vb.net 写入文件同步锁

 <SoapHeader("oHeader")> _
    <WebMethod()> _
    <ScriptMethod(ResponseFormat:=ResponseFormat.Json)> _
    Public Function Test_SyncLock() As String
        Dim threads(10) As Threading.Thread
        For i As Integer = 0 To 10
            threads(i) = New Threading.Thread(AddressOf PrintNumbers)
            threads(i).Name = String.Format("Worker thread #{0}", i)
        Next
        ' Now start each one.
        For Each t As Threading.Thread In threads
            t.Start()
        Next
        Return ""
    End Function

    Private Sub PrintNumbers()
        writeLog("", "a", Threading.Thread.CurrentThread.Name)
    End Sub

#Region "Write Log File"

    Private threadLock As Object = New Object()
    Public Sub writeLog(ByVal dir As String, ByVal fileName As String, ByVal log As String)

        Dim filePath As String = System.IO.Path.Combine(System.Web.Hosting.HostingEnvironment.MapPath("~/"),
                                                       "Log/" & dir & "/" & fileName & ".log")
        SyncLock threadLock
            '创建目录
            Dim dirPath As String = filePath.Substring(0, filePath.LastIndexOf("/"))
            If (Directory.Exists(dirPath) = False) Then
                Directory.CreateDirectory(dirPath)
            End If
            Dim aa As System.IO.StreamWriter = New System.IO.StreamWriter(filePath, True, System.Text.Encoding.UTF8)
            aa.WriteLine(log)
            aa.Close()
            aa.Dispose()
        End SyncLock
    End Sub
#End Region