c# - 条件变量的 TPL 等价物是什么？

Question

我正在学习任务并行库(结合 C# 5.0 async/await)，我想做这样的事情:

public class Foo
{
    public void UnblockDoSomething()
    {
        DoWork();
        // notify DoSomethingAsync
    }

    public async Task DoSomethingAsync()
    {
        DoSomeWork();
        await ... // Wait until UnblockDoSomething is called
        DoMoreWork();
    }
}

在传统的线程模型中，我可以使用条件变量来完成此操作。这个问题的 TPL 解决方案是什么？

Answer 1

如果你只有一次一个通知，你可以使用TaskCompletionSource:

public class Foo
{
  private TaskCompletionSource<object> _signal = new TaskCompletionSource<object>();

  public void UnblockDoSomething()
  {
    DoWork();
    _signal.SetResult(null);
    _signal = new TaskCompletionSource<object>();
  }

  public async Task DoSomethingAsync()
  {
    var continueSignal = _signal.Task;
    DoSomeWork();
    await continueSignal;
    DoMoreWork();
  }
}

另一种选择是使用信号量 (SemaphoreSlim)，如果之前收到过信号，它将“记住”:

public class Foo
{
  private readonly SemaphoreSlim _mutex = new SemaphoreSlim(0);

  public void UnblockDoSomething()
  {
    DoWork();
    _mutex.Release();
  }

  public async Task DoSomethingAsync()
  {
    DoSomeWork();
    await _mutex.WaitAsync();
    DoMoreWork();
  }
}

如果你真的需要一个条件变量，你可以使用AsyncConditionVariable来 self 的 AsyncEx library :

public class Foo
{
  private readonly AsyncLock _mutex = new AsyncLock();
  private readonly AsyncConditionVariable _cv = new AsyncConditionVariable(_mutex);

  public void UnblockDoSomething()
  {
    using (await _mutex.LockAsync())
    {
      DoWork();
      _cv.Notify();
    }
  }

  public async Task DoSomethingAsync()
  {
    using (await _mutex.LockAsync())
    {
      DoSomeWork();
      await _cv.WaitAsync();
      DoMoreWork();
    }
  }
}