Compiler warning about async shouldn't happen

Question

So the following code triggers the compiler warning:

"Async function without await operator will run synchronously"

    public async Task UpsertMariaDb()
    {
        IEnumerable<Task> insertTasks = InsertSomethingDb();
        IEnumerable<Task> updateTasks = UpdateSomethingDb();

        Task.WaitAll(insertTasks.ToArray());
        Task.WaitAll(updateTasks.ToArray());
    }

My question is the following, is there something very basic I don't understand about async/await or is this just a compiler warning bug because I haven't put an explicit "await"

You should use the `await` keyword in a method marked as `async`. If you are just calling `Task.Wait...` you don't need to mark the method as `async`. — rhughes, Jun 18 '20 at 18:16
Did you mean to use `await Task.WhenAll()` (asynchronous) instead of `Task.WaitAll()` (synchronous)? — itsme86, Jun 18 '20 at 18:17

Christoph Sonntag · Accepted Answer · 2020-06-19T13:52:55.987

9

Task.WaitAll blocks the current thread, so the warning is correct - you try to implement an async method, but it is not async as there is nothing being awaited.

You probably meant to do:

public async Task UpsertMariaDb()
{
    IEnumerable<Task> insertTasks = InsertSomethingDb();
    IEnumerable<Task> updateTasks = UpdateSomethingDb();

    await Task.WhenAll(insertTasks);
    await Task.WhenAll(updateTasks);
}

edited Jun 19 '20 at 13:52

answered Jun 18 '20 at 18:18

Christoph Sonntag

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3

Thanks for turning my comment into an actual answer. :) – itsme86 Jun 18 '20 at 18:19
3

Sorry your comment came up when I already started typing my answer so I thought I should continue anyways ;) – Christoph Sonntag Jun 18 '20 at 18:20
2

You can remove the `.ToArray()`, it is superfluous. `Task.WhenAll` has an overload that accepts `IEnumerable`. – Johnathan Barclay Jun 19 '20 at 13:39
Thanks for the hint @JohnathanBarclay, I edited my post accordingly ;) – Christoph Sonntag Jun 19 '20 at 13:53

Compiler warning about async shouldn't happen

1 Answers1