Question

当我尝试运行下面的代码时，执行同步操作。 为什么？

我收到以下警告......

警告1此异步方法缺少'await'运算符并将同步运行。考虑使用'await'运算符等待非阻塞API调用，或'await Task.Run（...）'在后台线程上执行CPU绑定工作。

private async void btProcessa_Click(object sender, EventArgs e)
{
    await ProcessaA();
    await ProcessaB();
}

public async Task ProcessaA()
{
    for (int i = 0; i <= 100; i++)
    {
        pbProcessoA.Value = i;
        Thread.Sleep(500);
    }
}

public async Task ProcessaB()
{
    for (int i = 0; i <= 100; i++)
    {
        pbProcessoB.Value = i;
        Thread.Sleep(500);
    }
}

Answer 1

async并不意味着“在后台线程上运行此代码”。如果您想了解async的更多信息，我有introductory blog post，MSDN docs很棒，而且full guide to the Task-based Asynchronous Pattern。

如果要对I / O绑定（或基于事件）的操作进行一些模拟，则应使用Task.Delay而不是Thread.Sleep：

public async Task ProcessaA()
{
  for (int i = 0; i <= 100; i++)
  {
    pbProcessoA.Value = i;
    await Task.Delay(500);
  }
}

如果您想模拟CPU绑定操作，那么您应该通过Task.Run将它们推送到后台任务：

public async Task ProcessaA()
{
  for (int i = 0; i <= 100; i++)
  {
    pbProcessoA.Value = i;
    await Task.Run(() => { Thread.Sleep(500); });
  }
}

Answer 2

我把这个例子写成了一个真实的生产系统。将实体保存在数据库中可能需要一些时间。看看这个优雅的模拟

class TestAsyncAwait
{
    public void GetEntities()
    {
        for (int i = 0; i < 4; i++)
        {
            var a = getEntities(i);
            saveEntitiesAsync(a);
        }
        Console.WriteLine("\nPress any key to close\n");
        Console.ReadKey();
    }

    private List<string> getEntities(int i)
    {
        Console.Write("getting Entities for id={0}...", i);
        Thread.Sleep(2000);
        var r = new List<string> { i.ToString(), " Hello!" };
        Console.WriteLine("done, has the Entities for id={0}\n", i);
        return r;
    }

    async void saveEntitiesAsync(List<string> a)
    {
        var sb = new StringBuilder();
        await Task.Run(() =>
        {
            Thread.Sleep(4000); // simulates long task
            foreach (string s in a) sb.Append(s);
        });
        // shows the thread in action
        Trace.WriteLine("saved: " + sb.ToString());
    }
}

等待异步不起作用。为什么？

2 个答案: