C# Asynchronous Programming Guideline Cheat Sheet

async_await_best_practices_cheatsheet.md

Async Await Best Practices Cheat Sheet

Summary of Asynchronous Programming Guidelines

Name	Description	Exceptions
Avoid async void	Prefer async Task methods over async void methods	Event handlers
Async all the way	Don't mix blocking and async code	Console main method
Configure context	Use ConfigureAwait(false) when you can	Methods that require con­text

The Async Way of Doing Things

To Do This ...	Instead of This ...	Use This
Retrieve the result of a background task	Task.Wait or Task.Result	await
Wait for any task to complete	Task.WaitAny	await Task.WhenAny
Retrieve the results of multiple tasks	Task.WaitAll	await Task.WhenAll
Wait a period of time	Thread.Sleep	await Task.Delay

Know Your Tools

There's a lot to learn about async and await, and it's natural to get a little disoriented. Here's a quick reference of solutions to common problems.

Solutions to Common Async Problems

Problem	Solution
Create a task to execute code	Task.Run or TaskFactory.StartNew (not the Task constructor or Task.Start)
Create a task wrapper for an operation or event	TaskFactory.FromAsync or TaskCompletionSource<T>
Support cancellation	CancellationTokenSource and CancellationToken
Report progress	IProgress<T> and Progress<T>
Handle streams of data	TPL Dataflow or Reactive Extensions
Synchronize access to a shared resource	SemaphoreSlim
Asynchronously initialize a resource	AsyncLazy<T>
Async-ready producer/consumer structures	TPL Dataflow or AsyncCollection<T>

Async and Await Guidelines

Read the Task-based Asynchronous Pattern (TAP) document. It is extremely well-written, and includes guidance on API design and the proper use of async/await (including cancellation and progress reporting).

There are many new await-friendly techniques that should be used instead of the old blocking techniques. If you have any of these Old examples in your new async code, you're Doing It Wrong(TM):

Old	New	Description
task.Wait	await task	Wait/await for a task to complete
task.Result	await task	Get the result of a completed task
Task.WaitAny	await Task.WhenAny	Wait/await for one of a collection of tasks to complete
Task.WaitAll	await Task.WhenAll	Wait/await for every one of a collection of tasks to complete
Thread.Sleep	await Task.Delay	Wait/await for a period of time
Task constructor	Task.Run or TaskFactory.StartNew	Create a code-based task

Source http://blog.stephencleary.com/2012/02/async-and-await.html

Source

• Async/Await - Best Practices in Asynchronous Programming