Критическая секция

object syncObj;
void WriteInFile1(string line)
{
    lock (syncObj)
    {
          StreamWriter LogStream;
          using (LogStream = new StreamWriter("file1.txt")
          {
                LogStream.WriteLine(line);
          }
          LogStream.Close();
    }
}
 
void WriteInFile2(string line)
{
    lock (syncObj)
    {
          StreamWriter LogStream;
          using (LogStream = new StreamWriter("file2.txt")
          {
                LogStream.WriteLine(line);
          }
          LogStream.Close();
    }
}

Dictionary<String, Object> lines = new Dictionary<String, String>();
Object getLockObject(string line)
{
   if(!lines.Contains(line)) lines.Add(line, line);
   return lines[line];
}
void WriteInFile1(string line)
{
    lock (getLockObject(line))
    {
          StreamWriter LogStream;
          using (LogStream = new StreamWriter(line)
          {
                LogStream.WriteLine(line);
          }
          LogStream.Close();
    }
}
 
void WriteInFile2(string line)
{
    lock (getLockObject(line))
    {
          StreamWriter LogStream;
          using (LogStream = new StreamWriter(line)
          {
                LogStream.WriteLine(line);
          }
          LogStream.Close();
    }
}