C# 如何創建, 暫停, 繼續, 終止一個執行緒(Thread)－天天向上

今天來複習一下執行緒, 先前有一些觀念錯誤: 關於暫停/關閉執行緒Suspend, Terminate

不該踩到地雷, 我一個都沒錯過@@

1. 本範例示範如何開一個worker執行緒, 呼叫Start開始不斷執行Job內容, 且不影響原本的主執行緒

2. 要暫停一個執行緒不建議使用Thread.Suspend, 這會讓你不曉得在你呼叫Suspend

當下該執行緒在幹甚麼;更準確地說, 你會不曉得worker在Job中已經
完成多少(停在Job中的哪個階段)
3. 不要使用Terminate, 建議使用Join

3. 透過ManualResetEvent搭配WaitOne 方法, 可以讓你更精準控制: 暫停, 繼續, 以及停止執行緒


public class Worker
   {
       /* Initializes a new instance of the ManualResetEvent class 
        * with a Boolean value indicating whether to set the initial state to signaled.
        */ 
       ManualResetEvent _shutdownEvent = new ManualResetEvent(false);
       ManualResetEvent _pauseEvent = new ManualResetEvent(true);
       Thread _thread;
       public Worker() { }
       public void Job()
       {
           int cnt = 0;
           while (true)
           {
               /* 封鎖目前執行緒, 直到waitHandle收到通知, 
                * Timeout.Infinite表示無限期等候
                */ 
               _pauseEvent.WaitOne(Timeout.Infinite);
               /* return true if the current instance receives a signal. 
                * If the current instance is never signaled, WaitOne never returns
                */ 
               if(_shutdownEvent.WaitOne(0))
                   break;
               /* if (_shutdownEvent.WaitOne(Timeout.Infinite))
                * 因為沒有收到signal, 所以會停在if()這一行, 造成cnt無法累加
                */
             
               Console.WriteLine("{0}", cnt++);
           }
       }
       public void Start()
       {
           _thread = new Thread(Job);
           _thread.Start();
           Console.WriteLine("Thread started running");
       }
       public void Pause()
       {
           /* Sets the state of the event to nonsignaled, 
            * causing threads to block.
            */ 
           _pauseEvent.Reset();  
           Console.WriteLine("Thread paused");
       }

       public void Resume()
       {
           /* Sets the state of the event to signaled, 
            * allowing one or more waiting threads to proceed.
            */ 
           _pauseEvent.Set();
           Console.WriteLine("Thread resuming ");
       }
       public void Stop()
       {
           // Signal the shutdown event
           _shutdownEvent.Set();
           Console.WriteLine("Thread Stopped ");

           // Make sure to resume any paused threads
           _pauseEvent.Set();

           // Wait for the thread to exit
           _thread.Join();
       }
   }

來測試Worker


static void Main(string[] args)
      {
          Worker w1 = new Worker();
          w1.Start();
          Thread.Sleep(500);
          w1.Pause();           
          Thread.Sleep(200);
          w1.Resume();
          Thread.Sleep(500);
          w1.Pause();
          Thread.Sleep(1000);
          w1.Resume();
          Thread.Sleep(200);
          w1.Stop();
          Console.Read();
      }

Pause()利用關閉_pauseEvent訊號, 即 _pauseEvent.Reset(),

來達到Job停在_pauseEvent.WaitOne(Timeout.Infinite);這一行程式碼,

這樣操作會比呼叫Thread.Suspend更好

   1: public void Pause()   2:        {   3:            /* Sets the state of the event to nonsignaled,    4:             * causing threads to block.   5:             */    6:            _pauseEvent.Reset();   7:            /* 在Job()中_pauseEvent.WaitOne(Timeout.Infinite);   8:             * 這一行因為在等signal回覆, 而Reset關閉signal,    9:             * 所以間接造成暫停Worker執行緒,   10:             * 這個方式會比Thread.Suspend()要好  11:             */   12:            Console.WriteLine("Thread paused");  13:        }

Stop()利用通知_shutdownEvent, 即_shutdownEvent.Set(),

讓Job中

if(_shutdownEvent.WaitOne(0))

  break;

條件成立, 跳離while-loop也就順利結束該執行緒

同時為了確保原本執行緒不是被暫停狀態

記得通知_pauseEvent, 即_pauseEvent.Set();

否則通知_shutdownEvent也枉然

最後在很優雅地等執行緒結束,

即呼叫_thread.Join(); 而不是Thread.Terminate

   1: public void Stop()   2: {   3:     // Signal the shutdown event   4:     _shutdownEvent.Set();   5:     Console.WriteLine("Thread Stopped ");   6:     7:     // Make sure to resume any paused threads   8:     _pauseEvent.Set();   9:    10:     // Wait for the thread to exit  11:     _thread.Join();  12: }