多個用戶寫入單個日志文本文件

Question

我試圖在任何用戶進行任何操作（例如登錄，編輯等）時，在MS Access 2016中的應用程序中使用日志系統。

到目前為止，我編寫的代碼使用open語句相當簡單，

Public Sub WriteLog(ByVal strContent As String)
    fileLog = FreeFile
    Open "D:/log.txt" For Output As fileLog

    Print #fileLog, strContent
    Close #fileLog
End Sub

這不好，因為我打算在共享網絡中寫日志文件，這意味着許多用戶可能會同時打開要寫入的文件。 這肯定會引發錯誤。 我想做一些排隊寫入文件但沒有找到任何解決方案。 這樣做是不是不可能嗎？

編輯：

在文件關閉后遞歸檢查文件是否打開並寫入文件，這是一種以某種方式“排隊”寫入文件的方法。 也許需要添加一些代碼來確保遞歸執行此函數的限制。

Function AvailableToWrite()

    ' Test to see if the file is open.
    If IsFileOpen("D:\log.txt") Then
        AvailableToWrite = IsFileOpen() ' Recursively check until file is closed
    Else
        AvailableToWrite = True
    End If

End Function

Function IsFileOpen(filename As String)
    Dim filenum As Integer, errnum As Integer

    On Error Resume Next
    filenum = FreeFile()
    ' Attempt to open the file and lock it.
    Open filename For Input Write As #filenum
    Close filenum
    errnum = Err           ' Save the error number that occurred.
    On Error GoTo 0        ' Turn error checking back on.

    ' Check to see which error occurred.
    Select Case errnum

        ' No error occurred.
        ' File is NOT already open by another user.
        Case 0
         IsFileOpen = False

        ' Error number for "Permission Denied."
        ' File is already opened by another user.
        Case 70
            IsFileOpen = True

    End Select

End Function

Answer 1

通常，在文本文件中寫一行只需要一瞬間。

因此，您可以簡單地在循環中捕獲錯誤，如果您的函數無法寫入文件，等待一小段隨機長度，然后重試直到成功。

附錄

在新嘗試完成之前塊的情況下的可變延遲的方法：

' Function to run a sequence of updates at random intervals for a preset
' duration while handling any concurrency issue that may arise.
' Run the function concurrently in two or more instances of Microsoft Access.
'
' Output logs the updates and lists the errors encountered when an update
' collides with an ongoing update from (one of) the other instance(s).
'
' 2016-01-31. Gustav Brock, Cactus Data ApS, CPH.
'
Public Sub ConcurrencyAwareTest()

    Dim db          As DAO.Database
    Dim rs          As DAO.Recordset
    Dim fd          As DAO.Field

    Dim StopTime    As Single
    Dim Delay       As Single
    Dim Attempts    As Long
    Dim LoopStart   As Single
    Dim LoopEnd     As Single
    Dim Loops       As Long

    Dim SQL         As String
    Dim Criteria    As String
    Dim NewValue    As Boolean

    SQL = "Select * From " & TableName & ""
    Criteria = KeyName & " = " & CStr(KeyValue) & ""

    Set db = CurrentDb
    Set rs = db.OpenRecordset(SQL, dbOpenDynaset, dbSeeChanges)

    rs.FindFirst Criteria
    Set fd = rs.Fields(FieldName)

    ' Set time for the test to stop.
    StopTime = Timer + Duration
    ' Let SetEdit and GetUpdate print debug information.
    DebugMode = True

    ' At random intervals, call updates of the field until StopTime is reached.
    While Timer < StopTime

        ' Postpone the next update.
        Delay = Timer + Rnd / 100
        While Timer < Delay
            DoEvents
        Wend
        Loops = Loops + 1
        LoopStart = Timer
        Debug.Print Loops, LoopStart

        ' Perform update.
        NewValue = Not fd.Value
        Do
            ' Count the attempts to update in this loop.
            Attempts = Attempts + 1
            ' Attempt edit and update until success.
            SetEdit rs
                fd.Value = NewValue
        Loop Until GetUpdate(rs)

        LoopEnd = Timer
        ' Print loop duration in milliseconds and edit attempts.
        Debug.Print , LoopEnd, Int(1000 * (LoopEnd - LoopStart)), Attempts
        Attempts = 0

    Wend
    rs.Close

    DebugMode = False
    Set fd = Nothing
    Set rs = Nothing
    Set db = Nothing

End Sub

目的是證明這篇文章中描述的概念：

以靜默方式處理Access中的並發更新沖突

Answer 2

表結構：

---

記錄事件的過程

Sub WriteLog(Optional note As String)
   'add event to log
    DoCmd.SetWarnings False
    DoCmd.RunSQL "INSERT INTO tblLog (logNote) SELECT """ & Replace(note,"""","'") & """"
    DoCmd.SetWarnings True

    'export to text file
    On Error Resume Next 'ignore error
    DoCmd.TransferText acExportDelim,,"tblLog","c:\LogFile.txt",True
    On Error Goto 0 'back to normal error handling
    Debug.Print "Wrote to log & updated text file."
End Sub

用法：

WriteLog "Your note here" ： 用當前日期/時間加上“你的筆記在這里”保存一條記錄
WriteLog ： 保存只有日期/時間的記錄

---

（我的）填表的例子：

_{（點擊Englarge）}

---

文本文件示例：

默認情況下它是逗號分隔的（因此可以在Excel中打開它），但是可以通過創建規范並使用acExportFixed標志以“固定寬度”導出一些額外的步驟。