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Async await meme
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Introduction
Imagine you’re a chef in a kitchen full of ingredients, some fresh, some a bit past their prime, all thanks to Microsoft’s “We never throw anything away” policy. This is what programming asynchronously in C# is like — an overwhelming mix of new and old syntax all in one big pot.
This pot can turn to be a big ball of code mud, you could end up with the coding equivalent of food poisoning: thread starvation, deadlocks, or even the dreaded application crashes. Most of these problems boil down to a lack of understanding of the underlying concepts such as state machines, the thread pool, context switching etc…
I drafted a document for my team explaining those concepts and decided to narrow it down to a simple 10 rule cook book here as those are pretty common in the industry. There’s a lot more than 10 rules, feel free to let me know if you want the rest !
1) Do not use Async void
From all the rules, this one is the most critical potentially crashing your whole application. async void can’t be tracked and if any exception is triggered, it will crash the whole application.
In a previous project, this caused our whole API to crash randomly on production because of an async void present in a background service.
public void BadAddUserAsync(User user); //You should not do this
public Task GoodAddUserAsync(User user); //Do this instead!
2) Use ValueTask or Task.FromResult for easy computations
The below example is considered bad, wasting a thread pool thread to return something that does not need an async call.
public Task<int> BadComputeDiscountAsync(User user) => Task.Run(()
=> 0.3 * user.BaskedAmount);
You should definitely use ValueTask<T> here to avoid using an extra thread AND save a minor Task allocation.
public Task<int> BestComputeDiscountAsync(User user)
=> new ValueTask<int>(0.3 * user.BaskedAmount);