如何在C＃中使受控无限循环异步？

Question

I found this

Run async method regularly with specified interval

which does half of what I want, but at the same time I want to be able to stop the loop whenever I want and then resume it as well. However while it's stopped, I don't want the infinite loop to keep running where the body gets skipped through a flag.

Basically I don't want this

while (true) {
    if (!paused) {
        // run work
    }
    // task delay
}

because then the while loop still runs.

How can I set it so that while its paused, nothing executes?

Answer 1

How can I set it so that while its paused, nothing executes?

That's hard to answer: if you define "pause" as: the object state remains valid while the loop doesn't use any resources then you'll have to stop and restart it (the loop).

All other timers, including Thread.Sleep , Task.Delay s etc. will put your thread in idle/suspended mode.

If that's not sufficient for your needs, you'll need to actually stop the "infinite" loop.

It will free up thread related resources as well.

More info about sleep:

Thread.Sleep

More about sleep

Answer 2

You could use System.Threading.Timer and dispose of it while it is not in use and re-create it when you are ready to "resume". These timers are light weight so creating and destroying them on demand is not a problem.

private System.Threading.Timer _timer;

public void StartResumeTimer()
{
  if(_timer == null)
    _timer = new System.Threading.Timer(async (e) => await DoWorkAsync(e), null, 0, 5000);
}

public void StopPauseTimer()
{
  _timer?.Dispose();
  _timer = null;
}

public async Task DoWorkAsync(object state)
{
   await Task.Delay(500); // do some work here, Task.Delay is just something to make the code compile
}

Answer 3

If you are really adverse to timers and want it to look like a while loop, then you can use TaskCompletionSource<T> :

private TaskCompletionSource<bool> _paused = null;

public async Task DoWork()
{
    while (true)
    {
        if (_paused != null)
        {
            await _paused.Task;
            _paused = null;
        }
        //run work
        await Task.Delay(100);
    }
}

public void Pause()
{
    _paused = _paused ?? new TaskCompletionSource<bool>();
}

public void UnPause()
{
    _paused?.SetResult(true);
}