c#Parallel多线程用法

  string a = "";
  List<int> list = new List<int>() { 1,2,3,4,5,6,7};
  var localobj=new object();
  var options = new ParallelOptions { MaxDegreeOfParallelism = 2 };
  await Parallel.ForEachAsync(list,options,async(number,_) =>
  {
      Console.WriteLine($"{Thread.CurrentThread.ManagedThreadId},{number}");

     
      lock(localobj)
      {
          a += $"{Thread.CurrentThread.ManagedThreadId},{number}\r\n";
      }
  });
  this.textBox1.Text = a;