scala - 在做 Future.sequence 时如何知道哪个 Future 失败？

Question

这是一个示例接收我正在处理的 Actor 的一部分:

def receive = {
        case "begin" =>
            val listOfFutures: IndexedSeq[Future[Any]] = workers.map(worker => worker ? Work("test"))
            val future: Future[IndexedSeq[Any]] = Future.sequence(listOfFutures)

            future onComplete {
                case Success(result) => println("Eventual result: "+result)
                case Failure(ex) =>  println("Failure: "+ex.getMessage)
            }
        case msg => println("A message received: "+msg)
    }

当对其中一个工作人员的询问失败时(在超时的情况下)，序列 future 以失败告终。但是我想知道哪些 worker 失败了。有没有更优雅的方法，而不是简单地将 listOfFutures 一一映射而不使用 Future.sequence ?

Answer 1

您可以使用 future 的recover映射或包装底层异常的方法:

import scala.concurrent.{Future, ExecutionContext}

case class WorkerFailed(name: String, cause: Throwable) 
  extends Exception(s"$name - ${cause.getMessage}", cause)

def mark[A](name: String, f: Future[A]): Future[A] = f.recover {
  case ex => throw WorkerFailed(name, ex)
}

import ExecutionContext.Implicits.global

val f = (0 to 10).map(i => mark(s"i = $i", Future { i / i }))
val g = Future.sequence(f)

g.value  // WorkerFailed: i = 0 - / by zero