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ThreadLocal<T> Class

Provides thread-local storage of data.


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

[HostProtectionAttribute(SecurityAction.LinkDemand, Synchronization = true, 
	ExternalThreading = true)]
public class ThreadLocal<T> : IDisposable

Type Parameters


Specifies the type of data stored per-thread.

The ThreadLocal<T> type exposes the following members.

Public methodThreadLocal<T>()Initializes the ThreadLocal<T> instance.
Public methodThreadLocal<T>(Func<T>)Initializes the ThreadLocal<T> instance with the specified valueFactory function.

Public propertyIsValueCreatedGets whether Value is initialized on the current thread.
Public propertyValueGets or sets the value of this instance for the current thread.

Public methodDispose()Releases all resources used by the current instance of the ThreadLocal<T> class.
Protected methodDispose(Boolean)Releases the resources used by this ThreadLocal<T> instance.
Public methodEquals(Object)Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected methodFinalizeReleases the resources used by this ThreadLocal<T> instance. (Overrides Object.Finalize().)
Public methodGetHashCodeServes as a hash function for a particular type. (Inherited from Object.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodToStringCreates and returns a string representation of this instance for the current thread. (Overrides Object.ToString().)


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

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

.NET Framework

Supported in: 4

.NET Framework Client Profile

Supported in: 4

Windows 7, Windows Vista SP1 or later, Windows XP SP3, 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.

With the exception of Dispose, all public and protected members of ThreadLocal<T> 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.