Task.Start/Wait vs. Async/Await in .NET: When Should I Use Each Approach?

.NET Asynchronous Programming: An in-depth discussion of Task.Start/Wait and Async/Await

.NET framework provides two asynchronous programming mechanisms: Task.Start/Wait and Async/Await. While the two have similarities, there are significant differences in behavior and impact.

Task.Start/Wait

The Task.Start/Wait method requires manually starting the task and then using the Wait() method to explicitly wait for its completion. This is a common pattern in synchronous programming and is suitable primarily for short-lived, non-blocking operations. The code using Task.Start/Wait is similar to:

<code class="language-csharp">public void MyMethod()
{
  Task t = Task.Factory.StartNew(DoSomethingThatTakesTime);
  t.Wait();
  UpdateLabelToSayItsComplete();
}</code>

Create and start a new background task by calling Task.StartNew(). The Wait() method blocks the current thread until the task is completed, ensuring that subsequent code (such as updating labels) is only executed after the task is completed.

Async/Await

Async/Await (introduced in .NET 4.5) provides a more natural and efficient way to handle asynchronous operations without blocking the current thread. This approach leverages the concepts of collaborative multitasking and continuation. The code using Async/Await looks like this:

<code class="language-csharp">public async void MyMethod()
{
  var result = Task.Factory.StartNew(DoSomethingThatTakesTime);
  await result;
  UpdateLabelToSayItsComplete();
}</code>

The async keyword instructs the compiler to treat the method as an asynchronous method. When the await keyword is encountered, the current method is suspended, the asynchronous operation continues on the thread pool thread, and control is returned to the caller. When the awaited task completes, the continuation associated with await returns execution to the original method.

Key differences

The main difference between Task.Start/Wait and Async/Await is the way they handle threads. Task.Start/Wait creates and starts a background task that runs independently of the current thread. This can lead to too many threads if a large number of background tasks are created simultaneously.

Async/Await, on the other hand, does not create new threads. It yields the current thread to the thread pool and waits for the asynchronous operation to complete. Once completed, the continuation is executed on the thread pool thread that originally called the wait operation, ensuring correct thread semantics and reducing the risk of over-threading.

When to use which method

Task.Start/Wait is suitable for simple asynchronous operations that do not require additional updates or responses. It can also be used in situations where you need to block a thread intentionally, such as waiting for the user to confirm an operation before continuing.

Async/Await is ideal for long-running, user-interactive operations where the user interface must remain responsive and updated. It simplifies the processing of multiple asynchronous operations, avoids the complexity of manual task management, and ensures efficient thread utilization.

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