socket 通讯 并发 问题
客户端通过socket与主机进行通讯，如果多个用户同时向主机发送数据，则返回结果是错误的，网上查了一些资料，说是数据并发的问题，现在我改怎样改进，才能不致数据错误。
服务端是UNIX C，客户端是vb.net，现把客户端代码贴出来，大家看我看下，该如何改进，才能满足要求。
客户端代码：
Public Class StateObject 'SOCKET ID Public workSocket As Socket = Nothing '可接收数据大小 Public Const BufferSize As Integer = 1024 * 512 'Public Const BufferSize As Integer = 1024 '接收数据缓冲区 Public buffer(BufferSize) As Byte '接收数据 Public sb As New StringBuilderEnd ClassPublic Class ESA_TCP_CLIENT '处理结果 Public Enum ExSocketState ExSocketSucceed = 0 '处理成功 ExSocketNoConnect = 1 '主机无连接 ExSocketUnKnown = 2 '未知状态（主机未响应） ExSocketAllUsed = 3 '无可用端口（没有空闲状态的端口） End Enum Private connectDone As New ManualResetEvent(False) Private sendDone As New ManualResetEvent(False) Private receiveDone As New ManualResetEvent(False) Private response As String = String.Empty '超时时间（毫秒） Private iTimeOutM As Integer Private isConn As Boolean = False Public Function SendTo(ByVal strHostIP As String, _ ByVal iPort As Integer, _ ByVal iTimeout As Integer, _ ByVal strSend As String, _ ByRef strRecv As String, _ ByVal Merch_ID As String, _ ByVal ULNm As String) As ExSocketState '增加Merch_ID,ULNm zfy 2011-1-6 用于生成Merch_ID.txt文件 On Error GoTo go_Err Dim ipHostInfo As IPHostEntry = Dns.GetHostEntry(strHostIP) Dim ipAddress As IPAddress = ipHostInfo.AddressList(0) Dim remoteEP As New IPEndPoint(ipAddress, iPort) Dim client As New Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp) strRecv = "" If iTimeout > 0 And iTimeout < 200000 Then '1000000 iTimeOutM = iTimeout Else iTimeOutM = 5000 '5000 End If SendTo = ExSocketState.ExSocketUnKnown client.BeginConnect(remoteEP, New AsyncCallback(AddressOf ConnectCallback), client) Dim s2 = Now() If connectDone.WaitOne(iTimeOutM, False) = True Then If isConn = True Then Send(client, strSend, Merch_ID, ULNm) '增加Merch_ID zfy 2011-1-6 用于生成Merch_ID.txt文件 If sendDone.WaitOne(iTimeOutM, False) = True Then If isConn = True Then '由于测试中出现异步通讯时接收主机报文有报文不完整情况 '所以在此处修改为在连接、发送时采用异步方式，而接收数据时采用同步方式 '此处还需要考虑同步接收的超时机制，暂略 Dim state As New StateObject state.workSocket = client If Receive(state, Merch_ID, ULNm) Then '增加Merch_ID,ULNm zfy 2011-1-6 用于生成Merch_ID.txt文件 'If Receive() Then strRecv = state.sb.ToString() If strRecv.Length > 10 Then strRecv = strRecv.Substring(10, strRecv.Length - 10) Else strRecv = "" End If SendTo = ExSocketState.ExSocketSucceed Else SendTo = ExSocketState.ExSocketUnKnown End If Else SendTo = ExSocketState.ExSocketUnKnown End If Else SendTo = ExSocketState.ExSocketUnKnown End If Else SendTo = ExSocketState.ExSocketNoConnect End If Else SendTo = ExSocketState.ExSocketNoConnect End Ifgo_Exit: If client.Connected = True Then client.Shutdown(SocketShutdown.Both) End If client.Close() Exit Functiongo_Err: GoTo go_Exit End Function Private Sub ConnectCallback(ByVal ar As IAsyncResult) On Error GoTo go_Err Dim client As Socket = TryCast(ar.AsyncState, Socket) If client IsNot Nothing Then client.EndConnect(ar) isConn = client.Connected Else isConn = False End If connectDone.Set()go_Exit: Exit Subgo_Err: isConn = False connectDone.Set() GoTo go_Exit End Sub Private Function Receive(ByRef state As StateObject, ByVal Merch_ID As String, ByVal ULNm As String) As Boolean '增加Merch_ID,ULNm zfy 2011-1-6 用于生成Merch_ID.txt文件 On Error GoTo go_Err Dim readStream As New NetworkStream(state.workSocket) Dim blnReturn As Boolean = False Dim intRcv As Integer Dim strTmp As String = "" state.buffer.Clear(state.buffer, 0, StateObject.BufferSize) readStream.ReadTimeout = iTimeOutM intRcv = readStream.Read(state.buffer, 0, StateObject.BufferSize) Do While intRcv > 0 strTmp = Encoding.Default.GetString(state.buffer, 0, intRcv) state.sb.Append(strTmp) If ConfigurationManager.AppSettings("g_IsDebug") = "1" Then Dim FileToWrite As System.IO.FileStream = System.IO.File.Create("D:\程序\ESA_OPR_New\debug\Receive" + Merch_ID + "_" + ULNm + ".txt") Dim rByte() As Byte = Encoding.Default.GetBytes(state.sb.ToString.ToCharArray) FileToWrite.Write(rByte, 0, rByte.Length) FileToWrite.Close() FileToWrite = Nothing End If '不按照报文头字符长度来取报文体字段，因为在测试中发现WINDOWS与UNIX在中文和特殊字符的长度判断上不相同 '所以采用查找结束符号的方式来判断报文尾 If InStr(strTmp, "</PACKAGE>") > 0 Then Exit Do Else state.buffer.Clear(state.buffer, 0, StateObject.BufferSize) intRcv = readStream.Read(state.buffer, 0, StateObject.BufferSize) End If Loop blnReturn = True readStream = Nothinggo_Exit: Return blnReturn Exit Functiongo_Err: blnReturn = False GoTo go_Exit End Function Private Sub Send(ByVal client As Socket, ByVal data As String, ByVal Merch_ID As String, ByVal ULNm As String) '增加Merch_ID,ULNm 2010-1-6 zfy On Error GoTo go_Err '2011-7-14 解决中文字符编码数量问题 Dim strLen As Integer For n = 1 To data.Length If AscW(Mid(data, n, 1)) > 256 Then strLen = strLen + 2 Else strLen = strLen + 1 Next data = Format(strLen, "0000000000") & data If ConfigurationManager.AppSettings("g_IsDebug") = "1" Then Dim FileToWrite As System.IO.FileStream = System.IO.File.Create("D:\程序\ESA_OPR_New\debug\Send" + Merch_ID + "_" + ULNm + ".txt") 'Dim rByte() As Byte = Encoding.Default.GetBytes(data.ToCharArray) Dim rByte() As Byte = Encoding.Default.GetBytes(data.ToCharArray) FileToWrite.Write(rByte, 0, rByte.Length) FileToWrite.Close() FileToWrite = Nothing End If Dim byteData As Byte() = Encoding.Default.GetBytes(data) '2011-7-15 zfy 解决报文发送乱码问题 client.BeginSend(byteData, 0, byteData.Length, 0, New AsyncCallback(AddressOf SendCallback), client)go_Exit: Exit Subgo_Err: GoTo go_Exit End Sub Private Sub SendCallback(ByVal ar As IAsyncResult) On Error GoTo go_Err Dim client As Socket = TryCast(ar.AsyncState, Socket) If client IsNot Nothing Then isConn = True Dim bytesSent As Integer = client.EndSend(ar) Else isConn = False End If sendDone.Set()go_Exit: Exit Subgo_Err: isConn = False sendDone.Set() GoTo go_Exit End SubEnd Class