System.Net.HttpListener.GetContextAsync C# (CSharp) Method

        public Task<HttpListenerContext> GetContextAsync()
        {
            throw new PlatformNotSupportedException();
        }

 //static SemaphoreSlim _semaphore = new SemaphoreSlim(100);
 public static async Task<Stopwatch> TestAsync()
 {
     var server = new HttpListener();
     server.Prefixes.Add($"http://{Constants.IpAddress}:{Constants.HttpPort}/");
     server.Start();
     Console.WriteLine("HTTP-сервер готов.");
     var stopwatch = new Stopwatch();
     var contexts = new List<HttpListenerContext>();
     var firstGetContextTask =server.GetContextAsync();
     contexts.Add(await firstGetContextTask);
     Console.WriteLine("Начался HTTP-тест.");
     stopwatch.Start();
     var getContextOtherTasks = Enumerable
         .Repeat((byte)0, Constants.ClientCount - 1)
         .Select(_ =>
         {
             //_semaphore.Wait();
             var contextTask = server.GetContextAsync();
             //_semaphore.Release();
             return contextTask;
         });
     var getContextTasks = new HashSet<Task<HttpListenerContext>>
         (getContextOtherTasks)
     {
         firstGetContextTask
     };
     await ProcessAllAsync(getContextTasks);
     stopwatch.Stop();
     server.Stop();
     return stopwatch;
 }