diff --git a/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/FlowProgrammer.java b/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/FlowProgrammer.java
index ebc86e4..b567a87 100644
--- a/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/FlowProgrammer.java
+++ b/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/FlowProgrammer.java
@@ -5,15 +5,20 @@
 import java.util.HashMap;
 import java.util.Map;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 import net.floodlightcontroller.core.IFloodlightProviderService;
 import net.floodlightcontroller.core.module.FloodlightModuleContext;
 import net.floodlightcontroller.core.module.FloodlightModuleException;
 import net.floodlightcontroller.core.module.IFloodlightModule;
 import net.floodlightcontroller.core.module.IFloodlightService;
-import net.floodlightcontroller.threadpool.IThreadPoolService;
 
 public class FlowProgrammer implements IFloodlightModule {
-	private static final boolean enableFlowSync = true;
+    @SuppressWarnings("unused")
+	private final static Logger log = LoggerFactory.getLogger(FlowProgrammer.class);
+
+	private static final boolean enableFlowSync = false;
 	
     protected volatile IFloodlightProviderService floodlightProvider;
 
@@ -79,5 +84,4 @@
 	return l;
     }
     
-
 }
diff --git a/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/FlowPusher.java b/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/FlowPusher.java
index 6379f26..f43a83e 100644
--- a/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/FlowPusher.java
+++ b/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/FlowPusher.java
@@ -9,6 +9,7 @@
 import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.ExecutionException;
+import java.util.concurrent.Semaphore;
 
 import org.openflow.protocol.*;
 import org.openflow.protocol.action.*;
@@ -47,6 +48,8 @@
 public class FlowPusher implements IFlowPusherService, IOFMessageListener {
     private final static Logger log = LoggerFactory.getLogger(FlowPusher.class);
 
+    private static boolean barrierIfEmpty = false;
+    
     // NOTE: Below are moved from FlowManager.
     // TODO: Values copied from elsewhere (class LearningSwitch).
     // The local copy should go away!
@@ -96,11 +99,20 @@
 				return true;
 			}
 			
+			if (current == last_sent_time) {
+				return false;
+			}
+			
 			// Check if sufficient time (from aspect of rate) elapsed or not.
 			long rate = last_sent_size / (current - last_sent_time);
 			return (rate < max_rate);
 		}
 		
+		/**
+		 * Log time and size of last sent data.
+		 * @param current Time to be sent.
+		 * @param size Size of sent data (in bytes).
+		 */
 		void logSentData(long current, long size) {
 			last_sent_time = current;
 			last_sent_size = size;
@@ -113,7 +125,7 @@
 
 	private FloodlightContext context = null;
 	private BasicFactory factory = null;
-	private Map<Long, FlowPusherProcess> threadMap = null;
+	private Map<Long, FlowPusherThread> threadMap = null;
 	private Map<Long, Map<Integer, OFBarrierReplyFuture>>
 		barrierFutures = new HashMap<Long, Map<Integer, OFBarrierReplyFuture>>();
 	
@@ -124,26 +136,31 @@
 	 * @author Naoki Shiota
 	 *
 	 */
-	private class FlowPusherProcess implements Runnable {
+	private class FlowPusherThread extends Thread {
 		private Map<IOFSwitch,SwitchQueue> queues
 		= new HashMap<IOFSwitch,SwitchQueue>();
 		
-		private boolean isStopped = false;
-		private boolean isMsgAdded = false;
+		private Semaphore mutex = new Semaphore(0);
 		
 		@Override
 		public void run() {
 			log.debug("Begin Flow Pusher Process");
 			
 			while (true) {
+				try {
+					// wait for message pushed to queue
+					mutex.acquire();
+				} catch (InterruptedException e) {
+					e.printStackTrace();
+					log.debug("FlowPusherThread is interrupted");
+					return;
+				}
+				
 				Set< Map.Entry<IOFSwitch,SwitchQueue> > entries;
 				synchronized (queues) {
 					entries = queues.entrySet();
 				}
 				
-				// Set taint flag to false at this moment.
-				isMsgAdded = false;
-				
 				for (Map.Entry<IOFSwitch,SwitchQueue> entry : entries) {
 					IOFSwitch sw = entry.getKey();
 					SwitchQueue queue = entry.getValue();
@@ -163,15 +180,14 @@
 							int i = 0;
 							while (! queue.isEmpty()) {
 								// Number of messages excess the limit
-								if (++i >= MAX_MESSAGE_SEND) {
+								if (i >= MAX_MESSAGE_SEND) {
 									// Messages remains in queue
-									isMsgAdded = true;
+									mutex.release();
 									break;
 								}
+								++i;
 								
 								OFMessage msg = queue.poll();
-								
-								// if need to send, call IOFSwitch#write()
 								try {
 									messageDamper.write(sw, msg, context);
 									log.debug("Pusher sends message : {}", msg);
@@ -183,27 +199,13 @@
 							}
 							sw.flush();
 							queue.logSentData(current_time, size);
+							
+							if (queue.isEmpty() && barrierIfEmpty) {
+								barrier(sw);
+							}
 						}
 					}
 				}
-				
-				// sleep while all queues are empty
-				while (! (isMsgAdded || isStopped)) {
-					try {
-						Thread.sleep(SLEEP_MILLI_SEC, SLEEP_NANO_SEC);
-					} catch (InterruptedException e) {
-						e.printStackTrace();
-						log.error("Thread.sleep failed");
-					}
-				}
-				
-				log.debug("Exit sleep loop.");
-				
-				if (isStopped) {
-					log.debug("Pusher Process finished.");
-					return;
-				}
-
 			}
 		}
 	}
@@ -261,12 +263,11 @@
 			return;
 		}
 		
-		threadMap = new HashMap<Long,FlowPusherProcess>();
+		threadMap = new HashMap<Long,FlowPusherThread>();
 		for (long i = 0; i < number_thread; ++i) {
-			FlowPusherProcess runnable = new FlowPusherProcess();
-			threadMap.put(i, runnable);
+			FlowPusherThread thread = new FlowPusherThread();
 			
-			Thread thread = new Thread(runnable);
+			threadMap.put(i, thread);
 			thread.start();
 		}
 	}
@@ -335,10 +336,8 @@
 			return;
 		}
 		
-		for (FlowPusherProcess runnable : threadMap.values()) {
-			if (! runnable.isStopped) {
-				runnable.isStopped = true;
-			}
+		for (FlowPusherThread t : threadMap.values()) {
+			t.interrupt();
 		}
 	}
 	
@@ -366,7 +365,7 @@
 	 */
 	@Override
 	public boolean add(IOFSwitch sw, OFMessage msg) {
-		FlowPusherProcess proc = getProcess(sw);
+		FlowPusherThread proc = getProcess(sw);
 		SwitchQueue queue = proc.queues.get(sw);
 
 		if (queue == null) {
@@ -382,8 +381,10 @@
 			log.debug("Message is pushed : {}", msg);
 		}
 		
-		proc.isMsgAdded = true;
-		
+		if (proc.mutex.availablePermits() == 0) {
+			proc.mutex.release();
+		}
+
 		return true;
 	}
 	
@@ -1041,14 +1042,18 @@
 	@Override
 	public OFBarrierReplyFuture barrierAsync(IOFSwitch sw) {
 		// TODO creation of message and future should be moved to OFSwitchImpl
+
+		if (sw == null) {
+			return null;
+		}
 		
-		OFMessage msg = factory.getMessage(OFType.BARRIER_REQUEST);
+		OFBarrierRequest msg = (OFBarrierRequest) factory.getMessage(OFType.BARRIER_REQUEST);
 		msg.setXid(sw.getNextTransactionId());
 		add(sw, msg);
 
 		// TODO create Future object of message
 		OFBarrierReplyFuture future = new OFBarrierReplyFuture(threadPool, sw, msg.getXid());
-		
+
 		synchronized (barrierFutures) {
 			Map<Integer,OFBarrierReplyFuture> map = barrierFutures.get(sw.getId());
 			if (map == null) {
@@ -1056,7 +1061,7 @@
 				barrierFutures.put(sw.getId(), map);
 			}
 			map.put(msg.getXid(), future);
-			log.debug("Created future for {}", msg.getXid());
+			log.debug("Inserted future for {}", msg.getXid());
 		}
 		
 		return future;
@@ -1076,7 +1081,7 @@
 		return sw.getId() % number_thread;
 	}
 	
-	protected FlowPusherProcess getProcess(IOFSwitch sw) {
+	protected FlowPusherThread getProcess(IOFSwitch sw) {
 		long hash = getHash(sw);
 		
 		return threadMap.get(hash);
@@ -1099,11 +1104,6 @@
 
 	@Override
 	public Command receive(IOFSwitch sw, OFMessage msg, FloodlightContext cntx) {
-		// This check can be skipped (since Controller must filter).
-//		if (msg.getType() != OFType.BARRIER_REPLY) {
-//			return Command.CONTINUE;
-//		}
-		
 		Map<Integer,OFBarrierReplyFuture> map = barrierFutures.get(sw.getId());
 		if (map == null) {
 			return Command.CONTINUE;
diff --git a/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/FlowSynchronizer.java b/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/FlowSynchronizer.java
index b2e4552..f3f5c50 100644
--- a/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/FlowSynchronizer.java
+++ b/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/FlowSynchronizer.java
@@ -2,7 +2,6 @@
 
 import java.io.IOException;
 import java.util.ArrayList;
-import java.util.Collection;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
@@ -13,23 +12,8 @@
 
 import org.openflow.protocol.OFFlowMod;
 import org.openflow.protocol.OFMatch;
-import org.openflow.protocol.OFMessage;
-import org.openflow.protocol.OFPacketOut;
 import org.openflow.protocol.OFPort;
 import org.openflow.protocol.OFStatisticsRequest;
-import org.openflow.protocol.action.OFAction;
-import org.openflow.protocol.action.OFActionDataLayerDestination;
-import org.openflow.protocol.action.OFActionDataLayerSource;
-import org.openflow.protocol.action.OFActionEnqueue;
-import org.openflow.protocol.action.OFActionNetworkLayerDestination;
-import org.openflow.protocol.action.OFActionNetworkLayerSource;
-import org.openflow.protocol.action.OFActionNetworkTypeOfService;
-import org.openflow.protocol.action.OFActionOutput;
-import org.openflow.protocol.action.OFActionStripVirtualLan;
-import org.openflow.protocol.action.OFActionTransportLayerDestination;
-import org.openflow.protocol.action.OFActionTransportLayerSource;
-import org.openflow.protocol.action.OFActionVirtualLanIdentifier;
-import org.openflow.protocol.action.OFActionVirtualLanPriorityCodePoint;
 import org.openflow.protocol.statistics.OFFlowStatisticsReply;
 import org.openflow.protocol.statistics.OFFlowStatisticsRequest;
 import org.openflow.protocol.statistics.OFStatistics;
@@ -37,36 +21,16 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import com.google.common.collect.Lists;
-import com.tinkerpop.blueprints.Direction;
-
 import net.floodlightcontroller.core.IFloodlightProviderService;
 import net.floodlightcontroller.core.IOFSwitch;
 import net.floodlightcontroller.core.IOFSwitchListener;
 import net.floodlightcontroller.core.module.FloodlightModuleContext;
 import net.floodlightcontroller.core.module.FloodlightModuleException;
-import net.floodlightcontroller.core.module.IFloodlightModule;
-import net.floodlightcontroller.core.module.IFloodlightService;
-import net.floodlightcontroller.restserver.IRestApiService;
-import net.onrc.onos.datagrid.IDatagridService;
 import net.onrc.onos.graph.GraphDBOperation;
 import net.onrc.onos.ofcontroller.core.INetMapTopologyObjects.IFlowEntry;
 import net.onrc.onos.ofcontroller.core.INetMapTopologyObjects.ISwitchObject;
-import net.onrc.onos.ofcontroller.core.module.IOnosService;
-import net.onrc.onos.ofcontroller.floodlightlistener.INetworkGraphService;
 import net.onrc.onos.ofcontroller.util.Dpid;
-import net.onrc.onos.ofcontroller.util.FlowEntryAction;
-import net.onrc.onos.ofcontroller.util.FlowEntryActions;
 import net.onrc.onos.ofcontroller.util.FlowEntryId;
-import net.onrc.onos.ofcontroller.util.FlowEntryAction.ActionEnqueue;
-import net.onrc.onos.ofcontroller.util.FlowEntryAction.ActionOutput;
-import net.onrc.onos.ofcontroller.util.FlowEntryAction.ActionSetEthernetAddr;
-import net.onrc.onos.ofcontroller.util.FlowEntryAction.ActionSetIPv4Addr;
-import net.onrc.onos.ofcontroller.util.FlowEntryAction.ActionSetIpToS;
-import net.onrc.onos.ofcontroller.util.FlowEntryAction.ActionSetTcpUdpPort;
-import net.onrc.onos.ofcontroller.util.FlowEntryAction.ActionSetVlanId;
-import net.onrc.onos.ofcontroller.util.FlowEntryAction.ActionSetVlanPriority;
-import net.onrc.onos.ofcontroller.util.FlowEntryAction.ActionStripVlan;
 import net.onrc.onos.registry.controller.IControllerRegistryService;
 
 public class FlowSynchronizer implements IFlowSyncService, IOFSwitchListener {
@@ -86,8 +50,8 @@
     public void synchronize(IOFSwitch sw) {
 	Synchroizer sync = new Synchroizer(sw);
 	Thread t = new Thread(sync);
-	t.start();
 	switchThread.put(sw, t);
+	t.start();
     }
 
     @Override
diff --git a/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/OFBarrierReplyFuture.java b/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/OFBarrierReplyFuture.java
new file mode 100644
index 0000000..3013f5a
--- /dev/null
+++ b/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/OFBarrierReplyFuture.java
@@ -0,0 +1,49 @@
+package net.onrc.onos.ofcontroller.flowprogrammer;
+
+import java.util.concurrent.TimeUnit;
+
+import org.openflow.protocol.OFBarrierReply;
+import org.openflow.protocol.OFMessage;
+import org.openflow.protocol.OFType;
+
+import net.floodlightcontroller.core.IOFSwitch;
+import net.floodlightcontroller.core.internal.OFMessageFuture;
+import net.floodlightcontroller.threadpool.IThreadPoolService;
+
+public class OFBarrierReplyFuture extends OFMessageFuture<OFBarrierReply> {
+
+    protected volatile boolean finished;
+
+    public OFBarrierReplyFuture(IThreadPoolService tp,
+            IOFSwitch sw, int transactionId) {
+        super(tp, sw, OFType.FEATURES_REPLY, transactionId);
+        init();
+    }
+
+    public OFBarrierReplyFuture(IThreadPoolService tp,
+            IOFSwitch sw, int transactionId, long timeout, TimeUnit unit) {
+        super(tp, sw, OFType.FEATURES_REPLY, transactionId, timeout, unit);
+        init();
+    }
+
+    private void init() {
+        this.finished = false;
+        this.result = null;
+    }
+
+    @Override
+    protected void handleReply(IOFSwitch sw, OFMessage msg) {
+        this.result = (OFBarrierReply) msg;
+        this.finished = true;
+    }
+
+    @Override
+    protected boolean isFinished() {
+        return finished;
+    }
+
+    @Override
+    protected void unRegister() {
+        super.unRegister();
+    }
+}