I had created two threads for two methds filewritting and filereading. By using synchronization only one thread should access either filewritting or filereading.

static void Main(string[] args)
        {
            demo Demo = new demo();
            Thread write = new Thread(new ThreadStart(Demo.FileWritting));
            write.Start();
            write.Join();
            Thread read = new Thread(new ThreadStart(Demo.FileReading));
            read.Start();
            read.Join();
        }
        
        public class demo
        {
            string path = @"D:/Demos.txt";
           public void FileWritting()
            {
               lock(this)
               {
                   if (!File.Exists(path)&&locking)
                   {
                       FileStream fs = new FileStream(path, FileMode.Append, FileAccess.Write);
                       StreamWriter sw = new StreamWriter(fs);
                       sw.WriteLine("Welcome to filehandling");
                       
                       sw.Close();
                       fs.Close();
                       Console.WriteLine("File creation of" + path + "is done successfully");
                   }
                   else if (File.Exists(path)&&locking==false)
                   {
                       Console.WriteLine("file already exists");
                   }
                      
               }
            }
           public static volatile bool locking = true;
           
            public void FileReading()
              {  
                   if (File.Exists(path)&&locking)
                   {
                       lock(this)
                       {
                       FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read);
                       StreamReader sr = new StreamReader(fs);

                       string s = sr.ReadToEnd();

                       Console.WriteLine(s);
                       sr.Close();
                       fs.Close();
                       }
                      
                   }
                   else if(!File.Exists(path)&&locking==false)
                       Console.WriteLine("file doent exists");
               }