AsyncLocal<T> Classe

Definizione

Rappresenta dati di ambiente locali rispetto a un flusso di controllo asincrono specificato, ad esempio un metodo asincrono.Represents ambient data that is local to a given asynchronous control flow, such as an asynchronous method.

generic <typename T>
public ref class AsyncLocal sealed
public sealed class AsyncLocal<T>
type AsyncLocal<'T> = class
Public NotInheritable Class AsyncLocal(Of T)

Parametri di tipo

T

Tipo dei dati di ambiente.The type of the ambient data.

Ereditarietà
AsyncLocal<T>

Esempi

Nell'esempio seguente viene usata la classe AsyncLocal<T> per salvare in modo permanente un valore stringa in un flusso asincrono.The following example uses the AsyncLocal<T> class to persist a string value across an asynchronous flow. Si differenzia anche l'uso di AsyncLocal<T> con ThreadLocal<T>.It also contrasts the use of AsyncLocal<T> with ThreadLocal<T>.

using System;
using System.Threading;
using System.Threading.Tasks;

class Example
{
    static AsyncLocal<string> _asyncLocalString = new AsyncLocal<string>();

    static ThreadLocal<string> _threadLocalString = new ThreadLocal<string>();

    static async Task AsyncMethodA()
    {
        // Start multiple async method calls, with different AsyncLocal values.
        // We also set ThreadLocal values, to demonstrate how the two mechanisms differ.
        _asyncLocalString.Value = "Value 1";
        _threadLocalString.Value = "Value 1";
        var t1 = AsyncMethodB("Value 1");

        _asyncLocalString.Value = "Value 2";
        _threadLocalString.Value = "Value 2";
        var t2 = AsyncMethodB("Value 2");

        // Await both calls
        await t1;
        await t2;
     }

    static async Task AsyncMethodB(string expectedValue)
    {
        Console.WriteLine("Entering AsyncMethodB.");
        Console.WriteLine("   Expected '{0}', AsyncLocal value is '{1}', ThreadLocal value is '{2}'", 
                          expectedValue, _asyncLocalString.Value, _threadLocalString.Value);
        await Task.Delay(100);
        Console.WriteLine("Exiting AsyncMethodB.");
        Console.WriteLine("   Expected '{0}', got '{1}', ThreadLocal value is '{2}'", 
                          expectedValue, _asyncLocalString.Value, _threadLocalString.Value);
    }

    static async Task Main(string[] args)
    {
        await AsyncMethodA();
    }
}
// The example displays the following output:
//   Entering AsyncMethodB.
//      Expected 'Value 1', AsyncLocal value is 'Value 1', ThreadLocal value is 'Value 1'
//   Entering AsyncMethodB.
//      Expected 'Value 2', AsyncLocal value is 'Value 2', ThreadLocal value is 'Value 2'
//   Exiting AsyncMethodB.
//      Expected 'Value 2', got 'Value 2', ThreadLocal value is ''
//   Exiting AsyncMethodB.
//      Expected 'Value 1', got 'Value 1', ThreadLocal value is ''
Imports System.Threading
Imports System.Threading.Tasks

Module Example
    Dim _asyncLocalString As New AsyncLocal(Of String)()

    Dim _threadLocalString As New ThreadLocal(Of String)()

    Async Function AsyncMethodA() As Task
        ' Start multiple async method calls, with different AsyncLocal values.
        ' We also set ThreadLocal values, to demonstrate how the two mechanisms differ.
        _asyncLocalString.Value = "Value 1"
        _threadLocalString.Value = "Value 1"
        Dim t1 = AsyncMethodB("Value 1")

        _asyncLocalString.Value = "Value 2"
        _threadLocalString.Value = "Value 2"
        Dim t2 = AsyncMethodB("Value 2")

        ' Await both calls
        await t1
        await t2
     End Function

    Async Function AsyncMethodB(expectedValue As String) As Task
        Console.WriteLine("Entering AsyncMethodB.")
        Console.WriteLine("   Expected '{0}', AsyncLocal value is '{1}', ThreadLocal value is '{2}'", 
                          expectedValue, _asyncLocalString.Value, _threadLocalString.Value)
        await Task.Delay(100)
        Console.WriteLine("Exiting AsyncMethodB.")
        Console.WriteLine("   Expected '{0}', got '{1}', ThreadLocal value is '{2}'", 
                          expectedValue, _asyncLocalString.Value, _threadLocalString.Value)
    End Function

   Public Sub Main()
       AsyncMethodA.Wait()
   End Sub
End Module
' The example displays the following output:
'   Entering AsyncMethodB.
'      Expected 'Value 1', AsyncLocal value is 'Value 1', ThreadLocal value is 'Value 1'
'   Entering AsyncMethodB.
'      Expected 'Value 2', AsyncLocal value is 'Value 2', ThreadLocal value is 'Value 2'
'   Exiting AsyncMethodB.
'      Expected 'Value 2', got 'Value 2', ThreadLocal value is ''
'   Exiting AsyncMethodB.
'      Expected 'Value 1', got 'Value 1', ThreadLocal value is ''

Commenti

Poiché il modello di programmazione asincrona basato su attività tende ad astrarre l'utilizzo dei thread, è possibile utilizzare le istanze AsyncLocal<T> per salvare in modo permanente i dati tra i thread.Because the task-based asynchronous programming model tends to abstract the use of threads, AsyncLocal<T> instances can be used to persist data across threads.

La classe AsyncLocal<T> fornisce inoltre notifiche facoltative quando viene modificato il valore associato al thread corrente, perché è stato modificato in modo esplicito impostando la proprietà Value oppure è stato modificato in modo implicito quando il thread ha rilevato un await o un'altra transizione del contesto.The AsyncLocal<T> class also provides optional notifications when the value associated with the current thread changes, either because it was explicitly changed by setting the Value property, or implicitly changed when the thread encountered an await or other context transition.

Costruttori

AsyncLocal<T>()

Crea un'istanza dell'istanza di AsyncLocal<T> che non riceve notifiche di modifica.Instantiates an AsyncLocal<T> instance that does not receive change notifications.

AsyncLocal<T>(Action<AsyncLocalValueChangedArgs<T>>)

Crea un'istanza dell'istanza di AsyncLocal<T> locale che riceve notifiche di modifica.Instantiates an AsyncLocal<T> local instance that receives change notifications.

Proprietà

Value

Ottiene o imposta il valore dei dati di ambiente.Gets or sets the value of the ambient data.

Metodi

Equals(Object)

Determina se l'oggetto specificato è uguale all'oggetto corrente.Determines whether the specified object is equal to the current object.

(Ereditato da Object)
GetHashCode()

Funge da funzione hash predefinita.Serves as the default hash function.

(Ereditato da Object)
GetType()

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

(Ereditato da Object)
MemberwiseClone()

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

(Ereditato da Object)
ToString()

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

(Ereditato da Object)

Si applica a