ManualResetEvent Class

Definition

Namespace:

System.Threading

Assembly:

System.Threading.dll

Source:

ManualResetEvent.cs

Represents a thread synchronization event that, when signaled, must be reset manually. This class cannot be inherited.

public ref class ManualResetEvent sealed : System::Threading::EventWaitHandle

public sealed class ManualResetEvent : System.Threading.EventWaitHandle

type ManualResetEvent = class
    inherit EventWaitHandle

Public NotInheritable Class ManualResetEvent
Inherits EventWaitHandle

Inheritance

Object

MarshalByRefObject

WaitHandle

EventWaitHandle

ManualResetEvent

Examples

The following example demonstrates how ManualResetEvent works. The example starts with a ManualResetEvent in the unsignaled state (that is, false is passed to the constructor). The example creates three threads, each of which blocks on the ManualResetEvent by calling its WaitOne method. When the user presses the Enter key, the example calls the Set method, which releases all three threads. Contrast this with the behavior of the AutoResetEvent class, which releases threads one at a time, resetting automatically after each release.

Pressing the Enter key again demonstrates that the ManualResetEvent remains in the signaled state until its Reset method is called: The example starts two more threads. These threads do not block when they call the WaitOne method, but instead run to completion.

Pressing the Enter key again causes the example to call the Reset method and to start one more thread, which blocks when it calls WaitOne. Pressing the Enter key one final time calls Set to release the last thread, and the program ends.

using namespace System;
using namespace System::Threading;

ref class Example
{
private:
    // mre is used to block and release threads manually. It is
    // created in the unsignaled state.
    static ManualResetEvent^ mre = gcnew ManualResetEvent(false);

    static void ThreadProc()
    {
        String^ name = Thread::CurrentThread->Name;

        Console::WriteLine(name + " starts and calls mre->WaitOne()");

        mre->WaitOne();

        Console::WriteLine(name + " ends.");
    }

public:
    static void Demo()
    {
        Console::WriteLine("\nStart 3 named threads that block on a ManualResetEvent:\n");

        for(int i = 0; i <=2 ; i++)
        {
            Thread^ t = gcnew Thread(gcnew ThreadStart(ThreadProc));
            t->Name = "Thread_" + i;
            t->Start();
        }

        Thread::Sleep(500);
        Console::WriteLine("\nWhen all three threads have started, press Enter to call Set()" +
                           "\nto release all the threads.\n");
        Console::ReadLine();

        mre->Set();

        Thread::Sleep(500);
        Console::WriteLine("\nWhen a ManualResetEvent is signaled, threads that call WaitOne()" +
                           "\ndo not block. Press Enter to show this.\n");
        Console::ReadLine();

        for(int i = 3; i <= 4; i++)
        {
            Thread^ t = gcnew Thread(gcnew ThreadStart(ThreadProc));
            t->Name = "Thread_" + i;
            t->Start();
        }

        Thread::Sleep(500);
        Console::WriteLine("\nPress Enter to call Reset(), so that threads once again block" +
                           "\nwhen they call WaitOne().\n");
        Console::ReadLine();

        mre->Reset();

        // Start a thread that waits on the ManualResetEvent.
        Thread^ t5 = gcnew Thread(gcnew ThreadStart(ThreadProc));
        t5->Name = "Thread_5";
        t5->Start();

        Thread::Sleep(500);
        Console::WriteLine("\nPress Enter to call Set() and conclude the demo.");
        Console::ReadLine();

        mre->Set();

        // If you run this example in Visual Studio, uncomment the following line:
        //Console::ReadLine();
    }
};

int main()
{
   Example::Demo();
}

/* This example produces output similar to the following:

Start 3 named threads that block on a ManualResetEvent:

Thread_0 starts and calls mre->WaitOne()
Thread_1 starts and calls mre->WaitOne()
Thread_2 starts and calls mre->WaitOne()

When all three threads have started, press Enter to call Set()
to release all the threads.


Thread_2 ends.
Thread_1 ends.
Thread_0 ends.

When a ManualResetEvent is signaled, threads that call WaitOne()
do not block. Press Enter to show this.


Thread_3 starts and calls mre->WaitOne()
Thread_3 ends.
Thread_4 starts and calls mre->WaitOne()
Thread_4 ends.

Press Enter to call Reset(), so that threads once again block
when they call WaitOne().


Thread_5 starts and calls mre->WaitOne()

Press Enter to call Set() and conclude the demo.

Thread_5 ends.
 */

using System;
using System.Threading;

public class Example
{
    // mre is used to block and release threads manually. It is
    // created in the unsignaled state.
    private static ManualResetEvent mre = new ManualResetEvent(false);

    static void Main()
    {
        Console.WriteLine("\nStart 3 named threads that block on a ManualResetEvent:\n");

        for(int i = 0; i <= 2; i++)
        {
            Thread t = new Thread(ThreadProc);
            t.Name = "Thread_" + i;
            t.Start();
        }

        Thread.Sleep(500);
        Console.WriteLine("\nWhen all three threads have started, press Enter to call Set()" +
                          "\nto release all the threads.\n");
        Console.ReadLine();

        mre.Set();

        Thread.Sleep(500);
        Console.WriteLine("\nWhen a ManualResetEvent is signaled, threads that call WaitOne()" +
                          "\ndo not block. Press Enter to show this.\n");
        Console.ReadLine();

        for(int i = 3; i <= 4; i++)
        {
            Thread t = new Thread(ThreadProc);
            t.Name = "Thread_" + i;
            t.Start();
        }

        Thread.Sleep(500);
        Console.WriteLine("\nPress Enter to call Reset(), so that threads once again block" +
                          "\nwhen they call WaitOne().\n");
        Console.ReadLine();

        mre.Reset();

        // Start a thread that waits on the ManualResetEvent.
        Thread t5 = new Thread(ThreadProc);
        t5.Name = "Thread_5";
        t5.Start();

        Thread.Sleep(500);
        Console.WriteLine("\nPress Enter to call Set() and conclude the demo.");
        Console.ReadLine();

        mre.Set();

        // If you run this example in Visual Studio, uncomment the following line:
        //Console.ReadLine();
    }

    private static void ThreadProc()
    {
        string name = Thread.CurrentThread.Name;

        Console.WriteLine(name + " starts and calls mre.WaitOne()");

        mre.WaitOne();

        Console.WriteLine(name + " ends.");
    }
}

/* This example produces output similar to the following:

Start 3 named threads that block on a ManualResetEvent:

Thread_0 starts and calls mre.WaitOne()
Thread_1 starts and calls mre.WaitOne()
Thread_2 starts and calls mre.WaitOne()

When all three threads have started, press Enter to call Set()
to release all the threads.


Thread_2 ends.
Thread_0 ends.
Thread_1 ends.

When a ManualResetEvent is signaled, threads that call WaitOne()
do not block. Press Enter to show this.


Thread_3 starts and calls mre.WaitOne()
Thread_3 ends.
Thread_4 starts and calls mre.WaitOne()
Thread_4 ends.

Press Enter to call Reset(), so that threads once again block
when they call WaitOne().


Thread_5 starts and calls mre.WaitOne()

Press Enter to call Set() and conclude the demo.

Thread_5 ends.
 */

Imports System.Threading

Public Class Example

    ' mre is used to block and release threads manually. It is
    ' created in the unsignaled state.
    Private Shared mre As New ManualResetEvent(False)

    <MTAThreadAttribute> _
    Shared Sub Main()

        Console.WriteLine(vbLf & _
            "Start 3 named threads that block on a ManualResetEvent:" & vbLf)

        For i As Integer = 0 To 2
            Dim t As New Thread(AddressOf ThreadProc)
            t.Name = "Thread_" & i
            t.Start()
        Next i

        Thread.Sleep(500)
        Console.WriteLine(vbLf & _
            "When all three threads have started, press Enter to call Set()" & vbLf & _
            "to release all the threads." & vbLf)
        Console.ReadLine()

        mre.Set()

        Thread.Sleep(500)
        Console.WriteLine(vbLf & _
            "When a ManualResetEvent is signaled, threads that call WaitOne()" & vbLf & _
            "do not block. Press Enter to show this." & vbLf)
        Console.ReadLine()

        For i As Integer = 3 To 4
            Dim t As New Thread(AddressOf ThreadProc)
            t.Name = "Thread_" & i
            t.Start()
        Next i

        Thread.Sleep(500)
        Console.WriteLine(vbLf & _
            "Press Enter to call Reset(), so that threads once again block" & vbLf & _
            "when they call WaitOne()." & vbLf)
        Console.ReadLine()

        mre.Reset()

        ' Start a thread that waits on the ManualResetEvent.
        Dim t5 As New Thread(AddressOf ThreadProc)
        t5.Name = "Thread_5"
        t5.Start()

        Thread.Sleep(500)
        Console.WriteLine(vbLf & "Press Enter to call Set() and conclude the demo.")
        Console.ReadLine()

        mre.Set()

        ' If you run this example in Visual Studio, uncomment the following line:
        'Console.ReadLine()

    End Sub


    Private Shared Sub ThreadProc()

        Dim name As String = Thread.CurrentThread.Name

        Console.WriteLine(name & " starts and calls mre.WaitOne()")

        mre.WaitOne()

        Console.WriteLine(name & " ends.")

    End Sub

End Class

' This example produces output similar to the following:
'
'Start 3 named threads that block on a ManualResetEvent:
'
'Thread_0 starts and calls mre.WaitOne()
'Thread_1 starts and calls mre.WaitOne()
'Thread_2 starts and calls mre.WaitOne()
'
'When all three threads have started, press Enter to call Set()
'to release all the threads.
'
'
'Thread_2 ends.
'Thread_0 ends.
'Thread_1 ends.
'
'When a ManualResetEvent is signaled, threads that call WaitOne()
'do not block. Press Enter to show this.
'
'
'Thread_3 starts and calls mre.WaitOne()
'Thread_3 ends.
'Thread_4 starts and calls mre.WaitOne()
'Thread_4 ends.
'
'Press Enter to call Reset(), so that threads once again block
'when they call WaitOne().
'
'
'Thread_5 starts and calls mre.WaitOne()
'
'Press Enter to call Set() and conclude the demo.
'
'Thread_5 ends.

Remarks

You use ManualResetEvent, AutoResetEvent, and EventWaitHandle for thread interaction (or thread signaling). For more information, see the Thread interaction, or signaling section of the Overview of synchronization primitives article.

When a thread begins an activity that must complete before other threads proceed, it calls ManualResetEvent.Reset to put ManualResetEvent in the non-signaled state. This thread can be thought of as controlling the ManualResetEvent. Threads that call ManualResetEvent.WaitOne block, awaiting the signal. When the controlling thread completes the activity, it calls ManualResetEvent.Set to signal that the waiting threads can proceed. All waiting threads are released.

Once it has been signaled, ManualResetEvent remains signaled until it is manually reset by calling the Reset() method. That is, calls to WaitOne return immediately.

You can control the initial state of a ManualResetEvent by passing a Boolean value to the constructor: true if the initial state is signaled, and false otherwise.

ManualResetEvent can also be used with the static WaitAll and WaitAny methods.

Beginning with the .NET Framework version 2.0, ManualResetEvent derives from the EventWaitHandle class. A ManualResetEvent is functionally equivalent to an EventWaitHandle created with EventResetMode.ManualReset.

Note

Unlike the ManualResetEvent class, the EventWaitHandle class provides access to named system synchronization events.

Beginning with the .NET Framework version 4.0, the System.Threading.ManualResetEventSlim class is a lightweight alternative to ManualResetEvent.

Constructors

ManualResetEvent(Boolean)

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

Fields

WaitTimeout

Indicates that a WaitAny(WaitHandle[], Int32, Boolean) operation timed out before any of the wait handles were signaled. This field is constant. (Inherited from WaitHandle)

Properties

Handle	Obsolete. Gets or sets the native operating system handle. (Inherited from WaitHandle)
SafeWaitHandle	Gets or sets the native operating system handle. (Inherited from WaitHandle)

Methods

Close()	Releases all resources held by the current WaitHandle. (Inherited from WaitHandle)
CreateObjRef(Type)	Creates an object that contains all the relevant information required to generate a proxy used to communicate with a remote object. (Inherited from MarshalByRefObject)
Dispose()	Releases all resources used by the current instance of the WaitHandle class. (Inherited from WaitHandle)
Dispose(Boolean)	When overridden in a derived class, releases the unmanaged resources used by the WaitHandle, and optionally releases the managed resources. (Inherited from WaitHandle)
Equals(Object)	Determines whether the specified object is equal to the current object. (Inherited from Object)
GetAccessControl()	Gets an EventWaitHandleSecurity object that represents the access control security for the named system event represented by the current EventWaitHandle object. (Inherited from EventWaitHandle)
GetHashCode()	Serves as the default hash function. (Inherited from Object)
GetLifetimeService()	Obsolete. Retrieves the current lifetime service object that controls the lifetime policy for this instance. (Inherited from MarshalByRefObject)
GetType()	Gets the Type of the current instance. (Inherited from Object)
InitializeLifetimeService()	Obsolete. Obtains a lifetime service object to control the lifetime policy for this instance. (Inherited from MarshalByRefObject)
MemberwiseClone()	Creates a shallow copy of the current Object. (Inherited from Object)
MemberwiseClone(Boolean)	Creates a shallow copy of the current MarshalByRefObject object. (Inherited from MarshalByRefObject)
Reset()	Sets the state of the event to nonsignaled, causing threads to block. (Inherited from EventWaitHandle)
Set()	Sets the state of the event to signaled, allowing one or more waiting threads to proceed. (Inherited from EventWaitHandle)
SetAccessControl(EventWaitHandleSecurity)	Sets the access control security for a named system event. (Inherited from EventWaitHandle)
ToString()	Returns a string that represents the current object. (Inherited from Object)
WaitOne()	Blocks the current thread until the current WaitHandle receives a signal. (Inherited from WaitHandle)
WaitOne(Int32, Boolean)	Blocks the current thread until the current WaitHandle receives a signal, using a 32-bit signed integer to specify the time interval and specifying whether to exit the synchronization domain before the wait. (Inherited from WaitHandle)
WaitOne(Int32)	Blocks the current thread until the current WaitHandle receives a signal, using a 32-bit signed integer to specify the time interval in milliseconds. (Inherited from WaitHandle)
WaitOne(TimeSpan, Boolean)	Blocks the current thread until the current instance receives a signal, using a TimeSpan to specify the time interval and specifying whether to exit the synchronization domain before the wait. (Inherited from WaitHandle)
WaitOne(TimeSpan)	Blocks the current thread until the current instance receives a signal, using a TimeSpan to specify the time interval. (Inherited from WaitHandle)

Extension Methods

GetSafeWaitHandle(WaitHandle)	Gets the safe handle for a native operating system wait handle.
SetSafeWaitHandle(WaitHandle, SafeWaitHandle)	Sets a safe handle for a native operating system wait handle.

Thread Safety

This class is thread safe.

See also

• WaitHandle
• Managed Threading
• Overview of synchronization primitives