Semaphore Costruttori

Definizione

Inizializza una nuova istanza della classe Semaphore.Initializes a new instance of the Semaphore class.

Overload

Semaphore(Int32, Int32)

Inizializza una nuova istanza della classe Semaphore, specificando il numero di voci iniziale e il numero massimo di voci contemporanei.Initializes a new instance of the Semaphore class, specifying the initial number of entries and the maximum number of concurrent entries.

Semaphore(Int32, Int32, String)

Inizializza una nuova istanza della classe Semaphore, specificando il numero di voci iniziale e il numero massimo di voci contemporanee, nonché indicando facoltativamente il nome di un oggetto semaforo di sistema.Initializes a new instance of the Semaphore class, specifying the initial number of entries and the maximum number of concurrent entries, and optionally specifying the name of a system semaphore object.

Semaphore(Int32, Int32, String, Boolean)

Inizializza una nuova istanza della classe Semaphore, specificando il numero di accessi iniziale e il numero massimo di accessi contemporanei, indicando facoltativamente il nome di un oggetto semaforo di sistema e specificando una variabile che riceve un valore che indica se è stato creato un nuovo semaforo di sistema.Initializes a new instance of the Semaphore class, specifying the initial number of entries and the maximum number of concurrent entries, optionally specifying the name of a system semaphore object, and specifying a variable that receives a value indicating whether a new system semaphore was created.

Semaphore(Int32, Int32, String, Boolean, SemaphoreSecurity)

Inizializza una nuova istanza della classe Semaphore, specificando il numero iniziale di accessi e il numero massimo di accessi contemporanei, indicando facoltativamente il nome di un oggetto semaforo di sistema, specificando una variabile che riceve un valore che indica se è stato creato un nuovo semaforo di sistema e specificando la sicurezza del controllo di accesso per il semaforo di sistema.Initializes a new instance of the Semaphore class, specifying the initial number of entries and the maximum number of concurrent entries, optionally specifying the name of a system semaphore object, specifying a variable that receives a value indicating whether a new system semaphore was created, and specifying security access control for the system semaphore.

Semaphore(Int32, Int32)

Inizializza una nuova istanza della classe Semaphore, specificando il numero di voci iniziale e il numero massimo di voci contemporanei.Initializes a new instance of the Semaphore class, specifying the initial number of entries and the maximum number of concurrent entries.

public:
 Semaphore(int initialCount, int maximumCount);
public Semaphore (int initialCount, int maximumCount);
new System.Threading.Semaphore : int * int -> System.Threading.Semaphore
Public Sub New (initialCount As Integer, maximumCount As Integer)

Parametri

initialCount
Int32

Numero iniziale delle richieste per il semaforo che possono essere concesse contemporaneamente.The initial number of requests for the semaphore that can be granted concurrently.

maximumCount
Int32

Numero massimo delle richieste per il semaforo che possono essere concesse contemporaneamente.The maximum number of requests for the semaphore that can be granted concurrently.

Eccezioni

initialCount è maggiore di maximumCount.initialCount is greater than maximumCount.

maximumCount è minore di 1.maximumCount is less than 1.

In alternativa-or- initialCount è minore di 0.initialCount is less than 0.

Esempi

Nell'esempio seguente viene creato un semaforo con un numero massimo di tre e un conteggio iniziale pari a zero.The following example creates a semaphore with a maximum count of three and an initial count of zero. L'esempio avvia cinque thread, che bloccano l'attesa del semaforo.The example starts five threads, which block waiting for the semaphore. Il thread principale usa l' Release(Int32) overload del metodo per aumentare il numero di semafori al massimo, consentendo a tre thread di accedere al semaforo.The main thread uses the Release(Int32) method overload to increase the semaphore count to its maximum, allowing three threads to enter the semaphore. Ogni thread usa il Thread.Sleep metodo per attendere un secondo, per simulare il lavoro e quindi chiama l' Release() overload del metodo per rilasciare il semaforo.Each thread uses the Thread.Sleep method to wait for one second, to simulate work, and then calls the Release() method overload to release the semaphore. Ogni volta che viene rilasciato il semaforo, viene visualizzato il numero di semafori precedente.Each time the semaphore is released, the previous semaphore count is displayed. I messaggi della console tengono traccia dell'uso del semaforo.Console messages track semaphore use. L'intervallo di lavoro simulato viene leggermente aumentato per ogni thread, per semplificare la lettura dell'output.The simulated work interval is increased slightly for each thread, to make the output easier to read.

#using <System.dll>
using namespace System;
using namespace System::Threading;

public ref class Example
{
private:
   // A semaphore that simulates a limited resource pool.
   //
   static Semaphore^ _pool;

   // A padding interval to make the output more orderly.
   static int _padding;

public:
   static void Main()
   {
      // Create a semaphore that can satisfy up to three
      // concurrent requests. Use an initial count of zero,
      // so that the entire semaphore count is initially
      // owned by the main program thread.
      //
      _pool = gcnew Semaphore( 0,3 );
      
      // Create and start five numbered threads.
      //
      for ( int i = 1; i <= 5; i++ )
      {
         Thread^ t = gcnew Thread(
            gcnew ParameterizedThreadStart( Worker ) );
         
         // Start the thread, passing the number.
         //
         t->Start( i );
      }
      
      // Wait for half a second, to allow all the
      // threads to start and to block on the semaphore.
      //
      Thread::Sleep( 500 );
      
      // The main thread starts out holding the entire
      // semaphore count. Calling Release(3) brings the
      // semaphore count back to its maximum value, and
      // allows the waiting threads to enter the semaphore,
      // up to three at a time.
      //
      Console::WriteLine( L"Main thread calls Release(3)." );
      _pool->Release( 3 );

      Console::WriteLine( L"Main thread exits." );
   }

private:
   static void Worker( Object^ num )
   {
      // Each worker thread begins by requesting the
      // semaphore.
      Console::WriteLine( L"Thread {0} begins and waits for the semaphore.", num );
      _pool->WaitOne();
      
      // A padding interval to make the output more orderly.
      int padding = Interlocked::Add( _padding, 100 );

      Console::WriteLine( L"Thread {0} enters the semaphore.", num );
      
      // The thread's "work" consists of sleeping for
      // about a second. Each thread "works" a little
      // longer, just to make the output more orderly.
      //
      Thread::Sleep( 1000 + padding );

      Console::WriteLine( L"Thread {0} releases the semaphore.", num );
      Console::WriteLine( L"Thread {0} previous semaphore count: {1}",
         num, _pool->Release() );
   }
};
using System;
using System.Threading;

public class Example
{
    // A semaphore that simulates a limited resource pool.
    //
    private static Semaphore _pool;

    // A padding interval to make the output more orderly.
    private static int _padding;

    public static void Main()
    {
        // Create a semaphore that can satisfy up to three
        // concurrent requests. Use an initial count of zero,
        // so that the entire semaphore count is initially
        // owned by the main program thread.
        //
        _pool = new Semaphore(0, 3);

        // Create and start five numbered threads. 
        //
        for(int i = 1; i <= 5; i++)
        {
            Thread t = new Thread(new ParameterizedThreadStart(Worker));

            // Start the thread, passing the number.
            //
            t.Start(i);
        }

        // Wait for half a second, to allow all the
        // threads to start and to block on the semaphore.
        //
        Thread.Sleep(500);

        // The main thread starts out holding the entire
        // semaphore count. Calling Release(3) brings the 
        // semaphore count back to its maximum value, and
        // allows the waiting threads to enter the semaphore,
        // up to three at a time.
        //
        Console.WriteLine("Main thread calls Release(3).");
        _pool.Release(3);

        Console.WriteLine("Main thread exits.");
    }

    private static void Worker(object num)
    {
        // Each worker thread begins by requesting the
        // semaphore.
        Console.WriteLine("Thread {0} begins " +
            "and waits for the semaphore.", num);
        _pool.WaitOne();

        // A padding interval to make the output more orderly.
        int padding = Interlocked.Add(ref _padding, 100);

        Console.WriteLine("Thread {0} enters the semaphore.", num);
        
        // The thread's "work" consists of sleeping for 
        // about a second. Each thread "works" a little 
        // longer, just to make the output more orderly.
        //
        Thread.Sleep(1000 + padding);

        Console.WriteLine("Thread {0} releases the semaphore.", num);
        Console.WriteLine("Thread {0} previous semaphore count: {1}",
            num, _pool.Release());
    }
}
Imports System.Threading

Public Class Example

    ' A semaphore that simulates a limited resource pool.
    '
    Private Shared _pool As Semaphore

    ' A padding interval to make the output more orderly.
    Private Shared _padding As Integer

    <MTAThread> _
    Public Shared Sub Main()
        ' Create a semaphore that can satisfy up to three
        ' concurrent requests. Use an initial count of zero,
        ' so that the entire semaphore count is initially
        ' owned by the main program thread.
        '
        _pool = New Semaphore(0, 3)

        ' Create and start five numbered threads. 
        '
        For i As Integer = 1 To 5
            Dim t As New Thread(New ParameterizedThreadStart(AddressOf Worker))
            'Dim t As New Thread(AddressOf Worker)

            ' Start the thread, passing the number.
            '
            t.Start(i)
        Next i

        ' Wait for half a second, to allow all the
        ' threads to start and to block on the semaphore.
        '
        Thread.Sleep(500)

        ' The main thread starts out holding the entire
        ' semaphore count. Calling Release(3) brings the 
        ' semaphore count back to its maximum value, and
        ' allows the waiting threads to enter the semaphore,
        ' up to three at a time.
        '
        Console.WriteLine("Main thread calls Release(3).")
        _pool.Release(3)

        Console.WriteLine("Main thread exits.")
    End Sub

    Private Shared Sub Worker(ByVal num As Object)
        ' Each worker thread begins by requesting the
        ' semaphore.
        Console.WriteLine("Thread {0} begins " _
            & "and waits for the semaphore.", num)
        _pool.WaitOne()

        ' A padding interval to make the output more orderly.
        Dim padding As Integer = Interlocked.Add(_padding, 100)

        Console.WriteLine("Thread {0} enters the semaphore.", num)
        
        ' The thread's "work" consists of sleeping for 
        ' about a second. Each thread "works" a little 
        ' longer, just to make the output more orderly.
        '
        Thread.Sleep(1000 + padding)

        Console.WriteLine("Thread {0} releases the semaphore.", num)
        Console.WriteLine("Thread {0} previous semaphore count: {1}", _
            num, _
            _pool.Release())
    End Sub
End Class

Commenti

Questo costruttore inizializza un semaforo senza nome.This constructor initializes an unnamed semaphore. Tutti i thread che usano un'istanza di tale semaforo devono avere riferimenti all'istanza.All threads that use an instance of such a semaphore must have references to the instance.

Se initialCount è minore di maximumCount, l'effetto è identico a quello in cui il thread corrente WaitOne hamaximumCount chiamato initialCount(meno) volte.If initialCount is less than maximumCount, the effect is the same as if the current thread had called WaitOne (maximumCount minus initialCount) times. Se non si desidera riservare alcuna voce per il thread che crea il semaforo, utilizzare lo stesso numero per maximumCount e. initialCountIf you do not want to reserve any entries for the thread that creates the semaphore, use the same number for maximumCount and initialCount.

Vedi anche

Semaphore(Int32, Int32, String)

Inizializza una nuova istanza della classe Semaphore, specificando il numero di voci iniziale e il numero massimo di voci contemporanee, nonché indicando facoltativamente il nome di un oggetto semaforo di sistema.Initializes a new instance of the Semaphore class, specifying the initial number of entries and the maximum number of concurrent entries, and optionally specifying the name of a system semaphore object.

public:
 Semaphore(int initialCount, int maximumCount, System::String ^ name);
public Semaphore (int initialCount, int maximumCount, string name);
new System.Threading.Semaphore : int * int * string -> System.Threading.Semaphore
Public Sub New (initialCount As Integer, maximumCount As Integer, name As String)

Parametri

initialCount
Int32

Numero iniziale delle richieste per il semaforo che possono essere concesse contemporaneamente.The initial number of requests for the semaphore that can be granted concurrently.

maximumCount
Int32

Numero massimo delle richieste per il semaforo che possono essere concesse contemporaneamente.The maximum number of requests for the semaphore that can be granted concurrently.

name
String

Nome di un oggetto semaforo di sistema denominato.The name of a named system semaphore object.

Eccezioni

initialCount è maggiore di maximumCount.initialCount is greater than maximumCount.

-oppure--or- La lunghezza diname supera i 260 caratteri.name is longer than 260 characters.

maximumCount è minore di 1.maximumCount is less than 1.

-oppure--or- initialCount è minore di 0.initialCount is less than 0.

Errore Win32.A Win32 error occurred.

Il semaforo denominato esiste e ha accesso alla sicurezza controllo, ma l'utente non dispone di FullControl.The named semaphore exists and has access control security, and the user does not have FullControl.

Il semaforo denominato non può essere creato, forse perché ha lo stesso nome di un handle di attesa di tipo diverso.The named semaphore cannot be created, perhaps because a wait handle of a different type has the same name.

Esempi

Nell'esempio di codice riportato di seguito viene illustrato il comportamento tra processi di un semaforo denominato.The following code example demonstrates the cross-process behavior of a named semaphore. Nell'esempio viene creato un semaforo denominato con un numero massimo di cinque e un conteggio iniziale pari a cinque.The example creates a named semaphore with a maximum count of five and an initial count of five. Il programma esegue tre chiamate al WaitOne metodo.The program makes three calls to the WaitOne method. Se quindi si esegue l'esempio compilato da due finestre di comando, la seconda copia si bloccherà alla terza chiamata a WaitOne.Thus, if you run the compiled example from two command windows, the second copy will block on the third call to WaitOne. Rilasciare una o più voci nella prima copia del programma per sbloccare il secondo.Release one or more entries in the first copy of the program to unblock the second.

#using <System.dll>
using namespace System;
using namespace System::Threading;

public ref class Example
{
public:
   static void main()
   {
      // Create a Semaphore object that represents the named
      // system semaphore "SemaphoreExample3". The semaphore has a
      // maximum count of five. The initial count is also five.
      // There is no point in using a smaller initial count,
      // because the initial count is not used if this program
      // doesn't create the named system semaphore, and with
      // this method overload there is no way to tell. Thus, this
      // program assumes that it is competing with other
      // programs for the semaphore.
      //
      Semaphore^ sem = gcnew Semaphore( 5,5,L"SemaphoreExample3" );
      
      // Attempt to enter the semaphore three times. If another
      // copy of this program is already running, only the first
      // two requests can be satisfied. The third blocks. Note
      // that in a real application, timeouts should be used
      // on the WaitOne calls, to avoid deadlocks.
      //
      sem->WaitOne();
      Console::WriteLine( L"Entered the semaphore once." );
      sem->WaitOne();
      Console::WriteLine( L"Entered the semaphore twice." );
      sem->WaitOne();
      Console::WriteLine( L"Entered the semaphore three times." );
      
      // The thread executing this program has entered the
      // semaphore three times. If a second copy of the program
      // is run, it will block until this program releases the
      // semaphore at least once.
      //
      Console::WriteLine( L"Enter the number of times to call Release." );
      int n;
      if ( Int32::TryParse( Console::ReadLine(),n ) )
      {
         sem->Release( n );
      }

      int remaining = 3 - n;
      if ( remaining > 0 )
      {
         Console::WriteLine( L"Press Enter to release the remaining "
         L"count ({0}) and exit the program.", remaining );
         Console::ReadLine();
         sem->Release( remaining );
      }
   }
};
using System;
using System.Threading;

public class Example
{
    public static void Main()
    {
        // Create a Semaphore object that represents the named 
        // system semaphore "SemaphoreExample3". The semaphore has a
        // maximum count of five. The initial count is also five. 
        // There is no point in using a smaller initial count,
        // because the initial count is not used if this program
        // doesn't create the named system semaphore, and with 
        // this method overload there is no way to tell. Thus, this
        // program assumes that it is competing with other
        // programs for the semaphore.
        //
        Semaphore sem = new Semaphore(5, 5, "SemaphoreExample3");

        // Attempt to enter the semaphore three times. If another 
        // copy of this program is already running, only the first
        // two requests can be satisfied. The third blocks. Note 
        // that in a real application, timeouts should be used
        // on the WaitOne calls, to avoid deadlocks.
        //
        sem.WaitOne();
        Console.WriteLine("Entered the semaphore once.");
        sem.WaitOne();
        Console.WriteLine("Entered the semaphore twice.");
        sem.WaitOne();
        Console.WriteLine("Entered the semaphore three times.");

        // The thread executing this program has entered the 
        // semaphore three times. If a second copy of the program
        // is run, it will block until this program releases the 
        // semaphore at least once.
        //
        Console.WriteLine("Enter the number of times to call Release.");
        int n;
        if (int.TryParse(Console.ReadLine(), out n))
        {
            sem.Release(n);
        }

        int remaining = 3 - n;
        if (remaining > 0)
        {
            Console.WriteLine("Press Enter to release the remaining " +
                "count ({0}) and exit the program.", remaining);
            Console.ReadLine();
            sem.Release(remaining);
        }
    }
}
Imports System.Threading

Public Class Example

    <MTAThread> _
    Public Shared Sub Main()
        ' Create a Semaphore object that represents the named 
        ' system semaphore "SemaphoreExample3". The semaphore has a
        ' maximum count of five. The initial count is also five. 
        ' There is no point in using a smaller initial count,
        ' because the initial count is not used if this program
        ' doesn't create the named system semaphore, and with 
        ' this method overload there is no way to tell. Thus, this
        ' program assumes that it is competing with other
        ' programs for the semaphore.
        '
        Dim sem As New Semaphore(5, 5, "SemaphoreExample3")

        ' Attempt to enter the semaphore three times. If another 
        ' copy of this program is already running, only the first
        ' two requests can be satisfied. The third blocks. Note 
        ' that in a real application, timeouts should be used
        ' on the WaitOne calls, to avoid deadlocks.
        '
        sem.WaitOne()
        Console.WriteLine("Entered the semaphore once.")
        sem.WaitOne()
        Console.WriteLine("Entered the semaphore twice.")
        sem.WaitOne()
        Console.WriteLine("Entered the semaphore three times.")

        ' The thread executing this program has entered the 
        ' semaphore three times. If a second copy of the program
        ' is run, it will block until this program releases the 
        ' semaphore at least once.
        '
        Console.WriteLine("Enter the number of times to call Release.")
        Dim n As Integer
        If Integer.TryParse(Console.ReadLine(), n) Then
            sem.Release(n)
        End If

        Dim remaining As Integer = 3 - n
        If (remaining) > 0 Then
            Console.WriteLine("Press Enter to release the remaining " _
                & "count ({0}) and exit the program.", remaining)
            Console.ReadLine()
            sem.Release(remaining)
        End If

    End Sub 
End Class 

Commenti

Questo costruttore inizializza un Semaphore oggetto che rappresenta un semaforo di sistema denominato.This constructor initializes a Semaphore object that represents a named system semaphore. È possibile creare più Semaphore oggetti che rappresentano lo stesso semaforo di sistema denominato.You can create multiple Semaphore objects that represent the same named system semaphore.

Se il semaforo di sistema denominato non esiste, viene creato con il conteggio iniziale e il conteggio massimo specificato da initialCount e maximumCount.If the named system semaphore does not exist, it is created with the initial count and maximum count specified by initialCount and maximumCount. Se il semaforo di sistema denominato esiste initialCount già e non vengono usati, sebbene i valori non validi continuano a maximumCount generare eccezioni.If the named system semaphore already exists, initialCount and maximumCount are not used, although invalid values still cause exceptions. Se è necessario determinare se è stato creato o meno un semaforo di sistema denominato, usare Semaphore(Int32, Int32, String, Boolean) invece l'overload del costruttore.If you need to determine whether or not a named system semaphore was created, use the Semaphore(Int32, Int32, String, Boolean) constructor overload instead.

Importante

Quando si utilizza questo overload del costruttore, la procedura consigliata consiste nello specificare lo stesso initialCount numero maximumCountper e.When you use this constructor overload, the recommended practice is to specify the same number for initialCount and maximumCount. Se initialCount è minore di maximumCounte viene creato un semaforo di sistema denominato, l'effetto è identico a quello di se il thread corrente WaitOne hamaximumCount chiamato initialCount(meno) volte.If initialCount is less than maximumCount, and a named system semaphore is created, the effect is the same as if the current thread had called WaitOne (maximumCount minus initialCount) times. Con questo overload del costruttore, tuttavia, non è possibile determinare se è stato creato un semaforo di sistema denominato.However, with this constructor overload there is no way to determine whether a named system semaphore was created.

Se si specifica null o una stringa vuota per name, viene creato un semaforo locale, come se fosse stato chiamato l' Semaphore(Int32, Int32) overload del costruttore.If you specify null or an empty string for name, a local semaphore is created, as if you had called the Semaphore(Int32, Int32) constructor overload.

Poiché i semafori denominati sono visibili in tutto il sistema operativo, possono essere usati per coordinare l'uso delle risorse tra i limiti dei processi.Because named semaphores are visible throughout the operating system, they can be used to coordinate resource use across process boundaries.

Se si desidera verificare se esiste un semaforo di sistema denominato, utilizzare il OpenExisting metodo.If you want to find out whether a named system semaphore exists, use the OpenExisting method. Il OpenExisting metodo tenta di aprire un semaforo denominato esistente e genera un'eccezione se il semaforo di sistema non esiste.The OpenExisting method attempts to open an existing named semaphore, and throws an exception if the system semaphore does not exist.

Sicurezza

SecurityPermission
per chiamare codice non gestito per creare un semaforo di sistema denominato.for calling unmanaged code to create a named system semaphore. Enumerazione associata: UnmanagedCode.Associated enumeration: UnmanagedCode. Azione di sicurezza LinkDemand:.Security action: LinkDemand.

Vedi anche

Semaphore(Int32, Int32, String, Boolean)

Inizializza una nuova istanza della classe Semaphore, specificando il numero di accessi iniziale e il numero massimo di accessi contemporanei, indicando facoltativamente il nome di un oggetto semaforo di sistema e specificando una variabile che riceve un valore che indica se è stato creato un nuovo semaforo di sistema.Initializes a new instance of the Semaphore class, specifying the initial number of entries and the maximum number of concurrent entries, optionally specifying the name of a system semaphore object, and specifying a variable that receives a value indicating whether a new system semaphore was created.

public:
 Semaphore(int initialCount, int maximumCount, System::String ^ name, [Runtime::InteropServices::Out] bool % createdNew);
public Semaphore (int initialCount, int maximumCount, string name, out bool createdNew);
new System.Threading.Semaphore : int * int * string * bool -> System.Threading.Semaphore
Public Sub New (initialCount As Integer, maximumCount As Integer, name As String, ByRef createdNew As Boolean)

Parametri

initialCount
Int32

Numero iniziale di richieste per il semaforo che possono essere soddisfatte contemporaneamente.The initial number of requests for the semaphore that can be satisfied concurrently.

maximumCount
Int32

Numero massimo di richieste per il semaforo che possono essere soddisfatte contemporaneamente.The maximum number of requests for the semaphore that can be satisfied concurrently.

name
String

Nome di un oggetto semaforo di sistema denominato.The name of a named system semaphore object.

createdNew
Boolean

Quando questo metodo viene restituito, contiene true se è stato creato un semaforo locale (ovvero, se il valore di name è null o una stringa vuota) oppure se è stato creato il semaforo di sistema denominato specificato; false se il semaforo di sistema denominato specificato è già esistente.When this method returns, contains true if a local semaphore was created (that is, if name is null or an empty string) or if the specified named system semaphore was created; false if the specified named system semaphore already existed. Questo parametro viene passato non inizializzato.This parameter is passed uninitialized.

Eccezioni

initialCount è maggiore di maximumCount.initialCount is greater than maximumCount.

In alternativa-or- La lunghezza diname supera i 260 caratteri.name is longer than 260 characters.

maximumCount è minore di 1.maximumCount is less than 1.

-oppure--or- initialCount è minore di 0.initialCount is less than 0.

Errore Win32.A Win32 error occurred.

Il semaforo denominato esiste e ha accesso alla sicurezza controllo, ma l'utente non dispone di FullControl.The named semaphore exists and has access control security, and the user does not have FullControl.

Il semaforo denominato non può essere creato, forse perché ha lo stesso nome di un handle di attesa di tipo diverso.The named semaphore cannot be created, perhaps because a wait handle of a different type has the same name.

Esempi

Nell'esempio di codice riportato di seguito viene illustrato il comportamento tra processi di un semaforo denominato.The following code example demonstrates the cross-process behavior of a named semaphore. Nell'esempio viene creato un semaforo denominato con un numero massimo di cinque e un conteggio iniziale pari a due.The example creates a named semaphore with a maximum count of five and an initial count of two. Ovvero si riservano tre voci per il thread che chiama il costruttore.That is, it reserves three entries for the thread that calls the constructor. Se createNew WaitOne è false, il programma effettua tre chiamate al metodo.If createNew is false, the program makes three calls to the WaitOne method. Se quindi si esegue l'esempio compilato da due finestre di comando, la seconda copia si bloccherà alla terza chiamata a WaitOne.Thus, if you run the compiled example from two command windows, the second copy will block on the third call to WaitOne. Rilasciare una o più voci nella prima copia del programma per sbloccare il secondo.Release one or more entries in the first copy of the program to unblock the second.

#using <System.dll>
using namespace System;
using namespace System::Threading;

public ref class Example
{
public:
   static void main()
   {
      // The value of this variable is set by the semaphore
      // constructor. It is true if the named system semaphore was
      // created, and false if the named semaphore already existed.
      //
      bool semaphoreWasCreated;
      
      // Create a Semaphore object that represents the named
      // system semaphore "SemaphoreExample". The semaphore has a
      // maximum count of five, and an initial count of two. The
      // Boolean value that indicates creation of the underlying
      // system object is placed in semaphoreWasCreated.
      //
      Semaphore^ sem = gcnew Semaphore( 2,5,L"SemaphoreExample",
         semaphoreWasCreated );
      if ( semaphoreWasCreated )
      {
         // If the named system semaphore was created, its count is
         // set to the initial count requested in the constructor.
         // In effect, the current thread has entered the semaphore
         // three times.
         //
         Console::WriteLine( L"Entered the semaphore three times." );
      }
      else
      {
         // If the named system semaphore was not created,
         // attempt to enter it three times. If another copy of
         // this program is already running, only the first two
         // requests can be satisfied. The third blocks.
         //
         sem->WaitOne();
         Console::WriteLine( L"Entered the semaphore once." );
         sem->WaitOne();
         Console::WriteLine( L"Entered the semaphore twice." );
         sem->WaitOne();
         Console::WriteLine( L"Entered the semaphore three times." );
      }
      
      // The thread executing this program has entered the
      // semaphore three times. If a second copy of the program
      // is run, it will block until this program releases the
      // semaphore at least once.
      //
      Console::WriteLine( L"Enter the number of times to call Release." );
      int n;
      if ( Int32::TryParse( Console::ReadLine(), n ) )
      {
         sem->Release( n );
      }

      int remaining = 3 - n;
      if ( remaining > 0 )
      {
         Console::WriteLine( L"Press Enter to release the remaining "
         L"count ({0}) and exit the program.", remaining );
         Console::ReadLine();
         sem->Release( remaining );
      }
   }
};
using System;
using System.Threading;

public class Example
{
    public static void Main()
    {
        // The value of this variable is set by the semaphore
        // constructor. It is true if the named system semaphore was
        // created, and false if the named semaphore already existed.
        //
        bool semaphoreWasCreated;

        // Create a Semaphore object that represents the named 
        // system semaphore "SemaphoreExample". The semaphore has a
        // maximum count of five, and an initial count of two. The
        // Boolean value that indicates creation of the underlying 
        // system object is placed in semaphoreWasCreated.
        //
        Semaphore sem = new Semaphore(2, 5, "SemaphoreExample", 
            out semaphoreWasCreated);

        if (semaphoreWasCreated)
        {
            // If the named system semaphore was created, its count is
            // set to the initial count requested in the constructor.
            // In effect, the current thread has entered the semaphore
            // three times.
            // 
            Console.WriteLine("Entered the semaphore three times.");
        }
        else
        {      
            // If the named system semaphore was not created,  
            // attempt to enter it three times. If another copy of
            // this program is already running, only the first two
            // requests can be satisfied. The third blocks.
            //
            sem.WaitOne();
            Console.WriteLine("Entered the semaphore once.");
            sem.WaitOne();
            Console.WriteLine("Entered the semaphore twice.");
            sem.WaitOne();
            Console.WriteLine("Entered the semaphore three times.");
        }

        // The thread executing this program has entered the 
        // semaphore three times. If a second copy of the program
        // is run, it will block until this program releases the 
        // semaphore at least once.
        //
        Console.WriteLine("Enter the number of times to call Release.");
        int n;
        if (int.TryParse(Console.ReadLine(), out n))
        {
            sem.Release(n);
        }

        int remaining = 3 - n;
        if (remaining > 0)
        {
            Console.WriteLine("Press Enter to release the remaining " +
                "count ({0}) and exit the program.", remaining);
            Console.ReadLine();
            sem.Release(remaining);
        }
    } 
} 
Imports System.Threading

Public Class Example

    <MTAThread> _
    Public Shared Sub Main()
        ' The value of this variable is set by the semaphore
        ' constructor. It is True if the named system semaphore was
        ' created, and False if the named semaphore already existed.
        '
        Dim semaphoreWasCreated As Boolean

        ' Create a Semaphore object that represents the named 
        ' system semaphore "SemaphoreExample". The semaphore has a
        ' maximum count of five, and an initial count of two. The
        ' Boolean value that indicates creation of the underlying 
        ' system object is placed in semaphoreWasCreated.
        '
        Dim sem As New Semaphore(2, 5, "SemaphoreExample", _
            semaphoreWasCreated)

        If semaphoreWasCreated Then
            ' If the named system semaphore was created, its count is
            ' set to the initial count requested in the constructor.
            ' In effect, the current thread has entered the semaphore
            ' three times.
            ' 
            Console.WriteLine("Entered the semaphore three times.")
        Else
            ' If the named system semaphore was not created,  
            ' attempt to enter it three times. If another copy of
            ' this program is already running, only the first two
            ' requests can be satisfied. The third blocks.
            '
            sem.WaitOne()
            Console.WriteLine("Entered the semaphore once.")
            sem.WaitOne()
            Console.WriteLine("Entered the semaphore twice.")
            sem.WaitOne()
            Console.WriteLine("Entered the semaphore three times.")
        End If

        ' The thread executing this program has entered the 
        ' semaphore three times. If a second copy of the program
        ' is run, it will block until this program releases the 
        ' semaphore at least once.
        '
        Console.WriteLine("Enter the number of times to call Release.")
        Dim n As Integer
        If Integer.TryParse(Console.ReadLine(), n) Then
            sem.Release(n)
        End If

        Dim remaining As Integer = 3 - n
        If (remaining) > 0 Then
            Console.WriteLine("Press Enter to release the remaining " _
                & "count ({0}) and exit the program.", remaining)
            Console.ReadLine()
            sem.Release(remaining)
        End If

    End Sub 
End Class 

Commenti

Questo costruttore inizializza un Semaphore oggetto che rappresenta un semaforo di sistema denominato.This constructor initializes a Semaphore object that represents a named system semaphore. È possibile creare più Semaphore oggetti che rappresentano lo stesso semaforo di sistema denominato.You can create multiple Semaphore objects that represent the same named system semaphore.

Se il semaforo di sistema denominato non esiste, viene creato con il conteggio iniziale e il conteggio massimo specificato da initialCount e maximumCount.If the named system semaphore does not exist, it is created with the initial count and maximum count specified by initialCount and maximumCount. Se il semaforo di sistema denominato esiste initialCount già e non vengono usati, sebbene i valori non validi continuano a maximumCount generare eccezioni.If the named system semaphore already exists, initialCount and maximumCount are not used, although invalid values still cause exceptions. Usare createdNew per determinare se il semaforo di sistema è stato creato.Use createdNew to determine whether the system semaphore was created.

Se initialCount è minore di maximumCounte createdNew è WaitOne maximumCount initialCount, l'effetto è identico a quello in cui il thread corrente ha chiamato (meno) volte. trueIf initialCount is less than maximumCount, and createdNew is true, the effect is the same as if the current thread had called WaitOne (maximumCount minus initialCount) times.

Se si specifica null o una stringa vuota per name, viene creato un semaforo locale, come se fosse stato chiamato l' Semaphore(Int32, Int32) overload del costruttore.If you specify null or an empty string for name, a local semaphore is created, as if you had called the Semaphore(Int32, Int32) constructor overload. In questo caso, createdNew è sempre true.In this case, createdNew is always true.

Poiché i semafori denominati sono visibili in tutto il sistema operativo, possono essere usati per coordinare l'uso delle risorse tra i limiti dei processi.Because named semaphores are visible throughout the operating system, they can be used to coordinate resource use across process boundaries.

Sicurezza

SecurityPermission
per chiamare codice non gestito per creare un semaforo di sistema denominato.for calling unmanaged code to create a named system semaphore. Enumerazione associata: UnmanagedCode.Associated enumeration: UnmanagedCode. Azione di sicurezza LinkDemand:.Security action: LinkDemand.

Vedi anche

Semaphore(Int32, Int32, String, Boolean, SemaphoreSecurity)

Inizializza una nuova istanza della classe Semaphore, specificando il numero iniziale di accessi e il numero massimo di accessi contemporanei, indicando facoltativamente il nome di un oggetto semaforo di sistema, specificando una variabile che riceve un valore che indica se è stato creato un nuovo semaforo di sistema e specificando la sicurezza del controllo di accesso per il semaforo di sistema.Initializes a new instance of the Semaphore class, specifying the initial number of entries and the maximum number of concurrent entries, optionally specifying the name of a system semaphore object, specifying a variable that receives a value indicating whether a new system semaphore was created, and specifying security access control for the system semaphore.

public:
 Semaphore(int initialCount, int maximumCount, System::String ^ name, [Runtime::InteropServices::Out] bool % createdNew, System::Security::AccessControl::SemaphoreSecurity ^ semaphoreSecurity);
public Semaphore (int initialCount, int maximumCount, string name, out bool createdNew, System.Security.AccessControl.SemaphoreSecurity semaphoreSecurity);
new System.Threading.Semaphore : int * int * string * bool * System.Security.AccessControl.SemaphoreSecurity -> System.Threading.Semaphore

Parametri

initialCount
Int32

Numero iniziale di richieste per il semaforo che possono essere soddisfatte contemporaneamente.The initial number of requests for the semaphore that can be satisfied concurrently.

maximumCount
Int32

Numero massimo di richieste per il semaforo che possono essere soddisfatte contemporaneamente.The maximum number of requests for the semaphore that can be satisfied concurrently.

name
String

Nome di un oggetto semaforo di sistema denominato.The name of a named system semaphore object.

createdNew
Boolean

Quando questo metodo viene restituito, contiene true se è stato creato un semaforo locale (ovvero, se il valore di name è null o una stringa vuota) oppure se è stato creato il semaforo di sistema denominato specificato; false se il semaforo di sistema denominato specificato è già esistente.When this method returns, contains true if a local semaphore was created (that is, if name is null or an empty string) or if the specified named system semaphore was created; false if the specified named system semaphore already existed. Questo parametro viene passato non inizializzato.This parameter is passed uninitialized.

semaphoreSecurity
SemaphoreSecurity

Oggetto SemaphoreSecurity che rappresenta la sicurezza del controllo di accesso da applicare al semaforo di sistema denominato.A SemaphoreSecurity object that represents the access control security to be applied to the named system semaphore.

Eccezioni

initialCount è maggiore di maximumCount.initialCount is greater than maximumCount.

-oppure--or- La lunghezza diname supera i 260 caratteri.name is longer than 260 characters.

maximumCount è minore di 1.maximumCount is less than 1.

-oppure--or- initialCount è minore di 0.initialCount is less than 0.

Il semaforo denominato esiste e ha accesso alla sicurezza controllo, ma l'utente non dispone di FullControl.The named semaphore exists and has access control security, and the user does not have FullControl.

Errore Win32.A Win32 error occurred.

Il semaforo denominato non può essere creato, forse perché ha lo stesso nome di un handle di attesa di tipo diverso.The named semaphore cannot be created, perhaps because a wait handle of a different type has the same name.

Esempi

Nell'esempio di codice seguente viene illustrato il comportamento tra processi di un semaforo denominato con sicurezza del controllo di accesso.The following code example demonstrates the cross-process behavior of a named semaphore with access control security. Nell'esempio viene usato OpenExisting(String) l'overload del metodo per verificare l'esistenza di un semaforo denominato.The example uses the OpenExisting(String) method overload to test for the existence of a named semaphore. Se il semaforo non esiste, viene creato con un numero massimo di due e con la sicurezza del controllo di accesso che nega all'utente corrente il diritto di usare il semaforo ma concede il diritto di leggere e modificare le autorizzazioni sul semaforo.If the semaphore does not exist, it is created with a maximum count of two and with access control security that denies the current user the right to use the semaphore but grants the right to read and change permissions on the semaphore. Se si esegue l'esempio compilato da due finestre di comando, la seconda copia genererà un'eccezione di violazione di accesso sulla chiamata OpenExisting(String) al metodo.If you run the compiled example from two command windows, the second copy will throw an access violation exception on the call to the OpenExisting(String) method. L'eccezione viene rilevata e l'esempio usa OpenExisting(String, SemaphoreRights) l'overload del metodo per aprire il semaforo con i diritti necessari per leggere e modificare le autorizzazioni.The exception is caught, and the example uses the OpenExisting(String, SemaphoreRights) method overload to open the semaphore with the rights needed to read and change the permissions.

Una volta modificate le autorizzazioni, il semaforo viene aperto con i diritti necessari per l'immissione e il rilascio.After the permissions are changed, the semaphore is opened with the rights required to enter and release. Se si esegue l'esempio compilato da una terza finestra di comando, questa viene eseguita utilizzando le nuove autorizzazioni.If you run the compiled example from a third command window, it runs using the new permissions.

#using <System.dll>
using namespace System;
using namespace System::Threading;
using namespace System::Security::AccessControl;
using namespace System::Security::Permissions;

public ref class Example
{
public:
   [SecurityPermissionAttribute(SecurityAction::Demand, Flags = SecurityPermissionFlag::UnmanagedCode)]
   static void main()
   {
      String^ semaphoreName = L"SemaphoreExample5";

      Semaphore^ sem = nullptr;
      bool doesNotExist = false;
      bool unauthorized = false;
      
      // Attempt to open the named semaphore.
      try
      {
         // Open the semaphore with (SemaphoreRights.Synchronize
         // | SemaphoreRights.Modify), to enter and release the
         // named semaphore.
         //
         sem = Semaphore::OpenExisting( semaphoreName );
      }
      catch ( WaitHandleCannotBeOpenedException^ ex ) 
      {
         Console::WriteLine( L"Semaphore does not exist." );
         doesNotExist = true;
      }
      catch ( UnauthorizedAccessException^ ex ) 
      {
         Console::WriteLine( L"Unauthorized access: {0}", ex->Message );
         unauthorized = true;
      }

      // There are three cases: (1) The semaphore does not exist.
      // (2) The semaphore exists, but the current user doesn't
      // have access. (3) The semaphore exists and the user has
      // access.
      //
      if ( doesNotExist )
      {
         // The semaphore does not exist, so create it.
         //
         // The value of this variable is set by the semaphore
         // constructor. It is true if the named system semaphore was
         // created, and false if the named semaphore already existed.
         //
         bool semaphoreWasCreated;
         
         // Create an access control list (ACL) that denies the
         // current user the right to enter or release the
         // semaphore, but allows the right to read and change
         // security information for the semaphore.
         //
         String^ user = String::Concat( Environment::UserDomainName,
            L"\\", Environment::UserName );
         SemaphoreSecurity^ semSec = gcnew SemaphoreSecurity;

         SemaphoreAccessRule^ rule = gcnew SemaphoreAccessRule( user,
            static_cast<SemaphoreRights>(
               SemaphoreRights::Synchronize |
               SemaphoreRights::Modify ),
            AccessControlType::Deny );
         semSec->AddAccessRule( rule );

         rule = gcnew SemaphoreAccessRule( user,
            static_cast<SemaphoreRights>(
               SemaphoreRights::ReadPermissions |
               SemaphoreRights::ChangePermissions ),
            AccessControlType::Allow );
         semSec->AddAccessRule( rule );
         
         // Create a Semaphore object that represents the system
         // semaphore named by the constant 'semaphoreName', with
         // maximum count three, initial count three, and the
         // specified security access. The Boolean value that
         // indicates creation of the underlying system object is
         // placed in semaphoreWasCreated.
         //
         sem = gcnew Semaphore( 3,3,semaphoreName,semaphoreWasCreated,semSec );
         
         // If the named system semaphore was created, it can be
         // used by the current instance of this program, even
         // though the current user is denied access. The current
         // program enters the semaphore. Otherwise, exit the
         // program.
         //
         if ( semaphoreWasCreated )
         {
            Console::WriteLine( L"Created the semaphore." );
         }
         else
         {
            Console::WriteLine( L"Unable to create the semaphore." );
            return;
         }

      }
      else if ( unauthorized )
      {
         // Open the semaphore to read and change the access
         // control security. The access control security defined
         // above allows the current user to do this.
         //
         try
         {
            sem = Semaphore::OpenExisting( semaphoreName,
               static_cast<SemaphoreRights>(
                  SemaphoreRights::ReadPermissions |
                  SemaphoreRights::ChangePermissions ));
            
            // Get the current ACL. This requires
            // SemaphoreRights.ReadPermissions.
            SemaphoreSecurity^ semSec = sem->GetAccessControl();

            String^ user = String::Concat( Environment::UserDomainName,
               L"\\", Environment::UserName );
            
            // First, the rule that denied the current user
            // the right to enter and release the semaphore must
            // be removed.
            SemaphoreAccessRule^ rule = gcnew SemaphoreAccessRule( user,
               static_cast<SemaphoreRights>(
                  SemaphoreRights::Synchronize |
                  SemaphoreRights::Modify ),
               AccessControlType::Deny );
            semSec->RemoveAccessRule( rule );
            
            // Now grant the user the correct rights.
            //
            rule = gcnew SemaphoreAccessRule( user,
               static_cast<SemaphoreRights>(
                  SemaphoreRights::Synchronize |
                  SemaphoreRights::Modify ),
               AccessControlType::Allow );
            semSec->AddAccessRule( rule );
            
            // Update the ACL. This requires
            // SemaphoreRights.ChangePermissions.
            sem->SetAccessControl( semSec );

            Console::WriteLine( L"Updated semaphore security." );
            
            // Open the semaphore with (SemaphoreRights.Synchronize
            // | SemaphoreRights.Modify), the rights required to
            // enter and release the semaphore.
            //
            sem = Semaphore::OpenExisting( semaphoreName );

         }
         catch ( UnauthorizedAccessException^ ex ) 
         {
            Console::WriteLine( L"Unable to change permissions: {0}", ex->Message );
            return;
         }
      }
      
      // Enter the semaphore, and hold it until the program
      // exits.
      //
      try
      {
         sem->WaitOne();
         Console::WriteLine( L"Entered the semaphore." );
         Console::WriteLine( L"Press the Enter key to exit." );
         Console::ReadLine();
         sem->Release();
      }
      catch ( UnauthorizedAccessException^ ex ) 
      {
         Console::WriteLine( L"Unauthorized access: {0}", ex->Message );
      }
   }
};
using System;
using System.Threading;
using System.Security.AccessControl;

internal class Example
{
    internal static void Main()
    {
        const string semaphoreName = "SemaphoreExample5";

        Semaphore sem = null;
        bool doesNotExist = false;
        bool unauthorized = false;

        // Attempt to open the named semaphore.
        try
        {
            // Open the semaphore with (SemaphoreRights.Synchronize
            // | SemaphoreRights.Modify), to enter and release the
            // named semaphore.
            //
            sem = Semaphore.OpenExisting(semaphoreName);
        }
        catch(WaitHandleCannotBeOpenedException)
        {
            Console.WriteLine("Semaphore does not exist.");
            doesNotExist = true;
        }
        catch(UnauthorizedAccessException ex)
        {
            Console.WriteLine("Unauthorized access: {0}", ex.Message);
            unauthorized = true;
        }

        // There are three cases: (1) The semaphore does not exist.
        // (2) The semaphore exists, but the current user doesn't 
        // have access. (3) The semaphore exists and the user has
        // access.
        //
        if (doesNotExist)
        {
            // The semaphore does not exist, so create it.
            //
            // The value of this variable is set by the semaphore
            // constructor. It is true if the named system semaphore was
            // created, and false if the named semaphore already existed.
            //
            bool semaphoreWasCreated;

            // Create an access control list (ACL) that denies the
            // current user the right to enter or release the 
            // semaphore, but allows the right to read and change
            // security information for the semaphore.
            //
            string user = Environment.UserDomainName + "\\" 
                + Environment.UserName;
            SemaphoreSecurity semSec = new SemaphoreSecurity();

            SemaphoreAccessRule rule = new SemaphoreAccessRule(
                user, 
                SemaphoreRights.Synchronize | SemaphoreRights.Modify, 
                AccessControlType.Deny);
            semSec.AddAccessRule(rule);

            rule = new SemaphoreAccessRule(
                user, 
                SemaphoreRights.ReadPermissions | SemaphoreRights.ChangePermissions,
                AccessControlType.Allow);
            semSec.AddAccessRule(rule);

            // Create a Semaphore object that represents the system
            // semaphore named by the constant 'semaphoreName', with
            // maximum count three, initial count three, and the
            // specified security access. The Boolean value that 
            // indicates creation of the underlying system object is
            // placed in semaphoreWasCreated.
            //
            sem = new Semaphore(3, 3, semaphoreName, 
                out semaphoreWasCreated, semSec);

            // If the named system semaphore was created, it can be
            // used by the current instance of this program, even 
            // though the current user is denied access. The current
            // program enters the semaphore. Otherwise, exit the
            // program.
            // 
            if (semaphoreWasCreated)
            {
                Console.WriteLine("Created the semaphore.");
            }
            else
            {
                Console.WriteLine("Unable to create the semaphore.");
                return;
            }

        }
        else if (unauthorized)
        {
            // Open the semaphore to read and change the access
            // control security. The access control security defined
            // above allows the current user to do this.
            //
            try
            {
                sem = Semaphore.OpenExisting(
                    semaphoreName, 
                    SemaphoreRights.ReadPermissions 
                        | SemaphoreRights.ChangePermissions);

                // Get the current ACL. This requires 
                // SemaphoreRights.ReadPermissions.
                SemaphoreSecurity semSec = sem.GetAccessControl();
                
                string user = Environment.UserDomainName + "\\" 
                    + Environment.UserName;

                // First, the rule that denied the current user 
                // the right to enter and release the semaphore must
                // be removed.
                SemaphoreAccessRule rule = new SemaphoreAccessRule(
                    user, 
                    SemaphoreRights.Synchronize | SemaphoreRights.Modify, 
                    AccessControlType.Deny);
                semSec.RemoveAccessRule(rule);

                // Now grant the user the correct rights.
                // 
                rule = new SemaphoreAccessRule(user, 
                     SemaphoreRights.Synchronize | SemaphoreRights.Modify, 
                     AccessControlType.Allow);
                semSec.AddAccessRule(rule);

                // Update the ACL. This requires
                // SemaphoreRights.ChangePermissions.
                sem.SetAccessControl(semSec);

                Console.WriteLine("Updated semaphore security.");

                // Open the semaphore with (SemaphoreRights.Synchronize 
                // | SemaphoreRights.Modify), the rights required to
                // enter and release the semaphore.
                //
                sem = Semaphore.OpenExisting(semaphoreName);

            }
            catch(UnauthorizedAccessException ex)
            {
                Console.WriteLine("Unable to change permissions: {0}", ex.Message);
                return;
            }
        }

        // Enter the semaphore, and hold it until the program
        // exits.
        //
        try
        {
            sem.WaitOne();
            Console.WriteLine("Entered the semaphore.");
            Console.WriteLine("Press the Enter key to exit.");
            Console.ReadLine();
            sem.Release();
        }
        catch(UnauthorizedAccessException ex)
        {
            Console.WriteLine("Unauthorized access: {0}", ex.Message);
        }
    }
}
Imports System.Threading
Imports System.Security.AccessControl

Friend Class Example

    <MTAThread> _
    Friend Shared Sub Main()
        Const semaphoreName As String = "SemaphoreExample5"

        Dim sem As Semaphore = Nothing
        Dim doesNotExist as Boolean = False
        Dim unauthorized As Boolean = False

        ' Attempt to open the named semaphore.
        Try
            ' Open the semaphore with (SemaphoreRights.Synchronize
            ' Or SemaphoreRights.Modify), to enter and release the
            ' named semaphore.
            '
            sem = Semaphore.OpenExisting(semaphoreName)
        Catch ex As WaitHandleCannotBeOpenedException
            Console.WriteLine("Semaphore does not exist.")
            doesNotExist = True
        Catch ex As UnauthorizedAccessException
            Console.WriteLine("Unauthorized access: {0}", ex.Message)
            unauthorized = True
        End Try

        ' There are three cases: (1) The semaphore does not exist.
        ' (2) The semaphore exists, but the current user doesn't 
        ' have access. (3) The semaphore exists and the user has
        ' access.
        '
        If doesNotExist Then
            ' The semaphore does not exist, so create it.
            '
            ' The value of this variable is set by the semaphore
            ' constructor. It is True if the named system semaphore was
            ' created, and False if the named semaphore already existed.
            '
            Dim semaphoreWasCreated As Boolean

            ' Create an access control list (ACL) that denies the
            ' current user the right to enter or release the 
            ' semaphore, but allows the right to read and change
            ' security information for the semaphore.
            '
            Dim user As String = Environment.UserDomainName _ 
                & "\" & Environment.UserName
            Dim semSec As New SemaphoreSecurity()

            Dim rule As New SemaphoreAccessRule(user, _
                SemaphoreRights.Synchronize Or SemaphoreRights.Modify, _
                AccessControlType.Deny)
            semSec.AddAccessRule(rule)

            rule = New SemaphoreAccessRule(user, _
                SemaphoreRights.ReadPermissions Or _
                SemaphoreRights.ChangePermissions, _
                AccessControlType.Allow)
            semSec.AddAccessRule(rule)

            ' Create a Semaphore object that represents the system
            ' semaphore named by the constant 'semaphoreName', with
            ' maximum count three, initial count three, and the
            ' specified security access. The Boolean value that 
            ' indicates creation of the underlying system object is
            ' placed in semaphoreWasCreated.
            '
            sem = New Semaphore(3, 3, semaphoreName, _
                semaphoreWasCreated, semSec)

            ' If the named system semaphore was created, it can be
            ' used by the current instance of this program, even 
            ' though the current user is denied access. The current
            ' program enters the semaphore. Otherwise, exit the
            ' program.
            ' 
            If semaphoreWasCreated Then
                Console.WriteLine("Created the semaphore.")
            Else
                Console.WriteLine("Unable to create the semaphore.")
                Return
            End If

        ElseIf unauthorized Then

            ' Open the semaphore to read and change the access
            ' control security. The access control security defined
            ' above allows the current user to do this.
            '
            Try
                sem = Semaphore.OpenExisting(semaphoreName, _
                    SemaphoreRights.ReadPermissions Or _
                    SemaphoreRights.ChangePermissions)

                ' Get the current ACL. This requires 
                ' SemaphoreRights.ReadPermissions.
                Dim semSec As SemaphoreSecurity = sem.GetAccessControl()
                
                Dim user As String = Environment.UserDomainName _ 
                    & "\" & Environment.UserName

                ' First, the rule that denied the current user 
                ' the right to enter and release the semaphore must
                ' be removed.
                Dim rule As New SemaphoreAccessRule(user, _
                    SemaphoreRights.Synchronize Or SemaphoreRights.Modify, _
                    AccessControlType.Deny)
                semSec.RemoveAccessRule(rule)

                ' Now grant the user the correct rights.
                ' 
                rule = New SemaphoreAccessRule(user, _
                    SemaphoreRights.Synchronize Or SemaphoreRights.Modify, _
                    AccessControlType.Allow)
                semSec.AddAccessRule(rule)

                ' Update the ACL. This requires
                ' SemaphoreRights.ChangePermissions.
                sem.SetAccessControl(semSec)

                Console.WriteLine("Updated semaphore security.")

                ' Open the semaphore with (SemaphoreRights.Synchronize 
                ' Or SemaphoreRights.Modify), the rights required to
                ' enter and release the semaphore.
                '
                sem = Semaphore.OpenExisting(semaphoreName)

            Catch ex As UnauthorizedAccessException
                Console.WriteLine("Unable to change permissions: {0}", _
                    ex.Message)
                Return
            End Try

        End If

        ' Enter the semaphore, and hold it until the program
        ' exits.
        '
        Try
            sem.WaitOne()
            Console.WriteLine("Entered the semaphore.")
            Console.WriteLine("Press the Enter key to exit.")
            Console.ReadLine()
            sem.Release()
        Catch ex As UnauthorizedAccessException
            Console.WriteLine("Unauthorized access: {0}", _
                ex.Message)
        End Try
    End Sub 
End Class 

Commenti

Utilizzare questo costruttore per applicare la sicurezza del controllo di accesso a un semaforo di sistema denominato quando viene creato, impedendo ad altro codice di assumere il controllo del semaforo.Use this constructor to apply access control security to a named system semaphore when it is created, preventing other code from taking control of the semaphore.

Questo costruttore inizializza un Semaphore oggetto che rappresenta un semaforo di sistema denominato.This constructor initializes a Semaphore object that represents a named system semaphore. È possibile creare più Semaphore oggetti che rappresentano lo stesso semaforo di sistema denominato.You can create multiple Semaphore objects that represent the same named system semaphore.

Se il semaforo di sistema denominato non esiste, viene creato con la sicurezza del controllo di accesso specificata.If the named system semaphore does not exist, it is created with the specified access control security. Se il semaforo denominato esiste, la sicurezza del controllo di accesso specificata viene ignorata.If the named semaphore exists, the specified access control security is ignored.

Nota

Il chiamante ha il controllo completo sull'oggetto appena Semaphore creato anche se semaphoreSecurity nega o non riesce a concedere alcuni diritti di accesso all'utente corrente.The caller has full control over the newly created Semaphore object even if semaphoreSecurity denies or fails to grant some access rights to the current user. Tuttavia, se l'utente corrente tenta di ottenere un Semaphore altro oggetto per rappresentare lo stesso semaforo denominato, usando un costruttore o il OpenExisting metodo, viene applicata la sicurezza del controllo di accesso di Windows.However, if the current user attempts to get another Semaphore object to represent the same named semaphore, using either a constructor or the OpenExisting method, Windows access control security is applied.

Se il semaforo di sistema denominato non esiste, viene creato con il conteggio iniziale e il conteggio massimo specificato da initialCount e maximumCount.If the named system semaphore does not exist, it is created with the initial count and maximum count specified by initialCount and maximumCount. Se il semaforo di sistema denominato esiste initialCount già e non vengono usati, sebbene i valori non validi continuano a maximumCount generare eccezioni.If the named system semaphore already exists, initialCount and maximumCount are not used, although invalid values still cause exceptions. Usare il createdNew parametro per determinare se il semaforo di sistema è stato creato da questo costruttore.Use the createdNew parameter to determine whether the system semaphore was created by this constructor.

Se initialCount è minore di maximumCounte createdNew è WaitOne maximumCount initialCount, l'effetto è identico a quello in cui il thread corrente ha chiamato (meno) volte. trueIf initialCount is less than maximumCount, and createdNew is true, the effect is the same as if the current thread had called WaitOne (maximumCount minus initialCount) times.

Se si specifica null o una stringa vuota per name, viene creato un semaforo locale, come se fosse stato chiamato l' Semaphore(Int32, Int32) overload del costruttore.If you specify null or an empty string for name, a local semaphore is created, as if you had called the Semaphore(Int32, Int32) constructor overload. In questo caso, createdNew è sempre true.In this case, createdNew is always true.

Poiché i semafori denominati sono visibili in tutto il sistema operativo, possono essere usati per coordinare l'uso delle risorse tra i limiti dei processi.Because named semaphores are visible throughout the operating system, they can be used to coordinate resource use across process boundaries.

Sicurezza

SecurityPermission
per chiamare codice non gestito per creare un semaforo di sistema denominato.for calling unmanaged code to create a named system semaphore. Enumerazione associata: UnmanagedCode.Associated enumeration: UnmanagedCode. Azione di sicurezza LinkDemand:.Security action: LinkDemand.

Vedi anche

Si applica a