Asynchronous Action Methods and I / O Termination Ports

Question

One of the reasons why it is important to use asynchronous programming, when our application relies on external services, is to allow ASP.NET to use I / O completion ports rather than blocking a thread waiting for an external service response, ASP.NET can park execution in the I / O completion port and use the thread to participate in another request, whenever the external service responds, then ASP.NET again executes this execution and resumes it. Thus, the thread is not a block.

An example of an asynchronous method:

[HttpPost]
public async Task<ActionResult> Open(String key)
{
    Foo foo= await _externalService.GetFoo(key);
    return View(foo);
}

But what happens if we use several requests to external services? How does ASP.NET handle this?

[HttpPost]
public async Task<ActionResult> Open()
{
    List<Task<Foo>> tasks = new List<Task<Foo>>();

    foreach (var key in this.Request.Form.AllKeys)
        tasks.Add(_externalService.GetFoo(key));

    var foos = await Task.WhenAll(tasks);

    Foo foo = null;
    foreach (var f in foos)
    {
        if (foo == null && f != null)
            foo = f;
        else
            foo.Merge(f);
    }
    return View(foo);
}

-? , Task.WhenAll ?

Answer 1

- -. WhenAll .