Excel process still runs in background

There was another similar question - and answer (https://stackoverflow.com/a/17367570/3063884), in which the solution was to avoid using double-dot notation. Instead, define variables for each object used along the way, and individually use Marshal.ReleaseComObject on each one.

Copying straight from the linked solution:

var workbook = excel.Workbooks.Open(/*params*/)

---> instead use -->

var workbooks = excel.Workbooks;
var workbook = workbooks.Open(/*params*/)

Then, when done, release each COM object:

Marshal.ReleaseComObject(workbook);
Marshal.ReleaseComObject(workbooks);
Marshal.ReleaseComObject(excel);

Long time no answer but what worked for me was to call the GC.Collect(); from the caller,

i.e. instead of

main()
{
    ...
    doexcelstuff();
    ...
}

void doexcelstuff()
{
    Excel.Application ExApp2 = new Excel.Application();
    Excel.Workbook excelWb = ExApp2 .Workbooks.Open(excelFName);
    Excel._Worksheet excelWorksheet = excelWb.Sheets[excelSName];
    //...
    excelWb.Close();
    ExApp2.Quit();     
    Marshal.ReleaseComObject(excelWb);
    Marshal.ReleaseComObject(excelWorksheet);
    Marshal.ReleaseComObject(ExApp2);
    excelWb = null;
    excelWorksheet= null;
    ExApp2= null;
    GC.Collect();
}

Using above Excel does not die

but a very small change, to where the GC is called from

main()
{
    ...
    doexcelstuff();
    GC.Collect();      // <<-- moved the GC to here (the caller)
    ...
}

void doexcelstuff()
{
    Excel.Application ExApp2 = new Excel.Application();
    Excel.Workbook excelWb = ExApp2 .Workbooks.Open(excelFName);
    Excel._Worksheet excelWorksheet = excelWb.Sheets[excelSName];
    //...
    excelWb.Close();
    ExApp2.Quit();     
    Marshal.ReleaseComObject(excelWb);
    Marshal.ReleaseComObject(excelWorksheet);
    Marshal.ReleaseComObject(ExApp2);
    excelWb = null;
    excelWorksheet= null;
    ExApp2= null;
    // removed the GC from here
}

My guess is the garbage collector needs to also quietly clean up internally created temp values (including refs/pointers) from the heap - some of which I guess in this case are pointing to COM objects.

(Just takes a smidgen of understanding of how machines work underneath the source code.)