using System;
using System.Collections.Generic;
using System.Text;
using System.IO;
using System.Threading;

namespace file_thread
{
    class Program
    {
        public static StreamWriter wr;
        
        static void Main(string[] args)
        {
            wr = new StreamWriter("output.txt");
            
            Thread t1 = new Thread(new ThreadStart(Thread1));
            Thread t2 = new Thread(new ThreadStart(Thread2));

            t1.Start();
            t2.Start();
        }

        public static void Thread1()
        {
            lock(wr)
            {
                for (int i = 0; i < 1000; i++)
                {
                    wr.WriteLine("Thread #1");
                }
            }
        }
        
        public static void Thread2()
        {
            lock (wr)
            {
                for (int i = 0; i < 1000; i++)
                {
                    wr.WriteLine("Thread #2");
                }
            }
        }

    }
}