TaskCompletionSource<TResult> Class
Definition
Important
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Represents the producer side of a Task<TResult> unbound to a delegate, providing access to the consumer side through the Task property.
generic <typename TResult>
public ref class TaskCompletionSource
public class TaskCompletionSource<TResult>
type TaskCompletionSource<'Result> = class
Public Class TaskCompletionSource(Of TResult)
Type Parameters
- TResult
The type of the result value associated with this TaskCompletionSource<TResult>.
- Inheritance
-
TaskCompletionSource<TResult>
Examples
The following example shows how to use a 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
Remarks
In many scenarios, it is useful to enable a Task<TResult> to represent an external asynchronous operation. TaskCompletionSource<TResult> is provided for this purpose. It enables the creation of a task that can be handed out to consumers. The consumers can use the members of the task the same way as they would in any other scenario handling task member variables. However, unlike most tasks, the state of a task created by a TaskCompletionSource is controlled explicitly by the methods on TaskCompletionSource. This enables the completion of the external asynchronous operation to be propagated to the underlying Task. The separation also ensures that consumers are not able to transition the state without access to the corresponding TaskCompletionSource. For more information, see the entry The Nature of TaskCompletionSource<TResult> in the Parallel Programming with .NET blog.
The Parallel Extensions samples also contain examples of how to use TaskCompletionSource<TResult>.
Constructors
TaskCompletionSource<TResult>() |
Creates a TaskCompletionSource<TResult>. |
TaskCompletionSource<TResult>(Object) |
Creates a TaskCompletionSource<TResult> with the specified state. |
TaskCompletionSource<TResult>(Object, TaskCreationOptions) |
Creates a TaskCompletionSource<TResult> with the specified state and options. |
TaskCompletionSource<TResult>(TaskCreationOptions) |
Creates a TaskCompletionSource<TResult> with the specified options. |
Properties
Task |
Gets the Task<TResult> created by this TaskCompletionSource<TResult>. |
Methods
Equals(Object) |
Determines whether the specified object is equal to the current object. (Inherited from Object) |
GetHashCode() |
Serves as the default hash function. (Inherited from Object) |
GetType() |
Gets the Type of the current instance. (Inherited from Object) |
MemberwiseClone() |
Creates a shallow copy of the current Object. (Inherited from Object) |
SetCanceled() |
Transitions the underlying Task<TResult> into the Canceled state. |
SetCanceled(CancellationToken) |
Transitions the underlying Task<TResult> into the Canceled state using the specified token. |
SetException(Exception) |
Transitions the underlying Task<TResult> into the Faulted state and binds it to a specified exception. |
SetException(IEnumerable<Exception>) |
Transitions the underlying Task<TResult> into the Faulted state and binds a collection of exception objects to it. |
SetFromTask(Task<TResult>) |
Transitions the underlying Task<TResult> into the same completion state as the specified |
SetResult(TResult) |
Transitions the underlying Task<TResult> into the RanToCompletion state. |
ToString() |
Returns a string that represents the current object. (Inherited from Object) |
TrySetCanceled() |
Attempts to transition the underlying Task<TResult> into the Canceled state. |
TrySetCanceled(CancellationToken) |
Attempts to transition the underlying Task<TResult> into the Canceled state and enables a cancellation token to be stored in the canceled task. |
TrySetException(Exception) |
Attempts to transition the underlying Task<TResult> into the Faulted state and binds it to a specified exception. |
TrySetException(IEnumerable<Exception>) |
Attempts to transition the underlying Task<TResult> into the Faulted state and binds a collection of exception objects to it. |
TrySetFromTask(Task<TResult>) |
Attempts to transition the underlying Task<TResult> into the same completion state as the specified |
TrySetResult(TResult) |
Attempts to transition the underlying Task<TResult> into the RanToCompletion state. |
Applies to
Thread Safety
All members of TaskCompletionSource<TResult> are thread-safe and may be used from multiple threads concurrently.