diff --git a/shadowsocks-csharp/Controller/Service/PortForwarder.cs b/shadowsocks-csharp/Controller/Service/PortForwarder.cs
index 5245bb7e..5429b053 100644
--- a/shadowsocks-csharp/Controller/Service/PortForwarder.cs
+++ b/shadowsocks-csharp/Controller/Service/PortForwarder.cs
@@ -39,6 +39,9 @@ namespace Shadowsocks.Controller
             // connection receive buffer
             private byte[] connetionRecvBuffer = new byte[RecvSize];
 
+            // instance-based lock
+            private readonly object _Lock = new object();
+
             public void Start(byte[] firstPacket, int length, Socket socket, int targetPort)
             {
                 this._firstPacket = firstPacket;
@@ -220,7 +223,7 @@ namespace Shadowsocks.Controller
 
             public void Close()
             {
-                lock (this)
+                lock (_Lock)
                 {
                     if (_closed)
                     {
diff --git a/shadowsocks-csharp/Controller/Service/TCPRelay.cs b/shadowsocks-csharp/Controller/Service/TCPRelay.cs
index 3ad3f4a3..c9e1ed25 100644
--- a/shadowsocks-csharp/Controller/Service/TCPRelay.cs
+++ b/shadowsocks-csharp/Controller/Service/TCPRelay.cs
@@ -160,8 +160,10 @@ namespace Shadowsocks.Controller
         private bool    _remoteShutdown = false;
         private bool    _closed = false;
 
-        private object  _encryptionLock = new object();
-        private object  _decryptionLock = new object();
+        // instance-based lock without static
+        private readonly object  _encryptionLock = new object();
+        private readonly object  _decryptionLock = new object();
+        private readonly object  _closeConnLock = new object();
 
         private DateTime _startConnectTime;
         private DateTime _startReceivingTime;
@@ -207,7 +209,7 @@ namespace Shadowsocks.Controller
 
         public void Close()
         {
-            lock (this)
+            lock (_closeConnLock)
             {
                 if (_closed) return;
                 _closed = true;
diff --git a/shadowsocks-csharp/Encryption/MbedTLSEncryptor.cs b/shadowsocks-csharp/Encryption/MbedTLSEncryptor.cs
index 4de20e70..5d958a1a 100644
--- a/shadowsocks-csharp/Encryption/MbedTLSEncryptor.cs
+++ b/shadowsocks-csharp/Encryption/MbedTLSEncryptor.cs
@@ -15,6 +15,9 @@ namespace Shadowsocks.Encryption
         private IntPtr _encryptCtx = IntPtr.Zero;
         private IntPtr _decryptCtx = IntPtr.Zero;
 
+        // instance based lock
+        private readonly object _Lock = new object();
+
         public MbedTLSEncryptor(string method, string password, bool onetimeauth, bool isudp)
             : base(method, password, onetimeauth, isudp)
         {
@@ -120,7 +123,7 @@ namespace Shadowsocks.Encryption
 
         protected virtual void Dispose(bool disposing)
         {
-            lock (this)
+            lock (_Lock)
             {
                 if (_disposed)
                 {
diff --git a/shadowsocks-csharp/View/LogForm.cs b/shadowsocks-csharp/View/LogForm.cs
index c29ff82d..f910a41a 100644
--- a/shadowsocks-csharp/View/LogForm.cs
+++ b/shadowsocks-csharp/View/LogForm.cs
@@ -34,6 +34,9 @@ namespace Shadowsocks.View
         const int BACK_OFFSET = 65536;
         ShadowsocksController controller;
 
+        // global traffic update lock, make it static
+        private static readonly object _lock = new object();
+
         #region chart
         long lastMaxSpeed;
         ShadowsocksController.QueueLast<TrafficInfo> traffic = new ShadowsocksController.QueueLast<TrafficInfo>();
@@ -71,7 +74,7 @@ namespace Shadowsocks.View
             long maxSpeed = 0;
             long lastInbound, lastOutbound;
 
-            lock (this)
+            lock (_lock)
             {
                 if (traffic.Count == 0)
                     return;
@@ -120,7 +123,7 @@ namespace Shadowsocks.View
 
         private void controller_TrafficChanged(object sender, EventArgs e)
         {
-            lock (this)
+            lock (_lock)
             {
                 traffic = new ShadowsocksController.QueueLast<TrafficInfo>();
                 foreach (var trafficPerSecond in controller.traffic)