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Thread.SetData Method

Sets the data in the specified slot on the currently running thread, for that thread's current domain. For better performance, use fields marked with the ThreadStaticAttribute attribute instead.

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

<HostProtectionAttribute(SecurityAction.LinkDemand, SharedState := True, ExternalThreading := True)> _
Public Shared Sub SetData ( _
	slot As LocalDataStoreSlot, _
	data As Object _


Type: System.LocalDataStoreSlot
The LocalDataStoreSlot in which to set the value.
Type: System.Object
The value to be set.

Important noteImportant

The .NET Framework provides two mechanisms for using thread local storage (TLS): thread-relative static fields (that is, fields that are marked with the ThreadStaticAttribute attribute) and data slots. Thread-relative static fields provide much better performance than data slots, and enable compile-time type checking. For more information about using TLS, see Thread Local Storage: Thread-Relative Static Fields and Data Slots.

Threads use a local store memory mechanism to store thread-specific data. The common language runtime allocates a multi-slot data store array to each process when it is created. The thread can allocate a data slot in the data store, store and retrieve a data value in the slot, and free the slot for reuse after the thread procedure ends and the Thread object has been reclaimed by garbage collection. Data slots are unique per thread. No other thread (not even a child thread) can get that data.

[Visual Basic]


SetData is a Shared method that always applies to the currently executing thread, even if you call it using a variable that refers to another thread. To avoid confusion, use the class name when calling Shared methods: Thread.SetData(testSlot, "test data").


The HostProtectionAttribute attribute applied to this type or member has the following Resources property value: SharedState | 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.

This section contains two code examples. The first example shows how to use a field that is marked with the ThreadStaticAttribute attribute to hold thread-specific information. The second example shows how to use a data slot to do the same thing.

First Example

The following example shows how to use a field that is marked with ThreadStaticAttribute to hold thread-specific information. This technique provides better performance than the technique that is shown in the second example.

Imports System
Imports System.Threading

Class Test

    <MTAThread> _
    Shared Sub Main()

        For i As Integer = 1 To 3
            Dim newThread As New Thread(AddressOf ThreadData.ThreadStaticDemo)
        Next i

    End Sub

End Class

Class ThreadData

    <ThreadStaticAttribute> _
    Shared threadSpecificData As Integer

    Shared Sub ThreadStaticDemo()

        ' Store the managed thread id for each thread in the static
        ' variable.
        threadSpecificData = Thread.CurrentThread.ManagedThreadId

        ' Allow other threads time to execute the same code, to show
        ' that the static data is unique to each thread.
        Thread.Sleep( 1000 )

        ' Display the static data.
        Console.WriteLine( "Data for managed thread {0}: {1}", _
            Thread.CurrentThread.ManagedThreadId, threadSpecificData )

    End Sub

End Class

' This code example produces output similar to the following:
'Data for managed thread 4: 4
'Data for managed thread 5: 5
'Data for managed thread 3: 3

Second Example

The following example demonstrates how to use a named data slot to store thread-specific information.

Imports System
Imports System.Threading

Class Test
    Public Shared Sub Main()
        Dim newThreads(3) As Thread
        Dim i As Integer
        For i = 0 To newThreads.Length - 1
            newThreads(i) = _
                New Thread(New ThreadStart(AddressOf Slot.SlotTest))
        Next i
        For i = 0 To newThreads.Length - 1
            Console.WriteLine("Thread_{0} finished.", _
        Next i
    End Sub
End Class

Class Slot
    Private Shared randomGenerator As New Random()

    Public Shared Sub SlotTest()
        ' Set random data in each thread's data slot.
        Dim slotData As Integer = randomGenerator.Next(1, 200)
        Dim threadId As Integer = Thread.CurrentThread.ManagedThreadId


        ' Show what was saved in the thread's data slot.
        Console.WriteLine("Data stored in thread_{0}'s data slot: {1,3}",
            threadId, slotData)

        ' Allow other threads time to execute SetData to show
        ' that a thread's data slot is unique to itself.

        Dim newSlotData As Integer = _
            CType(Thread.GetData(Thread.GetNamedDataSlot("Random")), Integer)

        If newSlotData = slotData Then
            Console.WriteLine("Data in thread_{0}'s data slot is still: {1,3}",
                threadId, newSlotData)
            Console.WriteLine("Data in thread_{0}'s data slot changed to: {1,3}",
                threadId, newSlotData)
        End If
    End Sub
End Class

.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

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.