Thread.Join
Method
Definition
Overloads
| Join() |
Blocks the calling thread until the thread represented by this instance terminates, while continuing to perform standard COM and |
| 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()
Blocks the calling thread until the thread represented by this instance terminates, while continuing to perform standard COM and SendMessage pumping.
public void Join ();
The caller attempted to join a thread that is in the Unstarted state.
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
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 hang because the current thread waits upon itself indefinitely,
This method changes the state of the calling thread to include ThreadState. You cannot invoke Join on a thread that is in the ThreadState state.
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.
public bool Join (int millisecondsTimeout);
- millisecondsTimeout
- Int32
The number of milliseconds to wait for the thread to terminate.
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 Infinite in milliseconds.
The thread has not been started.
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
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. You cannot invoke Join on a thread that is in the ThreadState state.
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.
public bool Join (TimeSpan timeout);
true if the thread terminated; false if the thread has not terminated after the amount of time specified by the timeout parameter has elapsed.
The value of timeout is negative and is not equal to Infinite in milliseconds, or is greater than MaxValue milliseconds.
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.
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
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 state.