Await Task.Run vs. Await Async: When Should You Choose Which?

.NET asynchronous programming: Choice of await Task.Run and await Async methods

In .NET asynchronous programming, the use of await Task.Run and await asynchronous methods is often confusing. This article will illustrate the difference between the two through a concrete scenario and provide a comprehensive understanding.

Scene:

Consider the following two code snippets:

<code class="language-csharp">await Task.Run(() => LongProcess());</code>

and

<code class="language-csharp">await LongProcess();</code>

where LongProcess is an asynchronous method containing asynchronous calls, such as await ExecuteReaderAsync().

Answer:

In this particular scenario, there is no significant difference between the two methods. Both use the await keyword to return control to the caller before the asynchronous operation in LongProcess is completed.

The nature of asynchronous execution

Contrary to popular belief, asynchronous code does not execute on multiple threads. Instead, it executes on a thread, utilizing a technique called "context switching."

When an asynchronous function calls another asynchronous function, the current thread temporarily suspends the execution of the caller and continues the execution of the callee. The operating system then assigns the suspended thread to other available tasks.

However, once a await statement is encountered in the callee, the current thread returns to the caller, effectively resuming the caller's execution.

DirectawaitAdvantages of asynchronous methods

In the given scenario, since LongProcess is already an async method, there is no need to explicitly wrap it in await before Task.Run it. Direct await asynchronous methods allow threads to immediately start performing other tasks while waiting for LongProcess to complete.

Task.Run usage scenarios

Task.Run has its specific use cases, for example:

• Start a new task without waiting for it, allowing non-blocking execution of time-consuming operations.
• Run potentially CPU-intensive operations on a background thread, freeing up the UI thread for responsive user interaction.

Summary

In the scenario given, both methods are functionally equivalent. However, the direct await asynchronous approach is preferable as it reduces thread switching and allows for more efficient use of the thread pool.

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