ONOS-3586: Move event handling in HostLocationProvider to a background thread to…

… avoid hogging event dispatcher thread

Change-Id: I41ada7a946743854228594345cb636d1c336a2af

@@ -67,8 +67,11 @@ import org.slf4j.Logger;
 
 import java.util.Dictionary;
 import java.util.Set;
+import java.util.concurrent.ExecutorService;
 
 import static com.google.common.base.Strings.isNullOrEmpty;
+import static java.util.concurrent.Executors.newSingleThreadScheduledExecutor;
+import static org.onlab.util.Tools.groupedThreads;
 import static org.slf4j.LoggerFactory.getLogger;
 
 /**
@@ -117,6 +120,8 @@ public class HostLocationProvider extends AbstractProvider implements HostProvid
                     "Host Location Provider; default is false")
     private boolean ipv6NeighborDiscovery = false;
 
+    protected ExecutorService eventHandler;
+
     /**
      * Creates an OpenFlow host provider.
      */
@@ -128,7 +133,7 @@ public class HostLocationProvider extends AbstractProvider implements HostProvid
     public void activate(ComponentContext context) {
         cfgService.registerProperties(getClass());
         appId = coreService.registerApplication("org.onosproject.provider.host");
-
+        eventHandler = newSingleThreadScheduledExecutor(groupedThreads("onos/host-loc-provider", "event-handler"));
         providerService = providerRegistry.register(this);
         packetService.addProcessor(processor, PacketProcessor.advisor(1));
         deviceService.addListener(deviceListener);
@@ -147,6 +152,7 @@ public class HostLocationProvider extends AbstractProvider implements HostProvid
         providerRegistry.unregister(this);
         packetService.removeProcessor(processor);
         deviceService.removeListener(deviceListener);
+        eventHandler.shutdown();
         providerService = null;
         log.info("Stopped");
     }
@@ -392,6 +398,10 @@ public class HostLocationProvider extends AbstractProvider implements HostProvid
     private class InternalDeviceListener implements DeviceListener {
         @Override
         public void event(DeviceEvent event) {
+            eventHandler.execute(() -> handleEvent(event));
+        }
+
+        private void handleEvent(DeviceEvent event) {
             Device device = event.subject();
             switch (event.type()) {
                 case DEVICE_ADDED:

@@ -16,6 +16,8 @@
 package org.onosproject.provider.host.impl;
 
 import com.google.common.collect.ImmutableSet;
+import com.google.common.util.concurrent.MoreExecutors;
+
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
@@ -170,6 +172,8 @@ public class HostLocationProviderTest {
         provider.hostService = hostService;
 
         provider.activate(CTX_FOR_NO_REMOVE);
+
+        provider.eventHandler = MoreExecutors.newDirectExecutorService();
     }
 
     @Test