Question

I am using an external DLL (pdfsharp) to open (then manipulate) lots of PDF files. I use:

Dim inputDocument = Pdf.IO.PdfReader.Open(PDFPath, IO.PdfDocumentOpenMode.ReadOnly)

Problem is – it seems to hang on certain, rare files. I don’t seem to get any timeout – it just hangs for hours on this line. We read thousands of files with this code, always on tiny files, so I was thinking that a quick workaround might be to somehow timeout if the this method takes more than a second or two. But I don’t see a simple way to do this. I am hoping to avoid spinning up a worker thread.

Any thoughts on how I might limit this threads allowed execution time, or is there a better (but simple) way?

Answer 1

We ended up working around this problem by creating an AbortableBackgroundWorker. I am not sure whose code this ended up being – but we found it online and sharing it here. In the rare case where one of the PDF’s hangs the PdfSharp Open() call, we abort the background worker.

  Public Class AbortableBackgroundWorker
    Inherits BackgroundWorker

    Private workerThread As Thread

    Protected Overrides Sub OnDoWork(e As DoWorkEventArgs)
        workerThread = Thread.CurrentThread
        Try
            MyBase.OnDoWork(e)
        Catch generatedExceptionName As ThreadAbortException
            e.Cancel = True
            'We must set Cancel property to true!
            'Prevents ThreadAbortException propagation
            Thread.ResetAbort()
        End Try
    End Sub


    Public Sub Abort()
        If workerThread IsNot Nothing Then
            workerThread.Abort()
            workerThread = Nothing
        End If
    End Sub

End Class