如何捕获 Task.Delay() 取消并进行回调？

Question

假设我有一个工人阶级。

public sealed class Worker : IDisposable
{
    private bool _isRunning;
    private CancellationTokenSource _cts;

    private readonly Action _action;
    private readonly int _millisecondsDelay;
    private readonly object _lock = new object();

    public Worker(Action action, int millisecondsDelay)
    {
        _action = action;
        _millisecondsDelay = millisecondsDelay = 5000;
    }

    public void Start()
    {
        lock (_lock)
        {
            if (!_isRunning)
            {
                _isRunning = true;
                Run();
            }
        }
    }

    public void Cancel()
    {
        lock (_lock)
        {
            if (_isRunning) _cts.Cancel();
        }
    }

    private void Run()
    {
        using (_cts) _cts = new CancellationTokenSource();
        Task.Run(async () => { await DoAsync(_cts.Token); });
    }

    private async Task DoAsync(CancellationToken cancellationToken)
    {
        while (!cancellationToken.IsCancellationRequested)
        {
            //Log.Message1("____REFRESHING STATUS____");
            _action();
            await Task.Delay(_millisecondsDelay, cancellationToken);
        }

        //this code is unreachable
        lock (_lock)
        {
            _isRunning = false;
        }
    }

    public void Dispose()
    {
        try
        {
            _cts?.Cancel();
        }
        finally
        {
            if (_cts != null)
            {
                _cts.Dispose();
                _cts = null;
            }
        }
    }
}

问题是代码_isRunning = false; 无法访问。我的意思是当调用者调用Cancel 方法时，工作人员更有可能等待Task.Delay。那么在我的任务被取消之后，我怎么能打电话给 smth（这里是 _isRunning = false;）？换句话说，我需要确保我的工人没有运行（它不是取消状态）

Answer 1

要回答您的字面问题，您可以使用finally 块：

private async Task DoAsync(CancellationToken cancellationToken)
{
  try
  {
    while (!cancellationToken.IsCancellationRequested)
    {
      //Log.Message1("____REFRESHING STATUS____");
      _action();
      await Task.Delay(_millisecondsDelay, cancellationToken);
    }
  }
  finally
  {
    lock (_lock)
    {
      _isRunning = false;
    }
  }
}

但我对这种“工人”方法有些担忧：

• 我不是Run 内部的即发即弃的超级粉丝。我怀疑你会想要改变它。
• 将lock 与异步代码混合可能会出现问题。您应该绝对确定这是您真正想做的事情。

也许值得退后一步，重新考虑一下你真正想要用这段代码做什么。