为什么我应该使用等待？

Question

I am new to async / await. but I created the POC but I am still confused.

Outcome of method

public async void WriteLineFunc(string str)
    {
        await Task.Factory.StartNew(() => WaitFor2Secs());
        //WaitFor2Secs();
        Console.WriteLine(str);
    }

and

public async void WriteLineFunc(string str)
    {
        //await Task.Factory.StartNew(() => WaitFor2Secs());
        WaitFor2Secs();
        Console.WriteLine(str);
    }

is same. What is point of making a method as await? Just to run a function on other thread and wait for its completion?

Answer 1

When a method uses await , it can return to its caller before it's complete.

Consider this example:

public async Task WriteLineFuncAsync(string str)
{
  await Task.Delay(2000);
  Console.WriteLine(str);
}

public void WriteLineFunc(string str)
{
  Thread.Sleep(2000);
  Console.WriteLine(str);
}

WriteLineFunc will synchronously block the running thread for 2 seconds and then write out the string. WriteLineFuncAsync will immediately return an incomplete Task to its caller; two seconds later, it will write out the string and then complete the Task .

For client-side applications, the main benefit is responsiveness (the GUI thread is not blocked). For server-side applications, the main benefit is scalability (you can have far more responses than threads).