Make NanosecondPrecisionSystemTimeProvider monotonic

src/main/java/net/openhft/chronicle/hash/ChronicleHashBuilder.java

@@ -396,7 +396,7 @@ public interface ChronicleHashBuilder<K, H extends ChronicleHash<K, ?, ?, ?>,
      * replication consensus protocol (conflicting data updates resolution).
      *
      * <p>Default time provider uses system time ({@link System#currentTimeMillis()}) in
-     * <i>nanosecond</i> precision.
+     * <i>nanosecond</i> precision, also it returns non-decreasing time.
      *
      * @param timeProvider a new time provider for replication needs
      * @return this builder back

src/main/java/net/openhft/chronicle/map/NanosecondPrecisionSystemTimeProvider.java

@@ -20,6 +20,7 @@ import net.openhft.chronicle.hash.replication.TimeProvider;
 
 import java.io.ObjectStreamException;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicLong;
 
 import static java.util.concurrent.TimeUnit.NANOSECONDS;
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
@@ -27,6 +28,8 @@ import static java.util.concurrent.TimeUnit.MILLISECONDS;
 final class NanosecondPrecisionSystemTimeProvider extends TimeProvider {
     private static final long serialVersionUID = 0L;
 
+    private static final AtomicLong lastTimeHolder = new AtomicLong();
+
     private static final NanosecondPrecisionSystemTimeProvider INSTANCE =
             new NanosecondPrecisionSystemTimeProvider();
 
@@ -38,7 +41,14 @@ final class NanosecondPrecisionSystemTimeProvider extends TimeProvider {
 
     @Override
     public long currentTime() {
-        return MILLISECONDS.toNanos(System.currentTimeMillis());
+        long now = MILLISECONDS.toNanos(System.currentTimeMillis());
+        while (true) {
+            long lastTime = lastTimeHolder.get();
+            if (now <= lastTime)
+                return lastTime;
+            if (lastTimeHolder.compareAndSet(lastTime, now))
+                return now;
+        }
     }
 
     @Override