How to ensure I don't keep keep creating additional EXCEL.EXE processes each time I call a routine in C# from a loop?

I am developing a C# Windows application using VS2005.
In the following routine which I call from a loop,
it seems that I create a new EXECEL.EXE process each time this routine is called
according to the Windows Task Manager.
Is there a way to ensure that I drop the EXCEL.EXE before I call this routine the next time?

public static void ExcelFormat(string filename, string footnote)
{
            Excel.Application oXL = new Excel.Application();
            oXL.Visible = false;
            oXL.DisplayAlerts = false;

            Excel._Workbook oWB = (Excel._Workbook)oXL.Workbooks.Open(filename, 0, false, 5, Missing.Value, Missing.Value, false, Missing.Value, Missing.Value, false, false, Missing.Value, false, false, false);
            Excel._Worksheet oSheet = (Excel._Worksheet)oWB.ActiveSheet;
            oSheet.Activate();

            try
            {

                oSheet.get_Range(oSheet.Cells[2, 1], oSheet.Cells[65535, 1]).EntireColumn.NumberFormat = "#,##0";

            }
            finally
            {                
                oXL.Workbooks.Close();
                oXL.Quit();
                System.Runtime.InteropServices.Marshal.ReleaseComObject(oXL);
                System.Runtime.InteropServices.Marshal.ReleaseComObject(oSheet);
                System.Runtime.InteropServices.Marshal.ReleaseComObject(oWB);
                oSheet = null;
                oWB = null;
                oXL = null;
            }
}
zimmer9Asked:
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Robert SchuttConnect With a Mentor Software EngineerCommented:
Michael's remark about creating the Excel object only once is pretty much a golden rule in general. However, in my testing I hardly noticed any delay while creating it over and over so I left this alone for the moment, also because I don't know the structure of the rest of your application, mainly if indeed you are talking about a loop that is calling this function lots of times right after each other or maybe 3 times a day.

His remark about garbage collection I was going to suggest to stay away from however on my own system I couldn't get it to work without it...

Killing a process should be a last resort but in some cases a nice option to have.

What I ended up doing in the 'finally' block is:
oXL.Workbooks.Close();
oXL.Quit();
System.Runtime.InteropServices.Marshal.ReleaseComObject(oSheet);
System.Runtime.InteropServices.Marshal.ReleaseComObject(oWB);
GC.Collect();
System.Runtime.InteropServices.Marshal.ReleaseComObject(oXL);

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One more remark: I haven't used code like this a lot but somewhere I read that you shouldn't use temporary objects like you do with get_Range. This could be causing stray object references which cause the behaviour you're experiencing (not in general but specifically with COM Interop objects). So you would need another object to hold the range, set the NumberFormat on that, and release the range object as well in the finally block. However, for this particular call (since you use .EntireColumn) you should be able to just use:
oSheet.Columns[1].NumberFormat = "#,##0";

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Michael FowlerConnect With a Mentor Solutions ConsultantCommented:
Instead of creating the excel object within the method you could create the object in the calling method and then pass this object to the method above. This  should prevent multiple objects being created. You can also call the garbage disposal directly to speed up the release of the memory.

Michael
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sognoctConnect With a Mentor Commented:
int pid = 0;
Excel.Application oXL = new Excel.Application();
Process p = Process.GetProcessById(GetWindowThreadProcessId(oXL.Hwnd, out pid));

now that you have the pid of the process you can kill it according to your needs
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