How to throttle multiple asynchronous tasks?

Question

I have some code of the following form:

static async Task DoSomething(int n) 
{
  ...
}

static void RunThreads(int totalThreads, int throttle) 
{
  var task         


        

Answer 1

First, abstract away from threads. Especially since your operation is asynchronous, you shouldn't be thinking about "threads" at all. In the asynchronous world, you have tasks, and you can have a huge number of tasks compared to threads.

Throttling asynchronous code can be done using SemaphoreSlim:

static async Task DoSomething(int n);

static void RunConcurrently(int total, int throttle) 
{
  var mutex = new SemaphoreSlim(throttle);
  var tasks = Enumerable.Range(0, total).Select(async item =>
  {
    await mutex.WaitAsync();
    try { await DoSomething(item); }
    finally { mutex.Release(); }
  });
  Task.WhenAll(tasks).Wait();
}