Fix unhandled exception during shutdown due to provider service being unavailable

Change-Id: I891b2d3c64576fe7cace80ff7907551b46054db6

@@ -177,6 +177,7 @@ public class OpenFlowDeviceProvider extends AbstractProvider implements DevicePr
     @Deactivate
     public void deactivate(ComponentContext context) {
         cfgService.unregisterProperties(getClass(), false);
+        listener.disable();
         controller.removeListener(listener);
         providerRegistry.unregister(this);
         collectors.values().forEach(PortStatsCollector::stop);
@@ -344,6 +345,7 @@ public class OpenFlowDeviceProvider extends AbstractProvider implements DevicePr
     private class InternalDeviceProvider implements OpenFlowSwitchListener, OpenFlowEventListener {
 
         private HashMap<Dpid, List<OFPortStatsEntry>> portStatsReplies = new HashMap<>();
+        private boolean isDisabled = false;
 
         @Override
         public void switchAdded(Dpid dpid) {
@@ -773,6 +775,11 @@ public class OpenFlowDeviceProvider extends AbstractProvider implements DevicePr
 
         @Override
         public void handleMessage(Dpid dpid, OFMessage msg) {
+            if (isDisabled) {
+                return;
+            }
+
+            try {
                 switch (msg.getType()) {
                     case STATS_REPLY:
                         if (((OFStatsReply) msg).getStatsType() == OFStatsType.PORT) {
@@ -796,6 +803,14 @@ public class OpenFlowDeviceProvider extends AbstractProvider implements DevicePr
                     default:
                         break;
                 }
+            } catch (IllegalStateException e) {
+                // system is shutting down and the providerService is no longer
+                // valid. Messages cannot be processed.
+            }
+        }
+
+        private void disable() {
+            isDisabled = true;
         }
     }