scala - 如何按顺序执行scala future list

Question

我想执行按顺序返回 future 的函数列表。

以下方法的可能实现是什么:

def runSequentially[A, B](lazyFutures: List[A ⇒ Future[B]])(input: A)
(implicit ec: ExecututionContext): Future[List[B]]

测试

test("execute futures sequentially") {
    import scala.concurrent.ExecutionContext.Implicits.global

    def runSequentially[A, B](lazyFutures: List[A ⇒ Future[B]])(input: A): Future[List[B]] = ???

    val l: List[Unit ⇒ Future[Unit]] = List(
      _ ⇒ Future { Thread.sleep(1000); println(1) },
      _ ⇒ Future { Thread.sleep(5000); println(2) },
      _ ⇒ Future { Thread.sleep(500); println(3) }
    )

    Await.result(runSequentially(l)(5), 20.seconds)

  }

这应该打印:

1
2
3

Answer 1

尝试用一个线程创建一个池并像这样使用 Future.traverse

implicit val singleThreadEc: ExecutionContext = 
  ExecutionContext.fromExecutor(Executors.newSingleThreadExecutor())

def runSequentially[A, B](lazyFutures: List[A ⇒ Future[B]])(input: A): Future[List[B]] =
  Future.traverse(lazyFutures)(f => f(input))