This documentation is archived and is not being maintained.

AutoResetEvent Constructor

Initializes a new instance of the AutoResetEvent class with a Boolean value indicating whether to set the initial state to signaled.

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

public AutoResetEvent(
	bool initialState


Type: System.Boolean

true to set the initial state to signaled; false to set the initial state to non-signaled.

The following example uses an AutoResetEvent to synchronize the activities of two threads. The first thread, which is the application thread, executes Main. It writes values to the protected resource, which is a static (Shared in Visual Basic) field named number. The second thread executes the static ThreadProc method, which reads the values written by Main.

The ThreadProc method waits for the AutoResetEvent. When Main calls the Set method on the AutoResetEvent, the ThreadProc method reads one value. The AutoResetEvent immediately resets, so the ThreadProc method waits again.

The program logic guarantees that the ThreadProc method will never read the same value two times. It does not guarantee that the ThreadProc method will read every value written by Main. That guarantee would require a second AutoResetEvent lock.

After each write operation, Main yields by calling the Thread.Sleep method, to give the second thread a chance to execute. Otherwise, on a single-processor computer Main would write many values between any two read operations.

using System;
using System.Threading;

namespace AutoResetEvent_Examples
	class MyMainClass
		//Initially not signaled. 
      const int numIterations = 100;
      static AutoResetEvent myResetEvent = new AutoResetEvent(false);
      static int number;

      static void Main()
         //Create and start the reader thread.
         Thread myReaderThread = new Thread(new ThreadStart(MyReadThreadProc));
         myReaderThread.Name = "ReaderThread";

         for(int i = 1; i <= numIterations; i++)
            Console.WriteLine("Writer thread writing value: {0}", i);
            number = i;

            //Signal that a value has been written.

            //Give the Reader thread an opportunity to act.

         //Terminate the reader thread.

      static void MyReadThreadProc()
            //The value will not be read until the writer has written 
            // at least once since the last read.
            Console.WriteLine("{0} reading value: {1}", Thread.CurrentThread.Name, number);

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, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

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, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0