Тайм-ауты, IProgress<T> и асинхронные освобождаемые ресурсы (эмуляция)

План

Тайм-аут через CancelAfter

using System;
using System.Threading;
using System.Threading.Tasks;

public class Program
{
  static async Task<string> SlowOpAsync(CancellationToken ct)
  {
    // Simulate slow I/O that honors cancellation
    await Task.Delay(500, ct);
    return "OK";
  }

  public static void Main(string[] args)
  {
    var cts = new CancellationTokenSource();
    cts.CancelAfter(150); // timeout after 150 ms

    Task<string> t = SlowOpAsync(cts.Token);
    try
    {
      string result = t.GetAwaiter().GetResult(); // demo only
      Console.WriteLine(result);
    }
    catch (OperationCanceledException)
    {
      Console.WriteLine("Timed out");
    }
  }
}

Тайм-аут через WhenAny

using System;
using System.Threading.Tasks;

public class Program
{
  // Wrap any Task<T> with a timeout using WhenAny
  static async Task<T> WithTimeoutAsync<T>(Task<T> work, int milliseconds)
  {
    Task delay = Task.Delay(milliseconds);
    Task first = await Task.WhenAny(work, delay);
    if (first == work) return await work; // completed in time
    throw new TimeoutException("Operation timed out");
  }

  static async Task<int> ComputeAsync()
  {
    await Task.Delay(300); // pretend work
    return 7;
  }

  public static void Main(string[] args)
  {
    try
    {
      int v = WithTimeoutAsync(ComputeAsync(), 100).GetAwaiter().GetResult();
      Console.WriteLine("Value " + v);
    }
    catch (TimeoutException ex)
    {
      Console.WriteLine(ex.Message);
    }
  }
}

Демонстрация IProgress<T>

using System;
using System.Threading.Tasks;

public class Program
{
  static async Task DownloadAsync(IProgress<int> progress)
  {
    // Report 0..100 in steps; UI would receive ProgressChanged on its context
    for (int p = 0; p <= 100; p += 25)
    {
      await Task.Delay(60);
      if (progress != null) progress.Report(p);
    }
  }

  public static void Main(string[] args)
  {
    Progress<int> prog = new Progress<int>(percent =>
    {
      Console.WriteLine("Progress: " + percent + "%");
    });

    DownloadAsync(prog).GetAwaiter().GetResult();
  }
}

Шаблон асинхронной очистки

using System;
using System.IO;
using System.Threading.Tasks;

public class Program
{
  static async Task WriteThenCloseAsync(string path)
  {
    // C# 6 has no IAsyncDisposable; emulate with try/finally.
    FileStream fs = null;
    StreamWriter sw = null;
    try
    {
      fs = new FileStream(path, FileMode.Create, FileAccess.Write, FileShare.None);
      sw = new StreamWriter(fs);
      await sw.WriteAsync("hello"); // do async work
      await sw.FlushAsync();        // ensure data is flushed
    }
    finally
    {
      // Dispose synchronously in finally
      if (sw != null) sw.Dispose();
      else if (fs != null) fs.Dispose();
    }
  }

  public static void Main(string[] args)
  {
    WriteThenCloseAsync("out.txt").GetAwaiter().GetResult();
    Console.WriteLine("Written");
  }
}

Рекомендации

Шаблон тайм-аута

Итоги