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Thread.Join.txt

Blocks the calling thread until the thread represented by this instance terminates, while continuing to perform standard COM and SendMessage pumping.


Remarks
Join is a synchronization method that blocks the calling thread (that is, the thread that calls the method) until the thread whose Join method is called has completed. Use this method to ensure that a thread has been terminated. The caller will block indefinitely if the thread does not terminate. In the following example, the Thread1 thread calls the Join() method of Thread2, which causes Thread1 to block until Thread2 has completed. 


using System;
using System.Threading;

public class Example
{
   static Thread thread1, thread2;
   
   public static void Main()
   {
      thread1 = new Thread(ThreadProc);
      thread1.Name = "Thread1";
      thread1.Start();
      
      thread2 = new Thread(ThreadProc);
      thread2.Name = "Thread2";
      thread2.Start();   
   }

   private static void ThreadProc()
   {
      Console.WriteLine("\nCurrent thread: {0}", Thread.CurrentThread.Name);

      // 若目前是Thread1 且 Thread2 還沒開始, 則等到 thread2 結束後, 再繼續執行!
	  if (Thread.CurrentThread.Name == "Thread1" && 
          thread2.ThreadState != ThreadState.Unstarted)
         thread2.Join();   
      
      Thread.Sleep(4000);
      Console.WriteLine("\nCurrent thread: {0}", Thread.CurrentThread.Name);
      Console.WriteLine("Thread1: {0}", thread1.ThreadState);
      Console.WriteLine("Thread2: {0}\n", thread2.ThreadState);
   }
}
// The example displays output like the following:
//       Current thread: Thread1
//       
//       Current thread: Thread2
//       
//       Current thread: Thread2
//       Thread1: WaitSleepJoin
//       Thread2: Running
//       
//       
//       Current thread: Thread1
//       Thread1: Running
//       Thread2: Stopped


If the thread has already terminated when Join is called, the method returns immediately. 
 Warning
You should never call the Join method of the Thread object that represents the current thread from the current thread. This causes your app to become unresponsive because the current thread waits upon itself indefinitely, 
注意 呼叫 Join() 的 Thread 物件, 不應為目前正在執行的主 thread, 否則會形成主 thread 等待自己結束, 結果為永遠無反應! 


This method changes the state of the calling thread to include ThreadState.WaitSleepJoin. You cannot invoke Join on a thread that is in the ThreadState.Unstarted state.

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Join(Int32) 
Blocks the calling thread until the thread represented by this instance terminates or the specified time elapses, while continuing to perform standard COM and SendMessage pumping.
C#

Copy
public bool Join (int millisecondsTimeout);
Parameters
millisecondsTimeout
Int32 
The number of milliseconds to wait for the thread to terminate.
Returns
Boolean 
true if the thread has terminated; false if the thread has not terminated after the amount of time specified by the millisecondsTimeout parameter has elapsed.
Exceptions
ArgumentOutOfRangeException 
The value of millisecondsTimeout is negative and is not equal to Infinite in milliseconds.
ThreadStateException 
The thread has not been started.
ArgumentException 
millisecondsTimeout is less than -1 (Timeout.Infinite).
ThreadInterruptedException 
The thread was interrupted while waiting.
Remarks
Join(Int32) is a synchronization method that blocks the calling thread (that is, the thread that calls the method) until either the thread whose Join method is called has completed or the time-out interval has elapsed. In the following example, the Thread1 thread calls the Join() method of Thread2, which causes Thread1 to block either until Thread2 has completed or 2 seconds have elapsed. 

using System;
using System.Threading;

public class Example
{
   static Thread thread1, thread2;
   
   public static void Main()
   {
      thread1 = new Thread(ThreadProc);
      thread1.Name = "Thread1";
      thread1.Start();
      
      thread2 = new Thread(ThreadProc);
      thread2.Name = "Thread2";
      thread2.Start();   
   }

   private static void ThreadProc()
   {
      Console.WriteLine("\nCurrent thread: {0}", Thread.CurrentThread.Name);
      if (Thread.CurrentThread.Name == "Thread1" && 
          thread2.ThreadState != ThreadState.Unstarted)
         if (thread2.Join(2000))
            Console.WriteLine("Thread2 has termminated.");
         else
            Console.WriteLine("The timeout has elapsed and Thread1 will resume.");   
      
      Thread.Sleep(4000);
      Console.WriteLine("\nCurrent thread: {0}", Thread.CurrentThread.Name);
      Console.WriteLine("Thread1: {0}", thread1.ThreadState);
      Console.WriteLine("Thread2: {0}\n", thread2.ThreadState);
   }
}
// The example displays the following output:
//       Current thread: Thread1
//       
//       Current thread: Thread2
//       The timeout has elapsed and Thread1 will resume.
//       
//       Current thread: Thread2
//       Thread1: WaitSleepJoin
//       Thread2: Running
//       
//       
//       Current thread: Thread1
//       Thread1: Running
//       Thread2: Stopped

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Join(TimeSpan) 
Blocks the calling thread until the thread represented by this instance terminates or the specified time elapses, while continuing to perform standard COM and SendMessage pumping.


using System;
using System.Threading;

class Test
{
    static TimeSpan waitTime = new TimeSpan(0, 0, 1);

    public static void Main() 
    {
        Thread newThread = new Thread(Work);
        newThread.Start();

        if(newThread.Join(waitTime + waitTime)) {
            Console.WriteLine("New thread terminated.");
        }
        else {
            Console.WriteLine("Join timed out.");
        }
    }

    static void Work()
    {
        Thread.Sleep(waitTime);
    }
}
// The example displays the following output:
//        New thread terminated.

Remarks
Join(TimeSpan) is a synchronization method that blocks the calling thread (that is, the thread that calls the method) until either the thread whose Join method is called has completed or the time-out interval has elapsed. In the following example, the Thread1 thread calls the Join() method of Thread2, which causes Thread1 to block either until Thread2 has completed or 2 seconds have elapsed. 

using System;
using System.Threading;

public class Example
{
   static Thread thread1, thread2;
   
   public static void Main()
   {
      thread1 = new Thread(ThreadProc);
      thread1.Name = "Thread1";
      thread1.Start();
      
      thread2 = new Thread(ThreadProc);
      thread2.Name = "Thread2";
      thread2.Start();   
   }

   private static void ThreadProc()
   {
      Console.WriteLine("\nCurrent thread: {0}", Thread.CurrentThread.Name);
      if (Thread.CurrentThread.Name == "Thread1" && 
          thread2.ThreadState != ThreadState.Unstarted)
         if (thread2.Join(TimeSpan.FromSeconds(2)))
            Console.WriteLine("Thread2 has termminated.");
         else
            Console.WriteLine("The timeout has elapsed and Thread1 will resume.");   
      
      Thread.Sleep(4000);
      Console.WriteLine("\nCurrent thread: {0}", Thread.CurrentThread.Name);
      Console.WriteLine("Thread1: {0}", thread1.ThreadState);
      Console.WriteLine("Thread2: {0}\n", thread2.ThreadState);
   }
}
// The example displays the following output:
//       Current thread: Thread1
//       
//       Current thread: Thread2
//       The timeout has elapsed and Thread1 will resume.
//       
//       Current thread: Thread2
//       Thread1: WaitSleepJoin
//       Thread2: Running
//       
//       
//       Current thread: Thread1
//       Thread1: Running
//       Thread2: Stopped


If Timeout.Infinite is specified for timeout, this method behaves identically to the Join() method overload, except for the return value. 
If the thread has already terminated when Join is called, the method returns immediately. 
This method changes the state of the current thread to include WaitSleepJoin. You cannot invoke Join on a thread that is in the ThreadState.Unstarted state.