C# async tasks in a queue or waiting list

问题:

i have an async Task like this:

public async Task DoWork()
{

}

And i have at the moment a:

List<Task> tmp = new List<Task>();

where i add the tasks.

I start the tasks like this:

foreach (Task t in tmp)
{
    await t;
}

Now my Question:

What`s the best way to start the tasks and only run 3 of them, at the same time (until the others are waiting)?

I think i need something like a queue/waiting list?

It should also be possible to add more tasks after the queue is started.

I`am using .NET 4.5.

Thank you for any suggestion

回答1:

Actually, the tasks start as soon as you call DoWork; when you await them, you are finishing the tasks.

One option for throttling tasks is SemaphoreSlim, which you can use as such:

private SemaphoreSlim _mutex = new SemaphoreSlim(3);
public async Task DoWorkAsync()
{
  await _mutex.WaitAsync();
  try
  {
    ...
  }
  finally
  {
    _mutex.Release();
  }
}

Another option is to use an actual queue, like an ActionBlock<T>, which has built-in throttling support.