C#

<br />
    private void NullAndRelease(object runtimeObject)<br />
    {<br />
      if (runtimeObject == null)<br />
        return;<br />
      try<br />
      {<br />
        System.Runtime.InteropServices.Marshal.FinalReleaseComObject(runtimeObject);<br />
      }<br />
      finally<br />
      { <br />
        runtimeObject = null; <br />
      }<br />
    }<br />
    private void button1_Click(object sender, EventArgs e)<br />
    {<br />
      Microsoft.Office.Interop.Excel.Application ExcelApp = new Microsoft.Office.Interop.Excel.Application();<br />
      object NullParam = System.Reflection.Missing.Value;<br />
      Workbook Book = ExcelApp.Workbooks.Open(FileName, 0, true, NullParam, NullParam, NullParam,<br />
        true, NullParam, NullParam, false, false, NullParam, false, true, NullParam);<br />
      Worksheet Sheet = Book.Worksheets[1] as Worksheet;<br />
      Range UsedRange = Sheet.UsedRange;<br />
<br />
      Range Cell = null;<br />
      int RowCount = UsedRange.Rows.Count;<br />
      for (int i = 2; i <= RowCount; i++)<br />
      {<br />
        Cell = UsedRange.Cells[i, 1] as Microsoft.Office.Interop.Excel.Range;<br />
        Cell = UsedRange.Cells[i, 2] as Microsoft.Office.Interop.Excel.Range;<br />
        Cell = UsedRange.Cells[i, 3] as Microsoft.Office.Interop.Excel.Range;<br />
        Cell = UsedRange.Cells[i, 4] as Microsoft.Office.Interop.Excel.Range;<br />
        Cell = UsedRange.Cells[i, 5] as Microsoft.Office.Interop.Excel.Range;<br />
        Cell = UsedRange.Cells[i, 6] as Microsoft.Office.Interop.Excel.Range;<br />
        NullAndRelease(Cell); <br />
      }<br />
      NullAndRelease(Cell);<br />
      NullAndRelease(UsedRange);<br />
      NullAndRelease(Sheet);<br />
      if (Book != null)<br />
        Book.Close(false, NullParam, false);<br />
      NullAndRelease(Book);<br />
      ExcelApp.Quit();<br />
      NullAndRelease(ExcelApp);<br />
      GC.Collect();<br />
      GC.WaitForPendingFinalizers();       <br />
    }<br />

<br />
      Cell = UsedRange.Cells[i, 7] as Microsoft.Office.Interop.Excel.Range;<br />

/// This method releases all references to a COM object. When
/// Visual Studio .NET calls a COM object from managed code, it
/// automatically creates a Runtime Callable Wrapper (RCW). The RCW
/// marshals calls between the .NET application and the COM object. The
/// RCW keeps a reference count on the COM object. Calling
/// ReleaseComObject when you are finished using an object will cause
/// the reference count of the RCW to be decremented.
/// param name="runtimeObject": The runtime callable wrapper whose
/// underlying COM object will be released.
private void NullAndRelease(object runtimeObject)
{
    try
    {

        if (runtimeObject != null)
        {

            // The RCW's reference count gets incremented each time the
            // COM pointer is passed from unmanaged to managed code.
            // Call ReleaseComObject in a loop until it returns 0 to be
            // sure that the underlying COM object gets released.
            int referenceCount = System.Runtime.InteropServices.
                Marshal.ReleaseComObject(runtimeObject);
    
            while (0 < referenceCount)
            {
                referenceCount = System.Runtime.InteropServices.
                    Marshal.ReleaseComObject(runtimeObject);
            }
        }
}
    finally
    {
        runtimeObject = null;
    }
}

JoeRip wrote:

Are changes to booleans already threadsafe?

Mark Churchill wrote:

Declare it as volatile