Killing EXCEL.exe Process from C# in a Windows Service

Question

I have a windows service that opens up an Excel spreadsheet via the Microsoft.Office.Interop.Excel.Application object.

Application xlApp = new Application();
Workbook workbook = xlApp.Workbooks.Open(fileName, 2, false);
...
...
workbook.Close();
xlApp.Quit();

I would like to kill the EXCEL.exe process that is left running after it is done working with the workbook.

I've tried the following with no success...

// This returns a processId of 0
IntPtr processId;
GetWindowThreadProcessId(new IntPtr(xlApp.Hwnd), out processId);
Process p = Process.GetProcessById(processId.ToInt32());   
p.Kill();

Anyone have any ideas as to how I can do this via a Windows Service?

Answer 1

After much reading and frustration I've found a solution!

All credit goes to dotNetkow, nightcoder and Mike Rosenblum for their solutions on this post: How do I properly clean up Excel interop objects?

Here is what I did...
1. Changed build mode of the project to "Release" (in DEBUG mode, COM objects have a hard time disposing of their references.
2. Removed all double dot expressions (all COM objects should be tied to a variable so they can be released)
3. Calling GC.Collect(), GC.WaitForPendingFinalizers(), and Marshal.FinalReleaseComObject() explicitly in a finally block

Here is the acutal code I am using:

Application xlApp = null;
Workbooks workbooks = null;
Workbook workbook = null;
Worksheet sheet = null;
Range r = null;
object obj = null;

try
{
    xlApp = new Application();
    xlApp.DisplayAlerts = false;
    xlApp.AskToUpdateLinks = false;
    workbooks = xlApp.Workbooks;
    workbook = workbooks.Open(fileName, 2, false);
    sheet = workbook.Worksheets[1];

    r = sheet.get_Range("F19");
    obj = r.get_Value(XlRangeValueDataType.xlRangeValueDefault);
}
finally
{
    GC.Collect();
    GC.WaitForPendingFinalizers();
    if (value != null) Marshal.FinalReleaseComObject(value);
    if (r != null) Marshal.FinalReleaseComObject(r);
    if (sheet != null) Marshal.FinalReleaseComObject(sheet);
    if (workbooks != null) Marshal.FinalReleaseComObject(workbooks);
    if (workbook != null)
    {
        workbook.Close(Type.Missing, Type.Missing, Type.Missing);
        Marshal.FinalReleaseComObject(workbook);
    }
    if (xlApp != null)
    {
        xlApp.Quit();
        Marshal.FinalReleaseComObject(xlApp);
    }
}