Example of semaphoreslim and wait timeout.

semaphoreslim_sample.cs

using System;
using System.Threading;
using System.Threading.Tasks;
using System.Collections.Generic;

namespace ConsoleApplication
{
    public class Program
    {
        public static void Main(string[] args)
        {
            Console.WriteLine("Hello World!");
            var lstFun = new List<Semafun>();
            lstFun.Add(new Semafun("a"));
            lstFun.Add(new Semafun("b"));
            lstFun.Add(new Semafun("c"));
            lstFun.Add(new Semafun("d"));

            var taskList = new List<Task>();

            foreach (var item in lstFun)
            {
                taskList.Add(item.StartAsync());
                //Task.Run(async() => await item.StartAsync()).Wait();
            }

            Task.WhenAll(taskList).Wait();
        }
    }
    
    public class Semafun{
        private readonly string _name;
        private readonly TimeSpan MaxTimeout = TimeSpan.FromSeconds(2);
        public Semafun(string name){
            _name = name;
        }

        private static SemaphoreSlim Sematest = new SemaphoreSlim(1,1);
        public async Task StartAsync(){
            try {
                Console.WriteLine("Start " + _name); 
                await Sematest.WaitAsync(MaxTimeout);
                Console.WriteLine("Wait completed"); 
                var result = _name  + " hello";
                await Task.Delay(1000).ConfigureAwait(false);
                Console.WriteLine(result);
                Sematest.Release();
            } catch (Exception e){
                Console.WriteLine("Errrrrrrr: " + e.Message);
            }
        }    
    }
}