ParameterizedThreadStart Delegate

Updated: September 2010

Represents the method that executes on a Thread.

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

[ComVisibleAttribute(false)]
public delegate void ParameterizedThreadStart(
	Object obj
)

Parameters

obj
Type: System.Object

An object that contains data for the thread procedure.

When a managed thread is created, the method that executes on the thread is represented by a ThreadStart delegate or a ParameterizedThreadStart delegate that is passed to the Thread constructor. The thread does not begin executing until the Thread.Start method is called. The System.Threading.ThreadStart or System.Threading.ParameterizedThreadStart delegate is invoked on the thread, and execution begins at the first line of the method represented by the delegate. In the case of the System.Threading.ParameterizedThreadStart delegate, the object that is passed to the Start(Object) method is passed to the delegate.

NoteNote:

Visual Basic and C# users can omit the ThreadStart or ParameterizedThreadStart delegate constructor when creating a thread. In Visual Basic, use the AddressOf operator when passing your method to the Thread constructor; for example, Dim t As New Thread(AddressOf ThreadProc). In C#, simply specify the name of the thread procedure. The compiler selects the correct delegate constructor.

NoteNote:

When you create a ParameterizedThreadStart delegate for an instance method in C++, the first parameter of the constructor is the instance variable. For a static method, the first parameter of the constructor is zero. For a static method, the delegate constructor requires only one parameter: the address of the callback method, qualified by the class name.

The ParameterizedThreadStart delegate and the Thread.Start(Object) method overload make it easy to pass data to a thread procedure, but this technique is not type safe because any object can be passed to Thread.Start(Object). 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 code example shows the syntax for creating and using a ParameterizedThreadStart delegate with a static method and an instance method.

NoteNote:

The Visual Basic and C# compilers infer the ParameterizedThreadStart delegate from the signatures of the DoWork and DoMoreWork methods, and call the correct constructor. Thus, there is no explicit constructor call in the code.

using System;
using System.Threading;

public class Work
{
    public static void Main()
    {
        // To start a thread using a shared thread procedure, use 
        // the class name and method name when you create the  
        // ParameterizedThreadStart delegate. C# infers the  
        // appropriate delegate creation syntax: 
        //    new ParameterizedThreadStart(Work.DoWork) 
        //
        Thread newThread = new Thread(Work.DoWork);

        // Use the overload of the Start method that has a 
        // parameter of type Object. You can create an object that 
        // contains several pieces of data, or you can pass any  
        // reference type or value type. The following code passes 
        // the integer value 42. 
        //
        newThread.Start(42);

        // To start a thread using an instance method for the thread  
        // procedure, use the instance variable and method name when  
        // you create the ParameterizedThreadStart delegate. C# infers  
        // the appropriate delegate creation syntax: 
        //    new ParameterizedThreadStart(w.DoMoreWork) 
        //
        Work w = new Work();
        newThread = new Thread(w.DoMoreWork);

        // Pass an object containing data for the thread. 
        //
        newThread.Start("The answer.");
    }

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

    public void DoMoreWork(object data)
    {
        Console.WriteLine("Instance thread procedure. Data='{0}'",
            data);
    }
}

/* This code example produces the following output (the order 
   of the lines might vary):

Static thread procedure. Data='42'
Instance thread procedure. Data='The answer'
*/

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0

Date

History

Reason

September 2010

Clarified that the example uses ParameterizedThreadStart.

Customer feedback.

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