“对象当前在其他地方使用”，但它在哪里使用，谁在使用它？

问：

有很多答案描述了为什么会发生这个错误，但我找不到任何答案来解释如何确定 （a） 哪个例程失败，（b） 我们在谈论哪个对象，以及 （c） 哪个其他代码位正在使用该对象。通常我们至少会得到一个行号，但出于某种原因，这个错误想让我猜测。有什么想法吗？（这是一个运行着多个线程的大型程序。

    System.Transactions Critical: 0 : <TraceRecord xmlns="http://schemas.microsoft.com/2004/10/E2ETraceEvent/TraceRecord" Severity="Critical"><TraceIdentifier>http://msdn.microsoft.com/TraceCodes/System/ActivityTracing/2004/07/Reliability/Exception/Unhandled</TraceIdentifier><Description>Unhandled exception</Description><AppDomain>MyLargeProgram.exe</AppDomain><Exception><ExceptionType>System.InvalidOperationException, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</ExceptionType><Message>Object is currently in use elsewhere.</Message><StackTrace>   at System.Drawing.Image.get_Width()
       at System.Drawing.Image.get_Size()
       at System.Windows.Forms.PictureBox.ImageRectangleFromSizeMode(PictureBoxSizeMode mode)
       at System.Windows.Forms.PictureBox.OnPaint(PaintEventArgs pe)
       at System.Windows.Forms.Control.PaintWithErrorHandling(PaintEventArgs e, Int16 layer)
       at System.Windows.Forms.Control.WmPaint(Message&amp;amp; m)
       at System.Windows.Forms.Control.WndProc(Message&amp;amp; m)
       at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message&amp;amp; m)
       at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message&amp;amp; m)
       at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)</StackTrace><ExceptionString>System.InvalidOperationException: Object is currently in use elsewhere.
       at System.Drawing.Image.get_Width()
       at System.Drawing.Image.get_Size()
       at System.Windows.Forms.PictureBox.ImageRectangleFromSizeMode(PictureBoxSizeMode mode)
       at System.Windows.Forms.PictureBox.OnPaint(PaintEventArgs pe)
       at System.Windows.Forms.Control.PaintWithErrorHandling(PaintEventArgs e, Int16 layer)
       at System.Windows.Forms.Control.WmPaint(Message&amp;amp; m)
       at System.Windows.Forms.Control.WndProc(Message&amp;amp; m)
       at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message&amp;amp; m)
       at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message&amp;amp; m)
       at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)</ExceptionString></Exception></TraceRecord>

应用程序创建一个大图像，该图像最终显示在 PictureBox 上。最终图像由线程分 4 个阶段从其他 4 个图像创建，线程复制其中一个现有图像，对其进行更改，然后再次将其保存到该图像。如果图像在其他地方使用，则有一些标志可以阻止图像被访问。最终线程获取第 4 个图像，对其进行更改，然后将修改后的图像的克隆设置为 PictureBox 图像。

    SyncLock bm
        PbWM.Image?.Dispose()
        PbWM.Image = CType(bm.Clone, Bitmap)
    End SyncLock

我以为我已经使用了足够的 SyncLock 和标志，但也许没有。我不知道为什么System.Transactions会出现在那里。我不是在导入它。

关于锁定的另一个问题：这是我用来替换图像内容的方法。有没有更好的方法？

    ' The Thread enters with Bitmap bm1..

    ' I make a working copy of bm1
    Using bm0 As Bitmap = CType(bm1.Clone, Bitmap)
        Using gr As Graphics = Graphics.FromImage(bm)
            ' Some image drawing is done here
        End Using

        SyncLock bm
            ' Replace bm1 with the altered image
            bm1 = CType(bm0.Clone, Bitmap)
        End SyncLock
    End Using

也许这是最好的方法？

    ' The Thread enters with Bitmap bm1..

    ' I make a working copy of bm1
    Using bm0 As Bitmap = CType(bm1.Clone, Bitmap)
        Using gr As Graphics = Graphics.FromImage(bm)
            ' Some image drawing is done here
        End Using

        Dim thisLock As New Object
        SyncLock thisLock
            ' Replace bm1 with the altered image
            bm1 = CType(bm0.Clone, Bitmap)
        End SyncLock
    End Using

还是这个？

    ' The Thread enters with Bitmap bm1..

    ' I make a working copy of bm1
    Using bm0 As Bitmap = CType(bm1.Clone, Bitmap)
        Using gr As Graphics = Graphics.FromImage(bm)
            ' Some image drawing is done here
        End Using

        Dim thisLock As New Object
        SyncLock thisLock
            ' Replace bm1 with the altered image
            bm1 = New Bitmap(bm0)
        End SyncLock
    End Using