EventWaitHandle.Set Metodo
Definizione
Importante
Alcune informazioni sono relative alla release non definitiva del prodotto, che potrebbe subire modifiche significative prima della release definitiva. Microsoft non riconosce alcuna garanzia, espressa o implicita, in merito alle informazioni qui fornite.
Imposta lo stato dell'evento su segnalato, per consentire a uno o più thread in attesa di procedere.
public:
bool Set();public bool Set ();member this.Set : unit -> boolPublic Function Set () As BooleanRestituisce
true se l'operazione ha esito positivo; in caso contrario, false.
Eccezioni
Il metodo Close() è già stato chiamato in precedenza su questo EventWaitHandle.
Esempio
Nell'esempio di codice seguente viene usato l'overload del SignalAndWait(WaitHandle, WaitHandle) metodo per consentire al thread principale di segnalare un thread bloccato e quindi attendere il completamento di un'attività.
L'esempio avvia cinque thread e consente loro di bloccare in un EventWaitHandle oggetto creato con il EventResetMode.AutoReset flag, quindi rilascia un thread ogni volta che l'utente preme il tasto INVIO . L'esempio esegue quindi una coda di altri cinque thread e li rilascia tutti usando un EventWaitHandle oggetto creato con il EventResetMode.ManualReset flag.
using namespace System;
using namespace System::Threading;
public ref class Example
{
private:
// The EventWaitHandle used to demonstrate the difference
// between AutoReset and ManualReset synchronization events.
//
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.
//
static __int64 threadCount = 0;
// An AutoReset event that allows the main thread to block
// until an exiting thread has decremented the count.
//
static EventWaitHandle^ clearCount =
gcnew EventWaitHandle( false,EventResetMode::AutoReset );
public:
[MTAThread]
static void main()
{
// Create an AutoReset EventWaitHandle.
//
ewh = gcnew 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 = gcnew Thread(
gcnew 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( threadCount ) < 5 )
{
Thread::Sleep( 500 );
}
// Release one thread each time the user presses ENTER,
// until all threads have been released.
//
while ( Interlocked::Read( threadCount ) > 0 )
{
Console::WriteLine( L"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 = gcnew EventWaitHandle( false,EventResetMode::ManualReset );
// Create and start five more numbered threads.
//
for ( int i = 0; i <= 4; i++ )
{
Thread^ t = gcnew Thread(
gcnew ParameterizedThreadStart( ThreadProc ) );
t->Start( i );
}
// Wait until all the threads have started and blocked.
//
while ( Interlocked::Read( threadCount ) < 5 )
{
Thread::Sleep( 500 );
}
// Because the EventWaitHandle was created with
// ManualReset mode, signaling it releases all the
// waiting threads.
//
Console::WriteLine( L"Press ENTER to release the waiting threads." );
Console::ReadLine();
ewh->Set();
}
static void ThreadProc( Object^ data )
{
int index = static_cast<Int32>(data);
Console::WriteLine( L"Thread {0} blocks.", data );
// Increment the count of blocked threads.
Interlocked::Increment( threadCount );
// Wait on the EventWaitHandle.
ewh->WaitOne();
Console::WriteLine( L"Thread {0} exits.", data );
// Decrement the count of blocked threads.
Interlocked::Decrement( threadCount );
// After signaling ewh, the main thread blocks on
// clearCount until the signaled thread has
// decremented the count. Signal it now.
//
clearCount->Set();
}
};
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();
}
}
Imports System.Threading
Public Class Example
' The EventWaitHandle used to demonstrate the difference
' between AutoReset and ManualReset synchronization events.
'
Private Shared ewh As EventWaitHandle
' 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 Shared threadCount As Long = 0
' An AutoReset event that allows the main thread to block
' until an exiting thread has decremented the count.
'
Private Shared clearCount As New EventWaitHandle(False, _
EventResetMode.AutoReset)
<MTAThread> _
Public Shared Sub 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 i As Integer = 0 To 4
Dim t As New Thread(AddressOf ThreadProc)
t.Start(i)
Next 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(threadCount) < 5
Thread.Sleep(500)
End While
' Release one thread each time the user presses ENTER,
' until all threads have been released.
'
While Interlocked.Read(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)
End While
Console.WriteLine()
' Create a ManualReset EventWaitHandle.
'
ewh = New EventWaitHandle(False, EventResetMode.ManualReset)
' Create and start five more numbered threads.
'
For i As Integer = 0 To 4
Dim t As New Thread(AddressOf ThreadProc)
t.Start(i)
Next i
' Wait until all the threads have started and blocked.
'
While Interlocked.Read(threadCount) < 5
Thread.Sleep(500)
End While
' 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()
End Sub
Public Shared Sub ThreadProc(ByVal data As Object)
Dim index As Integer = CInt(data)
Console.WriteLine("Thread {0} blocks.", data)
' Increment the count of blocked threads.
Interlocked.Increment(threadCount)
' Wait on the EventWaitHandle.
ewh.WaitOne()
Console.WriteLine("Thread {0} exits.", data)
' Decrement the count of blocked threads.
Interlocked.Decrement(threadCount)
' After signaling ewh, the main thread blocks on
' clearCount until the signaled thread has
' decremented the count. Signal it now.
'
clearCount.Set()
End Sub
End Class
Commenti
Per un EventWaitHandle oggetto con EventResetMode.AutoReset (incluso AutoResetEvent), il Set metodo rilascia un singolo thread. Se non sono presenti thread in attesa, l'handle di attesa rimane segnalato fino a quando un thread tenta di attendere o fino a quando Reset il metodo non viene chiamato.
Importante
Non vi è alcuna garanzia che ogni chiamata al Set metodo rilascia un thread da un EventWaitHandle cui modalità di reimpostazione è EventResetMode.AutoReset. Se due chiamate sono troppo vicine, in modo che la seconda chiamata si verifichi prima del rilascio di un thread, viene rilasciato un solo thread. È come se la seconda chiamata non si verificasse. Inoltre, se Set viene chiamato quando non sono presenti thread in attesa e l'oggetto EventWaitHandle è già segnalato, la chiamata non ha alcun effetto.
Per un EventWaitHandle con EventResetMode.ManualReset (incluso ManualResetEvent), la chiamata al metodo lascia l'handle di attesa in uno stato segnalato fino a quando non Set viene chiamato il Reset relativo metodo.