Make CoreEventDispatcher's listener processing time tracking thread-safe

Change-Id: Ib9f109e41fd1b78ce9771a2bb54e8bf3dda38d6c

@@ -27,11 +27,14 @@ import org.onosproject.event.EventDeliveryService;
 import org.onosproject.event.EventSink;
 import org.slf4j.Logger;
 
+import com.google.common.base.Stopwatch;
+
 import java.util.TimerTask;
 import java.util.concurrent.BlockingQueue;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Future;
 import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.TimeUnit;
 
 import static com.google.common.base.Preconditions.checkArgument;
 import static java.util.concurrent.Executors.newSingleThreadExecutor;
@@ -71,7 +74,7 @@ public class CoreEventDispatcher extends DefaultEventSinkRegistry
     // Means to detect long-running sinks
     private TimerTask watchdog;
     private EventSink lastSink;
-    private long lastStart = 0;
+    private final Stopwatch stopwatch = Stopwatch.createUnstarted();
     private Future<?> dispatchFuture;
 
     @Override
@@ -166,9 +169,9 @@ public class CoreEventDispatcher extends DefaultEventSinkRegistry
             EventSink sink = getSink(event.getClass());
             if (sink != null) {
                 lastSink = sink;
-                lastStart = System.currentTimeMillis();
+                stopwatch.start();
                 sink.process(event);
-                lastStart = 0;
+                stopwatch.reset();
             } else {
                 log.warn("No sink registered for event class {}",
                          event.getClass().getName());
@@ -184,11 +187,11 @@ public class CoreEventDispatcher extends DefaultEventSinkRegistry
     private class Watchdog extends TimerTask {
         @Override
         public void run() {
-            long delta = System.currentTimeMillis() - lastStart;
-            if (lastStart > 0 && delta > maxProcessMillis) {
-                lastStart = 0;
+            long elapsedTimeMillis = stopwatch.elapsed(TimeUnit.MILLISECONDS);
+            if (elapsedTimeMillis > maxProcessMillis) {
+                stopwatch.reset();
                 log.warn("Event sink {} exceeded execution time limit: {} ms; spawning new dispatch loop",
-                          lastSink.getClass().getName(), delta);
+                          lastSink.getClass().getName(), elapsedTimeMillis);
 
                 // Notify the sink that it has exceeded its time limit.
                 lastSink.onProcessLimit();