Await / Async in .NET

Asynchronous programming is not something that can be explained in comments. You should get out and read as many articles as possible. Be forewarned, though, that many tutorials out there have the mindset that asynchronous programming is about multi threading. It is NOT. Multi threading is just one form of asynchronous programming.

Imagine you are cooking mashed potatoes. Let's define the process in 5 tasks:

1. Dice potatoes.
2. Cook the diced potatoes.
3. Grate cheese.
4. Mash potatoes.
5. Mix the mashed potatoes with the grated cheese.

You will do this alone. You are the thread.

You could go through the list of tasks and do this list sequentially, one task after the other. You noticed, however, that you were doing nothing while the potatoes were being cooked. You could have grated the cheese while the potatoes were cooking. So you repeat the process, this time not waiting for the potatoes to cook. Clearly this is an improvement. Now you (the thread) are able to finish faster. You have made better use of the CPU time.

In code:

DicePotatoes(); // Synchronous task.
var cookTask = CookPotatoes(); // Asynchronous task.  You start it, but you don't await it.
GrateCheese(); // Synchronous task.
// Now you are ready to mash, then mix.
// Now you await.
await cookTask;
// Now you complete the recipe.
MashPotatoes(); // Synchronous task.
Mix(); // Synchronous task.

So the lesson here is twofold:

1. We did asynchronous programming, and we did not use another thread. We did single-threaded asynchronous programming.
2. You only await when you absolutely have to. Do not immediately and blindly await any async function. The await keyword synchronizes. Only use it when you need to synchronize.