Excel Process not closing in VB.net

Question

I am creating an excel file using interop.excel and the process is not closing. This is the code i am trying to use.

 Private Sub converToExcel(fileLoc As String, ds As DataSet)
    Dim xlApp As Excel.Application
    Dim xlWorkBook As Excel.Workbook
    Dim xlWorkBooks As Excel.Workbooks
    Dim xlWorkSheet As Excel.Worksheet
    Dim misValue As Object = System.Reflection.Missing.Value
    Dim i As Integer
    Dim j As Integer

    xlApp = New Excel.Application
    xlWorkBooks = xlApp.Workbooks
    xlWorkBook = xlWorkBooks.Add(misValue)
    xlWorkSheet = xlWorkBook.Sheets("sheet1")

    For i = 0 To ds.Tables(0).Rows.Count - 1
        For j = 0 To ds.Tables(0).Columns.Count - 1
            xlWorkSheet.Columns.NumberFormat = "@"
            xlWorkSheet.Cells(i + 1, j + 1) = String.Format("{0}", ds.Tables(0).Rows(i).Item(j).ToString())
        Next
    Next

    xlWorkSheet.SaveAs(fileLoc)
    xlWorkBook.Close()
    xlApp.Quit()

    releaseObject(xlWorkSheet)
    releaseObject(xlWorkBook)
    releaseObject(xlWorkBooks)
    releaseObject(xlApp)

End Sub
Private Sub releaseObject(ByVal obj As Object)
    Try
        System.Runtime.InteropServices.Marshal.ReleaseComObject(obj)
        obj = Nothing
    Catch ex As Exception
        obj = Nothing
    Finally
        GC.Collect()
    End Try
End Sub

I think i am missing a COM object but cant seem to find a solution. Also as a note, this is running on 64-bit Windows 8. Any help would be great! Thanks

Answer 1

Manual memory management like this just never works. This is a problem that's been known for very a long time and the core reason that garbage collectors were invented. Programmers just forever forget to release memory.

It gets extra hard when you can't see the memory being used. Which is certainly the case in your code, the xlWorkSheet.Cells(i + 1, j + 1) expression uses no less than three references. One for the range object returned by the Cells property, one for a sub-range object selected by i+1 and another for the sub-range object selected by j+1. Very nice syntax sugar provided by the VB.NET language, writing COM code without it is pretty doggone painful. But not helpful to let you see the references. Not only can't you see it in your source code, there is absolutely nothing the debugger can do to help you see them either.

This is very much a solved problem in .NET, it has a garbage collector and it can see everything. The most basic problem is that you don't give it a chance to solve your problem. The mistake you made is that you stopped. Probably by setting a breakpoint on the last statement and then looking in Task Manager and seeing Excel.exe still running. Yes, that's normal. Garbage collection is not instant.

Calling GC.Collect() is supposed to make it instant, but that doesn't work in the specific case of running the Debug build of your project. The lifetime of local variables gets then extended to the end of the method, help you see them in the Autos/Locals/Watch window. In other words, GC.Collect() doesn't actually collect any of the interface references. More about that behavior in this post.

The simple workaround is to not stop. Keep doing useful things to give the garbage collector a reason to run. Or letting your program terminate since it is done, Excel terminates when the finalizer thread runs for the last time. Which works because the local variables that had the references are not in scope anymore.

But everybody wants the instant fix anyway. You get it by deleting all the releaseObject() calls. And doing it like this instead:

converToExcel(path, dset)
GC.Collect()
GC.WaitForPendingFinalizers()

Or in other words, force a collection after the method has returned. The local variables are no longer in scope so they can't hold on to an Excel reference. It will now also work when you debug it, like it already did when you ran the Release build without a debugger.

Answer 2

Try System.Runtime.InteropServices.Marshal.FinalReleaseComObject, that should help... also you should call xlWorkBook.Close() and xlapp.quit, if I recall correctly. First call them and then set them to nothing.

Answer 3

I did not see anyone properly address what was occuring and instead, tried to create work arounds for it.

What is happening here is that the workbook is prompting, in the background, to be saved. In your code, you're saving the worksheet and not the workbook. You can either trick it and set the saved state of the workbook to true or save the workbook before exiting the excel applicaiton.

I was also having this issue. The Excel process would run the entire time the application was open. By adding the xlWorkBook.Saved = True line, the process would end after the call to xlApp.Quit(). In my case, I did not need to save the excel file, only reference it for values.

Option #1 - Do not save the workbook:

xlWorkSheet.SaveAs(fileLoc)
xlWorkBook.Saved = True       ' Add this line here.
'xlWorkBook.Close()           ' This line shouldn't be necessary anymore.
xlApp.Quit()

Option #2 - Save the workbook to a new file:

'xlWorkSheet.SaveAs(fileLoc)  ' Not needed
xlWorkBook.SaveAs(fileLoc)    ' If the file doesn't exist
'xlWorkBook.Close()           ' This line shouldn't be necessary anymore.
xlApp.Quit()

Option #3 - Save the workbook to an existing file:

'xlWorkSheet.SaveAs(fileLoc)  ' Not needed
xlWorkBook.Save(fileLoc)      ' If the file does exist
'xlWorkBook.Close()           ' This line shouldn't be necessary anymore.
xlApp.Quit()

.Quit() Method:
https://docs.microsoft.com/en-us/dotnet/api/microsoft.office.interop.excel._application.quit?view=excel-pia#Microsoft_Office_Interop_Excel__Application_Quit

.Saved() Method:
https://docs.microsoft.com/en-us/dotnet/api/microsoft.office.interop.excel._workbook.saved?view=excel-pia#Microsoft_Office_Interop_Excel__Workbook_Saved

Answer 4

The GC.Collect makes not much sense where you placed it, if anything you should call it after you return from converToExcel. Also you may need to wait for finalizers to run. Personally I think Hans' answer is the way to go, but I know from personal experience writing office addins in C# that sometimes its necessary to do manual reference counting, in particular when you need to be compatible with older office versions. (There are many documented problems, in particular when handling events from office, which can only be reliably solved by manual reference counting. Also some COM libraries don't like at all when released in the wrong order by GC, but thats not the case with office.)

So on to the actual problem in your code: there are three intermediate COM objects not released here:

• xlWorkBook.Sheets returns a collection of type Excel.Sheets
• xlWorkSheet.Columns returns a COM object of type Excel.Range
• xlWorkSheet.Cells also returns an Excel.Range object

Besides this, if Marshal.ReleaseComObject throws an exception you did something wrong in your manual reference counting, therefore I wouldn't wrap it in an exception handler. When doing manual reference counting you must release every COM object once for every time it crosses the COM->NET boundary, meaning the Excel.Range objects need to be released in every iteration of the loop.

Here's code which properly terminates Excel for me:

Imports Microsoft.Office.Interop
Imports System.Runtime.InteropServices

Private Sub converToExcel(fileLoc As String, ds As DataSet)
    Dim xlApp As New Excel.Application
    Dim xlWorkBooks As Excel.Workbooks = xlApp.Workbooks
    Dim xlWorkBook As Excel.Workbook = xlWorkBooks.Add(System.Reflection.Missing.Value)
    Dim xlWorkSheets As Excel.Sheets = xlWorkBook.Sheets
    ' accessing the sheet by index because name is localized and your code will fail in non-english office versions
    Dim xlWorkSheet As Excel.Worksheet = xlWorkSheets(1)

    For i = 0 To ds.Tables(0).Rows.Count - 1
        For j = 0 To ds.Tables(0).Columns.Count - 1
            ' couldn't this be moved outside the loop?
            Dim xlColumns As Excel.Range = xlWorkSheet.Columns
            xlColumns.NumberFormat = "@"
            Marshal.ReleaseComObject(xlColumns)

            Dim xlCells As Excel.Range = xlWorkSheet.Cells
            xlCells(i + 1, j + 1) = ds.Tables(0).Rows(i).Item(j).ToString()
            Marshal.ReleaseComObject(xlCells)
        Next
    Next

    xlWorkSheet.SaveAs(fileLoc)
    'xlWorkBook.Close() -- not really necessary
    xlApp.Quit()

    Marshal.ReleaseComObject(xlWorkSheet)
    Marshal.ReleaseComObject(xlWorkSheets)
    Marshal.ReleaseComObject(xlWorkBook)
    Marshal.ReleaseComObject(xlWorkBooks)
    Marshal.ReleaseComObject(xlApp)
End Sub

If you want to be extra careful you'd want to handle exceptions from the office API and call ReleaseComObject inside finally-clauses. It can be helpful to define a generic wrapper and write using-clauses instead of try-finally (make the wrapper a structure not a class so you don't allocate the wrappers on the heap).

Answer 5

It's just as simple as adding this line in your code, just after opening the Workbook:

oExcel.displayalerts = False

Answer 6

Finally solved :)

Private Function useSomeExcel(ByVal Excelfilename As String) 
  Dim objExcel As Excel.Application
  Dim objWorkBook As Excel.Workbook
  Dim objWorkSheets As Excel.Worksheet

  Dim datestart As Date = Date.Now
  objExcel = CreateObject("Excel.Application") 'This opens...  
  objWorkBook = objExcel.Workbooks.Open(Excelfilename) ' ... excel process
  Dim dateEnd As Date = Date.Now
  End_Excel_App(datestart, dateEnd) ' This closes excel proces
End Function

use this method

  Private Sub End_Excel_App(datestart As Date, dateEnd As Date)
    Dim xlp() As Process = Process.GetProcessesByName("EXCEL")
    For Each Process As Process In xlp
     If Process.StartTime >= datestart And Process.StartTime <= dateEnd Then
       Process.Kill()
       Exit For
     End If
    Next
  End Sub

This method closes especific process opened.