c# Task多线程并行任务中等待所有线程都执行完成

C#多线程中如何等待所有线程的任务都执行完成呢？在.net 4.0以4.0+中，有Task.WaitAll(params Task[] tasks)方法来等待所有Task[],而不需要更多的操作。按照微软官方的文档，我写了一个实例来调试和说明：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp
{
  class Program
  {

    static void Main(string[] args)
    {
      var bookShop = new BookShop();
      bookShop.Run();
    }

  }

  pulic class Book
  {
    public int Id { get; set; }

    public string Name { get; set; }
  }
  public class BookShop
  {
    Random rand = new Random();
    Queue<Book> queueBook = new Queue<Book>();
    int Max = 10000;
    int EachCount = 500;
    int Cur = 0;

    void LoadData()
    {
      if (Cur >= Max)
      {
        //when Cur>=Max,return
        Console.WriteLine("Reached max value!");
        return;
      }
      Console.WriteLine("Loading data...");
      for (int i = Cur; i < EachCount + Cur; i++)
      {
        Thread.Sleep(10);
        Console.Write(i + " ");
        //insert data into Queue<Book>
        queueBook.Enqueue(new Book { Id = i, Name = "Name_" + i });
      }
      Console.WriteLine("");
      Cur += EachCount;
      Console.WriteLine("Data loaded successful,{0}...", queueBook.Count);
    }

    public void Run()
    {
      LoadData();

      Console.WriteLine("Tasks have started...");
      do
      {
        Task[] tasks = new Task[10];
        for (int i = 0; i < 10; i++)
        {
          tasks[i] = Task.Factory.StartNew(() => DoSomeWork(1000 * 1));
        }
        //// Wait for all tasks to complete.
        Task.WaitAll(tasks);
        //when Queue<Book> is empty,reload data...
        LoadData();
      } while (queueBook.Count > 0);
      //when Cur>=Max,break the while loop
      Console.WriteLine("All tasks have completed.");

      Console.ReadKey();
    }

    void DoSomeWork(int val)
    {
      while (queueBook.Count > 0)
      {
        var m = queueBook.Dequeue();
        Console.WriteLine("DoSomeWork start,i={0},Current thread id:{1}...", m.Id, Thread.CurrentThread.ManagedThreadId);
        var sleep = rand.Next(10, 200);
        // Pretend to do something.
        Thread.Sleep(sleep);
        Console.WriteLine("DoSomeWork has completed,sleep:{0},i={1}", sleep, m.Id);
      }
    }
  }
}