scala - Scala future 的理解失败

Question

我有三个连续的 Futures 并在这样的理解中使用

val comF = for {
  f1 <- future1
  f2 <- future2
  f3 <- future3
} yield {
  // something
}

comF onSuccess { }
comF onFailure { 
  // ----------------      Here is the problem  --------------------------------
  //
  // How do I know which future failed(throw exception), when the callback comes here ?
  // Thanks for the help! Different futures using different exceptions can solve it.
}

现在我有一个像 List[Future[T]] 这样的 future 列表，首先我使用这个方法将它传输到 Future[List[T]] ( Why does this list-of-futures to future-of-list transformation compile and work? )。然后我得到了 future

val fList: Future[List[T]]
fList on Failure {
  // 
  // How do I know which is Fail now >??
}

Answer 1

考虑代码:

def func = {
  try {
    val x = maybeThrows
    val y = maybeThrowsToo
    val z = maybeThrowsAsWell
    result(x, y, x)
  } catch (RuntimeException e) {
    // How do I know which maybeThrows failed?
  }
}

Future case 的工作原理基本相同。

甚至在 List 中进行分组计算没有帮助:

def func = {
  try {
    val x = maybeThrows
    val y = maybeThrowsToo
    val z = maybeThrowsAsWell
    val list = List(x, y, z)
    result(list)
  } catch (RuntimeException e) {
    // How do I know which maybeThrows failed?
  }
}

剧透:您必须明确跟踪哪个计算失败。如果使用 try/catch 完成，会产生一些样板文件.但幸运的是 Future (和 Try )样板没有那么糟糕:

class TaggedException(val idx, exc: Exception)

def tagFailedWithIndex[T](idx: Int, f: Future[T]): Future[T] = 
  future recoverWith { case exc => Future.failed(new TaggedException(idx, exc)) }

val comF = for {
  f1 <- tagFailedWithIndex(0, future1)
  f2 <- tagFailedWithIndex(1, future2)
  f3 <- tagFailedWithIndex(2, future3)
} yield something(f1, f2, f3)

comF onFailure { 
  case exc: TaggedException => "%d computation failed".format(exc.idx)
}

剧透，您必须明确跟踪哪个计算失败。如果用 try/catch 完成，会产生很多样板文件.但幸运的是有 Try , 和 Future行为更加相同:

class TaggedException(val idx, exc: Exception)

def tagFailedWithIndex[T](idx: Int, f: Future[T]): Future[T] = 
  future recoverWith { case exc => Future.failed(new TaggedException(idx, exc)) }

val comF = for {
  f1 <- tagFailedWithIndex(0, future1)
  f2 <- tagFailedWithIndex(1, future2)
  f3 <- tagFailedWithIndex(2, future3)
} yield something(f1, f2, f3)

comF onFailure { 
  case exc: TaggedException => "%d computation failed".format(exc.idx)
}