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
Assemblies:   System.Threading (in System.Threading.dll)
  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);

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

Was this page helpful?
(1500 characters remaining)
Thank you for your feedback
© 2014 Microsoft