在同一任务上多次调用等待会降低性能

Question

Is it bad practice to call await on a task that has already been waited on? Is it bad for performance?

class SomeClass 
{ 
   string Prop1; 
   string Prop2; 
}

public void SomeMethod()
{
    Task<SomeClass>[] someClassInstanceTasks = Task<SomeClass>[10];
    foreach(var task in someClassInstanceTasks)
    {
        task = GetSomeClassInstanceAsync();
    }

    someClassInstanceTasks.WaitAll();

    SomeClass someClassInstance =  someClassInstanceTasks[0].Result;
     //OR (which is recommended)
    SomeClass someClassInstance =  await someClassInstanceTasks[0];
}

Personally, I prefer the await approach as an additional safeguard in case someone introduced a bug and mucked with the WaitAll() statement.

Answer 1

In your specific case, I would just use .Result . There is no reason to await on the completed Task to get the result. There is however a reason why you wouldn't want to await on a completed Task , simply due to the fact that you need to mark your method async , which will cause you to mark up all methods that calls that one either async or you would have to implement TaskCompletion , which is a lot of effort for no gain,