Code
using System;
using System.Collections.Generic;
using System.Text;
using System.IO;
using System.Runtime.Remoting.Messaging;

namespace WF
{    
    public class Program
    {
        static void Main()
        {
            BookmarkManager mgr = new BookmarkManager();
            OpenSesame os = new OpenSesame();
            os.Start(mgr);
            mgr.Resume("read", null); 
            Console.WriteLine("Press any key to continue  ");
            Console.ReadKey();
        }        
    }

/// <summary>
    /// 书签类
    /// </summary>
    [Serializable]
    public class Bookmark
    {
        private string name;
        private object payload;
        private BookmarkLocation bookmarkLocation;
        private BookmarkManager bookmarkManager;
        public Bookmark(string name, BookmarkLocation continueAt)
        {
            this.name = name;
            this.bookmarkLocation = continueAt;
        }
        public string Name { get { return this.name; } }
        public BookmarkLocation ContinueAt { get { return this.bookmarkLocation; } }
        public object Payload { get { return this.payload; } set { this.payload = value; } }
        /// <summary>
        /// 书签位置属性
        /// </summary>
        public BookmarkManager BookmarkManager { get { return this.bookmarkManager; } set { this.bookmarkManager = value; } }
    }
    /// <summary>
    /// 书签位置（委托类型）
    /// </summary>
    /// <param name="resumed"></param>
    public delegate void BookmarkLocation(Bookmark resumed);

public class BookmarkManager
    {
        private delegate string AsyncReadLine();
        private IList<Bookmark> bookmarks;
        private int currentIndex = -1;
        public void Add(Bookmark bookmark)
        {
            if (this.bookmarks == null)
                this.bookmarks = new List<Bookmark>();
            bookmark.BookmarkManager = this;
            bookmarks.Add(bookmark);
        }
        public void Remove(Bookmark bookmark)
        {
            if (this.bookmarks != null && this.bookmarks.Count > 0)
                this.bookmarks.Remove(bookmark);
        }
        public void Resume(string bookmarkName, object payload)
        {
            foreach (Bookmark bk in this.bookmarks)
                if (bk.Name.Equals(bookmarkName) && bk.ContinueAt != null)
                {
                    this.currentIndex = this.bookmarks.IndexOf(bk);
                    BeginReadLine(new AsyncCallback(AsyncCallback), payload);
                }
        }
        private void AsyncCallback(IAsyncResult ar)
        {
            Bookmark bk = this.bookmarks[currentIndex];
            bk.Payload = EndReadLine(ar);
            bk.ContinueAt.Invoke(bk);
        }
        private IAsyncResult BeginReadLine(AsyncCallback asyncCallback, object state)
        {
            AsyncReadLine asyncReadLine = new AsyncReadLine(Console.ReadLine);
            return asyncReadLine.BeginInvoke(asyncCallback, state);
        }
        private string EndReadLine(IAsyncResult ar)
        {
            AsyncReadLine reader = (AsyncReadLine)((AsyncResult)ar).AsyncDelegate;
            return reader.EndInvoke(ar);
        }
    }

[Serializable]
    public class OpenSesame
    {
        private string key;
        public void Start(BookmarkManager mgr)
        {
            this.key = DateTime.Now.Millisecond.ToString();
            Console.WriteLine("Here is the key: {0}", key);
            mgr.Add(new Bookmark("read", this.ContinueAt));
        }
        private void ContinueAt(Bookmark resumed)
        {
            string s = (string)resumed.Payload;
            BookmarkManager mgr = resumed.BookmarkManager;
            mgr.Remove(resumed);
            if (this.key.Equals(s))
                Console.WriteLine("Welcome, my friends!");
            else
                Console.WriteLine("Sorry, you press a wrong key.");
        }
    }
}