public class Asynchronous_methods_Example {
            // 1) modify method with async 2) return Task<T> (Object needed to proceed only if awaited on from caller)
            async Task<int> StartCPUTasksAsync()
            {
                System.Console.WriteLine("Before StartCPUTasks:");
                Random x = new Random();
                List<string> idList = new List<string> { "A", "B", "C", "D" };
                IEnumerable<Task> cpuTasks = idList.Select(id => CpuTaskAsync(id, x.Next(2000, 5000)));
                await Task.WhenAll(cpuTasks); // 3) starts all cpu tasks and yeild to caller of StartCPUTasksAsync
                System.Console.WriteLine("After StartCPUTasks:"); // note: await Task.WhenAll above prevents execution of this until all io tasks complete
                return idList.Count;
            }

            Task CpuTaskAsync(string taskid, int milliseconds = 1000)
            {
                // 4) use Task.Run to spawn thread for CPU bound task
                return Task.Run(() =>
                {
                    Console.WriteLine(taskid + ": (" + milliseconds + ") CpuTaskAsync start:" + System.DateTime.Now.ToString());
                    System.Threading.Thread.Sleep(milliseconds);
                    Console.WriteLine(taskid + ": CpuTaskAsync end:" + System.DateTime.Now.ToString());
                }
               );
            }

            // 1) modify method with async 2) return Task<T> (caller is able to force waiting for Object using await)
            async Task<int> StartIOTasksAsync()
            {
                System.Console.WriteLine("Before StartIOTasksAsync:");
                List<string> UriList = new List<string> { "https://microsoft.com", "http://apple.com", "https://code-sage.com" };
                IEnumerable<Task> ioTasks = UriList.Select(uri => IoTaskAsync(uri));
                await Task.WhenAll(ioTasks);  // starts all requests up to the "await GetByteArrayAsync statement in IoTaskAsync"
                System.Console.WriteLine("After StartIOTasksAsync:");  // note: await Task.WhenAll above prevents execution of this until all IoTaskAsync(s) complete
                return UriList.Count;
            }

            // 1) modify method with async that returns Task, void (send and forget)
            async Task IoTaskAsync(string URI)
            {
                System.Console.WriteLine("IoTaskAsync start:" + URI);
                HttpClient client = new HttpClient();
                byte[] response = await client.GetByteArrayAsync(URI);  // 2) yield control to caller (i.e. StartIOTasksAsync above starts next web request)
                System.Console.WriteLine("IoTaskAsync done:" + URI); // note: resumed by OS when response available (because of the await state above
            }

            // 1) modify method with async that returns Task, void (send and forget)
            public async void StartTasksNoBlockingAtAll()
            {
                System.Console.WriteLine("StartTasksNoBlockingAtAll start");
                StartCPUTasksAsync();  //note: without await this async method returns before all cputasks complete
                StartIOTasksAsync();  //note: without await this async method returns before all io tasks complete
                System.Console.WriteLine("StartTasksNoBlockingAtAll ends");  // this will displayed before either of the above "after cpu or io tasks" messages finish
            }
            // 1) modify method with async 2) return Task<T> (caller is able to force waiting for Object using await)
            public async Task<int> StartTasksinGroupsandWaitAsync()
            {
                System.Console.WriteLine("StartTasksinGroupsandWaitAsync start");
                int x = await StartCPUTasksAsync();  // note: this async will wait for all cputask initiated with this call
                int y = await StartIOTasksAsync();  //note: this async method returns before all io tasks complete
                System.Console.WriteLine("StartTasksinGroupsandWaitAsync ends");  // this will displayed before either of the above "after cpu or io tasks" messages finish
                return x+y;
            }
        }