Thread.IsBackground Property

 

Gets or sets a value indicating whether or not a thread is a background thread.

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

Public Property IsBackground As Boolean

Property Value

Type: System.Boolean

true if this thread is or is to become a background thread; otherwise, false.

Exception Condition
ThreadStateException

The thread is dead.

A thread is either a background thread or a foreground thread. Background threads are identical to foreground threads, except that background threads do not prevent a process from terminating. Once all foreground threads belonging to a process have terminated, the common language runtime ends the process. Any remaining background threads are stopped and do not complete.

By default, the following threads execute in the foreground (that is, their IsBackground property returns false):

  • The primary thread (or main application thread).

  • All threads created by calling a Thread class constructor.

By default, the following threads execute in the background (that is, their IsBackground property returns true):

  • Thread pool threads, which are a pool of worker threads maintained by the runtime. You can configure the thread pool and schedule work on thread pool threads by using the ThreadPool class.

    System_CAPS_noteNote

    Task-based asynchronous operations automatically execute on thread pool threads.

  • All threads that enter the managed execution environment from unmanaged code.

The following example contrasts the behavior of foreground and background threads. It creates a foreground thread and a background thread. The foreground thread keeps the process running until completes its for loop and terminates. However, as the output from the example shows, because the foreground thread has finished execution, the process is terminated before the background thread has completed execution.

Imports System.Threading

Public Module Example
    Public Sub Main()
        Dim shortTest As New BackgroundTest(10)
        Dim foregroundThread As New Thread(AddressOf shortTest.RunLoop)

        Dim longTest As New BackgroundTest(50)
        Dim backgroundThread As New Thread(AddressOf longTest.RunLoop)
        backgroundThread.IsBackground = True

        foregroundThread.Start()
        backgroundThread.Start()
    End Sub
End Module

Public Class BackgroundTest
    Dim maxIterations As Integer 

    Sub New(maximumIterations As Integer)
        maxIterations = maximumIterations
    End Sub

    Sub RunLoop()
        For i As Integer = 0 To maxIterations
            Console.WriteLine("{0} count: {1}", _
                    If(Thread.CurrentThread.IsBackground, 
                       "Background Thread", "Foreground Thread"), i)
            Thread.Sleep(250)
        Next 

        Console.WriteLine("{0} finished counting.", 
                          If(Thread.CurrentThread.IsBackground, 
                          "Background Thread", "Foreground Thread"))
    End Sub
End Class
' The example displays output like the following:
'    Foreground Thread count: 0
'    Background Thread count: 0
'    Background Thread count: 1
'    Foreground Thread count: 1
'    Foreground Thread count: 2
'    Background Thread count: 2
'    Foreground Thread count: 3
'    Background Thread count: 3
'    Background Thread count: 4
'    Foreground Thread count: 4
'    Foreground Thread count: 5
'    Background Thread count: 5
'    Foreground Thread count: 6
'    Background Thread count: 6
'    Background Thread count: 7
'    Foreground Thread count: 7
'    Background Thread count: 8
'    Foreground Thread count: 8
'    Foreground Thread count: 9
'    Background Thread count: 9
'    Background Thread count: 10
'    Foreground Thread count: 10
'    Background Thread count: 11
'    Foreground Thread finished counting.

.NET Framework
Available since 1.1
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
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