Thread.Start Method (Object)


Causes the operating system to change the state of the current instance to ThreadState.Running, and optionally supplies an object containing data to be used by the method the thread executes.

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

[HostProtectionAttribute(SecurityAction.LinkDemand, Synchronization = true, 
	ExternalThreading = true)]
public void Start(
	object parameter


Type: System.Object

An object that contains data to be used by the method the thread executes.

Exception Condition

The thread has already been started.


There is not enough memory available to start this thread.


This thread was created using a ThreadStart delegate instead of a ParameterizedThreadStart delegate.

Once a thread is in the ThreadState.Running state, the operating system can schedule it for execution. The thread begins executing at the first line of the method represented by the ThreadStart or ParameterizedThreadStart delegate supplied to the thread constructor. Note that the call to Start does not block the calling thread.

Once the thread terminates, it cannot be restarted with another call to Start.

This overload and the ParameterizedThreadStart delegate make it easy to pass data to a thread procedure, but the technique is not type safe because any object can be passed to this overload. A more robust way to pass data to a thread procedure is to put both the thread procedure and the data fields into a worker object. For more information, see Creating Threads and Passing Data at Start Time.

The following example creates a ParameterizedThreadStart delegate with a static method and an instance method.

using System;
using System.Threading;

public class Work
    public static void Main()
        // Start a thread that calls a parameterized static method.
        Thread newThread = new Thread(Work.DoWork);

        // Start a thread that calls a parameterized instance method.
        Work w = new Work();
        newThread = new Thread(w.DoMoreWork);
        newThread.Start("The answer.");

    public static void DoWork(object data)
        Console.WriteLine("Static thread procedure. Data='{0}'",

    public void DoMoreWork(object data)
        Console.WriteLine("Instance thread procedure. Data='{0}'",
// This example displays output like the following:
//       Static thread procedure. Data='42'
//       Instance thread procedure. Data='The answer.'

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