diff --git a/Example3/Example3.csproj b/Example3/Example3.csproj
index cfb81b7b..ce4fe265 100644
--- a/Example3/Example3.csproj
+++ b/Example3/Example3.csproj
@@ -8,7 +8,7 @@
     <ProjectGuid>{C648BA25-77E5-4A40-A97F-D0AA37B9FB26}</ProjectGuid>
     <OutputType>Exe</OutputType>
     <RootNamespace>Example3</RootNamespace>
-    <AssemblyName>Example3</AssemblyName>
+    <AssemblyName>example3</AssemblyName>
     <TargetFrameworkVersion>v3.5</TargetFrameworkVersion>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
diff --git a/websocket-sharp/Ext.cs b/websocket-sharp/Ext.cs
index 34a87f29..7f6aa368 100644
--- a/websocket-sharp/Ext.cs
+++ b/websocket-sharp/Ext.cs
@@ -49,6 +49,7 @@ using System.Security.Cryptography.X509Certificates;
 using System.Text;
 using WebSocketSharp.Net;
 using WebSocketSharp.Net.WebSockets;
+using WebSocketSharp.Server;
 
 namespace WebSocketSharp
 {
@@ -164,6 +165,20 @@ namespace WebSocketSharp
       }
     }
 
+    internal static string CheckIfStarted (this ServerState state)
+    {
+      return state != ServerState.START
+             ? "Not started, on shutdown or stopped."
+             : null;
+    }
+
+    internal static string CheckIfStopped (this ServerState state)
+    {
+      return state == ServerState.START || state == ServerState.SHUTDOWN
+             ? "Already started or on shutdown."
+             : null;
+    }
+
     internal static string CheckIfValidCloseData (this byte [] data)
     {
       return data.Length > 125
diff --git a/websocket-sharp/Server/HttpServer.cs b/websocket-sharp/Server/HttpServer.cs
index 7269f7fb..69d9fbc2 100644
--- a/websocket-sharp/Server/HttpServer.cs
+++ b/websocket-sharp/Server/HttpServer.cs
@@ -47,13 +47,15 @@ namespace WebSocketSharp.Server
     #region Private Fields
 
     private HttpListener                _listener;
-    private bool                        _listening;
+    private volatile bool               _listening;
     private Logger                      _logger;
     private int                         _port;
     private Thread                      _receiveRequestThread;
     private string                      _rootPath;
     private bool                        _secure;
     private WebSocketServiceHostManager _serviceHosts;
+    private volatile ServerState        _state;
+    private object                      _sync;
     private bool                        _windows;
 
     #endregion
@@ -308,12 +310,40 @@ namespace WebSocketSharp.Server
 
     #region Private Methods
 
+    private void abort ()
+    {
+      lock (_sync)
+      {
+        if (_state != ServerState.START)
+          return;
+
+        _state = ServerState.SHUTDOWN;
+      }
+
+      _listening = false;
+      _serviceHosts.Stop (((ushort) CloseStatusCode.SERVER_ERROR).ToByteArray (ByteOrder.BIG));
+      _listener.Abort ();
+
+      _state = ServerState.STOP;
+    }
+
+    private string checkIfCertExists ()
+    {
+      return _secure &&
+             !EndPointListener.CertificateExists (_port, _listener.CertificateFolderPath) &&
+             Certificate == null
+             ? "The secure connection requires a server certificate."
+             : null;
+    }
+
     private void init ()
     {
       _listener = new HttpListener ();
       _listening = false;
       _logger = new Logger ();
       _serviceHosts = new WebSocketServiceHostManager (_logger);
+      _state = ServerState.READY;
+      _sync = new object ();
 
       _windows = false;
       var os = Environment.OSVersion;
@@ -420,7 +450,8 @@ namespace WebSocketSharp.Server
           context.Response.Close ();
         }
         catch (Exception ex) {
-          _logger.Fatal (ex.Message);
+          _logger.Fatal (ex.ToString ());
+          context.Connection.Close (true);
         }
       };
 
@@ -434,15 +465,18 @@ namespace WebSocketSharp.Server
         try {
           processRequestAsync (_listener.GetContext ());
         }
-        catch (HttpListenerException) {
-          _logger.Info ("HttpListener has been stopped.");
+        catch (HttpListenerException ex) {
+          _logger.Warn (String.Format ("Receiving has been stopped.\nreason: {0}.", ex.Message));
           break;
         }
         catch (Exception ex) {
-          _logger.Fatal (ex.Message);
+          _logger.Fatal (ex.ToString ());
           break;
         }
       }
+
+      if (_listening)
+        abort ();
     }
 
     private void startReceiveRequestThread ()
@@ -452,20 +486,14 @@ namespace WebSocketSharp.Server
       _receiveRequestThread.Start ();
     }
 
-    private void stop (ushort code, string reason)
+    private void stopListener ()
     {
-      var data = code.Append (reason);
-      var msg = data.CheckIfValidCloseData ();
-      if (msg != null)
-      {
-        _logger.Error (String.Format ("{0}\ncode: {1}\nreason: {2}", msg, code, reason));
+      if (!_listening)
         return;
-      }
 
-      _serviceHosts.Stop (data);
+      _listening = false;
       _listener.Close ();
       _receiveRequestThread.Join (5 * 1000);
-      _listening = false;
     }
 
     #endregion
@@ -554,21 +582,22 @@ namespace WebSocketSharp.Server
     /// </summary>
     public void Start ()
     {
-      if (_listening)
-        return;
-
-      if (_secure &&
-          !EndPointListener.CertificateExists (_port, _listener.CertificateFolderPath) &&
-          Certificate == null
-      )
+      lock (_sync)
       {
-        _logger.Error ("Secure connection requires a server certificate.");
-        return;
-      }
+        var msg = _state.CheckIfStopped () ?? checkIfCertExists ();
+        if (msg != null)
+        {
+          _logger.Error (String.Format ("{0}\nstate: {1}\nsecure: {2}", msg, _state, _secure));
+          return;
+        }
 
-      _listener.Start ();
-      startReceiveRequestThread ();
-      _listening = true;
+        _serviceHosts.Start ();
+        _listener.Start ();
+        startReceiveRequestThread ();
+        _listening = true;
+
+        _state = ServerState.START;
+      }
     }
 
     /// <summary>
@@ -576,13 +605,22 @@ namespace WebSocketSharp.Server
     /// </summary>
     public void Stop ()
     {
-      if (!_listening)
-        return;
+      lock (_sync)
+      {
+        var msg = _state.CheckIfStarted ();
+        if (msg != null)
+        {
+          _logger.Error (String.Format ("{0}\nstate: {1}", msg, _state));
+          return;
+        }
+
+        _state = ServerState.SHUTDOWN;
+      }
 
       _serviceHosts.Stop ();
-      _listener.Close ();
-      _receiveRequestThread.Join (5 * 1000);
-      _listening = false;
+      stopListener ();
+
+      _state = ServerState.STOP;
     }
 
     /// <summary>
@@ -597,17 +635,26 @@ namespace WebSocketSharp.Server
     /// </param>
     public void Stop (ushort code, string reason)
     {
-      if (!_listening)
-        return;
-
-      var msg = code.CheckIfValidCloseStatusCode ();
-      if (msg != null)
+      byte [] data = null;
+      lock (_sync)
       {
-        _logger.Error (String.Format ("{0}\ncode: {1}", msg, code));
-        return;
+        var msg = _state.CheckIfStarted () ??
+                  code.CheckIfValidCloseStatusCode () ??
+                  (data = code.Append (reason)).CheckIfValidCloseData ();
+
+        if (msg != null)
+        {
+          _logger.Error (String.Format ("{0}\nstate: {1}\ncode: {2}\nreason: {3}", msg, _state, code, reason));
+          return;
+        }
+
+        _state = ServerState.SHUTDOWN;
       }
 
-      stop (code, reason);
+      _serviceHosts.Stop (data);
+      stopListener ();
+
+      _state = ServerState.STOP;
     }
 
     /// <summary>
@@ -615,17 +662,33 @@ namespace WebSocketSharp.Server
     /// and <see cref="string"/> used to stop the WebSocket services.
     /// </summary>
     /// <param name="code">
-    /// A <see cref="CloseStatusCode"/> that contains a status code indicating the reason for stop.
+    /// One of the <see cref="CloseStatusCode"/> values that represent the status codes indicating
+    /// the reasons for stop.
     /// </param>
     /// <param name="reason">
     /// A <see cref="string"/> that contains the reason for stop.
     /// </param>
     public void Stop (CloseStatusCode code, string reason)
     {
-      if (!_listening)
-        return;
+      byte [] data = null;
+      lock (_sync)
+      {
+        var msg = _state.CheckIfStarted () ??
+                  (data = ((ushort) code).Append (reason)).CheckIfValidCloseData ();
 
-      stop ((ushort) code, reason);
+        if (msg != null)
+        {
+          _logger.Error (String.Format ("{0}\nstate: {1}\nreason: {2}", msg, _state, reason));
+          return;
+        }
+
+        _state = ServerState.SHUTDOWN;
+      }
+
+      _serviceHosts.Stop (data);
+      stopListener ();
+
+      _state = ServerState.STOP;
     }
 
     #endregion
diff --git a/websocket-sharp/Server/ServerState.cs b/websocket-sharp/Server/ServerState.cs
new file mode 100644
index 00000000..1a4b9254
--- /dev/null
+++ b/websocket-sharp/Server/ServerState.cs
@@ -0,0 +1,40 @@
+#region License
+/*
+ * ServerState.cs
+ *
+ * The MIT License
+ *
+ * Copyright (c) 2013 sta.blockhead
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#endregion
+
+using System;
+
+namespace WebSocketSharp.Server
+{
+  internal enum ServerState
+  {
+    READY,
+    START,
+    SHUTDOWN,
+    STOP
+  }
+}
diff --git a/websocket-sharp/Server/WebSocketServer.cs b/websocket-sharp/Server/WebSocketServer.cs
index 0c44bde5..bd86ebe4 100644
--- a/websocket-sharp/Server/WebSocketServer.cs
+++ b/websocket-sharp/Server/WebSocketServer.cs
@@ -48,6 +48,8 @@ namespace WebSocketSharp.Server
     #region Private Fields
 
     private WebSocketServiceHostManager _serviceHosts;
+    private volatile ServerState        _state;
+    private object                      _sync;
 
     #endregion
 
@@ -87,6 +89,8 @@ namespace WebSocketSharp.Server
         throw new ArgumentException ("Must not contain the path component: " + url, "url");
 
       _serviceHosts = new WebSocketServiceHostManager (Log);
+      _state = ServerState.READY;
+      _sync = new object ();
     }
 
     /// <summary>
@@ -139,6 +143,8 @@ namespace WebSocketSharp.Server
       : base (address, port, "/", secure)
     {
       _serviceHosts = new WebSocketServiceHostManager (Log);
+      _state = ServerState.READY;
+      _sync = new object ();
     }
 
     #endregion
@@ -193,26 +199,30 @@ namespace WebSocketSharp.Server
 
     #endregion
 
-    #region Private Methods
+    #region Protected Methods
 
-    private void stop (ushort code, string reason)
+    /// <summary>
+    /// Aborts receiving the WebSocket connection requests.
+    /// </summary>
+    /// <remarks>
+    /// This method is called when an exception occurs while receiving the WebSocket connection requests.
+    /// </remarks>
+    protected override void Abort ()
     {
-      var data = code.Append (reason);
-      var msg = data.CheckIfValidCloseData ();
-      if (msg != null)
+      lock (_sync)
       {
-        Log.Error (String.Format ("{0}\ncode: {1}\nreason: {2}", msg, code, reason));
-        return;
+        if (_state != ServerState.START)
+          return;
+
+        _state = ServerState.SHUTDOWN;
       }
 
-      base.Stop ();
-      _serviceHosts.Stop (data);
+      StopListener ();
+      _serviceHosts.Stop (((ushort) CloseStatusCode.SERVER_ERROR).ToByteArray (ByteOrder.BIG));
+
+      _state = ServerState.STOP;
     }
 
-    #endregion
-
-    #region Protected Methods
-
     /// <summary>
     /// Accepts a WebSocket connection request.
     /// </summary>
@@ -301,13 +311,54 @@ namespace WebSocketSharp.Server
       return _serviceHosts.Remove (servicePath);
     }
 
+    /// <summary>
+    /// Starts to receive the WebSocket connection requests.
+    /// </summary>
+    public override void Start ()
+    {
+      lock (_sync)
+      {
+        var msg = _state.CheckIfStopped ();
+        if (msg != null)
+        {
+          Log.Error (String.Format ("{0}\nstate: {1}", msg, _state));
+          return;
+        }
+
+        _serviceHosts.Start ();
+
+        base.Start ();
+        if (!IsListening)
+        {
+          _serviceHosts.Stop ();
+          return;
+        }
+
+        _state = ServerState.START;
+      }
+    }
+
     /// <summary>
     /// Stops receiving the WebSocket connection requests.
     /// </summary>
     public override void Stop ()
     {
+      lock (_sync)
+      {
+        var msg = _state.CheckIfStarted ();
+        if (msg != null)
+        {
+          Log.Error (String.Format ("{0}\nstate: {1}", msg, _state));
+          return;
+        }
+
+        _state = ServerState.SHUTDOWN;
+      }
+
       base.Stop ();
       _serviceHosts.Stop ();
+
+      _state = ServerState.STOP;
     }
 
     /// <summary>
@@ -322,14 +373,26 @@ namespace WebSocketSharp.Server
     /// </param>
     public void Stop (ushort code, string reason)
     {
-      var msg = code.CheckIfValidCloseStatusCode ();
-      if (msg != null)
+      byte [] data = null;
+      lock (_sync)
       {
-        Log.Error (String.Format ("{0}\ncode: {1}", msg, code));
-        return;
+        var msg = _state.CheckIfStarted () ??
+                  code.CheckIfValidCloseStatusCode () ??
+                  (data = code.Append (reason)).CheckIfValidCloseData ();
+
+        if (msg != null)
+        {
+          Log.Error (String.Format ("{0}\nstate: {1}\ncode: {2}\nreason: {3}", msg, _state, code, reason));
+          return;
+        }
+
+        _state = ServerState.SHUTDOWN;
       }
 
-      stop (code, reason);
+      base.Stop ();
+      _serviceHosts.Stop (data);
+
+      _state = ServerState.STOP;
     }
 
     /// <summary>
@@ -337,14 +400,33 @@ namespace WebSocketSharp.Server
     /// and <see cref="string"/>.
     /// </summary>
     /// <param name="code">
-    /// A <see cref="CloseStatusCode"/> that contains a status code indicating the reason for stop.
+    /// One of the <see cref="CloseStatusCode"/> values that represent the status codes indicating
+    /// the reasons for stop.
     /// </param>
     /// <param name="reason">
     /// A <see cref="string"/> that contains the reason for stop.
     /// </param>
     public void Stop (CloseStatusCode code, string reason)
     {
-      stop ((ushort) code, reason);
+      byte [] data = null;
+      lock (_sync)
+      {
+        var msg = _state.CheckIfStarted () ??
+                  (data = ((ushort) code).Append (reason)).CheckIfValidCloseData ();
+
+        if (msg != null)
+        {
+          Log.Error (String.Format ("{0}\nstate: {1}\nreason: {2}", msg, _state, reason));
+          return;
+        }
+
+        _state = ServerState.SHUTDOWN;
+      }
+
+      base.Stop ();
+      _serviceHosts.Stop (data);
+
+      _state = ServerState.STOP;
     }
 
     #endregion
diff --git a/websocket-sharp/Server/WebSocketServerBase.cs b/websocket-sharp/Server/WebSocketServerBase.cs
index 711347f7..1901ba54 100644
--- a/websocket-sharp/Server/WebSocketServerBase.cs
+++ b/websocket-sharp/Server/WebSocketServerBase.cs
@@ -48,7 +48,7 @@ namespace WebSocketSharp.Server
 
     private IPAddress        _address;
     private X509Certificate2 _cert;
-    private bool             _listening;
+    private volatile bool    _listening;
     private Logger           _logger;
     private int              _port;
     private Thread           _receiveRequestThread;
@@ -339,8 +339,8 @@ namespace WebSocketSharp.Server
         }
         catch (Exception ex)
         {
+          _logger.Fatal (ex.ToString ());
           client.Close ();
-          _logger.Fatal (ex.Message);
         }
       };
 
@@ -354,15 +354,18 @@ namespace WebSocketSharp.Server
         try {
           processRequestAsync (_listener.AcceptTcpClient ());
         }
-        catch (SocketException) {
-          _logger.Info ("TcpListener has been stopped.");
+        catch (SocketException ex) {
+          _logger.Warn (String.Format ("Receiving has been stopped.\nreason: {0}.", ex.Message));
           break;
         }
         catch (Exception ex) {
-          _logger.Fatal (ex.Message);
+          _logger.Fatal (ex.ToString ());
           break;
         }
       }
+
+      if (_listening)
+        Abort ();
     }
 
     private void startReceiveRequestThread ()
@@ -392,6 +395,14 @@ namespace WebSocketSharp.Server
 
     #region Protected Methods
 
+    /// <summary>
+    /// Aborts receiving the WebSocket connection requests.
+    /// </summary>
+    /// <remarks>
+    /// This method is called when an exception occurs while receiving the WebSocket connection requests.
+    /// </remarks>
+    protected abstract void Abort ();
+
     /// <summary>
     /// Accepts a WebSocket connection request.
     /// </summary>
@@ -400,6 +411,18 @@ namespace WebSocketSharp.Server
     /// </param>
     protected abstract void AcceptWebSocket (TcpListenerWebSocketContext context);
 
+    /// <summary>
+    /// Stops the inner <see cref="TcpListener"/> used to receive the WebSocket connection requests.
+    /// </summary>
+    protected void StopListener ()
+    {
+      if (!_listening)
+        return;
+
+      _listening = false;
+      _listener.Stop ();
+    }
+
     #endregion
 
     #region Public Methods
@@ -414,7 +437,7 @@ namespace WebSocketSharp.Server
 
       if (_secure && _cert == null)
       {
-        _logger.Error ("Secure connection requires a server certificate.");
+        _logger.Error ("The secure connection requires a server certificate.");
         return;
       }
 
@@ -431,9 +454,9 @@ namespace WebSocketSharp.Server
       if (!_selfHost || !_listening)
         return;
 
+      _listening = false;
       _listener.Stop ();
       _receiveRequestThread.Join (5 * 1000);
-      _listening = false;
     }
 
     #endregion
diff --git a/websocket-sharp/Server/WebSocketServiceHost.cs b/websocket-sharp/Server/WebSocketServiceHost.cs
index c0680da7..1a6fb525 100644
--- a/websocket-sharp/Server/WebSocketServiceHost.cs
+++ b/websocket-sharp/Server/WebSocketServiceHost.cs
@@ -54,6 +54,8 @@ namespace WebSocketSharp.Server
 
     private string                  _servicePath;
     private WebSocketSessionManager _sessions;
+    private volatile ServerState    _state;
+    private object                  _sync;
 
     #endregion
 
@@ -63,6 +65,8 @@ namespace WebSocketSharp.Server
       : base (logger)
     {
       _sessions = new WebSocketSessionManager (logger);
+      _state = ServerState.READY;
+      _sync = new object ();
     }
 
     #endregion
@@ -92,6 +96,8 @@ namespace WebSocketSharp.Server
       : base (url)
     {
       _sessions = new WebSocketSessionManager (Log);
+      _state = ServerState.READY;
+      _sync = new object ();
     }
 
     /// <summary>
@@ -186,6 +192,8 @@ namespace WebSocketSharp.Server
       : base (address, port, servicePath, secure)
     {
       _sessions = new WebSocketSessionManager (Log);
+      _state = ServerState.READY;
+      _sync = new object ();
     }
 
     #endregion
@@ -267,26 +275,30 @@ namespace WebSocketSharp.Server
 
     #endregion
 
-    #region Private Methods
+    #region Protected Methods
 
-    private void stop (ushort code, string reason)
+    /// <summary>
+    /// Aborts receiving the WebSocket connection requests.
+    /// </summary>
+    /// <remarks>
+    /// This method is called when an exception occurs while receiving the WebSocket connection requests.
+    /// </remarks>
+    protected override void Abort ()
     {
-      var data = code.Append (reason);
-      var msg = data.CheckIfValidCloseData ();
-      if (msg != null)
+      lock (_sync)
       {
-        Log.Error (String.Format ("{0}\ncode: {1}\nreason: {2}", msg, code, reason));
-        return;
+        if (_state != ServerState.START)
+          return;
+
+        _state = ServerState.SHUTDOWN;
       }
 
-      base.Stop ();
-      _sessions.Stop (data);
+      StopListener ();
+      _sessions.Stop (((ushort) CloseStatusCode.SERVER_ERROR).ToByteArray (ByteOrder.BIG));
+
+      _state = ServerState.STOP;
     }
 
-    #endregion
-
-    #region Protected Methods
-
     /// <summary>
     /// Accepts a WebSocket connection request.
     /// </summary>
@@ -315,13 +327,54 @@ namespace WebSocketSharp.Server
 
     #region Public Methods
 
+    /// <summary>
+    /// Starts to receive the WebSocket connection requests.
+    /// </summary>
+    public override void Start ()
+    {
+      lock (_sync)
+      {
+        var msg = _state.CheckIfStopped ();
+        if (msg != null)
+        {
+          Log.Error (String.Format ("{0}\nstate: {1}", msg, _state));
+          return;
+        }
+
+        _sessions.Start ();
+
+        base.Start ();
+        if (!IsListening)
+        {
+          _sessions.Stop ();
+          return;
+        }
+
+        _state = ServerState.START;
+      }
+    }
+
     /// <summary>
     /// Stops receiving the WebSocket connection requests.
     /// </summary>
     public override void Stop ()
     {
+      lock (_sync)
+      {
+        var msg = _state.CheckIfStarted ();
+        if (msg != null)
+        {
+          Log.Error (String.Format ("{0}\nstate: {1}", msg, _state));
+          return;
+        }
+
+        _state = ServerState.SHUTDOWN;
+      }
+
       base.Stop ();
       _sessions.Stop ();
+
+      _state = ServerState.STOP;
     }
 
     /// <summary>
@@ -336,14 +389,26 @@ namespace WebSocketSharp.Server
     /// </param>
     public void Stop (ushort code, string reason)
     {
-      var msg = code.CheckIfValidCloseStatusCode ();
-      if (msg != null)
+      byte [] data = null;
+      lock (_sync)
       {
-        Log.Error (String.Format ("{0}\ncode: {1}", msg, code));
-        return;
+        var msg = _state.CheckIfStarted () ??
+                  code.CheckIfValidCloseStatusCode () ??
+                  (data = code.Append (reason)).CheckIfValidCloseData ();
+
+        if (msg != null)
+        {
+          Log.Error (String.Format ("{0}\nstate: {1}\ncode: {2}\nreason: {3}", msg, _state, code, reason));
+          return;
+        }
+
+        _state = ServerState.SHUTDOWN;
       }
 
-      stop (code, reason);
+      base.Stop ();
+      _sessions.Stop (data);
+
+      _state = ServerState.STOP;
     }
 
     /// <summary>
@@ -351,14 +416,33 @@ namespace WebSocketSharp.Server
     /// and <see cref="string"/>.
     /// </summary>
     /// <param name="code">
-    /// A <see cref="CloseStatusCode"/> that contains a status code indicating the reason for stop.
+    /// One of the <see cref="CloseStatusCode"/> values that represent the status codes indicating
+    /// the reasons for stop.
     /// </param>
     /// <param name="reason">
     /// A <see cref="string"/> that contains the reason for stop.
     /// </param>
     public void Stop (CloseStatusCode code, string reason)
     {
-      stop ((ushort) code, reason);
+      byte [] data = null;
+      lock (_sync)
+      {
+        var msg = _state.CheckIfStarted () ??
+                  (data = ((ushort) code).Append (reason)).CheckIfValidCloseData ();
+
+        if (msg != null)
+        {
+          Log.Error (String.Format ("{0}\nstate: {1}\nreason: {2}", msg, _state, reason));
+          return;
+        }
+
+        _state = ServerState.SHUTDOWN;
+      }
+
+      base.Stop ();
+      _sessions.Stop (data);
+
+      _state = ServerState.STOP;
     }
 
     #endregion
diff --git a/websocket-sharp/Server/WebSocketServiceHostManager.cs b/websocket-sharp/Server/WebSocketServiceHostManager.cs
index 95ab6e96..56b4be4f 100644
--- a/websocket-sharp/Server/WebSocketServiceHostManager.cs
+++ b/websocket-sharp/Server/WebSocketServiceHostManager.cs
@@ -45,6 +45,7 @@ namespace WebSocketSharp.Server
     private volatile bool                             _keepClean;
     private Logger                                    _logger;
     private Dictionary<string, IWebSocketServiceHost> _serviceHosts;
+    private volatile ServerState                      _state;
     private object                                    _sync;
 
     #endregion
@@ -61,6 +62,7 @@ namespace WebSocketSharp.Server
       _logger = logger;
       _keepClean = true;
       _serviceHosts = new Dictionary<string, IWebSocketServiceHost> ();
+      _state = ServerState.READY;
       _sync = new object ();
     }
 
@@ -78,7 +80,12 @@ namespace WebSocketSharp.Server
       get {
         var count = 0;
         foreach (var host in ServiceHosts)
+        {
+          if (_state != ServerState.START)
+            break;
+
           count += host.ConnectionCount;
+        }
 
         return count;
       }
@@ -143,12 +150,12 @@ namespace WebSocketSharp.Server
       internal set {
         lock (_sync)
         {
-          if (_keepClean ^ value)
-          {
-            _keepClean = value;
-            foreach (var host in _serviceHosts.Values)
-              host.KeepClean = value;
-          }
+          if (!(value ^ _keepClean))
+            return;
+
+          _keepClean = value;
+          foreach (var host in _serviceHosts.Values)
+            host.KeepClean = value;
         }
       }
     }
@@ -192,7 +199,12 @@ namespace WebSocketSharp.Server
     {
       var result = new Dictionary<string, Dictionary<string, bool>> ();
       foreach (var host in ServiceHosts)
+      {
+        if (_state != ServerState.START)
+          break;
+
         result.Add (host.ServicePath, host.Sessions.BroadpingInternally (data));
+      }
 
       return result;
     }
@@ -214,6 +226,9 @@ namespace WebSocketSharp.Server
           return;
         }
 
+        if (_state == ServerState.START)
+          serviceHost.Sessions.Start ();
+
         _serviceHosts.Add (servicePath, serviceHost);
       }
     }
@@ -234,18 +249,33 @@ namespace WebSocketSharp.Server
         _serviceHosts.Remove (servicePath);
       }
 
-      host.Sessions.Stop (((ushort) CloseStatusCode.AWAY).ToByteArray (ByteOrder.BIG));
+      if (host.Sessions.State == ServerState.START)
+        host.Sessions.Stop (((ushort) CloseStatusCode.AWAY).ToByteArray (ByteOrder.BIG));
+
       return true;
     }
 
+    internal void Start ()
+    {
+      lock (_sync)
+      {
+        foreach (var host in _serviceHosts.Values)
+          host.Sessions.Start ();
+
+        _state = ServerState.START;
+      }
+    }
+
     internal void Stop ()
     {
       lock (_sync)
       {
+        _state = ServerState.SHUTDOWN;
         foreach (var host in _serviceHosts.Values)
           host.Sessions.Stop ();
 
         _serviceHosts.Clear ();
+        _state = ServerState.STOP;
       }
     }
 
@@ -253,10 +283,12 @@ namespace WebSocketSharp.Server
     {
       lock (_sync)
       {
+        _state = ServerState.SHUTDOWN;
         foreach (var host in _serviceHosts.Values)
           host.Sessions.Stop (data);
 
         _serviceHosts.Clear ();
+        _state = ServerState.STOP;
       }
     }
 
@@ -282,7 +314,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public void Broadcast (byte [] data)
     {
-      var msg = data.CheckIfValidSendData ();
+      var msg = _state.CheckIfStarted () ?? data.CheckIfValidSendData ();
       if (msg != null)
       {
         _logger.Error (msg);
@@ -290,7 +322,12 @@ namespace WebSocketSharp.Server
       }
 
       foreach (var host in ServiceHosts)
+      {
+        if (_state != ServerState.START)
+          break;
+
         host.Sessions.BroadcastInternally (data);
+      }
     }
 
     /// <summary>
@@ -302,7 +339,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public void Broadcast (string data)
     {
-      var msg = data.CheckIfValidSendData ();
+      var msg = _state.CheckIfStarted () ?? data.CheckIfValidSendData ();
       if (msg != null)
       {
         _logger.Error (msg);
@@ -310,7 +347,12 @@ namespace WebSocketSharp.Server
       }
 
       foreach (var host in ServiceHosts)
+      {
+        if (_state != ServerState.START)
+          break;
+
         host.Sessions.BroadcastInternally (data);
+      }
     }
 
     /// <summary>
@@ -328,7 +370,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public bool BroadcastTo (byte [] data, string servicePath)
     {
-      var msg = data.CheckIfValidSendData () ?? servicePath.CheckIfValidServicePath ();
+      var msg = _state.CheckIfStarted () ?? data.CheckIfValidSendData () ?? servicePath.CheckIfValidServicePath ();
       if (msg != null)
       {
         _logger.Error (msg);
@@ -361,7 +403,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public bool BroadcastTo (string data, string servicePath)
     {
-      var msg = data.CheckIfValidSendData () ?? servicePath.CheckIfValidServicePath ();
+      var msg = _state.CheckIfStarted () ?? data.CheckIfValidSendData () ?? servicePath.CheckIfValidServicePath ();
       if (msg != null)
       {
         _logger.Error (msg);
@@ -389,6 +431,13 @@ namespace WebSocketSharp.Server
     /// </returns>
     public Dictionary<string, Dictionary<string, bool>> Broadping ()
     {
+      var msg = _state.CheckIfStarted ();
+      if (msg != null)
+      {
+        _logger.Error (msg);
+        return null;
+      }
+
       return broadping (new byte [] {});
     }
 
@@ -408,10 +457,10 @@ namespace WebSocketSharp.Server
     public Dictionary<string, Dictionary<string, bool>> Broadping (string message)
     {
       if (message == null || message.Length == 0)
-        return broadping (new byte [] {});
+        return Broadping ();
 
       var data = Encoding.UTF8.GetBytes (message);
-      var msg = data.CheckIfValidPingData ();
+      var msg = _state.CheckIfStarted () ?? data.CheckIfValidPingData ();
       if (msg != null)
       {
         _logger.Error (msg);
@@ -434,7 +483,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public Dictionary<string, bool> BroadpingTo (string servicePath)
     {
-      var msg = servicePath.CheckIfValidServicePath ();
+      var msg = _state.CheckIfStarted () ?? servicePath.CheckIfValidServicePath ();
       if (msg != null)
       {
         _logger.Error (msg);
@@ -472,7 +521,7 @@ namespace WebSocketSharp.Server
         return BroadpingTo (servicePath);
 
       var data = Encoding.UTF8.GetBytes (message);
-      var msg = data.CheckIfValidPingData () ?? servicePath.CheckIfValidServicePath ();
+      var msg = _state.CheckIfStarted () ?? data.CheckIfValidPingData () ?? servicePath.CheckIfValidServicePath ();
       if (msg != null)
       {
         _logger.Error (msg);
@@ -501,7 +550,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public void CloseSession (string id, string servicePath)
     {
-      var msg = servicePath.CheckIfValidServicePath ();
+      var msg = _state.CheckIfStarted () ?? servicePath.CheckIfValidServicePath ();
       if (msg != null)
       {
         _logger.Error (msg);
@@ -536,7 +585,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public void CloseSession (ushort code, string reason, string id, string servicePath)
     {
-      var msg = servicePath.CheckIfValidServicePath ();
+      var msg = _state.CheckIfStarted () ?? servicePath.CheckIfValidServicePath ();
       if (msg != null)
       {
         _logger.Error (msg);
@@ -571,7 +620,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public void CloseSession (CloseStatusCode code, string reason, string id, string servicePath)
     {
-      var msg = servicePath.CheckIfValidServicePath ();
+      var msg = _state.CheckIfStarted () ?? servicePath.CheckIfValidServicePath ();
       if (msg != null)
       {
         _logger.Error (msg);
@@ -604,7 +653,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public bool PingTo (string id, string servicePath)
     {
-      var msg = servicePath.CheckIfValidServicePath ();
+      var msg = _state.CheckIfStarted () ?? servicePath.CheckIfValidServicePath ();
       if (msg != null)
       {
         _logger.Error (msg);
@@ -640,7 +689,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public bool PingTo (string message, string id, string servicePath)
     {
-      var msg = servicePath.CheckIfValidServicePath ();
+      var msg = _state.CheckIfStarted () ?? servicePath.CheckIfValidServicePath ();
       if (msg != null)
       {
         _logger.Error (msg);
@@ -675,7 +724,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public bool SendTo (byte [] data, string id, string servicePath)
     {
-      var msg = servicePath.CheckIfValidServicePath ();
+      var msg = _state.CheckIfStarted () ?? servicePath.CheckIfValidServicePath ();
       if (msg != null)
       {
         _logger.Error (msg);
@@ -710,7 +759,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public bool SendTo (string data, string id, string servicePath)
     {
-      var msg = servicePath.CheckIfValidServicePath ();
+      var msg = _state.CheckIfStarted () ?? servicePath.CheckIfValidServicePath ();
       if (msg != null)
       {
         _logger.Error (msg);
@@ -744,7 +793,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public bool TryGetServiceHost (string servicePath, out IWebSocketServiceHost serviceHost)
     {
-      var msg = servicePath.CheckIfValidServicePath ();
+      var msg = _state.CheckIfStarted () ?? servicePath.CheckIfValidServicePath ();
       if (msg != null)
       {
         _logger.Error (msg);
diff --git a/websocket-sharp/Server/WebSocketSessionManager.cs b/websocket-sharp/Server/WebSocketSessionManager.cs
index 30135d53..713c2f82 100644
--- a/websocket-sharp/Server/WebSocketSessionManager.cs
+++ b/websocket-sharp/Server/WebSocketSessionManager.cs
@@ -42,9 +42,10 @@ namespace WebSocketSharp.Server
     #region Private Fields
 
     private object                               _forSweep;
+    private volatile bool                        _keepClean;
     private Logger                               _logger;
     private Dictionary<string, WebSocketService> _sessions;
-    private volatile bool                        _stopped;
+    private volatile ServerState                 _state;
     private volatile bool                        _sweeping;
     private Timer                                _sweepTimer;
     private object                               _sync;
@@ -62,21 +63,30 @@ namespace WebSocketSharp.Server
     {
       _logger = logger;
       _forSweep = new object ();
+      _keepClean = true;
       _sessions = new Dictionary<string, WebSocketService> ();
-      _stopped = false;
+      _state = ServerState.READY;
       _sweeping = false;
       _sync = new object ();
 
-      setSweepTimer ();
-      startSweepTimer ();
+      setSweepTimer (60 * 1000);
     }
 
     #endregion
 
     #region Internal Properties
 
+    internal ServerState State {
+      get {
+        return _state;
+      }
+    }
+
     internal IEnumerable<WebSocketService> ServiceInstances {
       get {
+        if (_state != ServerState.START)
+          return new List<WebSocketService> ();
+
         lock (_sync)
         {
           return _sessions.Values.ToList ();
@@ -158,7 +168,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public IWebSocketSession this [string id] {
       get {
-        var msg = id.CheckIfValidSessionID ();
+        var msg = _state.CheckIfStarted () ?? id.CheckIfValidSessionID ();
         if (msg != null)
         {
           _logger.Error (msg);
@@ -182,17 +192,16 @@ namespace WebSocketSharp.Server
     /// </value>
     public bool KeepClean {
       get {
-        return _sweepTimer.Enabled;
+        return _keepClean;
       }
 
       internal set {
-        if (value)
-        {
-          if (!_stopped)
-            startSweepTimer ();
-        }
-        else
-          stopSweepTimer ();
+        if (!(value ^ _keepClean))
+          return;
+
+        _keepClean = value;
+        if (_state == ServerState.START)
+          _sweepTimer.Enabled = value;
       }
     }
 
@@ -213,72 +222,20 @@ namespace WebSocketSharp.Server
 
     #region Private Methods
 
-    private void broadcast (byte [] data)
-    {
-      foreach (var service in ServiceInstances)
-        service.Send (data);
-    }
-
-    private void broadcast (string data)
-    {
-      foreach (var service in ServiceInstances)
-        service.Send (data);
-    }
-
-    private void broadcastAsync (byte [] data)
-    {
-      var services = ServiceInstances.GetEnumerator ();
-      Action completed = null;
-      completed = () =>
-      {
-        if (services.MoveNext ())
-          services.Current.SendAsync (data, completed);
-      };
-
-      if (services.MoveNext ())
-        services.Current.SendAsync (data, completed);
-    }
-
-    private void broadcastAsync (string data)
-    {
-      var services = ServiceInstances.GetEnumerator ();
-      Action completed = null;
-      completed = () =>
-      {
-        if (services.MoveNext ())
-          services.Current.SendAsync (data, completed);
-      };
-
-      if (services.MoveNext ())
-        services.Current.SendAsync (data, completed);
-    }
-
     private static string createID ()
     {
       return Guid.NewGuid ().ToString ("N");
     }
 
-    private void setSweepTimer ()
+    private void setSweepTimer (double interval)
     {
-      _sweepTimer = new Timer (60 * 1000);
+      _sweepTimer = new Timer (interval);
       _sweepTimer.Elapsed += (sender, e) =>
       {
         Sweep ();
       };
     }
 
-    private void startSweepTimer ()
-    {
-      if (!_sweepTimer.Enabled)
-        _sweepTimer.Start ();
-    }
-
-    private void stopSweepTimer ()
-    {
-      if (_sweepTimer.Enabled)
-        _sweepTimer.Stop ();
-    }
-
     #endregion
 
     #region Internal Methods
@@ -287,7 +244,7 @@ namespace WebSocketSharp.Server
     {
       lock (_sync)
       {
-        if (_stopped)
+        if (_state != ServerState.START)
           return null;
 
         var id = createID ();
@@ -299,25 +256,42 @@ namespace WebSocketSharp.Server
 
     internal void BroadcastInternally (byte [] data)
     {
-      if (_stopped)
-        broadcast (data);
-      else
-        broadcastAsync (data);
+      var services = ServiceInstances.GetEnumerator ();
+      Action completed = null;
+      completed = () =>
+      {
+        if (_state == ServerState.START && services.MoveNext ())
+          services.Current.SendAsync (data, completed);
+      };
+
+      if (_state == ServerState.START && services.MoveNext ())
+        services.Current.SendAsync (data, completed);
     }
 
     internal void BroadcastInternally (string data)
     {
-      if (_stopped)
-        broadcast (data);
-      else
-        broadcastAsync (data);
+      var services = ServiceInstances.GetEnumerator ();
+      Action completed = null;
+      completed = () =>
+      {
+        if (_state == ServerState.START && services.MoveNext ())
+          services.Current.SendAsync (data, completed);
+      };
+
+      if (_state == ServerState.START && services.MoveNext ())
+        services.Current.SendAsync (data, completed);
     }
 
     internal Dictionary<string, bool> BroadpingInternally (byte [] data)
     {
       var result = new Dictionary<string, bool> ();
       foreach (var session in ServiceInstances)
+      {
+        if (_state != ServerState.START)
+          break;
+
         result.Add (session.ID, session.Context.WebSocket.Ping (data));
+      }
 
       return result;
     }
@@ -330,31 +304,37 @@ namespace WebSocketSharp.Server
       }
     }
 
+    internal void Start ()
+    {
+      _sweepTimer.Enabled = _keepClean;
+      _state = ServerState.START;
+    }
+
     internal void Stop ()
     {
-      stopSweepTimer ();
       lock (_sync)
       {
-        if (_stopped)
-          return;
+        _state = ServerState.SHUTDOWN;
 
-        _stopped = true;
-        foreach (var session in ServiceInstances)
+        _sweepTimer.Enabled = false;
+        foreach (var session in _sessions.Values.ToList ())
           session.Context.WebSocket.Close ();
+
+        _state = ServerState.STOP;
       }
     }
 
     internal void Stop (byte [] data)
     {
-      stopSweepTimer ();
       lock (_sync)
       {
-        if (_stopped)
-          return;
+        _state = ServerState.SHUTDOWN;
 
-        _stopped = true;
-        foreach (var session in ServiceInstances)
+        _sweepTimer.Enabled = false;
+        foreach (var session in _sessions.Values.ToList ())
           session.Context.WebSocket.Close (data);
+
+        _state = ServerState.STOP;
       }
     }
 
@@ -378,7 +358,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public void Broadcast (byte [] data)
     {
-      var msg = data.CheckIfValidSendData ();
+      var msg = _state.CheckIfStarted () ?? data.CheckIfValidSendData ();
       if (msg != null)
       {
         _logger.Error (msg);
@@ -396,7 +376,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public void Broadcast (string data)
     {
-      var msg = data.CheckIfValidSendData ();
+      var msg = _state.CheckIfStarted () ?? data.CheckIfValidSendData ();
       if (msg != null)
       {
         _logger.Error (msg);
@@ -415,6 +395,13 @@ namespace WebSocketSharp.Server
     /// </returns>
     public Dictionary<string, bool> Broadping ()
     {
+      var msg = _state.CheckIfStarted ();
+      if (msg != null)
+      {
+        _logger.Error (msg);
+        return null;
+      }
+
       return BroadpingInternally (new byte [] {});
     }
 
@@ -431,10 +418,10 @@ namespace WebSocketSharp.Server
     public Dictionary<string, bool> Broadping (string message)
     {
       if (message == null || message.Length == 0)
-        return BroadpingInternally (new byte [] {});
+        return Broadping ();
 
       var data = Encoding.UTF8.GetBytes (message);
-      var msg = data.CheckIfValidPingData ();
+      var msg = _state.CheckIfStarted () ?? data.CheckIfValidPingData ();
       if (msg != null)
       {
         _logger.Error (msg);
@@ -452,7 +439,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public void CloseSession (string id)
     {
-      var msg = id.CheckIfValidSessionID ();
+      var msg = _state.CheckIfStarted () ?? id.CheckIfValidSessionID ();
       if (msg != null)
       {
         _logger.Error (msg);
@@ -484,7 +471,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public void CloseSession (ushort code, string reason, string id)
     {
-      var msg = id.CheckIfValidSessionID ();
+      var msg = _state.CheckIfStarted () ?? id.CheckIfValidSessionID ();
       if (msg != null)
       {
         _logger.Error (msg);
@@ -516,7 +503,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public void CloseSession (CloseStatusCode code, string reason, string id)
     {
-      var msg = id.CheckIfValidSessionID ();
+      var msg = _state.CheckIfStarted () ?? id.CheckIfValidSessionID ();
       if (msg != null)
       {
         _logger.Error (msg);
@@ -545,7 +532,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public bool PingTo (string id)
     {
-      var msg = id.CheckIfValidSessionID ();
+      var msg = _state.CheckIfStarted () ?? id.CheckIfValidSessionID ();
       if (msg != null)
       {
         _logger.Error (msg);
@@ -578,7 +565,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public bool PingTo (string message, string id)
     {
-      var msg = id.CheckIfValidSessionID ();
+      var msg = _state.CheckIfStarted () ?? id.CheckIfValidSessionID ();
       if (msg != null)
       {
         _logger.Error (msg);
@@ -610,7 +597,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public bool SendTo (byte [] data, string id)
     {
-      var msg = id.CheckIfValidSessionID ();
+      var msg = _state.CheckIfStarted () ?? id.CheckIfValidSessionID ();
       if (msg != null)
       {
         _logger.Error (msg);
@@ -643,7 +630,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public bool SendTo (string data, string id)
     {
-      var msg = id.CheckIfValidSessionID ();
+      var msg = _state.CheckIfStarted () ?? id.CheckIfValidSessionID ();
       if (msg != null)
       {
         _logger.Error (msg);
@@ -666,7 +653,7 @@ namespace WebSocketSharp.Server
     /// </summary>
     public void Sweep ()
     {
-      if (_stopped || _sweeping || Count == 0)
+      if (_state != ServerState.START || _sweeping || Count == 0)
         return;
 
       lock (_forSweep)
@@ -674,11 +661,11 @@ namespace WebSocketSharp.Server
         _sweeping = true;
         foreach (var id in InactiveIDs)
         {
+          if (_state != ServerState.START)
+            break;
+
           lock (_sync)
           {
-            if (_stopped)
-              break;
-
             WebSocketService session;
             if (_sessions.TryGetValue (id, out session))
             {
@@ -714,7 +701,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public bool TryGetSession (string id, out IWebSocketSession session)
     {
-      var msg = id.CheckIfValidSessionID ();
+      var msg = _state.CheckIfStarted () ?? id.CheckIfValidSessionID ();
       if (msg != null)
       {
         _logger.Error (msg);
diff --git a/websocket-sharp/websocket-sharp.csproj b/websocket-sharp/websocket-sharp.csproj
index 0774bf83..13553bcf 100644
--- a/websocket-sharp/websocket-sharp.csproj
+++ b/websocket-sharp/websocket-sharp.csproj
@@ -129,6 +129,7 @@
     <Compile Include="WebSocketState.cs" />
     <Compile Include="Server\IWebSocketSession.cs" />
     <Compile Include="Server\WebSocketSessionManager.cs" />
+    <Compile Include="Server\ServerState.cs" />
   </ItemGroup>
   <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
   <ItemGroup>