具有超时的WriteAsync

本文介绍了具有超时的WriteAsync的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我尝试编写一个具有超时的简单异步写入，如下所示，并且在缓冲区很大且等待时间很小的情况下，我希望该函数抛出TaskCanceledException。但是，这不会发生。 WriteAsync将阻塞许多秒钟，直到写入完成。我想念什么？

I try to code a simple async write with timeout as below and expect the function to throw a TaskCanceledException given a very large buffer and small waitTime. However, this does not happen. WriteAsync will block for many seconds until the write completes. What am I missing?

public async void WriteWithTimeout(Stream os, byte[] buf, int waitMs) { CancellationTokenSource tokenSource = new CancellationTokenSource(waitMs); // cancel after waitMs milliseconds. await os.WriteAsync(buf, 0, buf.Length, tokenSource.Token); return; }

从GUI线程调用：

try { WriteWithTimeout(response.OutputStream, buf100M, w1ms); } catch(OperationCanceledException e) { ConsoleWriteLine("Failed with exception: {0}", e.Message); }

推荐答案

异步无效。它必须返回一个任务，您必须等待它。

You can't catch a async void. It must return a task and you have to await it.

public async Task WriteWithTimeout(Stream os, byte[] buf, int waitMs) { CancellationTokenSource tokenSource = new CancellationTokenSource(waitMs); // cancel after waitMs milliseconds. await os.WriteAsync(buf, 0, buf.Length, tokenSource.Token); return; }

gui代码

try { await WriteWithTimeout(response.OutputStream, buf100M, w1ms); } catch(OperationCanceledException e) { ConsoleWriteLine("Failed with exception: {0}", e.Message); }

取消仍会发生，但您只是看不到它们。

The cancellations still happen but you just don't observe them.

更新：

os.WriteAsync（只是一个同步完成，由 Task.Run（在幕后 1 支持。取消令牌不会取消已经运行的 Task.Run（。在这种情况下，最好的方法是将取消内容包装在 Task.WhenAny（令牌也通过无限长的 Task.Delay（。

It is possible that os.WriteAsync( is just a synchronous completion just backed by a Task.Run( behind the scenes1. The cancellation token won't cancel a already running Task.Run(. In that case the best way is to wrap the cancellation up in a Task.WhenAny( and pass in the token to there too via a infinitely long Task.Delay(.

public async Task WriteWithTimeout(Stream os, byte[] buf, int waitMs) { CancellationTokenSource tokenSource = new CancellationTokenSource(waitMs); // cancel after waitMs milliseconds. var task = os.WriteAsync(buf, 0, buf.Length, tokenSource.Token); var waitedTask = await Task.WhenAny(task, Task.Delay(-1, token)); await waitedTask; //Wait on the returned task to observe any exceptions. }

1。例如，如果不将 FileOptions.Asynchronous 传递给构造函数，则这是 FileStream 的默认行为

1. For example that is the default behavior of a FileStream if you don't pass inFileOptions.Asynchronous to the constructor