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();
}