Use Monitors : Monitor « Thread « C# / CSharp Tutorial

1. C# / CSharp Tutorial
2. Thread
3. Monitor

using System;
using System.Collections;
using System.Threading;

class MainClass
{
  public static ArrayList MyList = new ArrayList();
  
  static void Main(string[] args)
  {
      Thread ThreadOne = new Thread(new ThreadStart(MonitorExample));
    ThreadOne.Start();
  }
  static void MonitorExample()
  {
    Monitor.Enter(MyList);
    MyList.Add("a value");
    Monitor.Exit(MyList);
  }
}