没有等待的异步任务的第二次实现

Question

What can I do when I have an interface that returns a task (void) but one of the implementations has no async action?

My interface IDatabaseService has two implementations: FirestoreDatabaseService and CacheDatabaseService . It makes sense for FirestoreDatabaseService to use the Method async Task AddResult(ResultDto result) as result of a method but the CacheDatabaseService has only a list and needs no await, it is basically a void method.

I get a warning "Warning CS1998 This async method lacks 'await' operators and will run synchronously. Consider using the 'await' operator to await non-blocking API calls, or 'await Task.Run(...)'" when I implement the method in CacheDatabaseService async. If I remove the async I have to return a task but Task.FromResult does not work for void Tasks.

Answer 1

That warning almost always means your method should not be async .

The async keyword really just enables the use of await . So if you aren't using await , you don't need async .

If AddResult must return a Task , then return a Task . If you aren't actually doing anything asynchronous, then you can return Task.CompletedTask .

For example:

public Task AddResult(ResultDto result) {
    ...
    return Task.CompletedTask;
}

If you have to return a value ( Task<T> ), then you can use Task.FromResult() .

An interface that specifies that a method should return a Task is just a way of making it possible to make the method async . It doesn't mean it must.