gh-10: Added nanoseconds support for the WallClock classes

util-core/src/main/java/com/indeed/util/core/time/DefaultWallClock.java

@@ -11,4 +11,9 @@ public class DefaultWallClock implements WallClock {
     public long currentTimeMillis() {
         return System.currentTimeMillis();
     }
+
+    @Override
+    public long nanoTime() {
+        return System.nanoTime();
+    }
 }

util-core/src/main/java/com/indeed/util/core/time/StoppedClock.java

@@ -10,13 +10,13 @@
  * @author matts
  */
 public final class StoppedClock implements WallClock {
-    @Nonnull private final AtomicLong millis;
+    @Nonnull private final AtomicLong nanos;
 
     /**
      * Creates a new stopped clock frozen at the current moment in time.
      */
     public StoppedClock() {
-        this(System.currentTimeMillis());
+        this(System.nanoTime(), TimeUnit.NANOSECONDS);
     }
 
     /**
@@ -25,7 +25,18 @@ public StoppedClock() {
      * @param millis The current time to use for the stopped clock.
      */
     public StoppedClock(final long millis) {
-        this.millis = new AtomicLong(millis);
+        this(millis, TimeUnit.MILLISECONDS);
+    }
+
+    /**
+     * Creates a new stopped clock frozen at the given moment in time with the
+     * specified time unit.
+     *
+     * @param time The time to use for the stopped clock.
+     * @param timeUnit The time unit that {@code time} is measured in.
+     */
+    public StoppedClock(final long time, final TimeUnit timeUnit) {
+        nanos = new AtomicLong(timeUnit.toNanos(time));
     }
 
     /**
@@ -34,23 +45,38 @@ public StoppedClock(final long millis) {
      * @param millis The new time to set the stopped clock to.
      */
     public final void set(final long millis) {
-        this.millis.set(millis);
+        set(millis, TimeUnit.MILLISECONDS);
+    }
+
+    /**
+     * Reset this stopped clock to the given moment in time.
+     *
+     * @param time The new time to set the stopped clock to.
+     * @param timeUnit The time unit that {@code time} is measured in.
+     */
+    public final void set(final long time, final TimeUnit timeUnit) {
+        this.nanos.set(timeUnit.toNanos(time));
     }
 
     /**
      * Add the specified amount of time to the current clock.
      *
-     * @param value The numeric value to add to the clock after converting
+     * @param time The numeric value to add to the clock after converting
      *              based on the provided {@code timeUnit}.
-     * @param timeUnit The time unit that {@code value} is measured in.
+     * @param timeUnit The time unit that {@code time} is measured in.
      * @return The time after being adjusted by the provided offset.
      */
-    public final long plus(final long value, @Nonnull final TimeUnit timeUnit) {
-        return this.millis.addAndGet(timeUnit.toMillis(value));
+    public final long plus(final long time, @Nonnull final TimeUnit timeUnit) {
+        return this.nanos.addAndGet(timeUnit.toNanos(time));
     }
 
     @Override
     public long currentTimeMillis () {
-        return millis.get();
+        return TimeUnit.NANOSECONDS.toMillis(nanos.get());
+    }
+
+    @Override
+    public long nanoTime() {
+        return nanos.get();
     }
 }

util-core/src/main/java/com/indeed/util/core/time/WallClock.java

@@ -7,4 +7,6 @@
  */
 public interface WallClock {
     long currentTimeMillis();
+
+    long nanoTime();
 }