Experimenting with Apache 2 copyright on the onos-cli module. More later...
diff --git a/core/api/src/main/java/org/onlab/onos/event/AbstractListenerRegistry.java b/core/api/src/main/java/org/onlab/onos/event/AbstractListenerRegistry.java
index 9710306..95581e3 100644
--- a/core/api/src/main/java/org/onlab/onos/event/AbstractListenerRegistry.java
+++ b/core/api/src/main/java/org/onlab/onos/event/AbstractListenerRegistry.java
@@ -19,6 +19,7 @@
     private final Logger log = getLogger(getClass());
 
     private final Set<L> listeners = new CopyOnWriteArraySet<>();
+    private volatile boolean shutdown = false;
 
     /**
      * Adds the specified listener.
@@ -58,7 +59,24 @@
      * @param error error encountered while processing
      */
     protected void reportProblem(E event, Throwable error) {
-        log.warn("Exception encountered while processing event " + event, error);
+        if (!shutdown) {
+            log.warn("Exception encountered while processing event " + event, error);
+        }
     }
 
+    /**
+     * Prepares the registry for normal operation.
+     */
+    public void activate() {
+        shutdown = false;
+    }
+
+    /**
+     * Prepares the registry for shutdown.
+     */
+    public void deactivate() {
+        shutdown = true;
+    }
+
+
 }