Should I Await or Return Tasks in Async C# Methods?

Awaiting vs Returning in Async Methods: Consequences Explored

When working with asynchronous programming in C#, developers often encounter the question of whether to await an async method call within another async method or simply return the task. While both approaches may seem valid, each option has distinct consequences that warrant consideration.

Option A: Returning the Task Directly

In this approach, the async method directly returns the task obtained from the nested async call. This is akin to writing:

Task FooAsync()
{
    return BazAsync();  // Option A
}

Consequences:

• The caller is responsible for awaiting the returned task.
• The method can be called from both synchronous and asynchronous contexts.
• Exceptions thrown within the synchronous code in the method will be delivered synchronously.
• Argument validation can be performed synchronously.

Option B: Awaiting the Task

When awaiting the task, the async method explicitly waits for the nested async call to complete. This is written as:

async Task BarAsync()
{
    await BazAsync(); // Option B
}

Consequences:

• The method must be declared as async since it performs an await operation.
• The caller does not need to await the method itself.
• Exceptions thrown within the asynchronous code will be delivered asynchronously.
• Argument validation cannot be performed synchronously.

Choosing the Right Option

The choice between returning or awaiting depends on the specific scenario and requirements.

If the method performs a small amount of synchronous work and calls only one async method, returning the task (Option A) can be a more efficient approach. However, if the method needs to do additional asynchronous work or handle exceptions asynchronously, then awaiting the task (Option B) is the appropriate choice.

It's important to note that methods declared as async cannot return tasks directly. If a method must return a task, it must itself be declared as async.

Practical Example

Consider the following code snippet:

// Version 1:
Task BarAsync()
{
    // No need to gronkle yet...
    return BazAsync();
}

// Oops, for version 2 I need to do some more work...
async Task BarAsync()
{
    int gronkle = await GronkleAsync();
    // Do something with gronkle

    // Now we have to await BazAsync as we're now in an async method
    await BazAsync();
}

Initially, the method BarAsync didn't need to await BazAsync, so it returned the task directly. However, when additional asynchronous work was introduced, BarAsync had to be converted into an asynchronous method and await BazAsync.

By understanding the consequences of returning or awaiting in async methods, developers can implement asynchronous code effectively and avoid potential pitfalls.

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