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EventResetMode Enumeration

Indicates whether an EventWaitHandle is reset automatically or manually after receiving a signal.

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

[ComVisibleAttribute(false)]
public enum EventResetMode

Member nameDescription
Supported by the .NET Compact FrameworkSupported by the XNA FrameworkAutoResetWhen signaled, the EventWaitHandle resets automatically after releasing a single thread. If no threads are waiting, the EventWaitHandle remains signaled until a thread blocks, and resets after releasing the thread.
Supported by the .NET Compact FrameworkSupported by the XNA FrameworkManualResetWhen signaled, the EventWaitHandle releases all waiting threads and remains signaled until it is manually reset.

The following code example uses the SignalAndWait(WaitHandle, WaitHandle) method overload to allow the main thread to signal a blocked thread and then wait until the thread finishes a task.

The example starts five threads and allows them to block on an EventWaitHandle created with the EventResetMode.AutoReset flag, then releases one thread each time the user presses the ENTER key. The example then queues another five threads and releases them all using an EventWaitHandle created with the EventResetMode.ManualReset flag.

using System;
using System.Threading;

public class Example
{
    // The EventWaitHandle used to demonstrate the difference 
    // between AutoReset and ManualReset synchronization events. 
    // 
    private static EventWaitHandle ewh;

    // A counter to make sure all threads are started and 
    // blocked before any are released. A Long is used to show 
    // the use of the 64-bit Interlocked methods. 
    // 
    private static long threadCount = 0;

    // An AutoReset event that allows the main thread to block 
    // until an exiting thread has decremented the count. 
    // 
    private static EventWaitHandle clearCount = 
        new EventWaitHandle(false, EventResetMode.AutoReset);

    [MTAThread]
    public static void Main()
    {
        // Create an AutoReset EventWaitHandle. 
        //
        ewh = new EventWaitHandle(false, EventResetMode.AutoReset);

        // Create and start five numbered threads. Use the 
        // ParameterizedThreadStart delegate, so the thread 
        // number can be passed as an argument to the Start  
        // method. 
        for (int i = 0; i <= 4; i++)
        {
            Thread t = new Thread(
                new ParameterizedThreadStart(ThreadProc)
            );
            t.Start(i);
        }

        // Wait until all the threads have started and blocked. 
        // When multiple threads use a 64-bit value on a 32-bit 
        // system, you must access the value through the 
        // Interlocked class to guarantee thread safety. 
        // 
        while (Interlocked.Read(ref threadCount) < 5)
        {
            Thread.Sleep(500);
        }

        // Release one thread each time the user presses ENTER, 
        // until all threads have been released. 
        // 
        while (Interlocked.Read(ref threadCount) > 0)
        {
            Console.WriteLine("Press ENTER to release a waiting thread.");
            Console.ReadLine();

            // SignalAndWait signals the EventWaitHandle, which 
            // releases exactly one thread before resetting,  
            // because it was created with AutoReset mode.  
            // SignalAndWait then blocks on clearCount, to  
            // allow the signaled thread to decrement the count 
            // before looping again. 
            //
            WaitHandle.SignalAndWait(ewh, clearCount);
        }
        Console.WriteLine();

        // Create a ManualReset EventWaitHandle. 
        //
        ewh = new EventWaitHandle(false, EventResetMode.ManualReset);

        // Create and start five more numbered threads. 
        // 
        for(int i=0; i<=4; i++)
        {
            Thread t = new Thread(
                new ParameterizedThreadStart(ThreadProc)
            );
            t.Start(i);
        }

        // Wait until all the threads have started and blocked. 
        // 
        while (Interlocked.Read(ref threadCount) < 5)
        {
            Thread.Sleep(500);
        }

        // Because the EventWaitHandle was created with 
        // ManualReset mode, signaling it releases all the 
        // waiting threads. 
        //
        Console.WriteLine("Press ENTER to release the waiting threads.");
        Console.ReadLine();
        ewh.Set();

    }

    public static void ThreadProc(object data)
    {
        int index = (int) data;

        Console.WriteLine("Thread {0} blocks.", data);
        // Increment the count of blocked threads.
        Interlocked.Increment(ref threadCount);

        // Wait on the EventWaitHandle.
        ewh.WaitOne();

        Console.WriteLine("Thread {0} exits.", data);
        // Decrement the count of blocked threads.
        Interlocked.Decrement(ref threadCount);

        // After signaling ewh, the main thread blocks on 
        // clearCount until the signaled thread has  
        // decremented the count. Signal it now. 
        //
        clearCount.Set();
    }
}

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

.NET Compact Framework

Supported in: 3.5

XNA Framework

Supported in: 3.0, 2.0, 1.0

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