When Should I Use `await Task.WhenAll` Instead of Multiple `await` Statements?

Why choose await Task.WhenAll instead of multiple await?

When dealing with asynchronous tasks, a common question is whether you should use await Task.WhenAll instead of multiple await statements. This article explores the advantages of using Task.WhenAll in specific scenarios.

Consider the following methods (DoWork1 and DoWork2) that perform a series of asynchronous tasks:

<code class="language-csharp">static async Task DoWork1()
{
    await DoTaskAsync("t1.1", 3000);
    await DoTaskAsync("t1.2", 2000);
    await DoTaskAsync("t1.3", 1000);
}

static async Task DoWork2()
{
    var t1 = DoTaskAsync("t2.1", 3000);
    var t2 = DoTaskAsync("t2.2", 2000);
    var t3 = DoTaskAsync("t2.3", 1000);
    await Task.WhenAll(t1, t2, t3);
}</code>

In both cases, the goal is to execute tasks asynchronously and continue execution after all tasks are completed. However, there are key differences between the two approaches.

1. Error handling:

Task.WhenAll has the advantage of propagating errors for all tasks at once. In DoWork1, if any tasks fail, these errors will be lost because they will be overwritten by subsequent await statements. DoWork2 on the other hand will collect and display all errors that occur during task execution.

2. Task completion semantics:

Task.WhenAll Wait for all tasks to complete, even if some tasks failed or were cancelled. This is evident in situations where a task may throw an exception or timeout. In DoWork1, if one task fails or times out, the program continues execution without waiting for other tasks. This can lead to unexpected behavior and race conditions.

3. Code readability:

Using Task.WhenAll improves the readability of your code because it clearly indicates the intention to wait for all tasks to complete. It encapsulates the async await aspect of the code, making it easier to understand the overall flow of execution.

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