使用任务。然后等待结果:

var tCat = FeedCat();
var tHouse = SellHouse();
var tCar = BuyCar();
await Task.WhenAll(tCat, tHouse, tCar);
Cat cat = await tCat;
House house = await tHouse;
Tesla car = await tCar; 
//as they have all definitely finished, you could also use Task.Value.

The three tasks in your example differ greatly in importance. In case one of them fails, you probably want to know what happened with the others. For example in case the communication with the automatic cat feeder failed, you don't want to miss whether selling your house succeeded or failed. So it makes sense to return back not just a Cat, a House and a Tesla, but the tasks themselves. The calling code will then be able to query separately each of the three tasks, and react appropriately to their successful or failed completions:

public async Task<(Task<Cat>, Task<House>, Task<Tesla>)> FeedCatSellHouseBuyCar()
{
    Task<Cat> task1 = FeedCat();
    Task<House> task2 = SellHouse();
    Task<Tesla> task3 = BuyCar();

    // All three tasks are launched at this point.

    try { await Task.WhenAll(task1, task2, task3).ConfigureAwait(false); } catch { }

    // All three tasks are completed at this point.
    
    return (task1, task2, task3);
}

使用的例子:

var (catTask, houseTask, teslaTask) = await FeedCatSellHouseBuyCar();

// All three tasks are completed at this point.

if (catTask.IsCompletedSuccessfully)
    Console.WriteLine($"{catTask.Result.Name} is eating her healthy meal.");
else
    Console.WriteLine("Your cat is starving!");

if (houseTask.IsCompletedSuccessfully)
    Console.WriteLine($"Your house at {houseTask.Result.Address} was sold. You are now rich and homeless!");
else
    Console.WriteLine("You are still the poor owner of your house.");

if (teslaTask.IsCompletedSuccessfully)
    Console.WriteLine($"You are now the owner a battery-powered {teslaTask.Result.Name}.");
else
    Console.WriteLine("You are still driving a Hyundai.");

带有空catch的try块是必需的，因为. net 7仍然没有提供适当的方法来等待任务，而不会在取消或失败时抛出。

提出警告

对于那些访问这个线程和其他类似线程寻找使用async+await+task工具集并行化EntityFramework的方法的人来说，这里显示的模式是合理的，然而，当涉及到EF的特殊雪花时，除非在每个* async()调用中使用单独的(新的)db-context-instance，否则无法实现并行执行。

这类事情是必要的，因为ef-db-context固有的设计限制禁止在同一个ef-db-context实例中并行运行多个查询。

利用已经给出的答案，这是确保你收集所有值的方法，即使在一个或多个任务导致异常的情况下:

  public async Task<string> Foobar() {
    async Task<string> Awaited(Task<Cat> a, Task<House> b, Task<Tesla> c) {
        return DoSomething(await a, await b, await c);
    }

    using (var carTask = BuyCarAsync())
    using (var catTask = FeedCatAsync())
    using (var houseTask = SellHouseAsync())
    {
        if (carTask.Status == TaskStatus.RanToCompletion //triple
            && catTask.Status == TaskStatus.RanToCompletion //cache
            && houseTask.Status == TaskStatus.RanToCompletion) { //hits
            return Task.FromResult(DoSomething(catTask.Result, carTask.Result, houseTask.Result)); //fast-track
        }

        cat = await catTask;
        car = await carTask;
        house = await houseTask;
        //or Task.AwaitAll(carTask, catTask, houseTask);
        //or await Task.WhenAll(carTask, catTask, houseTask);
        //it depends on how you like exception handling better

        return Awaited(catTask, carTask, houseTask);
   }
 }

具有或多或少相同性能特征的替代实现可以是:

 public async Task<string> Foobar() {
    using (var carTask = BuyCarAsync())
    using (var catTask = FeedCatAsync())
    using (var houseTask = SellHouseAsync())
    {
        cat = catTask.Status == TaskStatus.RanToCompletion ? catTask.Result : (await catTask);
        car = carTask.Status == TaskStatus.RanToCompletion ? carTask.Result : (await carTask);
        house = houseTask.Status == TaskStatus.RanToCompletion ? houseTask.Result : (await houseTask);

        return DoSomething(cat, car, house);
     }
 }

var dn = await Task.WhenAll<dynamic>(FeedCat(),SellHouse(),BuyCar());

如果你想访问Cat，你可以这样做:

var ct = (Cat)dn[0];

这是非常简单的做法和非常有用的使用，没有必要去追求一个复杂的解决方案。

如果你正在使用c# 7，你可以使用一个方便的包装方法，像这样…

public static class TaskEx
{
    public static async Task<(T1, T2)> WhenAll<T1, T2>(Task<T1> task1, Task<T2> task2)
    {
        return (await task1, await task2);
    }
}

.．.当您希望等待多个具有不同返回类型的任务时，可以启用这样的方便语法。当然，您必须对等待的不同数量的任务进行多次重载。

var (someInt, someString) = await TaskEx.WhenAll(GetIntAsync(), GetStringAsync());

但是，如果您打算把这个例子变成现实，请参阅Marc Gravell对ValueTask和已经完成的任务的一些优化的回答。

await语句不是使代码按顺序运行吗?考虑以下代码

class Program
{
    static Stopwatch _stopwatch = new();

    static async Task Main(string[] args)
    {
        Console.WriteLine($"fire hot");
        _stopwatch.Start();
        var carTask = BuyCar();
        var catTask = FeedCat();
        var houseTask = SellHouse();
        await carTask;
        await catTask;
        await houseTask;
        Console.WriteLine($"{_stopwatch.ElapsedMilliseconds} done!");

        Console.WriteLine($"using await");
        _stopwatch.Restart();
        await BuyCar();
        await FeedCat();
        await SellHouse();            

        Console.WriteLine($"{_stopwatch.ElapsedMilliseconds} done!");
    }

    static async Task BuyCar()
    {
        Console.WriteLine($"{_stopwatch.ElapsedMilliseconds} buy car started");
        await Task.Delay(2000);
        Console.WriteLine($"{_stopwatch.ElapsedMilliseconds} buy car done");
    }

    static async Task FeedCat()
    {
        Console.WriteLine($"{_stopwatch.ElapsedMilliseconds} feed cat started");
        await Task.Delay(1000);
        Console.WriteLine($"{_stopwatch.ElapsedMilliseconds} feed cat done");
    }

    static async Task SellHouse()
    {
        Console.WriteLine($"{_stopwatch.ElapsedMilliseconds} sell house started");
        await Task.Delay(10);
        Console.WriteLine($"{_stopwatch.ElapsedMilliseconds} sell house done");
    }
}

fire hot
0 buy car started
3 feed cat started
4 sell house started
18 sell house done
1004 feed cat done
2013 buy car done
2014 done!
using await
0 buy car started
2012 buy car done
2012 feed cat started
3018 feed cat done
3018 sell house started
3033 sell house done
3034 done!