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Join Method (Int32)
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Thread.Join Method (Int32)

Blocks the calling thread until a thread terminates or the specified time elapses, while continuing to perform standard COM and SendMessage pumping.

Namespace:  System.Threading
Assembly:  mscorlib (in mscorlib.dll)

[HostProtectionAttribute(SecurityAction.LinkDemand, Synchronization = true, 
	ExternalThreading = true)]
public bool Join(
	int millisecondsTimeout


Type: System.Int32

The number of milliseconds to wait for the thread to terminate.

Return Value

Type: System.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.


The value of millisecondsTimeout is negative and is not equal to Timeout.Infinite in milliseconds.


The thread has not been started.

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 mainThread, thread1, thread2;

   public static void Main()
      mainThread = Thread.CurrentThread;
      thread1 = new Thread(ThreadProc);
      thread1.Name = "Thread1";

      thread2 = new Thread(ThreadProc);
      thread2.Name = "Thread2";

   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.");
            Console.WriteLine("The timeout has elapsed and Thread1 will resume.");   

      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 the millisecondsTimeout parameter, 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 calling thread to include ThreadState.WaitSleepJoin. You cannot invoke Join on a thread that is in the ThreadState.Unstarted state.


The HostProtectionAttribute attribute applied to this type or member has the following Resources property value: Synchronization | ExternalThreading. The HostProtectionAttribute does not affect desktop applications (which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser). For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes.

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8
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