AutoResetEvent Classe

Definizione

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

public ref class AutoResetEvent sealed : System::Threading::WaitHandle

public sealed class AutoResetEvent : System.Threading.EventWaitHandle

public sealed class AutoResetEvent : System.Threading.WaitHandle

[System.Runtime.InteropServices.ComVisible(true)]
public sealed class AutoResetEvent : System.Threading.EventWaitHandle

type AutoResetEvent = class
    inherit EventWaitHandle

type AutoResetEvent = class
    inherit WaitHandle

[<System.Runtime.InteropServices.ComVisible(true)>]
type AutoResetEvent = class
    inherit EventWaitHandle

Public NotInheritable Class AutoResetEvent
Inherits EventWaitHandle

Public NotInheritable Class AutoResetEvent
Inherits WaitHandle

Ereditarietà

Object

WaitHandle

EventWaitHandle

AutoResetEvent

Ereditarietà

Object

MarshalByRefObject

WaitHandle

EventWaitHandle

AutoResetEvent

Ereditarietà

Object

MarshalByRefObject

WaitHandle

AutoResetEvent

Attributi

ComVisibleAttribute

Esempio

Nell'esempio seguente viene illustrato come usare AutoResetEvent per rilasciare un thread alla volta chiamando il metodo Set (nella classe base) ogni volta che l'utente preme il tasto Invio. L'esempio avvia tre thread, che attendono un AutoResetEvent creato nello stato segnalato. Il primo thread viene rilasciato immediatamente, perché il AutoResetEvent è già nello stato segnalato. In questo modo il AutoResetEvent viene reimpostato sullo stato non segnalato, in modo che i thread successivi si blocchino. I thread bloccati non vengono rilasciati finché l'utente non li rilascia uno alla volta premendo il tasto Invio.

Dopo il rilascio dei thread dal primo AutoResetEvent, attende un altro AutoResetEvent creato nello stato non segnalato. Tutti e tre i thread bloccano, quindi il metodo Set deve essere chiamato tre volte per rilasciarli tutti.

using namespace System;
using namespace System::Threading;

ref class Example
{
private:
    static AutoResetEvent^ event_1 = gcnew AutoResetEvent(true);
    static AutoResetEvent^ event_2 = gcnew AutoResetEvent(false);

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

        Console::WriteLine("{0} waits on AutoResetEvent #1.", name);
        event_1->WaitOne();
        Console::WriteLine("{0} is released from AutoResetEvent #1.", name);

        Console::WriteLine("{0} waits on AutoResetEvent #2.", name);
        event_2->WaitOne();
        Console::WriteLine("{0} is released from AutoResetEvent #2.", name);

        Console::WriteLine("{0} ends.", name);
    }

public:
    static void Demo()
    {
        Console::WriteLine("Press Enter to create three threads and start them.\r\n" +
                           "The threads wait on AutoResetEvent #1, which was created\r\n" +
                           "in the signaled state, so the first thread is released.\r\n" +
                           "This puts AutoResetEvent #1 into the unsignaled state.");
        Console::ReadLine();
            
        for (int i = 1; i < 4; i++)
        {
            Thread^ t = gcnew Thread(gcnew ThreadStart(&ThreadProc));
            t->Name = "Thread_" + i;
            t->Start();
        }
        Thread::Sleep(250);

        for (int i = 0; i < 2; i++)
        {
            Console::WriteLine("Press Enter to release another thread.");
            Console::ReadLine();
            event_1->Set();
            Thread::Sleep(250);
        }

        Console::WriteLine("\r\nAll threads are now waiting on AutoResetEvent #2.");
        for (int i = 0; i < 3; i++)
        {
            Console::WriteLine("Press Enter to release a thread.");
            Console::ReadLine();
            event_2->Set();
            Thread::Sleep(250);
        }

        // Visual Studio: Uncomment the following line.
        //Console::Readline();
    }
};

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

/* This example produces output similar to the following:

Press Enter to create three threads and start them.
The threads wait on AutoResetEvent #1, which was created
in the signaled state, so the first thread is released.
This puts AutoResetEvent #1 into the unsignaled state.

Thread_1 waits on AutoResetEvent #1.
Thread_1 is released from AutoResetEvent #1.
Thread_1 waits on AutoResetEvent #2.
Thread_3 waits on AutoResetEvent #1.
Thread_2 waits on AutoResetEvent #1.
Press Enter to release another thread.

Thread_3 is released from AutoResetEvent #1.
Thread_3 waits on AutoResetEvent #2.
Press Enter to release another thread.

Thread_2 is released from AutoResetEvent #1.
Thread_2 waits on AutoResetEvent #2.

All threads are now waiting on AutoResetEvent #2.
Press Enter to release a thread.

Thread_2 is released from AutoResetEvent #2.
Thread_2 ends.
Press Enter to release a thread.

Thread_1 is released from AutoResetEvent #2.
Thread_1 ends.
Press Enter to release a thread.

Thread_3 is released from AutoResetEvent #2.
Thread_3 ends.
 */

using System;
using System.Threading;

// Visual Studio: Replace the default class in a Console project with 
//                the following class.
class Example
{
    private static AutoResetEvent event_1 = new AutoResetEvent(true);
    private static AutoResetEvent event_2 = new AutoResetEvent(false);

    static void Main()
    {
        Console.WriteLine("Press Enter to create three threads and start them.\r\n" +
                          "The threads wait on AutoResetEvent #1, which was created\r\n" +
                          "in the signaled state, so the first thread is released.\r\n" +
                          "This puts AutoResetEvent #1 into the unsignaled state.");
        Console.ReadLine();
            
        for (int i = 1; i < 4; i++)
        {
            Thread t = new Thread(ThreadProc);
            t.Name = "Thread_" + i;
            t.Start();
        }
        Thread.Sleep(250);

        for (int i = 0; i < 2; i++)
        {
            Console.WriteLine("Press Enter to release another thread.");
            Console.ReadLine();
            event_1.Set();
            Thread.Sleep(250);
        }

        Console.WriteLine("\r\nAll threads are now waiting on AutoResetEvent #2.");
        for (int i = 0; i < 3; i++)
        {
            Console.WriteLine("Press Enter to release a thread.");
            Console.ReadLine();
            event_2.Set();
            Thread.Sleep(250);
        }

        // Visual Studio: Uncomment the following line.
        //Console.Readline();
    }

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

        Console.WriteLine("{0} waits on AutoResetEvent #1.", name);
        event_1.WaitOne();
        Console.WriteLine("{0} is released from AutoResetEvent #1.", name);

        Console.WriteLine("{0} waits on AutoResetEvent #2.", name);
        event_2.WaitOne();
        Console.WriteLine("{0} is released from AutoResetEvent #2.", name);

        Console.WriteLine("{0} ends.", name);
    }
}

/* This example produces output similar to the following:

Press Enter to create three threads and start them.
The threads wait on AutoResetEvent #1, which was created
in the signaled state, so the first thread is released.
This puts AutoResetEvent #1 into the unsignaled state.

Thread_1 waits on AutoResetEvent #1.
Thread_1 is released from AutoResetEvent #1.
Thread_1 waits on AutoResetEvent #2.
Thread_3 waits on AutoResetEvent #1.
Thread_2 waits on AutoResetEvent #1.
Press Enter to release another thread.

Thread_3 is released from AutoResetEvent #1.
Thread_3 waits on AutoResetEvent #2.
Press Enter to release another thread.

Thread_2 is released from AutoResetEvent #1.
Thread_2 waits on AutoResetEvent #2.

All threads are now waiting on AutoResetEvent #2.
Press Enter to release a thread.

Thread_2 is released from AutoResetEvent #2.
Thread_2 ends.
Press Enter to release a thread.

Thread_1 is released from AutoResetEvent #2.
Thread_1 ends.
Press Enter to release a thread.

Thread_3 is released from AutoResetEvent #2.
Thread_3 ends.
 */

Imports System.Threading

' Visual Studio: Replace the default class in a Console project with 
'                the following class.
Class Example

    Private Shared event_1 As New AutoResetEvent(True)
    Private Shared event_2 As New AutoResetEvent(False)

    <MTAThread()> _
    Shared Sub Main()
    
        Console.WriteLine("Press Enter to create three threads and start them." & vbCrLf & _
                          "The threads wait on AutoResetEvent #1, which was created" & vbCrLf & _
                          "in the signaled state, so the first thread is released." & vbCrLf & _
                          "This puts AutoResetEvent #1 into the unsignaled state.")
        Console.ReadLine()
            
        For i As Integer = 1 To 3
            Dim t As New Thread(AddressOf ThreadProc)
            t.Name = "Thread_" & i
            t.Start()
        Next
        Thread.Sleep(250)

        For i As Integer = 1 To 2
            Console.WriteLine("Press Enter to release another thread.")
            Console.ReadLine()

            event_1.Set()
            Thread.Sleep(250)
        Next

        Console.WriteLine(vbCrLf & "All threads are now waiting on AutoResetEvent #2.")
        For i As Integer = 1 To 3
            Console.WriteLine("Press Enter to release a thread.")
            Console.ReadLine()

            event_2.Set()
            Thread.Sleep(250)
        Next

        ' Visual Studio: Uncomment the following line.
        'Console.Readline()
    End Sub

    Shared Sub ThreadProc()
    
        Dim name As String = Thread.CurrentThread.Name

        Console.WriteLine("{0} waits on AutoResetEvent #1.", name)
        event_1.WaitOne()
        Console.WriteLine("{0} is released from AutoResetEvent #1.", name)

        Console.WriteLine("{0} waits on AutoResetEvent #2.", name)
        event_2.WaitOne()
        Console.WriteLine("{0} is released from AutoResetEvent #2.", name)

        Console.WriteLine("{0} ends.", name)
    End Sub
End Class

' This example produces output similar to the following:
'
'Press Enter to create three threads and start them.
'The threads wait on AutoResetEvent #1, which was created
'in the signaled state, so the first thread is released.
'This puts AutoResetEvent #1 into the unsignaled state.
'
'Thread_1 waits on AutoResetEvent #1.
'Thread_1 is released from AutoResetEvent #1.
'Thread_1 waits on AutoResetEvent #2.
'Thread_3 waits on AutoResetEvent #1.
'Thread_2 waits on AutoResetEvent #1.
'Press Enter to release another thread.
'
'Thread_3 is released from AutoResetEvent #1.
'Thread_3 waits on AutoResetEvent #2.
'Press Enter to release another thread.
'
'Thread_2 is released from AutoResetEvent #1.
'Thread_2 waits on AutoResetEvent #2.
'
'All threads are now waiting on AutoResetEvent #2.
'Press Enter to release a thread.
'
'Thread_2 is released from AutoResetEvent #2.
'Thread_2 ends.
'Press Enter to release a thread.
'
'Thread_1 is released from AutoResetEvent #2.
'Thread_1 ends.
'Press Enter to release a thread.
'
'Thread_3 is released from AutoResetEvent #2.
'Thread_3 ends.

Commenti

Si usano AutoResetEvent, ManualResetEvente EventWaitHandle per l'interazione tra thread (o segnalazione di thread). Per altre informazioni, vedere Interazione tra thread.

Un thread attende un segnale chiamando AutoResetEvent.WaitOne. Se il AutoResetEvent è nello stato non segnalato, il thread si blocca fino a quando non viene chiamato il AutoResetEvent.Set. La chiamata di Set segnala AutoResetEvent di rilasciare un thread in attesa. AutoResetEvent rimane segnalato fino a quando non viene chiamato Reset o viene rilasciato un singolo thread in attesa, in cui torna automaticamente allo stato non segnalato.

Se nessun thread è in attesa quando il AutoResetEvent entra in uno stato segnalato, lo stato rimane segnalato fino a quando un thread non osserva il segnale (chiamando WaitOne). Tale thread non si blocca: il AutoResetEvent rilascia immediatamente il thread e torna allo stato non segnalato.

È possibile controllare lo stato iniziale di un AutoResetEvent passando un valore booleano al costruttore: true se lo stato iniziale viene segnalato e false in caso contrario.

AutoResetEvent possono essere usati anche con i metodi staticWaitAll e WaitAny.

AutoResetEvent deriva dalla classe EventWaitHandle. Un AutoResetEvent equivale funzionalmente a un EventWaitHandle creato con EventResetMode.AutoReset.

Costruttori

Campi

Proprietà

Metodi

Implementazioni dell'interfaccia esplicita

Metodi di estensione

Si applica a

Thread safety

Questa classe è thread-safe.

Vedi anche

• WaitHandle
• di threading gestito
• Panoramica delle primitive di sincronizzazione