C# 异步函数 - 一起使用 WhenAll 函数和 await word

Question

I need to understand something, i have a function, for example:

public static class classExample
{
     public async Task funcAsync()
    {

        List<Task<string>> exampleList= new List<Task<string>>();
        // do stuff          
        await Task.WhenAll(exampleList);
    }
}

and in my main method i have:

 main()
 {
       classExample.funcAsync();         
 }

If i use await word in main like this:

await classExample.funcAsync();

is different from without await in main? i asking because i have

await Task.WhenAll(exampleList);

inside the function.

What the different?

And more question, i have this example:

async Task function2()
{
    // do stuff
    await //for some code will be done
}

main()
{
    function2();
    function3();
}

If i not use await word so the function will continue to function3, in this case i not need that function3 waiting to function2 and this is can to continue but the question: will the function2 do all the work? in case function3 will end all the work before function2 will end. after function3 will end all the work the main function wait to function2 will ended?

Thanks!

Answer 1

If I use await word in main like this: await classExample.funcAsync(); is different from without await in main?

Yes, funcAsync returns a Task which will complete when all the exampleList Task s have completed (due to the use of Task.WhenAll ), so without using await , your Main will likely exit before those have all completed.

In your second example, not awaiting function2 will allow function3 to execute without waiting for function2 to complete, however, if function3 completes before the Task returned from function2 has completed, then your code will exit prematurely.

You can mitigate this by storing a reference to the Task and awaiting later:

var task = function2();
function3();
await task;

Or if function3 also returns a Task :

await Task.WhenAll(function2(), function3());