diff --git a/src/org/hwo/servicelink/ServiceLink.java b/src/org/hwo/servicelink/ServiceLink.java
index d0301a5..91a328c 100644
--- a/src/org/hwo/servicelink/ServiceLink.java
+++ b/src/org/hwo/servicelink/ServiceLink.java
@@ -64,6 +64,8 @@ public class ServiceLink implements NewSerialPortListener {
 	RxWorker	rxWorker;
 	TxWorker	txWorker;
 	
+	boolean		closing;
+	
 	private List<ServiceLinkListener> serviceLinkListeners;
 	
 	public ServiceLink(NewSerialPort serialPort)
@@ -114,31 +116,35 @@ public class ServiceLink implements NewSerialPortListener {
 		this.serialPort.close();
 	}
 	
-	public synchronized void open() throws ServiceLinkException
+	public void open() throws ServiceLinkException
 	{
-		close();
-		
-		if (serialPort != null){
-			_open();
-		} else {
-			throwNotOpen();
+		if (!closing){
+			close();
+			
+			if (serialPort != null){
+				_open();
+			} else {
+				throwNotOpen();
+			}
 		}
 	}
 	
-	public synchronized void close()
+	public void close()
 	{
-		if (txWorker != null){
-			_close();
-		}			
+		if (!closing){
+			if (txWorker != null){
+				_close();
+			}
+		}
 	}
 	
-	private synchronized void throwNotOpen() throws ServiceLinkException
+	private void throwNotOpen() throws ServiceLinkException
 	{
 		if (!isOpen())
 			throw new ServiceLinkException("serial port not opened!");		
 	}
 	
-	public synchronized boolean isOpen()
+	public boolean isOpen()
 	{
 		return (this.serialPort != null) && (this.serialPort.isOpen()) && (this.txWorker != null);
 	}	
@@ -344,11 +350,11 @@ public class ServiceLink implements NewSerialPortListener {
 		queueRequest(request);
 	}
 
-	public synchronized NewSerialPort getSerialPort() {
+	public NewSerialPort getSerialPort() {
 		return serialPort;
 	}
 
-	public synchronized void setSerialPort(NewSerialPort serialPort) {
+	public void setSerialPort(NewSerialPort serialPort) {
 		if (isOpen()){
 			this.close();
 			this.serialPort.removeNewSerialPortListener(this);
@@ -373,6 +379,9 @@ public class ServiceLink implements NewSerialPortListener {
 			if (!isAlive())
 				return;
 
+			if (exit)
+				return;
+			
 			exit = true;
 			this.notifyAll();
 			try {
@@ -413,6 +422,7 @@ public class ServiceLink implements NewSerialPortListener {
 
 				} catch (Exception io){
 					log(io);
+					exit = true;
 					ServiceLink.this.close();
 				};
 			}
@@ -430,9 +440,17 @@ public class ServiceLink implements NewSerialPortListener {
 			if (!isAlive())
 				return;
 			
+			if (exit)
+				return;
+			
 			exit = true;
 			try {
-				this.wait();
+				this.notifyAll();
+				this.wait(250);
+				
+				if (this.isAlive())
+					this.stop();
+				
 			} catch (InterruptedException e) {
 				log(e);
 			}
@@ -464,13 +482,14 @@ public class ServiceLink implements NewSerialPortListener {
 					tx = txQueue.pollFirst();
 				}
 
-				while (tx != null){
+				while ((tx != null)&&(!exit)&&(ServiceLink.this.isOpen())){
 					byte[] txbytes = tx.toByteArray();
 					try {
 						log(DEBUGDETAIL,"TX BYTES: %s",ByteArrayHexlifier.byteArrayToString(txbytes));
-						serialPort.getOutputStream().write(txbytes);						
+						serialPort.getOutputStream().write(txbytes);					
 					} catch (IOException io) {
 						log(io);
+						exit = true;
 						ServiceLink.this.close();
 					}