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Thread.Join Method

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

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

'Declaration
<HostProtectionAttribute(SecurityAction.LinkDemand, Synchronization := True,  _
	ExternalThreading := True)> _
Public Sub Join
'Usage
Dim instance As Thread

instance.Join()

ExceptionCondition
ThreadStateException

The caller attempted to join a thread that is in the ThreadState.Unstarted state.

ThreadInterruptedException

The thread is interrupted while waiting.

NoteNote:

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.

Use this method to ensure a thread has terminated. The caller will block indefinitely if the thread does not terminate. 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 following code example shows how to use Join to wait for a thread to terminate.

Option Explicit
Option Strict

Imports System
Imports System.Threading

Public Class IsThreadPool

    <MTAThread> _
    Shared Sub Main()
        Dim autoEvent As New AutoResetEvent(False)

        Dim regularThread As New Thread(AddressOf ThreadMethod)
        regularThread.Start()
        ThreadPool.QueueUserWorkItem(AddressOf WorkMethod, autoEvent)

        ' Wait for foreground thread to end.
        regularThread.Join()

        ' Wait for background thread to end.
        autoEvent.WaitOne()
    End Sub 

    Shared Sub ThreadMethod()
        Console.WriteLine("ThreadOne, executing ThreadMethod, " & _
            "is from the thread pool? {0}", _
            Thread.CurrentThread.IsThreadPoolThread)
    End Sub 

    Shared Sub WorkMethod(stateInfo As Object)
        Console.WriteLine("ThreadTwo, executing WorkMethod, " & _
            "is from the thread pool? {0}", _
            Thread.CurrentThread.IsThreadPoolThread)

        ' Signal that this thread is finished.
        DirectCast(stateInfo, AutoResetEvent).Set()
    End Sub 

End Class

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0

XNA Framework

Supported in: 3.0, 2.0, 1.0
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