multiple awaits vs Task.WaitAll – equivalent?

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The first option will not execute the two operations concurrently. It will execute the first and await its completion, and only then the second.

The second option will execute both concurrently but will wait for them synchronously (i.e. while blocking a thread).

You shouldn’t use both options since the first completes slower than the second and the second blocks a thread without need.

You should wait for both operations asynchronously with Task.WhenAll:

public async Task<IHttpActionResult> MethodB()
{
    var customer = new Customer();

    var getAllWidgetsTask = _widgetService.GetAllWidgets();
    var getAllFoosTask = _fooService.GetAllFos();

    await Task.WhenAll(getAllWidgetsTask, getAllFoosTask);

    customer.Widgets = await getAllWidgetsTask;
    customer.Foos = await getAllFoosTask;

    return Ok(customer);
}

Note that after Task.WhenAll completed both tasks already completed so awaiting them completes immediately.

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