.net - 在.Net中打开XPS文档会导致内存泄漏

Question

以下代码片段说明了打开 XPS 文件时的内存泄漏。如果您运行它并观察任务管理器，它会增长并且不会释放内存，直到应用程序退出。

'***** 控制台应用程序开始。

Module Main

    Const DefaultTestFilePath As String = "D:\Test.xps"
    Const DefaultLoopRuns As Integer = 1000

    Public Sub Main(ByVal Args As String())
        Dim PathToTestXps As String = DefaultTestFilePath
        Dim NumberOfLoops As Integer = DefaultLoopRuns

        If (Args.Count >= 1) Then PathToTestXps = Args(0)
        If (Args.Count >= 2) Then NumberOfLoops = CInt(Args(1))

        Console.Clear()
        Console.WriteLine("Start - {0}", GC.GetTotalMemory(True))
        For LoopCount As Integer = 1 To NumberOfLoops

            Console.CursorLeft = 0
            Console.Write("Loop {0:d5}", LoopCount)

            ' The more complex the XPS document and the more loops, the more memory is lost.
            Using XPSItem As New Windows.Xps.Packaging.XpsDocument(PathToTestXps, System.IO.FileAccess.Read)
                Dim FixedDocSequence As Windows.Documents.FixedDocumentSequence

                ' This line leaks a chunk of memory each time, when commented out it does not.
                FixedDocSequence = XPSItem.GetFixedDocumentSequence
            End Using
        Next
        Console.WriteLine()
        GC.Collect() ' This line has no effect, I think the memory that has leaked is unmanaged (C++ XPS internals).
        Console.WriteLine("Complete - {0}", GC.GetTotalMemory(True))

        Console.WriteLine("Loop complete but memory not released, will release when app exits (press a key to exit).")
        Console.ReadKey()

    End Sub

End Module

'***** 控制台应用程序结束。

它循环一千次的原因是因为我的代码处理大量文件并快速泄漏内存，从而导致 OutOfMemoryException。强制垃圾收集不起作用(我怀疑它是 XPS 内部的非托管内存块)。

代码最初位于另一个线程和类中，但已简化为这样。

非常感谢任何帮助。

瑞恩

Answer 1

嗯，我找到了。这是框架中的一个错误，要解决它，您需要添加对 UpdateLayout 的调用。 using 语句可以更改为以下内容以提供修复；

        Using XPSItem As New Windows.Xps.Packaging.XpsDocument(PathToTestXps, System.IO.FileAccess.Read)
            Dim FixedDocSequence As Windows.Documents.FixedDocumentSequence
            Dim DocPager As Windows.Documents.DocumentPaginator

            FixedDocSequence = XPSItem.GetFixedDocumentSequence
            DocPager = FixedDocSequence.DocumentPaginator
            DocPager.ComputePageCount()

            ' This is the fix, each page must be laid out otherwise resources are never released.'
            For PageIndex As Integer = 0 To DocPager.PageCount - 1
                DirectCast(DocPager.GetPage(PageIndex).Visual, Windows.Documents.FixedPage).UpdateLayout()
            Next
            FixedDocSequence = Nothing
        End Using