C# · 12月 26, 2021

c# – 使用TaskCompletionSource实现异步方法

我有一个黑盒子对象暴露一个异步操作的方法,当操作完成时触发一个事件.我把它包装成一个任务< OpResult> Black@R_946_2419@OperationAysnc()方法使用TaskCompletionSource – 这很好.

但是,在该异步包装器中,如果在给定超时后未收到事件,我想管理异步调用与超时错误.目前我用一个计时器来管理它:

public Task<OpResult> Black@R_946_2419@OperationAysnc() { var tcs = new TaskCompletionSource<TestResult>(); const int timeoutMs = 20000; Timer timer = new Timer(_ => tcs.TrySetResult(OpResult.Timeout),null,timeoutMs,Timeout.Infinite); EventHandler<EndOpEventArgs> eventHandler = (sender,args) => { … tcs.TrySetResult(OpResult.BlarBlar); } black@R_946_2419@.EndAsyncOpEvent += eventHandler; black@R_946_2419@.StartAsyncOp(); return tcs.Task;}

这是管理超时的唯一方法吗?有没有设置自己的计时器 – 我看不到任何超时内置在TaskCompletionSource?

解决方法 您可以使用 CancellationTokenSource超时.与您的TaskCompletionSource一起使用,如 this.

例如.:

public Task<OpResult> Black@R_946_2419@OperationAysnc() { var tcs = new TaskCompletionSource<TestResult>(); const int timeoutMs = 20000; var ct = new CancellationTokenSource(timeoutMs); ct.Token.Register(() => tcs.TrySetCanceled(),useSynchronizationContext: false); EventHandler<EndOpEventArgs> eventHandler = (sender,args) => { … tcs.TrySetResult(OpResult.BlarBlar); } black@R_946_2419@.EndAsyncOpEvent += eventHandler; black@R_946_2419@.StartAsyncOp(); return tcs.Task;}

更新了,这里有一个完整的功能示例:

using System;using System.ComponentModel;using System.Threading;using System.Threading.Tasks;namespace ConsoleApplication{ public class Program { // .NET 4.5/C# 5.0: convert EAP pattern into TAP pattern with timeout public async Task<AsyncCompletedEventArgs> Black@R_946_2419@OperationAsync( object state,CancellationToken token,int timeout = Timeout.Infinite) { var tcs = new TaskCompletionSource<AsyncCompletedEventArgs>(); // prepare the timeout CancellationToken newToken; if (timeout != Timeout.Infinite) { var cts = CancellationTokenSource.CreateLinkedTokenSource(token); cts.CancelAfter(timeout); newToken = cts.Token; } else newToken = token; // handle completion AsyncCompletedEventHandler handler = (sender,args) => { if (args.Cancelled) tcs.TrySetCanceled(); else if (args.Error != null) tcs.SetException(args.Error); else tcs.SetResult(args); }; this.Black@R_946_2419@OperationCompleted += handler; try { using (newToken.Register(() => tcs.SetCanceled(),useSynchronizationContext: false)) { this.StartBlack@R_946_2419@Operation(null); return await tcs.Task.ConfigureAwait(continueOnCapturedContext: false); } } finally { this.Black@R_946_2419@OperationCompleted -= handler; } } // emulate async operation AsyncCompletedEventHandler Black@R_946_2419@OperationCompleted = delegate { }; void StartBlack@R_946_2419@Operation(object state) { ThreadPool.QueueUserWorkItem(s => { Thread.Sleep(1000); this.Black@R_946_2419@OperationCompleted(this,new AsyncCompletedEventArgs(error: null,cancelled: false,userState: state)); },state); } // test static void Main() { try { new Program().Black@R_946_2419@OperationAsync(null,CancellationToken.None,1200).Wait(); Console.WriteLine(“Completed.”); new Program().Black@R_946_2419@OperationAsync(null,900).Wait(); } catch (Exception ex) { while (ex is AggregateException) ex = ex.InnerException; Console.WriteLine(ex.Message); } Console.ReadLine(); } }}

可以找到.NET 4.0 / C#4.0 vesion here,它利用编译器生成的IEnumerator状态机.