ThreadStaticAttribute ThreadStaticAttribute ThreadStaticAttribute ThreadStaticAttribute Class

Definizione

Indica che il valore di un campo statico è univoco per ogni thread.Indicates that the value of a static field is unique for each thread.

public ref class ThreadStaticAttribute : Attribute
[System.AttributeUsage(System.AttributeTargets.Field, Inherited=false)]
[System.Runtime.InteropServices.ComVisible(true)]
[System.Serializable]
public class ThreadStaticAttribute : Attribute
type ThreadStaticAttribute = class
    inherit Attribute
Public Class ThreadStaticAttribute
Inherits Attribute
Ereditarietà
ThreadStaticAttributeThreadStaticAttributeThreadStaticAttributeThreadStaticAttribute
Attributi

Esempi

Nell'esempio seguente viene creata un'istanza di un generatore di numeri casuali, vengono creati 10 thread oltre al thread principale ed infine vengono generati due milioni di numeri casuali in ogni thread.The following example instantiates a random number generator, creates ten threads in addition to the main thread, and then generates two million random numbers in each thread. Utilizza l'attributo ThreadStaticAttribute per calcolare la somma e il conteggio dei numeri casuali per ogni thread.It uses the ThreadStaticAttribute attribute to calculate the sum and the count of random numbers per thread. Definisce inoltre due campi aggiuntivi per ogni singolo thread, previous e abnormal per rilevare il danneggiamento del generatore di numeri casuali.It also defines two additional per-thread fields, previous and abnormal, that allows it to detect corruption of the random number generator.

using System;
using System.Threading;

public class Example
{
   [ThreadStatic] static double previous = 0.0;
   [ThreadStatic] static double sum = 0.0;
   [ThreadStatic] static int calls = 0;
   [ThreadStatic] static bool abnormal;
   static int totalNumbers = 0;
   static CountdownEvent countdown;
   private static Object lockObj;
   Random rand;
   
   public Example()
   { 
      rand = new Random();
      lockObj = new Object();
      countdown = new CountdownEvent(1);
   } 

   public static void Main()
   {
      Example ex = new Example();
      Thread.CurrentThread.Name = "Main";
      ex.Execute();
      countdown.Wait();
      Console.WriteLine("{0:N0} random numbers were generated.", totalNumbers);
   }

   private void Execute()
   {   
      for (int threads = 1; threads <= 10; threads++)
      {
         Thread newThread = new Thread(new ThreadStart(this.GetRandomNumbers));
         countdown.AddCount();
         newThread.Name = threads.ToString();
         newThread.Start();
      }
      this.GetRandomNumbers();
   }

   private void GetRandomNumbers()
   {
      double result = 0.0;
      
       
      for (int ctr = 0; ctr < 2000000; ctr++)
      {
         lock (lockObj) {
            result = rand.NextDouble();
            calls++;
            Interlocked.Increment(ref totalNumbers);
            // We should never get the same random number twice.
            if (result == previous) {
               abnormal = true;
               break;
            }
            else {
               previous = result;
               sum += result;
            }   
         }
      }
      // get last result
      if (abnormal)
         Console.WriteLine("Result is {0} in {1}", previous, Thread.CurrentThread.Name);
       
      Console.WriteLine("Thread {0} finished random number generation.", Thread.CurrentThread.Name);
      Console.WriteLine("Sum = {0:N4}, Mean = {1:N4}, n = {2:N0}\n", sum, sum/calls, calls);        
      countdown.Signal();
   }
}
// The example displays output similar to the following:
//    Thread 1 finished random number generation.
//    Total = 1,000,556.7483, Mean = 0.5003, n = 2,000,000
//    
//    Thread 6 finished random number generation.
//    Total = 999,704.3865, Mean = 0.4999, n = 2,000,000
//    
//    Thread 2 finished random number generation.
//    Total = 999,680.8904, Mean = 0.4998, n = 2,000,000
//    
//    Thread 10 finished random number generation.
//    Total = 999,437.5132, Mean = 0.4997, n = 2,000,000
//    
//    Thread 8 finished random number generation.
//    Total = 1,000,663.7789, Mean = 0.5003, n = 2,000,000
//    
//    Thread 4 finished random number generation.
//    Total = 999,379.5978, Mean = 0.4997, n = 2,000,000
//    
//    Thread 5 finished random number generation.
//    Total = 1,000,011.0605, Mean = 0.5000, n = 2,000,000
//    
//    Thread 9 finished random number generation.
//    Total = 1,000,637.4556, Mean = 0.5003, n = 2,000,000
//    
//    Thread Main finished random number generation.
//    Total = 1,000,676.2381, Mean = 0.5003, n = 2,000,000
//    
//    Thread 3 finished random number generation.
//    Total = 999,951.1025, Mean = 0.5000, n = 2,000,000
//    
//    Thread 7 finished random number generation.
//    Total = 1,000,844.5217, Mean = 0.5004, n = 2,000,000
//    
//    22,000,000 random numbers were generated.
Imports System.Threading

Public Class Example
   <ThreadStatic> Shared previous As Double = 0.0
   <ThreadStatic> Shared sum As Double = 0.0
   <ThreadStatic> Shared calls As Integer = 0
   <ThreadStatic> Shared abnormal As Boolean
   Shared totalNumbers As Integer = 0
   Shared countdown As CountdownEvent
   Private Shared lockObj As Object
   Dim rand As Random

   Public Sub New()
      rand = New Random()
      lockObj = New Object()
      countdown = New CountdownEvent(1)
   End Sub

   Public Shared Sub Main()
      Dim ex As New Example()
      Thread.CurrentThread.Name = "Main"
      ex.Execute()
      countdown.Wait()
      Console.WriteLine("{0:N0} random numbers were generated.", totalNumbers)
   End Sub

   Private Sub Execute()
      For threads As Integer = 1 To 10
         Dim newThread As New Thread(New ThreadStart(AddressOf GetRandomNumbers))
         countdown.AddCount()
         newThread.Name = threads.ToString()
         newThread.Start()
      Next
      Me.GetRandomNumbers()
   End Sub

   Private Sub GetRandomNumbers()
      Dim result As Double = 0.0
      
       
      For ctr As Integer = 1 To 2000000
         SyncLock lockObj
            result = rand.NextDouble()
            calls += 1
            Interlocked.Increment(totalNumbers)
            ' We should never get the same random number twice.
            If result = previous Then
               abnormal = True
               Exit For
            Else
               previous = result
               sum += result
            End If   
         End SyncLock
      Next
      ' Get last result.
      If abnormal Then
         Console.WriteLine("Result is {0} in {1}", previous, Thread.CurrentThread.Name)
      End If       
      
      Console.WriteLine("Thread {0} finished random number generation.", Thread.CurrentThread.Name)
      Console.WriteLine("Sum = {0:N4}, Mean = {1:N4}, n = {2:N0}", sum, sum/calls, calls)
      Console.WriteLine()        
      countdown.Signal()
   End Sub
End Class
' The example displays output similar to the following:
'    Thread 1 finished random number generation.
'    Total = 1,000,556.7483, Mean = 0.5003, n = 2,000,000
'    
'    Thread 6 finished random number generation.
'    Total = 999,704.3865, Mean = 0.4999, n = 2,000,000
'    
'    Thread 2 finished random number generation.
'    Total = 999,680.8904, Mean = 0.4998, n = 2,000,000
'    
'    Thread 10 finished random number generation.
'    Total = 999,437.5132, Mean = 0.4997, n = 2,000,000
'    
'    Thread 8 finished random number generation.
'    Total = 1,000,663.7789, Mean = 0.5003, n = 2,000,000
'    
'    Thread 4 finished random number generation.
'    Total = 999,379.5978, Mean = 0.4997, n = 2,000,000
'    
'    Thread 5 finished random number generation.
'    Total = 1,000,011.0605, Mean = 0.5000, n = 2,000,000
'    
'    Thread 9 finished random number generation.
'    Total = 1,000,637.4556, Mean = 0.5003, n = 2,000,000
'    
'    Thread Main finished random number generation.
'    Total = 1,000,676.2381, Mean = 0.5003, n = 2,000,000
'    
'    Thread 3 finished random number generation.
'    Total = 999,951.1025, Mean = 0.5000, n = 2,000,000
'    
'    Thread 7 finished random number generation.
'    Total = 1,000,844.5217, Mean = 0.5004, n = 2,000,000
'    
'    22,000,000 random numbers were generated.

Nell'esempio viene utilizzata l'istruzione lock in C# e il costrutto SyncLock in Visual Basic per sincronizzare l'accesso al generatore di numeri casuali.The example uses the lock statement in C# and the SyncLock construct in Visual Basic to synchronize access to the random number generator. Ciò impedisce il danneggiamento del generatore di numeri casuali, che in genere comporta la restituzione del valore zero per tutte le chiamate successive.This prevents corruption of the random number generator, which typically results in its returning a value of zero for all subsequent calls.

Nell'esempio viene anche utilizzata la classe CountdownEvent per garantire che la generazione di numeri casuali sia stata completata da ogni thread prima che venga visualizzato il numero totale di chiamate.The example also uses the CountdownEvent class to ensure that each thread has finished generating random numbers before it displays the total number of calls. In caso contrario, se il thread principale viene completato prima degli altri thread generati, viene visualizzato un valore impreciso relativo al numero totale di chiamate al metodo.Otherwise, if the main thread completes execution before the additional threads that it spawns, it displays an inaccurate value for the total number of method calls.

Commenti

Oggetto static campo contrassegnato con ThreadStaticAttribute non è condivisa tra thread.A static field marked with ThreadStaticAttribute is not shared between threads. Ogni thread in esecuzione dispone di un'istanza separata del campo, in modo indipendente imposta e ottiene i valori per il campo.Each executing thread has a separate instance of the field, and independently sets and gets values for that field. Se si accede al campo in un thread diverso, conterrà un valore diverso.If the field is accessed on a different thread, it will contain a different value.

Si noti che oltre ad applicare l'attributo ThreadStaticAttribute a un campo, è inoltre necessario definirlo come campo static (in C#) o campo Shared (in Visual Basic).Note that in addition to applying the ThreadStaticAttribute attribute to a field, you must also define it as a static field (in C#) or a Shared field (in Visual Basic).

Nota

Non specificare i valori iniziali per i campi contrassegnati con ThreadStaticAttribute, perché tale inizializzazione viene eseguita solo una volta, quando viene eseguito il costruttore della classe e quindi influisce su un solo thread.Do not specify initial values for fields marked with ThreadStaticAttribute, because such initialization occurs only once, when the class constructor executes, and therefore affects only one thread. Se non si specifica un valore iniziale, è possibile basarsi sul campo in fase di inizializzazione per il valore predefinito se è un tipo di valore o per null se è un tipo di riferimento.If you do not specify an initial value, you can rely on the field being initialized to its default value if it is a value type, or to null if it is a reference type.

Usare questo attributo così com'è e non derivano da essa.Use this attribute as it is, and do not derive from it.

Per altre informazioni sull'utilizzo di attributi, vedere attributi.For more information about using attributes, see Attributes.

Costruttori

ThreadStaticAttribute() ThreadStaticAttribute() ThreadStaticAttribute() ThreadStaticAttribute()

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

Metodi

Equals(Object) Equals(Object) Equals(Object) Equals(Object)

Restituisce un valore che indica se questa istanza è uguale a un oggetto specificato.Returns a value that indicates whether this instance is equal to a specified object.

(Inherited from Attribute)
GetHashCode() GetHashCode() GetHashCode() GetHashCode()

Restituisce il codice hash per l'istanza.Returns the hash code for this instance.

(Inherited from Attribute)
GetType() GetType() GetType() GetType()

Ottiene l'oggetto Type dell'istanza corrente.Gets the Type of the current instance.

(Inherited from Object)
IsDefaultAttribute() IsDefaultAttribute() IsDefaultAttribute() IsDefaultAttribute()

In caso di override in una classe derivata, indica se il valore di questa istanza è il valore predefinito per la classe derivata.When overridden in a derived class, indicates whether the value of this instance is the default value for the derived class.

(Inherited from Attribute)
Match(Object) Match(Object) Match(Object) Match(Object)

Quando è sottoposto a override in una classe derivata, restituisce un valore che indica se questa istanza equivale a un oggetto specificato.When overridden in a derived class, returns a value that indicates whether this instance equals a specified object.

(Inherited from Attribute)
MemberwiseClone() MemberwiseClone() MemberwiseClone() MemberwiseClone()

Crea una copia superficiale dell'oggetto Object corrente.Creates a shallow copy of the current Object.

(Inherited from Object)
ToString() ToString() ToString() ToString()

Restituisce una stringa che rappresenta l'oggetto corrente.Returns a string that represents the current object.

(Inherited from Object)

Implementazioni dell'interfaccia esplicita

_Attribute.GetIDsOfNames(Guid, IntPtr, UInt32, UInt32, IntPtr) _Attribute.GetIDsOfNames(Guid, IntPtr, UInt32, UInt32, IntPtr) _Attribute.GetIDsOfNames(Guid, IntPtr, UInt32, UInt32, IntPtr) _Attribute.GetIDsOfNames(Guid, IntPtr, UInt32, UInt32, IntPtr)

Esegue il mapping di un set di nomi a un set corrispondente di ID dispatch.Maps a set of names to a corresponding set of dispatch identifiers.

(Inherited from Attribute)
_Attribute.GetTypeInfo(UInt32, UInt32, IntPtr) _Attribute.GetTypeInfo(UInt32, UInt32, IntPtr) _Attribute.GetTypeInfo(UInt32, UInt32, IntPtr) _Attribute.GetTypeInfo(UInt32, UInt32, IntPtr)

Recupera le informazioni sul tipo relative a un oggetto, che possono essere usate per ottenere informazioni sul tipo relative a un'interfaccia.Retrieves the type information for an object, which can be used to get the type information for an interface.

(Inherited from Attribute)
_Attribute.GetTypeInfoCount(UInt32) _Attribute.GetTypeInfoCount(UInt32) _Attribute.GetTypeInfoCount(UInt32) _Attribute.GetTypeInfoCount(UInt32)

Recupera il numero delle interfacce di informazioni sul tipo fornite da un oggetto (0 o 1).Retrieves the number of type information interfaces that an object provides (either 0 or 1).

(Inherited from Attribute)
_Attribute.Invoke(UInt32, Guid, UInt32, Int16, IntPtr, IntPtr, IntPtr, IntPtr) _Attribute.Invoke(UInt32, Guid, UInt32, Int16, IntPtr, IntPtr, IntPtr, IntPtr) _Attribute.Invoke(UInt32, Guid, UInt32, Int16, IntPtr, IntPtr, IntPtr, IntPtr) _Attribute.Invoke(UInt32, Guid, UInt32, Int16, IntPtr, IntPtr, IntPtr, IntPtr)

Fornisce l'accesso a proprietà e metodi esposti da un oggetto.Provides access to properties and methods exposed by an object.

(Inherited from Attribute)

Proprietà

TypeId TypeId TypeId TypeId

Quando è implementata in una classe derivata, ottiene un identificatore univoco della classe Attribute.When implemented in a derived class, gets a unique identifier for this Attribute.

(Inherited from Attribute)

Si applica a

Vedi anche