WaitHandles 的数目必须少于或等于 64 个

1、用于同步 在多线程(并发)或异步运行的程序的时候，我们常会这样做：

using System;
using System.Threading;

namespace ThreadPoolTest
{
  class Program
  {
    private const int NumThreads = 5;

    private static int[] inputArray;
    private static double[] resultArray;
    private static ManualResetEvent[] resetEvents;

    private static void Main(string[] args)
    {
      inputArray = new int[NumThreads];
      resultArray = new double[NumThreads];
      resetEvents = new ManualResetEvent[NumThreads];

      Random rand = new Random();
      for (int s = 0; s < NumThreads; s++)
      {
        inputArray[s] = rand.Next(1,5000000);
        resetEvents[s] = new ManualResetEvent(false);
        ThreadPool.QueueUserWorkItem(new WaitCallback(DoWork), (object)s);
      }

      Console.WriteLine("Waiting...");

      WaitHandle.WaitAll(resetEvents);

      Console.WriteLine("And the answers are: ");
      for (int i = 0; i < NumThreads; i++)
        Console.WriteLine(inputArray[i] + " -> " + resultArray[i]);
    }

    private static void DoWork(object o)
    {
      int index = (int)o;

      for (int i = 1; i < inputArray[index]; i++)
        resultArray[index] += 1.0 / (i * (i + 1));

      resetEvents[index].Set();
    }
  }
}

 但是，现在的问题是当ManualResetEvent数组的元素个数超过（>）64时，就会报如标题所示的异常（System.NotSupportedException: WaitHandle 的数目必须少于或等于 64 个）。 如何解决：

2、解决问题

    方法一、设置计数标示，当完成我们线程数激发完成事件的响应标志。

using System;
using System.Threading;

namespace ThreadPoolTest
{
    class Program
    {
        private static int _numerOfThreadsNotYetCompleted = 100;
        private static ManualResetEvent _doneEvent = new ManualResetEvent(false);

        private static void Main(string[] args)
        {
            for (int threadNumber = 0; threadNumber < 100; threadNumber++)
                ThreadPool.QueueUserWorkItem(new WaitCallback(DoWork), 
					(object)threadNumber);

            _doneEvent.WaitOne();

            Console.WriteLine("All done.");
        }

        private static void DoWork(object o)
        {
            try
            {
                Console.WriteLine("Thread number: {0}", (int)o);
            }
            finally
            {
                if (Interlocked.Decrement(ref _numerOfThreadsNotYetCompleted) == 0)
                    _doneEvent.Set();
            }
        }
    }
}

参考：http://www.codeproject.com/Articles/142341/Solved-The-number-of-WaitHandles-must-be-less-than

方法二、还用ManualResetEvent resetEvents = new ManualResetEvent[NumThreads]; 只不过对线程数分组，每组不超过64个。循环组数。

方法三、.NET4.0中可以通过 CountdownEvent 类解决。具体参见http://msdn.microsoft.com/en-us/library/system.threading.countdownevent.aspx

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over！