diff --git a/Modbus.Net/Modbus.Net.CodeGenerator/ConnectorWithControllerByteArrayCodeGenerator.cs b/Modbus.Net/Modbus.Net.CodeGenerator/ConnectorWithControllerByteArrayCodeGenerator.cs
index 1eb9c69..74dcb4f 100644
--- a/Modbus.Net/Modbus.Net.CodeGenerator/ConnectorWithControllerByteArrayCodeGenerator.cs
+++ b/Modbus.Net/Modbus.Net.CodeGenerator/ConnectorWithControllerByteArrayCodeGenerator.cs
@@ -112,7 +112,7 @@ namespace Modbus.Net
             IDisposable asyncLock = null;
             try
             {
-                if (Controller.IsSending != true)
+                if (!Controller.IsSending)
                 {
                     Controller.SendStart();
                 }
diff --git a/Modbus.Net/Modbus.Net/Connector/ComConnector.cs b/Modbus.Net/Modbus.Net/Connector/ComConnector.cs
index a2a84af..8694a69 100644
--- a/Modbus.Net/Modbus.Net/Connector/ComConnector.cs
+++ b/Modbus.Net/Modbus.Net/Connector/ComConnector.cs
@@ -82,10 +82,6 @@ namespace Modbus.Net
         ///     获取线程
         /// </summary>
         private Task _receiveThread;
-        /// <summary>
-        ///     获取线程关闭
-        /// </summary>
-        private bool _taskCancel = false;
 
         /// <summary>
         /// 缓冲的字节流
@@ -276,23 +272,23 @@ namespace Modbus.Net
                 // Release managed resources               
             }
             // Release unmanaged resources
-            if (SerialPort != null)
+            Linkers?.Remove((_slave, _com));
+            logger.LogInformation("Com connector {ConnectionToken} Removed", _com);
+            if (Linkers?.Count(p => p.Item2 == _com) == 0)
             {
-                Linkers.Remove((_slave, _com));
-                logger.LogInformation("Com connector {ConnectionToken} Removed", _com);
-                if (Linkers.Count(p => p.Item2 == _com) == 0)
+                if (SerialPort?.IsOpen == true)
+                {
+                    SerialPort?.Close();
+                }
+                SerialPort?.Dispose();
+                logger.LogInformation("Com interface {Com} Disposed", _com);
+                Controller?.SendStop();
+                if (Connectors.ContainsKey(_com))
                 {
-                    if (SerialPort.IsOpen)
-                    {
-                        SerialPort.Close();
-                    }
-                    SerialPort.Dispose();
-                    logger.LogInformation("Com interface {Com} Disposed", _com);
-                    Controller.SendStop();
                     Connectors[_com] = null;
                     Connectors.Remove(_com);
-                    ReceiveMsgThreadStop();
                 }
+                ReceiveMsgThreadStop();
             }
         }
 
@@ -365,7 +361,7 @@ namespace Modbus.Net
                     {
                         lock (SerialPort)
                         {
-                            _taskCancel = false;
+                            ReceiveMsgThreadStop();
                             SerialPort.Open();
                             ReceiveMsgThreadStart();
                             Controller.SendStart();
@@ -496,18 +492,35 @@ namespace Modbus.Net
         /// <inheritdoc />
         protected override void ReceiveMsgThreadStart()
         {
-            _receiveThread = Task.Run(ReceiveMessage);
+            if (_receiveThread == null)
+            {
+                _receiveThread = Task.Run(ReceiveMessage);
+            }
         }
 
         /// <inheritdoc />
         protected override void ReceiveMsgThreadStop()
         {
-            _taskCancel = true;
+            _receiveThread?.Dispose();
+            _receiveThread = null;
+            CacheClear();
+            Controller?.Clear();
+        }
+
+        private void CacheClear()
+        {
+            if (CacheBytes != null)
+            {
+                lock (CacheBytes)
+                {
+                    CacheBytes.Clear();
+                }
+            }
         }
 
         private async Task ReceiveMessage()
         {
-            while (!_taskCancel)
+            while (true)
             {
                 try
                 {
@@ -532,10 +545,7 @@ namespace Modbus.Net
                                     CacheBytes.Count);
                             logger.LogError(
                                 $"Com client {ConnectionToken} cached msg: {string.Concat(CacheBytes.Select(p => " " + p.ToString("X2")))}");
-                            lock (CacheBytes)
-                            {
-                                CacheBytes.Clear();
-                            }
+                            CacheClear();
                         }
                         else
                         {
@@ -569,6 +579,7 @@ namespace Modbus.Net
                 }
                 catch (Exception e)
                 {
+                    CacheClear();
                     logger.LogError(e, "Com client {ConnectionToken} read msg error", ConnectionToken);
                 }
             }
diff --git a/Modbus.Net/Modbus.Net/Controller/BaseController.cs b/Modbus.Net/Modbus.Net/Controller/BaseController.cs
index b921b62..0f6869b 100644
--- a/Modbus.Net/Modbus.Net/Controller/BaseController.cs
+++ b/Modbus.Net/Modbus.Net/Controller/BaseController.cs
@@ -24,7 +24,7 @@ namespace Modbus.Net
         /// <summary>
         ///     ��Ϣά���߳��Ƿ�������
         /// </summary>
-        public virtual bool? IsSending => SendingThread?.Status == TaskStatus.Running || SendingThread?.Status == TaskStatus.WaitingToRun || SendingThread?.Status == TaskStatus.Created;
+        public virtual bool IsSending => SendingThread != null;
 
         /// <summary>
         ///     ���з�λ�ú���
@@ -73,7 +73,8 @@ namespace Modbus.Net
         /// <inheritdoc />
         public virtual void SendStop()
         {
-            SendingThread.Dispose();
+            Clear();
+            SendingThread?.Dispose();
             SendingThread = null;
             Clear();
         }
@@ -81,7 +82,7 @@ namespace Modbus.Net
         /// <inheritdoc />
         public virtual void SendStart()
         {
-            if (IsSending != true)
+            if (!IsSending)
             {
                 SendingThread = Task.Run(() => SendingMessageControlInner());
             }
@@ -90,9 +91,12 @@ namespace Modbus.Net
         /// <inheritdoc />
         public void Clear()
         {
-            lock (WaitingMessages)
+            if (WaitingMessages != null)
             {
-                WaitingMessages.Clear();
+                lock (WaitingMessages)
+                {
+                    WaitingMessages.Clear();
+                }
             }
         }
 
@@ -196,13 +200,7 @@ namespace Modbus.Net
                     if (def != null)
                     {
                         def.ReceiveMessage = message.Item1;
-                        lock (WaitingMessages)
-                        {
-                            if (WaitingMessages.IndexOf(def) >= 0)
-                            {
-                                WaitingMessages.Remove(def);
-                            }
-                        }
+                        ForceRemoveWaitingMessage(def);
                         def.ReceiveMutex.Set();
                         ans.Add((message.Item1, true));
                     }
diff --git a/Modbus.Net/Modbus.Net/Controller/FifoController.cs b/Modbus.Net/Modbus.Net/Controller/FifoController.cs
index a14b478..592d3eb 100644
--- a/Modbus.Net/Modbus.Net/Controller/FifoController.cs
+++ b/Modbus.Net/Modbus.Net/Controller/FifoController.cs
@@ -14,8 +14,6 @@ namespace Modbus.Net
 
         private MessageWaitingDef _currentSendingPos;
 
-        private bool _taskCancel = false;
-
         private int _waitingListMaxCount;
 
         /// <summary>
@@ -40,7 +38,7 @@ namespace Modbus.Net
         /// <inheritdoc />
         protected override void SendingMessageControlInner()
         {
-            while (!_taskCancel)
+            while (true)
             {
                 if (AcquireTime > 0)
                 {
@@ -79,25 +77,10 @@ namespace Modbus.Net
                     catch (Exception e)
                     {
                         logger.LogError(e, "Controller throws exception");
-                        _taskCancel = true;
+                        SendStop();
                     }
                 }
             }
-            SendStop();
-        }
-
-        /// <inheritdoc />
-        public override void SendStart()
-        {
-            _taskCancel = false;
-            base.SendStart();
-        }
-
-        /// <inheritdoc />
-        public override void SendStop()
-        {
-            _taskCancel = true;
-            base.SendStop();
         }
 
         /// <inheritdoc />
@@ -124,7 +107,7 @@ namespace Modbus.Net
             {
                 return false;
             }
-            if (_taskCancel)
+            if (!IsSending)
             {
                 return false;
             }
diff --git a/Modbus.Net/Modbus.Net/Controller/MatchDirectlySendController.cs b/Modbus.Net/Modbus.Net/Controller/MatchDirectlySendController.cs
index 7401a7c..b6e1627 100644
--- a/Modbus.Net/Modbus.Net/Controller/MatchDirectlySendController.cs
+++ b/Modbus.Net/Modbus.Net/Controller/MatchDirectlySendController.cs
@@ -11,7 +11,7 @@ namespace Modbus.Net
         /// <summary>
         ///     消息维护线程是否在运行
         /// </summary>
-        public override bool? IsSending => true;
+        public override bool IsSending => true;
 
         /// <inheritdoc />
         public MatchDirectlySendController(ICollection<(int, int)>[] keyMatches,
diff --git a/Modbus.Net/Modbus.Net/Interface/IController.cs b/Modbus.Net/Modbus.Net/Interface/IController.cs
index c3fd62e..2cb9431 100644
--- a/Modbus.Net/Modbus.Net/Interface/IController.cs
+++ b/Modbus.Net/Modbus.Net/Interface/IController.cs
@@ -10,7 +10,7 @@ namespace Modbus.Net
         /// <summary>
         ///     ��Ϣά���߳��Ƿ�������
         /// </summary>
-        bool? IsSending { get; }
+        bool IsSending { get; }
 
         /// <summary>
         ///     ������Ϣ