Thread.Join Method

Reference

Definition

Namespace:: System.Threading

Assembly:: System.Threading.Thread.dll

Assembly:: mscorlib.dll

Assembly:: netstandard.dll

Important

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Blocks the calling thread until the thread represented by this instance terminates.

Overloads

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

Join()

Source:: Thread.cs

Source:: Thread.cs

Source:: Thread.cs

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

public:
 void Join();

public void Join ();

member this.Join : unit -> unit

Public Sub Join ()

Exceptions

ThreadStateException

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

ThreadInterruptedException

The thread is interrupted while waiting.

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);
      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

open System.Threading

let mutable thread1, thread2 =
    Unchecked.defaultof<Thread>, Unchecked.defaultof<Thread>

let threadProc () =
    printfn $"\nCurrent thread: {Thread.CurrentThread.Name}"

    if
        Thread.CurrentThread.Name = "Thread1"
        && thread2.ThreadState <> ThreadState.Unstarted
    then
        thread2.Join()

    Thread.Sleep 4000
    printfn $"\nCurrent thread: {Thread.CurrentThread.Name}"
    printfn $"Thread1: {thread1.ThreadState}"
    printfn $"Thread2: {thread2.ThreadState}\n"

thread1 <- Thread threadProc
thread1.Name <- "Thread1"
thread1.Start()

thread2 <- Thread threadProc
thread2.Name <- "Thread2"
thread2.Start()

// 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

Imports System.Threading

Module Example
   Dim thread1, thread2 As Thread

   Public Sub Main()
      thread1 = new Thread(AddressOf ThreadProc)
      thread1.Name = "Thread1"
      thread1.Start()
      
      thread2 = New Thread(AddressOf ThreadProc)
      thread2.Name = "Thread2"
      thread2.Start()   
   End Sub

   Private Sub ThreadProc()
      Console.WriteLine()
      Console.WriteLine("Current thread: {0}", Thread.CurrentThread.Name)
      If (Thread.CurrentThread.Name = "Thread1" And 
          thread2.ThreadState <> ThreadState.Unstarted)
         thread2.Join()
      End If
      Thread.Sleep(4000)
      Console.WriteLine()
      Console.WriteLine("Current thread: {0}", Thread.CurrentThread.Name)
      Console.WriteLine("Thread1: {0}", thread1.ThreadState)
      Console.WriteLine("Thread2: {0}", thread2.ThreadState)
      Console.WriteLine()
   End Sub
End Module
' 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,

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.

Applies to

Join(Int32)

Source:: Thread.cs

Source:: Thread.cs

Source:: Thread.cs

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.

public:
 bool Join(int millisecondsTimeout);

public bool Join (int millisecondsTimeout);

member this.Join : int -> bool

Public Function Join (millisecondsTimeout As Integer) As Boolean

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

open System.Threading

let mutable thread1, thread2 =
    Unchecked.defaultof<Thread>, Unchecked.defaultof<Thread>

let threadProc () =
    printfn $"\nCurrent thread: {Thread.CurrentThread.Name}"

    if
        Thread.CurrentThread.Name = "Thread1"
        && thread2.ThreadState <> ThreadState.Unstarted
    then
        if thread2.Join 2000 then
            printfn "Thread2 has termminated."
        else
            printfn "The timeout has elapsed and Thread1 will resume."

    Thread.Sleep 4000
    printfn $"\nCurrent thread: {Thread.CurrentThread.Name}"
    printfn $"Thread1: {thread1.ThreadState}"
    printfn $"Thread2: {thread2.ThreadState}\n"

thread1 <- Thread threadProc
thread1.Name <- "Thread1"
thread1.Start()

thread2 <- Thread threadProc
thread2.Name <- "Thread2"
thread2.Start()

// 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

Imports System.Threading

Module Example
   Dim thread1, thread2 As Thread

   Public Sub Main()
      thread1 = new Thread(AddressOf ThreadProc)
      thread1.Name = "Thread1"
      thread1.Start()
      
      thread2 = New Thread(AddressOf ThreadProc)
      thread2.Name = "Thread2"
      thread2.Start()   
   End Sub

   Private Sub ThreadProc()
      Console.WriteLine()
      Console.WriteLine("Current thread: {0}", Thread.CurrentThread.Name)
      If (Thread.CurrentThread.Name = "Thread1" And 
          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.")
         End If      
      End If
      Thread.Sleep(4000)
      Console.WriteLine()
      Console.WriteLine("Current thread: {0}", Thread.CurrentThread.Name)
      Console.WriteLine("Thread1: {0}", thread1.ThreadState)
      Console.WriteLine("Thread2: {0}", thread2.ThreadState)
      Console.WriteLine()
   End Sub
End Module
' The example displays the following output:
'       Current thread: Thread1
'       
'       Current thread: Thread2
'       
'       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.

Applies to

Join(TimeSpan)

Source:: Thread.cs

Source:: Thread.cs

Source:: Thread.cs

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.

public:
 bool Join(TimeSpan timeout);

public bool Join (TimeSpan timeout);

member this.Join : TimeSpan -> bool

Public Function Join (timeout As TimeSpan) As Boolean

Parameters

timeout: TimeSpan

A TimeSpan set to the amount of time to wait for the thread to terminate.

Returns

Boolean

true if the thread terminated; false if the thread has not terminated after the amount of time specified by the timeout parameter has elapsed.

Exceptions

ArgumentOutOfRangeException

The value of timeout is negative and is not equal to Infinite in milliseconds, or is greater than Int32.MaxValue milliseconds.

ThreadStateException

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

Examples

The following code example demonstrates how to use a TimeSpan value with the Join method.

using namespace System;
using namespace System::Threading;

static TimeSpan waitTime = TimeSpan(0,0,1);

ref class Test
{
public:
   static void Work()
   {
      Thread::Sleep( waitTime );
   }

};

int main()
{
   Thread^ newThread = gcnew Thread( gcnew ThreadStart( Test::Work ) );
   newThread->Start();
   if ( newThread->Join( waitTime + waitTime ) )
   {
      Console::WriteLine( "New thread terminated." );
   }
   else
   {
      Console::WriteLine( "Join timed out." );
   }
}
// The example displays the following output:
//        New thread terminated.

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.

open System
open System.Threading

let waitTime = TimeSpan(0, 0, 1)

let work () =
    Thread.Sleep waitTime

let newThread = Thread work
newThread.Start()

if waitTime + waitTime |> newThread.Join then
    printfn "New thread terminated."
else
    printfn "Join timed out."

// The example displays the following output:
//        New thread terminated.

Imports System.Threading

Public Module Test
    Dim waitTime As New TimeSpan(0, 0, 1)

    Public Sub Main() 
        Dim newThread As New Thread(AddressOf Work)
        newThread.Start()

        If newThread.Join(waitTime + waitTime) Then
            Console.WriteLine("New thread terminated.")
        Else
            Console.WriteLine("Join timed out.")
        End If
    End Sub

    Private Sub Work()
        Thread.Sleep(waitTime)
    End Sub
End Module
' 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

open System
open System.Threading

let mutable thread1, thread2 =
    Unchecked.defaultof<Thread>, Unchecked.defaultof<Thread>

let threadProc () =
    printfn $"\nCurrent thread: {Thread.CurrentThread.Name}"

    if
        Thread.CurrentThread.Name = "Thread1"
        && thread2.ThreadState <> ThreadState.Unstarted
    then
        if TimeSpan.FromSeconds 2 |> thread2.Join then
            printfn "Thread2 has termminated."
        else
            printfn "The timeout has elapsed and Thread1 will resume."

    Thread.Sleep 4000
    printfn $"\nCurrent thread: {Thread.CurrentThread.Name}"
    printfn $"Thread1: {thread1.ThreadState}"
    printfn $"Thread2: {thread2.ThreadState}\n"

thread1 <- Thread threadProc
thread1.Name <- "Thread1"
thread1.Start()

thread2 <- Thread threadProc
thread2.Name <- "Thread2"
thread2.Start()

// 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

Imports System.Threading

Module Example
   Dim thread1, thread2 As Thread

   Public Sub Main()
      thread1 = new Thread(AddressOf ThreadProc)
      thread1.Name = "Thread1"
      thread1.Start()
      
      thread2 = New Thread(AddressOf ThreadProc)
      thread2.Name = "Thread2"
      thread2.Start()   
   End Sub

   Private Sub ThreadProc()
      Console.WriteLine()
      Console.WriteLine("Current thread: {0}", Thread.CurrentThread.Name)
      If (Thread.CurrentThread.Name = "Thread1" And 
          thread2.ThreadState <> ThreadState.Unstarted)
         If thread2.Join(2000)
            Console.WriteLine("Thread2 has termminated.")
         Else
            Console.WriteLine("The timeout has elapsed and Thread1 will resume.")
         End If      
      End If
      Thread.Sleep(4000)
      Console.WriteLine()
      Console.WriteLine("Current thread: {0}", Thread.CurrentThread.Name)
      Console.WriteLine("Thread1: {0}", thread1.ThreadState)
      Console.WriteLine("Thread2: {0}", thread2.ThreadState)
      Console.WriteLine()
   End Sub
End Module
' The example displays the following output:
'       Current thread: Thread1
'       
'       Current thread: Thread2
'       
'       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.

Applies to

Share via

Thread.Join Method

Definition

Overloads

Join()

Exceptions

Remarks

See also

Applies to

Join(Int32)

Parameters

Returns

Exceptions

Remarks

See also

Applies to

Join(TimeSpan)

Parameters

Returns

Exceptions

Examples

Remarks

See also

Applies to

Additional resources