C# interop: excel process not exiting after adding new worksheet to existing file

Question

I've read many of the other threads here about managing COM references while using the .Net-Excel interop to make sure the Excel process exits correctly upon exit, and so far the techniques have been working very well, but I recently came across a problem when adding new worksheets to an existing workbook file.

The code below leaves a zombie Excel process.

If I add a worksheet to a newly created workbook file, it exits fine. If I run the code excluding the .Add() line, it exits fine. (The existing file I'm reading from is an empty file created by the commented out code)

Any ideas?

//using Excel = Microsoft.Office.Interop.Excel;
//using System.Runtime.InteropServices;
public static void AddTest()
{
  string filename = @"C:\addtest.xls";
  object m = Type.Missing;
  Excel.Application excelapp = new Excel.Application();
  if (excelapp == null) throw new Exception("Can't start Excel");
  Excel.Workbooks wbs = excelapp.Workbooks;

  //if I create a new file and then add a worksheet,
  //it will exit normally (i.e. if you uncomment the next two lines
  //and comment out the .Open() line below):
  //Excel.Workbook wb = wbs.Add(Excel.XlWBATemplate.xlWBATWorksheet);
  //wb.SaveAs(filename, m, m, m, m, m, 
  //          Excel.XlSaveAsAccessMode.xlExclusive,
  //          m, m, m, m, m);

  //but if I open an existing file and add a worksheet,
  //it won't exit (leaves zombie excel processes)
  Excel.Workbook wb = wbs.Open(filename,
                               m, m, m, m, m, m,
                               Excel.XlPlatform.xlWindows,
                               m, m, m, m, m, m, m);

  Excel.Sheets sheets = wb.Worksheets;

  //This is the offending line:
  Excel.Worksheet wsnew = sheets.Add(m, m, m, m) as Excel.Worksheet; 

  //N.B. it doesn't help if I try specifying the parameters in Add() above

  wb.Save();
  wb.Close(m, m, m);

  //overkill to do GC so many times, but shows that doesn't fix it
  GC();
  //cleanup COM references
  //changing these all to FinalReleaseComObject doesn't help either
  while (Marshal.ReleaseComObject(wsnew) > 0) { } 
  wsnew = null;
  while (Marshal.ReleaseComObject(sheets) > 0) { }
  sheets = null;
  while (Marshal.ReleaseComObject(wb) > 0) { }
  wb = null;
  while (Marshal.ReleaseComObject(wbs) > 0) { }
  wbs = null;
  GC();
  excelapp.Quit();
  while (Marshal.ReleaseComObject(excelapp) > 0) { }
  excelapp = null;
  GC();
}

public static void GC()
{
  System.GC.Collect();
  System.GC.WaitForPendingFinalizers();
  System.GC.Collect();
  System.GC.WaitForPendingFinalizers();
}

Answer 1

I don't have the code to hand, but I did run into a similar problem. If I recall correctly, I ended up retrieving the process id of the excel instance, and killing it (after a suitable wait period, and when the other method failed).

I think I used:

GetWindowThreadProcessId (via P/Invoke) on the excel object hwnd property to get the process id, and then used Process.GetProcessById to get a process object. Once I'd done that, I'd call Kill on the process.

EDIT: I have to admit, this isn't the ideal solution, but if you can't find the rogue interface that isn't being released, then this will fix it in true eggshell/sledgehammer fashion. ;)

EDIT2: You don't have to call Kill on the process object immediately... You could first try calling Close before resorting to Kill.

Answer 2

Not very constructive I know but I tested the code exactly as shown above and my Excel process exits as expected, my C:\addtest.xls is sitting with 8 new sheets and no Excel process is running.
Could the interop version be the cause I wonder? I tested with 11 & 12.

Answer 3

I have done a similar thing. I create an Excel file or open an existing. I delete all the sheets and add my own. here is the code I use to ensure all references are closed:

            workbook.Close(true, null, null);
            excelApp.Quit();

            if (newSheet != null)
            {
                System.Runtime.InteropServices.Marshal.ReleaseComObject(newSheet);
            }
            if (rangeSelection != null)
            {
            System.Runtime.InteropServices.Marshal.ReleaseComObject(rangeSelection);
            }
            if (sheets != null)
            {
                System.Runtime.InteropServices.Marshal.ReleaseComObject(sheets);
            }
            if (workbook != null)
            {
                System.Runtime.InteropServices.Marshal.ReleaseComObject(workbook);
            }
            if (excelApp != null)
            {
                System.Runtime.InteropServices.Marshal.ReleaseComObject(excelApp);
            }

            newSheet = null;
            rangeSelection = null;
            sheets = null;
            workbook = null;
            excelApp = null;

            GC.Collect();

I have tested this with many different options and not had it fail on me yet.

Answer 4

I'm using VB.NET 3.5 SP1 and the following code STILL leaves EXCEL.EXE open:

        xlWorkbook.Close(SaveChanges:=False)
        xlApplication.Quit()

        System.Runtime.InteropServices.Marshal.ReleaseComObject(xlRange)
        System.Runtime.InteropServices.Marshal.ReleaseComObject(xlWorksheet)
        System.Runtime.InteropServices.Marshal.ReleaseComObject(xlSheets)
        System.Runtime.InteropServices.Marshal.ReleaseComObject(xlWorkbook)
        System.Runtime.InteropServices.Marshal.ReleaseComObject(xlApplication)

        xlRange = Nothing
        xlWorksheet = Nothing
        xlSheets = Nothing
        xlWorkbook = Nothing
        xlApplication = Nothing

        GC.GetTotalMemory(False)
        GC.Collect()
        GC.WaitForPendingFinalizers()

        GC.Collect()
        GC.WaitForPendingFinalizers()
        GC.Collect()
        GC.GetTotalMemory(True)

Answer 5

Andrew, here is the code I've found that works. I thought I post post it here for others who come across:

namespace WindowHandler
{
using System;
using System.Text;
using System.Collections;
using System.Runtime.InteropServices;

/// <summary>
/// Window class for handling window stuff.
/// This is really a hack and taken from Code Project and mutilated to this small thing.
/// </summary>
public class Window
{
    /// <summary>
    /// Win32 API import for getting the process Id.
    /// The out param is the param we are after. I have no idea what the return value is.
    /// </summary>
    [DllImport("user32.dll")]
    private static extern IntPtr GetWindowThreadProcessId(IntPtr hWnd, out IntPtr ProcessId);

    /// <summary>
    /// Gets a Window's process Id.
    /// </summary>
    /// <param name="hWnd">Handle Id.</param>
    /// <returns>ID of the process.</returns>
    public static IntPtr GetWindowThreadProcessId(IntPtr hWnd)
    {
        IntPtr processId;
        IntPtr returnResult = GetWindowThreadProcessId(hWnd, out processId);

        return processId;
    }
}
}

Answer 6

here's my full code to kill the Excel you created with the Office12 .Net interop library: Enjoy, -Alan.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;
using System.Diagnostics;
using Microsoft.Office.Interop.Excel;

class Program
{

    /// <summary> 
    /// Win32 API import for getting the process Id. 
    /// The out param is the param we are after. I have no idea what the return value is. 
    /// </summary> 
    [DllImport("user32.dll")]
    private static extern IntPtr GetWindowThreadProcessId(IntPtr hWnd, out IntPtr ProcessId); 

    static void Main(string[] args)
    {
        var app = new Application();
        IntPtr hwnd = new IntPtr(app.Hwnd);
        IntPtr processId;
        IntPtr foo = GetWindowThreadProcessId(hwnd, out processId);
        Process proc = Process.GetProcessById(processId.ToInt32());
        proc.Kill(); // set breakpoint here and watch the Windows Task Manager kill this exact EXCEL.EXE
        app.Quit(); // should give you a "Sorry, I can't find this Excel session since you killed it" Exception.
    }
}