TaskCompletionSource<TResult> 类
定义
重要
一些信息与预发行产品相关，相应产品在发行之前可能会进行重大修改。 对于此处提供的信息，Microsoft 不作任何明示或暗示的担保。
表示 Task<TResult> 未绑定的委托的生成方，通过 Task 属性提供对使用者端的访问权限。
generic <typename TResult>
public ref class TaskCompletionSourcepublic class TaskCompletionSource<TResult>type TaskCompletionSource<'Result> = classPublic Class TaskCompletionSource(Of TResult)类型参数
- TResult
与此 TaskCompletionSource<TResult>关联的结果值的类型。
- 继承
-
TaskCompletionSource<TResult>
示例
以下示例演示如何使用 TaskCompletionSource<TResult>：
using System;
using System.Diagnostics;
using System.Threading;
using System.Threading.Tasks;
class TCSDemo
{
// Demonstrated features:
// TaskCompletionSource ctor()
// TaskCompletionSource.SetResult()
// TaskCompletionSource.SetException()
// Task.Result
// Expected results:
// The attempt to get t1.Result blocks for ~1000ms until tcs1 gets signaled. 15 is printed out.
// The attempt to get t2.Result blocks for ~1000ms until tcs2 gets signaled. An exception is printed out.
static void Main()
{
TaskCompletionSource<int> tcs1 = new TaskCompletionSource<int>();
Task<int> t1 = tcs1.Task;
// Start a background task that will complete tcs1.Task
Task.Factory.StartNew(() =>
{
Thread.Sleep(1000);
tcs1.SetResult(15);
});
// The attempt to get the result of t1 blocks the current thread until the completion source gets signaled.
// It should be a wait of ~1000 ms.
Stopwatch sw = Stopwatch.StartNew();
int result = t1.Result;
sw.Stop();
Console.WriteLine("(ElapsedTime={0}): t1.Result={1} (expected 15) ", sw.ElapsedMilliseconds, result);
// ------------------------------------------------------------------
// Alternatively, an exception can be manually set on a TaskCompletionSource.Task
TaskCompletionSource<int> tcs2 = new TaskCompletionSource<int>();
Task<int> t2 = tcs2.Task;
// Start a background Task that will complete tcs2.Task with an exception
Task.Factory.StartNew(() =>
{
Thread.Sleep(1000);
tcs2.SetException(new InvalidOperationException("SIMULATED EXCEPTION"));
});
// The attempt to get the result of t2 blocks the current thread until the completion source gets signaled with either a result or an exception.
// In either case it should be a wait of ~1000 ms.
sw = Stopwatch.StartNew();
try
{
result = t2.Result;
Console.WriteLine("t2.Result succeeded. THIS WAS NOT EXPECTED.");
}
catch (AggregateException e)
{
Console.Write("(ElapsedTime={0}): ", sw.ElapsedMilliseconds);
Console.WriteLine("The following exceptions have been thrown by t2.Result: (THIS WAS EXPECTED)");
for (int j = 0; j < e.InnerExceptions.Count; j++)
{
Console.WriteLine("\n-------------------------------------------------\n{0}", e.InnerExceptions[j].ToString());
}
}
}
}
Imports System.Diagnostics
Imports System.Threading
Imports System.Threading.Tasks
Module TCSDemo
' Demonstrated features:
' TaskCompletionSource ctor()
' TaskCompletionSource.SetResult()
' TaskCompletionSource.SetException()
' Task.Result
' Expected results:
' The attempt to get t1.Result blocks for ~1000ms until tcs1 gets signaled. 15 is printed out.
' The attempt to get t2.Result blocks for ~1000ms until tcs2 gets signaled. An exception is printed out.
Private Sub Main()
Dim tcs1 As New TaskCompletionSource(Of Integer)()
Dim t1 As Task(Of Integer) = tcs1.Task
' Start a background task that will complete tcs1.Task
Task.Factory.StartNew(Sub()
Thread.Sleep(1000)
tcs1.SetResult(15)
End Sub)
' The attempt to get the result of t1 blocks the current thread until the completion source gets signaled.
' It should be a wait of ~1000 ms.
Dim sw As Stopwatch = Stopwatch.StartNew()
Dim result As Integer = t1.Result
sw.Stop()
Console.WriteLine("(ElapsedTime={0}): t1.Result={1} (expected 15) ", sw.ElapsedMilliseconds, result)
' ------------------------------------------------------------------
' Alternatively, an exception can be manually set on a TaskCompletionSource.Task
Dim tcs2 As New TaskCompletionSource(Of Integer)()
Dim t2 As Task(Of Integer) = tcs2.Task
' Start a background Task that will complete tcs2.Task with an exception
Task.Factory.StartNew(Sub()
Thread.Sleep(1000)
tcs2.SetException(New InvalidOperationException("SIMULATED EXCEPTION"))
End Sub)
' The attempt to get the result of t2 blocks the current thread until the completion source gets signaled with either a result or an exception.
' In either case it should be a wait of ~1000 ms.
sw = Stopwatch.StartNew()
Try
result = t2.Result
Console.WriteLine("t2.Result succeeded. THIS WAS NOT EXPECTED.")
Catch e As AggregateException
Console.Write("(ElapsedTime={0}): ", sw.ElapsedMilliseconds)
Console.WriteLine("The following exceptions have been thrown by t2.Result: (THIS WAS EXPECTED)")
For j As Integer = 0 To e.InnerExceptions.Count - 1
Console.WriteLine(vbLf & "-------------------------------------------------" & vbLf & "{0}", e.InnerExceptions(j).ToString())
Next
End Try
End Sub
End Module
注解
在许多情况下，使 Task<TResult> 能够表示外部异步操作非常有用。 为此，提供了 TaskCompletionSource<TResult>。 它允许创建可分发给使用者的任务。 使用者可以像处理任务成员变量的任何其他方案一样使用任务的成员。 但是，与大多数任务不同，TaskCompletionSource 创建的任务的状态由 TaskCompletionSource 上的方法显式控制。 这样就可以将外部异步操作的完成传播到基础任务。 分离还可确保使用者在无法访问相应的 TaskCompletionSource 的情况下无法转换状态。 有关详细信息，请参阅 .NET 并行编程博客中 TaskCompletionSource<TResult> 的条目。
并行扩展示例 还包含如何使用 TaskCompletionSource<TResult>的示例。
构造函数
属性
| Task |
方法
适用于
线程安全性
TaskCompletionSource<TResult> 的所有成员都是线程安全的，可以同时从多个线程使用。
另请参阅
- 将 TPL 与其他异步模式配合使用
- 如何：在任务 中包装 EAP 模式
