ThreadStaticAttribute Classe

Definizione

public ref class ThreadStaticAttribute : Attribute

[System.AttributeUsage(System.AttributeTargets.Field, Inherited=false)]
public class ThreadStaticAttribute : Attribute

[System.AttributeUsage(System.AttributeTargets.Field, Inherited=false)]
[System.Serializable]
public class ThreadStaticAttribute : Attribute

[System.AttributeUsage(System.AttributeTargets.Field, Inherited=false)]
[System.Serializable]
[System.Runtime.InteropServices.ComVisible(true)]
public class ThreadStaticAttribute : Attribute

[<System.AttributeUsage(System.AttributeTargets.Field, Inherited=false)>]
type ThreadStaticAttribute = class
    inherit Attribute

[<System.AttributeUsage(System.AttributeTargets.Field, Inherited=false)>]
[<System.Serializable>]
type ThreadStaticAttribute = class
    inherit Attribute

[<System.AttributeUsage(System.AttributeTargets.Field, Inherited=false)>]
[<System.Serializable>]
[<System.Runtime.InteropServices.ComVisible(true)>]
type ThreadStaticAttribute = class
    inherit Attribute

Public Class ThreadStaticAttribute
Inherits Attribute

Ereditarietà

Object

Attribute

ThreadStaticAttribute

Attributi

AttributeUsageAttribute SerializableAttribute ComVisibleAttribute

Esempio

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. Utilizza l'attributo ThreadStaticAttribute per calcolare la somma e il conteggio dei numeri casuali per ogni thread. Definisce inoltre due campi aggiuntivi per ogni singolo thread, previous e abnormal per rilevare il danneggiamento del generatore di numeri casuali.

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.
//    Sum = 1,000,556.7483, Mean = 0.5003, n = 2,000,000
//    
//    Thread 6 finished random number generation.
//    Sum = 999,704.3865, Mean = 0.4999, n = 2,000,000
//    
//    Thread 2 finished random number generation.
//    Sum = 999,680.8904, Mean = 0.4998, n = 2,000,000
//    
//    Thread 10 finished random number generation.
//    Sum = 999,437.5132, Mean = 0.4997, n = 2,000,000
//    
//    Thread 8 finished random number generation.
//    Sum = 1,000,663.7789, Mean = 0.5003, n = 2,000,000
//    
//    Thread 4 finished random number generation.
//    Sum = 999,379.5978, Mean = 0.4997, n = 2,000,000
//    
//    Thread 5 finished random number generation.
//    Sum = 1,000,011.0605, Mean = 0.5000, n = 2,000,000
//    
//    Thread 9 finished random number generation.
//    Sum = 1,000,637.4556, Mean = 0.5003, n = 2,000,000
//    
//    Thread Main finished random number generation.
//    Sum = 1,000,676.2381, Mean = 0.5003, n = 2,000,000
//    
//    Thread 3 finished random number generation.
//    Sum = 999,951.1025, Mean = 0.5000, n = 2,000,000
//    
//    Thread 7 finished random number generation.
//    Sum = 1,000,844.5217, Mean = 0.5004, n = 2,000,000
//    
//    22,000,000 random numbers were generated.

open System
open System.Threading

type Example() =
    [<ThreadStatic; DefaultValue>] 
    static val mutable private previous : double

    [<ThreadStatic; DefaultValue>] 
    static val mutable private sum : double
    
    [<ThreadStatic; DefaultValue>] 
    static val mutable private calls : int

    [<ThreadStatic; DefaultValue>] 
    static val mutable private abnormal : bool
   
    static let mutable totalNumbers = 0
    static let countdown = new CountdownEvent(1)
    static let lockObj = obj ()
    let rand = Random()


    member this.Execute() =
        for threads = 1 to 10 do
            let newThread = new Thread(ThreadStart this.GetRandomNumbers)
            countdown.AddCount()
            newThread.Name <- threads.ToString()
            newThread.Start()
        this.GetRandomNumbers()
        countdown.Wait()
        printfn $"{totalNumbers:N0} random numbers were generated."

    member _.GetRandomNumbers() =
        let mutable i = 0
        while i < 2000000 do
            lock lockObj (fun () ->
                let result = rand.NextDouble()
                Example.calls <- Example.calls + 1
                Interlocked.Increment &totalNumbers |> ignore
                // We should never get the same random number twice.
                if result = Example.previous then
                    Example.abnormal <- true
                    i <- 2000001 // break
                else
                    Example.previous <- result
                    Example.sum <- Example.sum + result )
            i <- i + 1
        // get last result
        if Example.abnormal then
            printfn $"Result is {Example.previous} in {Thread.CurrentThread.Name}"
        
        printfn $"Thread {Thread.CurrentThread.Name} finished random number generation."
        printfn $"Sum = {Example.sum:N4}, Mean = {Example.sum / float Example.calls:N4}, n = {Example.calls:N0}\n"
        countdown.Signal() |> ignore

let ex = Example()
Thread.CurrentThread.Name <- "Main"
ex.Execute()

// The example displays output similar to the following:
//    Thread 1 finished random number generation.
//    Sum = 1,000,556.7483, Mean = 0.5003, n = 2,000,000
//    
//    Thread 6 finished random number generation.
//    Sum = 999,704.3865, Mean = 0.4999, n = 2,000,000
//    
//    Thread 2 finished random number generation.
//    Sum = 999,680.8904, Mean = 0.4998, n = 2,000,000
//    
//    Thread 10 finished random number generation.
//    Sum = 999,437.5132, Mean = 0.4997, n = 2,000,000
//    
//    Thread 8 finished random number generation.
//    Sum = 1,000,663.7789, Mean = 0.5003, n = 2,000,000
//    
//    Thread 4 finished random number generation.
//    Sum = 999,379.5978, Mean = 0.4997, n = 2,000,000
//    
//    Thread 5 finished random number generation.
//    Sum = 1,000,011.0605, Mean = 0.5000, n = 2,000,000
//    
//    Thread 9 finished random number generation.
//    Sum = 1,000,637.4556, Mean = 0.5003, n = 2,000,000
//    
//    Thread Main finished random number generation.
//    Sum = 1,000,676.2381, Mean = 0.5003, n = 2,000,000
//    
//    Thread 3 finished random number generation.
//    Sum = 999,951.1025, Mean = 0.5000, n = 2,000,000
//    
//    Thread 7 finished random number generation.
//    Sum = 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.
'    Sum = 1,000,556.7483, Mean = 0.5003, n = 2,000,000
'    
'    Thread 6 finished random number generation.
'    Sum = 999,704.3865, Mean = 0.4999, n = 2,000,000
'    
'    Thread 2 finished random number generation.
'    Sum = 999,680.8904, Mean = 0.4998, n = 2,000,000
'    
'    Thread 10 finished random number generation.
'    Sum = 999,437.5132, Mean = 0.4997, n = 2,000,000
'    
'    Thread 8 finished random number generation.
'    Sum = 1,000,663.7789, Mean = 0.5003, n = 2,000,000
'    
'    Thread 4 finished random number generation.
'    Sum = 999,379.5978, Mean = 0.4997, n = 2,000,000
'    
'    Thread 5 finished random number generation.
'    Sum = 1,000,011.0605, Mean = 0.5000, n = 2,000,000
'    
'    Thread 9 finished random number generation.
'    Sum = 1,000,637.4556, Mean = 0.5003, n = 2,000,000
'    
'    Thread Main finished random number generation.
'    Sum = 1,000,676.2381, Mean = 0.5003, n = 2,000,000
'    
'    Thread 3 finished random number generation.
'    Sum = 999,951.1025, Mean = 0.5000, n = 2,000,000
'    
'    Thread 7 finished random number generation.
'    Sum = 1,000,844.5217, Mean = 0.5004, n = 2,000,000
'    
'    22,000,000 random numbers were generated.

Nell'esempio viene usata l'istruzione lock in C#, la lock funzione in F# e il SyncLock costrutto in Visual Basic per sincronizzare l'accesso al generatore di numeri casuali. Ciò impedisce il danneggiamento del generatore di numeri casuali, che in genere comporta la restituzione del valore zero per tutte le chiamate successive.

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. 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.

Commenti

Un static campo contrassegnato con ThreadStaticAttribute non è condiviso tra thread. Ogni thread in esecuzione ha un'istanza separata del campo e imposta in modo indipendente e ottiene i valori per tale campo. Se si accede al campo in un thread diverso, conterrà un valore diverso.

Si noti che, oltre ad applicare l'attributo ThreadStaticAttribute a un campo, è necessario definirlo anche come static campo (in C# o F#) o Shared come campo (in Visual Basic).

Usare questo attributo così come è e non derivare da esso.

Per altre informazioni sull'uso degli attributi, vedere Attributi.

Costruttori

Proprietà

Metodi

Implementazioni dell'interfaccia esplicita

Si applica a

Vedi anche

• Attribute
• Thread
• AsyncLocal<T>
• Estensione di metadati mediante attributi
• Threading gestito