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

interface Task{
	void doTask();
}
class TaskA : Task{
	public void doTask(){
		Console.WriteLine("ABC");
	}
}
class TaskB : Task{
	public void doTask(){
		for(;;){
			Console.Write(".");
			Thread.Sleep(0); //Cancel用
		}
	}
}

class Tasker{
	private Thread th;
	private EventWaitHandle wh = new ManualResetEvent(false);
	private Queue<Task> queue = new Queue<Task>();
	private bool end = false;
	
	public void Start(){
		if(th!=null){throw new Exception();}
		th = new Thread(ThreadMain);
		th.Start();
	}
	public void AddTask(Task t){
		lock(queue){
			queue.Enqueue(t);
			wh.Set();
		}
	}
	public void Cancel(){
		th.Interrupt();
	}
	public void Join(){
		lock(queue){
			end = true;
			wh.Set();
		}
		th.Join();
	}
	
	private void ThreadMain(){
		try{
			Console.WriteLine("Start");
			for(;;){
				Task t;
				lock(queue){
					t = queue.Count==0 ? null : queue.Dequeue();
					if(t==null){
						if(end){
							Console.WriteLine("End");
							return;
						}
						wh.Reset();
					}
				}
				if(t==null){
					Console.WriteLine("Wait");
					wh.WaitOne(Timeout.Infinite);
				}
				else{
					t.doTask();
					Thread.Sleep(0); //Cancel用
				}
			}
		}
		catch(ThreadInterruptedException){
			Console.WriteLine();
			Console.WriteLine("Cancel");
		}
	}
}

class Test{
	public static void Main(){
		{
			Tasker te = new Tasker();
			te.Start();
			Thread.Sleep(50); //Taskが無いのでスレッドはWaitになる
			te.AddTask(new TaskA());
			Thread.Sleep(50); //TaskAはすぐ終わるのでスレッドはWaitになる
			te.AddTask(new TaskB());
			Thread.Sleep(1);
			te.Cancel(); //TaskBは終わらないので中断
			te.Join(); //Threadの終了を待つ
		}
		Console.WriteLine("--------------");
		{
			Tasker te = new Tasker();
			te.AddTask(new TaskA());
			te.Start();
			Thread.Sleep(50); //TaskAはすぐ終わるのでスレッドはWaitになる
			te.Join(); //Waitから復帰させThreadの終了を待つ
		}
	}
}