AsyncLocal<T> Class

Definition

Stellt Umgebungsdaten dar, die für eine angegebene asynchrone Ablaufsteuerung lokal sind, wie etwa eine asynchrone Methode.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)

Type Parameters

T

Der Typ der Umgebungsdaten.The type of the ambient data.

Inheritance
AsyncLocal<T>

Examples

Im folgenden Beispiel wird die AsyncLocal<T>-Klasse verwendet, um einen Zeichen folgen Wert über einen asynchronen Fluss hinweg beizubehalten.The following example uses the AsyncLocal<T> class to persist a string value across an asynchronous flow. Außerdem wird die Verwendung von AsyncLocal<T> mit ThreadLocal<T>kontrastiert.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 ''

Remarks

Da das aufgabenbasierte asynchrone Programmiermodell tendenziell die Verwendung von Threads abstrahiert, können AsyncLocal<T> Instanzen verwendet werden, um Daten Thread übergreifend beizubehalten.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.

Die AsyncLocal<T>-Klasse stellt auch optionale Benachrichtigungen bereit, wenn sich der Wert ändert, der dem aktuellen Thread zugeordnet ist, da er entweder explizit durch Festlegen der Value-Eigenschaft geändert oder implizit geändert wurde, als der Thread einen await oder einen anderen Kontext Übergang gefunden hat.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.

Constructors

AsyncLocal<T>()

Instanziiert eine AsyncLocal<T>-Instanz, die keine Änderungsbenachrichtigungen empfängt.Instantiates an AsyncLocal<T> instance that does not receive change notifications.

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

Instanziiert eine lokale AsyncLocal<T>-Instanz, die Änderungsbenachrichtigungen empfängt.Instantiates an AsyncLocal<T> local instance that receives change notifications.

Properties

Value

Ruft den Wert der Umgebungsdaten ab oder legt ihn fest.Gets or sets the value of the ambient data.

Methods

Equals(Object)

Bestimmt, ob das angegebene Objekt mit dem aktuellen Objekt identisch ist.Determines whether the specified object is equal to the current object.

(Inherited from Object)
GetHashCode()

Fungiert als Standardhashfunktion.Serves as the default hash function.

(Inherited from Object)
GetType()

Ruft den Type der aktuellen Instanz ab.Gets the Type of the current instance.

(Inherited from Object)
MemberwiseClone()

Erstellt eine flache Kopie des aktuellen Object.Creates a shallow copy of the current Object.

(Inherited from Object)
ToString()

Gibt eine Zeichenfolge zurück, die das aktuelle Objekt darstellt.Returns a string that represents the current object.

(Inherited from Object)

Applies to