期货/成功竞赛

我正在学习期货,我正在尝试创建一种方法,将两个期货作为参数(f和g)并返回成功完成的第一个未来,否则它返回f或g.

一些用例来说明我的方法的行为是:

Future 1        | Future 2         | Result
Success First     Success Second     Future 1
Success First     Failure Second     Future 1
Success Second    Success First      Future 2
Success Second    Failure First      Future 1
Failure First     Failure Second     Future 2 (because we had a failure on Future 1, so try to see what is the result Future 2)

所以我创建了这个方法:

def successRace(f: Future[T], g: Future[T]): Future[T] = {
        val p1 = Promise[T]()
        val p2 = Promise[T]()
        val p3 = Promise[T]()
        p1.completeWith(f)
        p2.completeWith(g)
        p3. ????
        p3.future
}

而现在,我怎么知道哪一个先完成了？