Different behavior async/await in almost the same methods

Question

Let\'s say I have two async methods

public async static Task RunAsync1()
{
    await Task.Delay(2000);
    await Task.Delay(2000);
}

and

Answer 1

In the second method 2 tasks are started at the same time. They will both finish in 2 seconds (as they are running in parallel). In the first method you first run one method (2 seconds), wait for it to complete, then start the second one (2 more seconds). The key point here is Task.Delay(..) starts right when you call it, not when you await it.

To clarify more, first method:

var t1 = Task.Delay(2000); // this task is running now
await t1; // returns 2 seconds later
var t2 = Task.Delay(2000); // this task is running now
await t2; // returns 2 more seconds later

Second method:

var t1 = Task.Delay(2000); 
var t2 = Task.Delay(2000); // both are running now

await t1; // returns in about 2 seconds
await t2; // returns almost immediately, because t2 is already running for 2 seconds