[.NET] Thread Separate Event

撰写多线程对象时，执行速度是一项很重要的设计考虑。通常为了加快执行速度，会将执行运作逻辑的主线程，跟发出事件的事件线程做隔离设计。这样的隔离设计可以不让主线程，因为外部事件处理而停顿。而这样的设计下，为了简化线程管理，可以采用ThreadPool来完成事件线程的工作。简单的程序范例如下：

 

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namespace ConsoleApplication1 {     class Program     {         static void Main(string[] args)         {             var obj = new ClassA();             obj.NotifyArrived += new Action<int>(obj_NotifyArrived);             obj.Start();             Console.ReadLine();             obj.Stop();         }           static void obj_NotifyArrived(int data)         {             Console.WriteLine(data);         }     }       public class ClassA     {         // Fields         private bool _isRunning = true;             // Methods            public void Start()         {             Thread thread = new Thread(this.Run);             thread.Start();         }           public void Stop()         {             _isRunning = false;         }           private void Run()         {             int i = 0;             while (_isRunning == true)             {                 Thread.Sleep(100);                 this.OnNotifyArrived(i++);             }         }             // Events         public event System.Action<int> NotifyArrived;         private void OnNotifyArrived(int data)         {             WaitCallback handlerDelegate = delegate(object state)             {                 var handler = this.NotifyArrived;                 if (handler != null)                 {                     handler(data);                 }             };             ThreadPool.QueueUserWorkItem(handlerDelegate);         }     } }

 

但是这样的隔离设计，却无法满足「必须按照先来后到去处理事件」这样的行为要求。因为ThreadPool只是单纯的为每一个WaitCallback委派，分派一条线程去做处理，而每条线程之间并没有设定执行先后顺序的能力。

 

这个问题困扰了我几天，后来想到一个解法。在主线程跟事件线程之间，垫一层Queue做隔离，将要执行的WaitCallback委派都存放进这个Queue。并且通过Lock的机制，强迫一次只能有一个线程去处理Queue里面的WaitCallback委派。透过这样的设计，就可以完成将执行运作逻辑的主线程，跟发出事件的事件线程做隔离设计的工作。范例程序代码如下：

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namespace ConsoleApplication1 {     class Program     {         static void Main(string[] args)         {             var obj = new ClassB();             obj.NotifyArrived += new Action<int>(obj_NotifyArrived);             obj.Start();             Console.ReadLine();             obj.Stop();         }           static void obj_NotifyArrived(int data)         {             Console.WriteLine(data);         }     }       public class ClassB     {         // Fields         private bool _isRunning = true;           private readonly object _eventSyncRoot = new object();           private readonly Queue<WaitCallback> _eventDelegateQueue = new Queue<WaitCallback>();             // Methods            public void Start()         {             Thread thread = new Thread(this.Run);             thread.Start();         }           public void Stop()         {             _isRunning = false;         }           private void Run()         {             int i = 0;             while (_isRunning == true)             {                 Thread.Sleep(100);                 this.OnNotifyArrived(i++);             }         }             // Events         public event System.Action<int> NotifyArrived;         private void OnNotifyArrived(int data)         {             // Queue EventDelegate             WaitCallback eventDelegate = delegate(object state)             {                 var handler = this.NotifyArrived;                 if (handler != null)                 {                     handler(data);                 }             };               lock (_eventDelegateQueue)             {                 _eventDelegateQueue.Enqueue(eventDelegate);             }               // Run EventDelegate             WaitCallback handlerDelegate = delegate(object state)             {                 lock (_eventSyncRoot)                 {                     WaitCallback runEventDelegate = null;                     lock (_eventDelegateQueue)                     {                         if (_eventDelegateQueue.Count > 0)                         {                             runEventDelegate = _eventDelegateQueue.Dequeue();                         }                     }                       if (runEventDelegate != null)                     {                         runEventDelegate(null);                     }                 }             };             ThreadPool.QueueUserWorkItem(handlerDelegate);         }     } }

 

最后说一下，要完成这样的隔离设计。不使用ThreadPool，而改用一个独立Thread去处理WaitCallback委派，也是可行的设计。只不过独立一个线程去处理，就需要额外增加管理这个独立线程的工作，这就看每个人的选择跟考虑了。