According to MSDN:
Creates a task that will complete when all of the supplied tasks have completed.
When Task.WhenAll() is called, it creates a task but does that necessarily mean that it creates a new thread to execute that task? For example, how many threads are created in this console application below?
class Program { static void Main(string[] args) { RunAsync(); Console.ReadKey(); } public static async Task RunAsync() { Stopwatch sw = new Stopwatch(); sw.Start(); Task<string> google = GetString("http://www.google.com"); Task<string> microsoft = GetString("http://www.microsoft.com"); Task<string> lifehacker = GetString("http://www.lifehacker.com"); Task<string> engadget = GetString("http://www.engadget.com"); await Task.WhenAll(google, microsoft, lifehacker, engadget); sw.Stop(); Console.WriteLine("Time elapsed: " + sw.Elapsed.TotalSeconds); } public static async Task<string> GetString(string url) { using (var client = new HttpClient()) { return await client.GetStringAsync(url); } } } 
