Need to understand the usage of SemaphoreSlim

Question

Here is the code I have but I don\'t understand what SemaphoreSlim is doing.

async Task WorkerMainAsync()
{
    SemaphoreSlim ss = new Semaphore         


        

Answer 1

i guess that if i run 50 thread at a time then code like SemaphoreSlim ss = new SemaphoreSlim(10); will force to run 10 active thread at time

That is correct; the use of the semaphore ensures that there won't be more than 10 workers doing this work at the same time.

Calling WaitAsync on the semaphore produces a task that will be completed when that thread has been given "access" to that token. await-ing that task lets the program continue execution when it is "allowed" to do so. Having an asynchronous version, rather than calling Wait, is important both to ensure that the method stays asynchronous, rather than being synchronous, as well as deals with the fact that an async method can be executing code across several threads, due to the callbacks, and so the natural thread affinity with semaphores can be a problem.

A side note: DoPollingThenWorkAsync shouldn't have the Async postfix because it's not actually asynchronous, it's synchronous. Just call it DoPollingThenWork. It will reduce confusion for the readers.