AsyncLocal<T> 類別

定義

表示對於指定的非同步控制流程為本機的環境資料,例如非同步方法。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)

類型參數

T

環境資料的類型。The type of the ambient data.

繼承
AsyncLocal<T>

範例

下列範例會使用AsyncLocal<T>類別, 將字串值保存在非同步流程中。The following example uses the AsyncLocal<T> class to persist a string value across an asynchronous flow. 它也會比較使用AsyncLocal<T>ThreadLocal<T>的差異。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 ''

備註

因為以工作為基礎的非同步程式設計模型傾向于使用執行緒, AsyncLocal<T>所以實例可以用來跨執行緒保存資料。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.

當與目前線程相關聯的值變更時, Value 類別也會提供選擇性通知,因為它是透過設定屬性進行明確變更,或線上程遇到下列情況時隱含變更:AsyncLocal<T> await或其他內容轉換。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.

建構函式

AsyncLocal<T>()

具現化不會接收變更告知的 AsyncLocal<T> 執行個體。Instantiates an AsyncLocal<T> instance that does not receive change notifications.

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

具現化會接收變更告知的 AsyncLocal<T> 本機執行個體。Instantiates an AsyncLocal<T> local instance that receives change notifications.

屬性

Value

取得或設定環境資料的值。Gets or sets the value of the ambient data.

方法

Equals(Object)

判斷指定的物件是否等於目前的物件。Determines whether the specified object is equal to the current object.

(繼承來源 Object)
GetHashCode()

作為預設雜湊函數。Serves as the default hash function.

(繼承來源 Object)
GetType()

取得目前執行個體的 TypeGets the Type of the current instance.

(繼承來源 Object)
MemberwiseClone()

建立目前 Object 的淺層複製。Creates a shallow copy of the current Object.

(繼承來源 Object)
ToString()

傳回代表目前物件的字串。Returns a string that represents the current object.

(繼承來源 Object)

適用於