ThreadLocal<T> Class

Definition

Namespace:

System.Threading

Assembly:

System.Threading.dll

Source:

ThreadLocal.cs

Provides thread-local storage of data.

generic <typename T>
public ref class ThreadLocal : IDisposable

public class ThreadLocal<T> : IDisposable

type ThreadLocal<'T> = class
    interface IDisposable

Public Class ThreadLocal(Of T)
Implements IDisposable

Type Parameters

T

Specifies the type of data stored per-thread.

Inheritance

Object

ThreadLocal<T>

Implements

IDisposable

Examples

The following example shows how to use ThreadLocal<T>:

using System;
using System.Threading;
using System.Threading.Tasks;

class ThreadLocalDemo
{
    
        // Demonstrates:
        //      ThreadLocal(T) constructor
        //      ThreadLocal(T).Value
        //      One usage of ThreadLocal(T)
        static void Main()
        {
            // Thread-Local variable that yields a name for a thread
            ThreadLocal<string> ThreadName = new ThreadLocal<string>(() =>
            {
                return "Thread" + Thread.CurrentThread.ManagedThreadId;
            });

            // Action that prints out ThreadName for the current thread
            Action action = () =>
            {
                // If ThreadName.IsValueCreated is true, it means that we are not the
                // first action to run on this thread.
                bool repeat = ThreadName.IsValueCreated;

                Console.WriteLine("ThreadName = {0} {1}", ThreadName.Value, repeat ? "(repeat)" : "");
            };

            // Launch eight of them.  On 4 cores or less, you should see some repeat ThreadNames
            Parallel.Invoke(action, action, action, action, action, action, action, action);

            // Dispose when you are done
            ThreadName.Dispose();
        }
}
// This multithreading example can produce different outputs for each 'action' invocation and will vary with each run.
// Therefore, the example output will resemble but may not exactly match the following output (from a 4 core processor):
// ThreadName = Thread5 
// ThreadName = Thread6 
// ThreadName = Thread4 
// ThreadName = Thread6 (repeat)
// ThreadName = Thread1 
// ThreadName = Thread4 (repeat)
// ThreadName = Thread7 
// ThreadName = Thread5 (repeat)

Imports System.Threading
Imports System.Threading.Tasks

Module ThreadLocalDemo

    ' Demonstrates:
    ' ThreadLocal(T) constructor
    ' ThreadLocal(T).Value
    ' One usage of ThreadLocal(T)
    Sub Main()
        ' Thread-Local variable that yields a name for a thread
        Dim ThreadName As New ThreadLocal(Of String)(
            Function()
                Return "Thread" & Thread.CurrentThread.ManagedThreadId
            End Function)

        ' Action that prints out ThreadName for the current thread
        Dim action As Action =
            Sub()
                ' If ThreadName.IsValueCreated is true, it means that we are not the
                ' first action to run on this thread.
                Dim repeat As Boolean = ThreadName.IsValueCreated

                Console.WriteLine("ThreadName = {0} {1}", ThreadName.Value, If(repeat, "(repeat)", ""))
            End Sub

        ' Launch eight of them. On 4 cores or less, you should see some repeat ThreadNames
        Parallel.Invoke(action, action, action, action, action, action, action, action)

        ' Dispose when you are done
        ThreadName.Dispose()
    End Sub
End Module
' This multithreading example can produce different outputs for each 'action' invocation and will vary with each run.
' Therefore, the example output will resemble but may not exactly match the following output (from a 4 core processor):
' ThreadName = Thread5 
' ThreadName = Thread6 
' ThreadName = Thread4 
' ThreadName = Thread6 (repeat)
' ThreadName = Thread1 
' ThreadName = Thread4 (repeat)
' ThreadName = Thread7 
' ThreadName = Thread5 (repeat)

Constructors

ThreadLocal<T>()	Initializes the ThreadLocal<T> instance.
ThreadLocal<T>(Boolean)	Initializes the ThreadLocal<T> instance and specifies whether all values are accessible from any thread.
ThreadLocal<T>(Func<T>)	Initializes the ThreadLocal<T> instance with the specified valueFactory function.
ThreadLocal<T>(Func<T>, Boolean)	Initializes the ThreadLocal<T> instance with the specified valueFactory function and a flag that indicates whether all values are accessible from any thread.

Properties

IsValueCreated	Gets whether Value is initialized on the current thread.
Value	Gets or sets the value of this instance for the current thread.
Values	Gets a list containing the values stored by all threads that have accessed this instance.

Methods

Dispose()	Releases all resources used by the current instance of the ThreadLocal<T> class.
Dispose(Boolean)	Releases the resources used by this ThreadLocal<T> instance.
Equals(Object)	Determines whether the specified object is equal to the current object. (Inherited from Object)
Finalize()	Releases the resources used by this ThreadLocal<T> instance.
GetHashCode()	Serves as the default hash function. (Inherited from Object)
GetType()	Gets the Type of the current instance. (Inherited from Object)
MemberwiseClone()	Creates a shallow copy of the current Object. (Inherited from Object)
ToString()	Creates and returns a string representation of this instance for the current thread.

Thread Safety

With the exception of Dispose(), all public and protected members of ThreadLocal<T> are thread-safe and may be used concurrently from multiple threads. The value returned for the Value and IsValueCreated properties is specific for the thread on which the property is accessed.

See also

• Lazy<T>
• AsyncLocal<T>
• Lazy Initialization
• How to: Perform Lazy Initialization of Objects