Await Task.Run vs. Await: When Should I Use Each Approach in Asynchronous Programming?

C# Asynchronous Programming: Differences and Applications of await Task.Run and await

In C# asynchronous programming, the use of await Task.Run and await is often confusing, especially when the difference between the two is not obvious. Understanding their differences is critical to optimizing code execution and avoiding potential problems.

Basics of asynchronous programming

Before we dive into specific scenarios, let’s briefly review the basics of asynchronous programming. Asynchronous methods in C# allow for non-blocking execution, enabling tasks to be performed in parallel without blocking the UI thread.

When an asynchronous method is called, it forms a state machine to control its execution. When the await keyword is encountered in a method, it hands control to the caller while the asynchronous operation continues in the background. After the operation is completed, the state machine resumes execution from await.

await Task.Run vs. await

In certain scenarios, await Task.Run(() => LongProcess()) and await LongProcess() may look like equivalent expressions, but there are subtle differences underneath.

await Task.Run(() => LongProcess()) will start a background thread to execute the LongProcess method, freeing the current thread to perform other tasks. After the background task completes, the thread returns to the caller and continues execution.

On the other hand, await LongProcess() means that the LongProcess method itself is an asynchronous method. In this case, the current thread does not give control to the background thread. Instead, an asynchronous state machine is formed for LongProcess, and the await keyword enables the state machine to continue execution after the asynchronous operation in LongProcess is completed.

Impact of thread behavior

The difference between

await Task.Run and await affects thread behavior:

• await Task.Run: Create a background thread to perform asynchronous operations. While the background task is running, other threads can continue executing.
• await: The current thread will be paused, and other threads can execute while the asynchronous operation in the asynchronous method is in progress.

When to use which method

In most cases, it is recommended to use LongProcess instead of await LongProcess() if await Task.Run(() => LongProcess()) is already an asynchronous method. This keeps the current thread responsive while the asynchronous operation in LongProcess is running.

However, if LongProcess is not an asynchronous method, or it performs very heavy calculations that would block the UI thread, it is recommended to use await Task.Run(() => LongProcess()) to delegate execution to a background thread.

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