C# async og await

CSharp kode 

 private void CopyFile(string source, string dest)
         {
             using (FileStream sourceStream = new FileStream(source, FileMode.Open))
             {
                 byte[] buffer = new byte[256 * 1024]; // Change to suitable size after testing performance
                 using (FileStream destStream = new FileStream(dest, FileMode.Create))
                 {
                     int i;
                     while ((i = sourceStream.Read(buffer, 0, buffer.Length)) > 0)
                     {
                         destStream.Write(buffer, 0, i);
                     }
                 }
             }
         }

CSharp kode 

 public List<BufferBits> BufferList = new List<BufferBits>();
         public bool ReadToEnd = false;
 
 
 private void button2_Click(object sender, EventArgs e)
         {
             string source = @"Y:\Film\Coming To America (1988)\Coming To America 1988.mp4";
             string dest = @"C:\Temp\xx.tmp";
             ReadWriteFile(source, dest);
         }
 
 public async Task ReadWriteFile(string source, string dest)
         {
             Task<long> InputLengthTask = ReadFile(source); //Burde fortsætte til WriteFile fordi ReadFile er async?
             Task<long> OutputLengthTask = WriteFile(dest);
             long InputResult = await InputLengthTask;
             long OutputResult = await OutputLengthTask;
         }
 
         public async Task<long> WriteFile(string destination)
         {
             int i = 0;
             MemoryStream memStream = new MemoryStream();
             BufferBits bb;
             while (!ReadToEnd)
             {
                 bb = null;
                 try
                 {
                     bb = BufferList.ElementAt(i);
                 }
                 catch (Exception ex)
                 {
                     continue;
                 }
 
 
                 if (bb != null)
                 {
                     i++;
                     memStream.Write(bb.ByteArray, bb.Offset, bb.Count);
                 }
             }
             return memStream.Length;
         }
 
 public class BufferBits
     {
         public byte[] ByteArray { get; set; }
         public int Offset { get; set; }
         public int Count { get; set; }
 
         public BufferBits(byte[] buffer, int offset, int count)
         {
             this.ByteArray = buffer;
             this.Offset = offset;
             this.Count = count;
         }
     }