本文件說明如何將目標資料流區塊與其來源區塊解除連結。
備註
TPL 資料流函式庫（命名 System.Threading.Tasks.Dataflow 空間）包含在 .NET 6 及更新版本中。 對於 .NET Framework 和 .NET Standard 專案，你需要安裝 📦 System.Threading.Tasks.Dataflow NuGet 套件。
Example
以下範例建立三個 TransformBlock<TInput,TOutput> 物件，每個 TrySolution 物件呼叫方法來計算一個值。 此範例只需從第一次呼叫到 TrySolution 結束的結果。
using System;
using System.Threading;
using System.Threading.Tasks.Dataflow;
// Demonstrates how to unlink dataflow blocks.
class DataflowReceiveAny
{
// Receives the value from the first provided source that has
// a message.
public static T ReceiveFromAny<T>(params ISourceBlock<T>[] sources)
{
// Create a WriteOnceBlock<T> object and link it to each source block.
var writeOnceBlock = new WriteOnceBlock<T>(e => e);
foreach (var source in sources)
{
// Setting MaxMessages to one instructs
// the source block to unlink from the WriteOnceBlock<T> object
// after offering the WriteOnceBlock<T> object one message.
source.LinkTo(writeOnceBlock, new DataflowLinkOptions { MaxMessages = 1 });
}
// Return the first value that is offered to the WriteOnceBlock object.
return writeOnceBlock.Receive();
}
// Demonstrates a function that takes several seconds to produce a result.
static int TrySolution(int n, CancellationToken ct)
{
// Simulate a lengthy operation that completes within three seconds
// or when the provided CancellationToken object is cancelled.
SpinWait.SpinUntil(() => ct.IsCancellationRequested,
new Random().Next(3000));
// Return a value.
return n + 42;
}
static void Main(string[] args)
{
// Create a shared CancellationTokenSource object to enable the
// TrySolution method to be cancelled.
var cts = new CancellationTokenSource();
// Create three TransformBlock<int, int> objects.
// Each TransformBlock<int, int> object calls the TrySolution method.
Func<int, int> action = n => TrySolution(n, cts.Token);
var trySolution1 = new TransformBlock<int, int>(action);
var trySolution2 = new TransformBlock<int, int>(action);
var trySolution3 = new TransformBlock<int, int>(action);
// Post data to each TransformBlock<int, int> object.
trySolution1.Post(11);
trySolution2.Post(21);
trySolution3.Post(31);
// Call the ReceiveFromAny<T> method to receive the result from the
// first TransformBlock<int, int> object to finish.
int result = ReceiveFromAny(trySolution1, trySolution2, trySolution3);
// Cancel all calls to TrySolution that are still active.
cts.Cancel();
// Print the result to the console.
Console.WriteLine($"The solution is {result}.");
cts.Dispose();
}
}
/* Sample output:
The solution is 53.
*/
Imports System.Threading
Imports System.Threading.Tasks.Dataflow
' Demonstrates how to unlink dataflow blocks.
Friend Class DataflowReceiveAny
' Receives the value from the first provided source that has
' a message.
Public Shared Function ReceiveFromAny(Of T)(ParamArray ByVal sources() As ISourceBlock(Of T)) As T
' Create a WriteOnceBlock<T> object and link it to each source block.
Dim writeOnceBlock = New WriteOnceBlock(Of T)(Function(e) e)
For Each source In sources
' Setting MaxMessages to one instructs
' the source block to unlink from the WriteOnceBlock<T> object
' after offering the WriteOnceBlock<T> object one message.
source.LinkTo(writeOnceBlock, New DataflowLinkOptions With {.MaxMessages = 1})
Next source
' Return the first value that is offered to the WriteOnceBlock object.
Return writeOnceBlock.Receive()
End Function
' Demonstrates a function that takes several seconds to produce a result.
Private Shared Function TrySolution(ByVal n As Integer, ByVal ct As CancellationToken) As Integer
' Simulate a lengthy operation that completes within three seconds
' or when the provided CancellationToken object is cancelled.
SpinWait.SpinUntil(Function() ct.IsCancellationRequested, New Random().Next(3000))
' Return a value.
Return n + 42
End Function
Shared Sub Main(ByVal args() As String)
' Create a shared CancellationTokenSource object to enable the
' TrySolution method to be cancelled.
Dim cts = New CancellationTokenSource()
' Create three TransformBlock<int, int> objects.
' Each TransformBlock<int, int> object calls the TrySolution method.
Dim action As Func(Of Integer, Integer) = Function(n) TrySolution(n, cts.Token)
Dim trySolution1 = New TransformBlock(Of Integer, Integer)(action)
Dim trySolution2 = New TransformBlock(Of Integer, Integer)(action)
Dim trySolution3 = New TransformBlock(Of Integer, Integer)(action)
' Post data to each TransformBlock<int, int> object.
trySolution1.Post(11)
trySolution2.Post(21)
trySolution3.Post(31)
' Call the ReceiveFromAny<T> method to receive the result from the
' first TransformBlock<int, int> object to finish.
Dim result As Integer = ReceiveFromAny(trySolution1, trySolution2, trySolution3)
' Cancel all calls to TrySolution that are still active.
cts.Cancel()
' Print the result to the console.
Console.WriteLine("The solution is {0}.", result)
cts.Dispose()
End Sub
End Class
' Sample output:
'The solution is 53.
'
為了從第一個TransformBlock<TInput,TOutput>完成的物件獲得值，此範例定義了ReceiveFromAny(T)方法。 此 ReceiveFromAny(T) 方法接受一組 ISourceBlock<TOutput> 物件，並將每個物件連結到一個 WriteOnceBlock<T> 物件。 當你使用此 LinkTo 方法將來源資料流區塊與目標區塊連結時，來源會隨著資料的出現向目標區塊傳遞訊息。 由於 WriteOnceBlock<T> 類別只接受第一個提供的訊息，因此 ReceiveFromAny(T) 方法透過呼叫 Receive 方法來產生其結果。 這會產生第一個提供給物件 WriteOnceBlock<T> 的訊息。 此 LinkTo 方法有一個超載版本，接受一個 DataflowLinkOptions 物件，其屬性 MaxMessages 設定為 1 時，指示來源區塊在目標接收到從來源來的一個訊息後從目標解除連結。
WriteOnceBlock<T>物件從來源解除連結非常重要，因為在WriteOnceBlock<T>物件收到訊息後，來源陣列與WriteOnceBlock<T>物件之間的關係不再必要。
為了讓剩下的呼叫 TrySolution 在其中一個計算出值後結束，該TrySolution 方法會採用一個CancellationToken 物件，該物件在呼叫 ReceiveFromAny(T) 返回後被取消。 當該SpinUntil物件被取消時，該CancellationToken方法會回傳。
