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

Properly closing the open Excel workbook and quitting the app is extremely difficult. If I can find the links I'll post them, but essentially you must clean up all references to any COM object that you create. This includes everything from ODBCConnections (data connections), Worksheets, Workbooks, and the Excel application. A combination I got to work involved garbage collection and the System.Runtime.InteropServices.Marshal object:

// Garbage collecting
GC.Collect();
GC.WaitForPendingFinalizers();
// Clean up references to all COM objects
// As per above, you're just using a Workbook and Excel Application instance, so release them:
workbook.Close(false, Missing.Value, Missing.Value);
xlApp.Quit();
Marshal.FinalReleaseComObject(workbook);
Marshal.FinalReleaseComObject(xlApp);

Like you mentioned, looping through and killing each Excel process is usually not a good idea, since if you're running this as a Windows app you may close Excel on your user, or in a service also close an instance of Excel that is running via some other program.

Edit: See this question for more info.

You need to check file handles and get PID, that are opened by process and then kill it. It worked for me.

private void genExcel(
{
   int pid = -1;
   //Get PID
   xlApp = new Excel.Application();
   HandleRef hwnd = new HandleRef(xlApp, (IntPtr)xlApp.Hwnd);
   GetWindowThreadProcessId(hwnd, out pid);
   .
   .
   .
   .
   //Finally
   KillProcess(pid,"EXCEL");
}

[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
public static extern int GetWindowThreadProcessId(HandleRef handle, out int processId);

private void KillProcess(int pid, string processName)
{
    // to kill current process of excel
    System.Diagnostics.Process[] AllProcesses = System.Diagnostics.Process.GetProcessesByName(processName);
    foreach (System.Diagnostics.Process process in AllProcesses)
    {
       if (process.Id == pid)
       {
         process.Kill();
       }
    }
    AllProcesses = null;
}

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);
    }
}