = MillisecondsTimePoint.now();
+                }
+            }, /* delay 0 means immediate execution */ 0l, /* period 1s */ 1000l);
+    }
+    
+    /**
+     * A time point that is approximately the current time, up to one second late. Obtaining a time point
+     * this way is much less expensive than using {@link #now()} which really generates a new time point
+     * upon each invocation and as such does not qualify for high-frequency operations, particularly when
+     * the timer is used for some human time-based timeout of several seconds.
+     */
+    public static TimePoint approximateNow() {
+        return timePointNoOlderThanOneSecond;
+    }
+    
+    /**
+     * A time point as exact as {@link System#currentTimeMillis()}
+     */
+    public static TimePoint now() {
         return new MillisecondsTimePoint(System.currentTimeMillis());
     }