Thread.Interrupt Method (System.Threading)

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.NET Framework Class Library
Thread.Interrupt Method

Interrupts a thread that is in the WaitSleepJoin thread state.

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

Visual Basic
<SecurityPermissionAttribute(SecurityAction.Demand, ControlThread := True)> _
Public Sub Interrupt
C#
[SecurityPermissionAttribute(SecurityAction.Demand, ControlThread = true)]
public void Interrupt()
Visual C++
[SecurityPermissionAttribute(SecurityAction::Demand, ControlThread = true)]
public:
void Interrupt()
F#
[<SecurityPermissionAttribute(SecurityAction.Demand, ControlThread = true)>]
member Interrupt : unit -> unit 

Exceptions

Exception Condition
SecurityException

The caller does not have the appropriate SecurityPermission.

Remarks

If this thread is not currently blocked in a wait, sleep, or join state, it will be interrupted when it next begins to block.

ThreadInterruptedException is thrown in the interrupted thread, but not until the thread blocks. If the thread never blocks, the exception is never thrown, and thus the thread might complete without ever being interrupted.

Examples

The following code example shows the behavior of a running thread when it is interrupted and subsequently gets blocked.

Visual Basic

Option Explicit
Option Strict

Imports System
Imports System.Security.Permissions
Imports System.Threading

Public Class ThreadInterrupt

    <MTAThread> _
    Shared Sub Main()
        Dim stayAwake As New StayAwake()
        Dim newThread As New Thread(AddressOf stayAwake.ThreadMethod)
        newThread.Start()

        ' The following line causes an exception to be thrown 
        ' in ThreadMethod if newThread is currently blocked
        ' or becomes blocked in the future.
        newThread.Interrupt()
        Console.WriteLine("Main thread calls Interrupt on newThread.")

        ' Tell newThread to go to sleep.
        stayAwake.SleepSwitch = True

        ' Wait for newThread to end.
        newThread.Join()
    End Sub

End Class

Public Class StayAwake

    Dim sleepSwitchValue As Boolean = False

    WriteOnly Property SleepSwitch As Boolean
        Set
            sleepSwitchValue = Value
        End Set
    End Property 

    Sub New()
    End Sub

    Sub ThreadMethod()
        Console.WriteLine("newThread is executing ThreadMethod.")
        While Not sleepSwitchValue

            ' Use SpinWait instead of Sleep to demonstrate the 
            ' effect of calling Interrupt on a running thread.
            Thread.SpinWait(10000000)
        End While
        Try
            Console.WriteLine("newThread going to sleep.")

            ' When newThread goes to sleep, it is immediately 
            ' woken up by a ThreadInterruptedException.
            Thread.Sleep(Timeout.Infinite)
        Catch ex As ThreadInterruptedException
            Console.WriteLine("newThread cannot go to " & _
                "sleep - interrupted by main thread.")
        End Try
    End Sub

End Class


C#

using System;
using System.Security.Permissions;
using System.Threading;

class ThreadInterrupt
{
    static void Main()
    {
        StayAwake stayAwake = new StayAwake();
        Thread newThread = 
            new Thread(new ThreadStart(stayAwake.ThreadMethod));
        newThread.Start();

        // The following line causes an exception to be thrown 
        // in ThreadMethod if newThread is currently blocked
        // or becomes blocked in the future.
        newThread.Interrupt();
        Console.WriteLine("Main thread calls Interrupt on newThread.");

        // Tell newThread to go to sleep.
        stayAwake.SleepSwitch = true;

        // Wait for newThread to end.
        newThread.Join();
    }
}

class StayAwake
{
    bool sleepSwitch = false;

    public bool SleepSwitch
    {
        set{ sleepSwitch = value; }
    }

    public StayAwake(){}

    public void ThreadMethod()
    {
        Console.WriteLine("newThread is executing ThreadMethod.");
        while(!sleepSwitch)
        {
            // Use SpinWait instead of Sleep to demonstrate the 
            // effect of calling Interrupt on a running thread.
            Thread.SpinWait(10000000);
        }
        try
        {
            Console.WriteLine("newThread going to sleep.");

            // When newThread goes to sleep, it is immediately 
            // woken up by a ThreadInterruptedException.
            Thread.Sleep(Timeout.Infinite);
        }
        catch(ThreadInterruptedException e)
        {
            Console.WriteLine("newThread cannot go to sleep - " +
                "interrupted by main thread.");
        }
    }
}


Visual C++

using namespace System;
using namespace System::Security::Permissions;
using namespace System::Threading;

ref class StayAwake
{
private:
   bool sleepSwitch;

public:

   property bool SleepSwitch 
   {
      void set( bool value )
      {
         sleepSwitch = value;
      }

   }
   StayAwake()
   {
      sleepSwitch = false;
   }

   void ThreadMethod()
   {
      Console::WriteLine( "newThread is executing ThreadMethod." );
      while (  !sleepSwitch )
      {

         // Use SpinWait instead of Sleep to demonstrate the 
         // effect of calling Interrupt on a running thread.
         Thread::SpinWait( 10000000 );
      }

      try
      {
         Console::WriteLine( "newThread going to sleep." );

         // When newThread goes to sleep, it is immediately 
         // woken up by a ThreadInterruptedException.
         Thread::Sleep( Timeout::Infinite );
      }
      catch ( ThreadInterruptedException^ /*e*/ ) 
      {
         Console::WriteLine( "newThread cannot go to sleep - "
         "interrupted by main thread." );
      }

   }

};

int main()
{
   StayAwake^ stayAwake = gcnew StayAwake;
   Thread^ newThread = gcnew Thread( gcnew ThreadStart( stayAwake, &StayAwake::ThreadMethod ) );
   newThread->Start();

   // The following line causes an exception to be thrown 
   // in ThreadMethod if newThread is currently blocked
   // or becomes blocked in the future.
   newThread->Interrupt();
   Console::WriteLine( "Main thread calls Interrupt on newThread." );

   // Then tell newThread to go to sleep.
   stayAwake->SleepSwitch = true;

   // Wait for newThread to end.
   newThread->Join();
}



Version Information

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1
.NET Framework Security

Platforms

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
See Also

Reference

Other Resources

Community Content

Jim Fr
incorrect documentation if blocked in catch or finally
Interrupt() will not interrupt a Sleep if the Sleep statement is inside a catch or finally block.  The same may be true for other blocking calls in addition to Sleep, but I didn't test that.  Can you please update this page to document this behavior.

Lander Verhack
Incorrect example

The code in the example is incorrect: The property 'SleepSwitch' in the class 'StayAwake' doesn't contain a setter. Therefore the code will not compile. The solution is to add a getter, so the property will become this:

    
      public
      bool SleepSwitch
    { 
get { return sleepSwitch; } set{ sleepSwitch = value; } }
Or you could use an automatic property, like this:
    
      public
      bool SleepSwitch
    { 
get; set; }
Example has been changed to meet this comment

Lander Verhack
Watch out for Console.WriteLine
In this example the interrupt raises the error, not when the thread is sleeping, but in the in the first statement of the Threadmethod:
    Console.WriteLine("newThread is executing ThreadMethod.");

Console.WriteLine will block the thread until the output is written, therefore the ThreadInterruptedException is thrown before newThread has entered the try block and causing an unhandled exception.