diff --git a/shadowsocks-csharp/Controller/Local.cs b/shadowsocks-csharp/Controller/Local.cs
index 8eb2384b..64663c2c 100755
--- a/shadowsocks-csharp/Controller/Local.cs
+++ b/shadowsocks-csharp/Controller/Local.cs
@@ -151,30 +151,30 @@ namespace Shadowsocks.Controller
                     return;
                 }
                 closed = true;
-            }
-            if (connection != null)
-            {
-                try
-                {
-                    connection.Shutdown(SocketShutdown.Send);
-                }
-                catch (Exception e)
-                {
-                    Console.WriteLine(e.Message);
-                }
-            }
-            if (remote != null)
-            {
-                try
+                if (connection != null)
                 {
-                    remote.Shutdown(SocketShutdown.Send);
+                    try
+                    {
+                        connection.Shutdown(SocketShutdown.Send);
+                    }
+                    catch (Exception e)
+                    {
+                        Console.WriteLine(e.Message);
+                    }
                 }
-                catch (SocketException e)
+                if (remote != null)
                 {
-                    Console.WriteLine(e.Message);
+                    try
+                    {
+                        remote.Shutdown(SocketShutdown.Send);
+                    }
+                    catch (SocketException e)
+                    {
+                        Console.WriteLine(e.Message);
+                    }
                 }
+                ((IDisposable)encryptor).Dispose();
             }
-            ((IDisposable)encryptor).Dispose();
         }
 
         private void ConnectCallback(IAsyncResult ar)
diff --git a/shadowsocks-csharp/Encrypt/PolarSSLEncryptor.cs b/shadowsocks-csharp/Encrypt/PolarSSLEncryptor.cs
index 3b00c6cb..9bfa3dde 100755
--- a/shadowsocks-csharp/Encrypt/PolarSSLEncryptor.cs
+++ b/shadowsocks-csharp/Encrypt/PolarSSLEncryptor.cs
@@ -165,38 +165,38 @@ namespace Shadowsocks.Encrypt
 
         public override void Encrypt(byte[] buf, int length, byte[] outbuf, out int outlength)
         {
-            if (_encryptCtx == null)
+            lock (this)
             {
-                randBytes(outbuf, ivLen);
-                InitCipher(ref _encryptCtx, outbuf, true);
-                outlength = length + ivLen;
-                lock (tempbuf)
+                if (_disposed)
                 {
+                    outbuf = null;
+                    outlength = 0;
+                    return;
+                }
+                if (_encryptCtx == null)
+                {
+                    randBytes(outbuf, ivLen);
+                    InitCipher(ref _encryptCtx, outbuf, true);
+                    outlength = length + ivLen;
                     // C# could be multi-threaded
-                    lock (_encryptCtx)
+                    switch (_cipher)
                     {
-                        switch (_cipher)
-                        {
-                            case CIPHER_AES:
-                                PolarSSL.aes_crypt_cfb128(_encryptCtx, PolarSSL.AES_ENCRYPT, length, ref _encryptIVOffset, _encryptIV, buf, tempbuf);
-                                break;
-                            case CIPHER_BF:
-                                PolarSSL.blowfish_crypt_cfb64(_encryptCtx, PolarSSL.BLOWFISH_ENCRYPT, length, ref _encryptIVOffset, _encryptIV, buf, tempbuf);
-                                break;
-                            case CIPHER_RC4:
-                                PolarSSL.arc4_crypt(_encryptCtx, length, buf, tempbuf);
-                                break;
-                        }
-                        outlength = length + ivLen;
-                        Buffer.BlockCopy(tempbuf, 0, outbuf, ivLen, outlength);
+                        case CIPHER_AES:
+                            PolarSSL.aes_crypt_cfb128(_encryptCtx, PolarSSL.AES_ENCRYPT, length, ref _encryptIVOffset, _encryptIV, buf, tempbuf);
+                            break;
+                        case CIPHER_BF:
+                            PolarSSL.blowfish_crypt_cfb64(_encryptCtx, PolarSSL.BLOWFISH_ENCRYPT, length, ref _encryptIVOffset, _encryptIV, buf, tempbuf);
+                            break;
+                        case CIPHER_RC4:
+                            PolarSSL.arc4_crypt(_encryptCtx, length, buf, tempbuf);
+                            break;
                     }
+                    outlength = length + ivLen;
+                    Buffer.BlockCopy(tempbuf, 0, outbuf, ivLen, outlength);
                 }
-            }
-            else
-            {
-                outlength = length;
-                lock (_encryptCtx)
+                else
                 {
+                    outlength = length;
                     switch (_cipher)
                     {
                         case CIPHER_AES:
@@ -215,36 +215,36 @@ namespace Shadowsocks.Encrypt
 
         public override void Decrypt(byte[] buf, int length, byte[] outbuf, out int outlength)
         {
-            if (_decryptCtx == null)
+            lock (this)
             {
-                InitCipher(ref _decryptCtx, buf, false);
-                outlength = length - ivLen;
-                lock (tempbuf)
+                if (_disposed)
                 {
+                    outbuf = null;
+                    outlength = 0;
+                    return;
+                }
+                if (_decryptCtx == null)
+                {
+                    InitCipher(ref _decryptCtx, buf, false);
+                    outlength = length - ivLen;
                     // C# could be multi-threaded
                     Buffer.BlockCopy(buf, ivLen, tempbuf, 0, length - ivLen);
-                    lock (_decryptCtx)
+                    switch (_cipher)
                     {
-                        switch (_cipher)
-                        {
-                            case CIPHER_AES:
-                                PolarSSL.aes_crypt_cfb128(_decryptCtx, PolarSSL.AES_DECRYPT, length - ivLen, ref _decryptIVOffset, _decryptIV, tempbuf, outbuf);
-                                break;
-                            case CIPHER_BF:
-                                PolarSSL.blowfish_crypt_cfb64(_decryptCtx, PolarSSL.BLOWFISH_DECRYPT, length - ivLen, ref _decryptIVOffset, _decryptIV, tempbuf, outbuf);
-                                break;
-                            case CIPHER_RC4:
-                                PolarSSL.arc4_crypt(_decryptCtx, length - ivLen, tempbuf, outbuf);
-                                break;
-                        }
+                        case CIPHER_AES:
+                            PolarSSL.aes_crypt_cfb128(_decryptCtx, PolarSSL.AES_DECRYPT, length - ivLen, ref _decryptIVOffset, _decryptIV, tempbuf, outbuf);
+                            break;
+                        case CIPHER_BF:
+                            PolarSSL.blowfish_crypt_cfb64(_decryptCtx, PolarSSL.BLOWFISH_DECRYPT, length - ivLen, ref _decryptIVOffset, _decryptIV, tempbuf, outbuf);
+                            break;
+                        case CIPHER_RC4:
+                            PolarSSL.arc4_crypt(_decryptCtx, length - ivLen, tempbuf, outbuf);
+                            break;
                     }
                 }
-            }
-            else
-            {
-                outlength = length;
-                lock (_decryptCtx)
+                else
                 {
+                    outlength = length;
                     switch (_cipher)
                     {
                         case CIPHER_AES:
@@ -284,13 +284,10 @@ namespace Shadowsocks.Encrypt
                     return;
                 }
                 _disposed = true;
-            }
 
-            if (disposing)
-            {
-                if (_encryptCtx != null)
+                if (disposing)
                 {
-                    lock (_encryptCtx)
+                    if (_encryptCtx != null)
                     {
                         switch (_cipher)
                         {
@@ -306,10 +303,7 @@ namespace Shadowsocks.Encrypt
                         }
                         _encryptCtx = null;
                     }
-                }
-                if (_decryptCtx != null)
-                {
-                    lock (_decryptCtx)
+                    if (_decryptCtx != null)
                     {
                         switch (_cipher)
                         {