using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using ClosedXML.Excel;

namespace TestSavingTwoBigFiles
{
    public class Program
    {
        private static string folderPath = @"C:FOLDERPATH";
        private static string fileName1 = folderPath + "FILENAME1.xlsm";
        private static string fileName2 = folderPath + "FILENAME2.xlsm";

        public static void StartThread1()
        {
            Console.WriteLine("Creating first file...");
            var wb = new XLWorkbook(fileName1, XLEventTracking.Disabled);
            try
            {
                using (wb)
                {
                    using (var ms = new MemoryStream())
                    {
                        Console.WriteLine("Saving first file...");
                        wb.SaveAs(ms);
                    }
                }
                Console.WriteLine("First file saved successfully");
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex);
                Console.ReadLine();
            }
        }

        public static void StartThread2()
        {
            Console.WriteLine("Creating second file...");
            var wb = new XLWorkbook(fileName2, XLEventTracking.Disabled);
            try
            {
                using (wb)
                {
                    using (var ms = new MemoryStream())
                    {
                        Console.WriteLine("Saving second file...");
                        wb.SaveAs(ms);
                    }
                }
                Console.WriteLine("Second file saved successfully");
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex);
                Console.ReadLine();
            }
        }

        public static void Main(string[] args)
        {
            var thread1Start = new ThreadStart(StartThread1);
            var thread1 = new Thread(thread1Start);
            Console.WriteLine("Starting first thread");
            thread1.Start();

            var thread2Start = new ThreadStart(StartThread2);
            var thread2 = new Thread(thread2Start);
            Console.WriteLine("Starting second thread");
            thread2.Start();
        }
    }
}