无法初始化类$line10.$read$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$

Question

我用一个奇怪的问题开始了我的一天。我真的看不出我的代码有什么问题。取下面的几行

import scala.concurrent._
import scala.concurrent.duration._
import scala.util._
import scala.concurrent.ExecutionContext.Implicits.global

def f2 = Future.failed(new Exception("I do nothing"))
def f1 = Future { println("working"); Thread.sleep(5000); 1 }

val list = List(f2, f1)
val consolidated = Future.sequence(list)
consolidated.onComplete {
  case Success(_) => println("completed successfully")
  case Failure(e) => println(s"failed with ${e.getMessage}")
}
Await.result(consolidated, Duration.Inf)

然后在REPL中做一个:paste。我看到了一个奇怪的例外

~ > scala
Welcome to Scala 2.12.1 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_121).
Type in expressions for evaluation. Or try :help.

scala> :paste
// Entering paste mode (ctrl-D to finish)

import scala.concurrent._
import scala.concurrent.duration._
import scala.util._
import scala.concurrent.ExecutionContext.Implicits.global

def f2 = Future.failed(new Exception("no work"))
def f1 = Future { println("working"); Thread.sleep(5000); 1 }

val list = List(f2, f1)
val consolidated = Future.sequence(list)
consolidated.onComplete {
  case Success(_) => println("completed successfully")
  case Failure(e) => println(s"failed with ${e.getMessage}")
}
Await.result(consolidated, Duration.Inf)


// Exiting paste mode, now interpreting.

java.lang.NoClassDefFoundError: Could not initialize class $line3.$read$$iw$$iw$
    at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:60)
    at scala.concurrent.impl.ExecutionContextImpl$AdaptedForkJoinTask.exec(ExecutionContextImpl.scala:140)
    at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
    at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056)
    at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692)
    at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157)
java.lang.NoClassDefFoundError: Could not initialize class $line3.$read$$iw$$iw$
    at scala.runtime.java8.JFunction0$mcI$sp.apply(JFunction0$mcI$sp.java:12)
    at scala.concurrent.Future$.$anonfun$apply$1(Future.scala:653)
    at scala.util.Success.$anonfun$map$1(Try.scala:251)
    at scala.util.Success.map(Try.scala:209)
    at scala.concurrent.Future.$anonfun$map$1(Future.scala:287)
    at scala.concurrent.impl.Promise.liftedTree1$1(Promise.scala:29)
    at scala.concurrent.impl.Promise.$anonfun$transform$1(Promise.scala:29)
    at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:60)
    at scala.concurrent.impl.ExecutionContextImpl$AdaptedForkJoinTask.exec(ExecutionContextImpl.scala:140)
    at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
    at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056)
    at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692)
    at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157)
java.lang.Exception: I do nothing
  at .f2(<console>:16)
  ... 29 elided

scala>

我真的看不到Could not initialize class错误的原因。根据我的说法，代码应该只是打印"failed with no work“

Answer 1

问题是：

Await.result(consolidated, Duration.Inf)

当您对Future执行Await操作时，该操作将失败，它包含的异常将被抛出。由于REPL的工作方式，有一个未捕获的异常会导致它的一些机器崩溃。这看起来像是REPL中的一个bug，但似乎还没有被报道。

请注意，onComplete不会更改Future的结果。它只是在Future完成后安排要做的事情。具体地说，它不消耗Future。如果你打算转换Future，你可以这样做：

val transformed: Future[String] = consolidated.andThen {
  case Success(v) => "Completed successfully"
  case Failure(e) => s"Failed with ${e.getMessage}"
}

println(Await.result(transformed, Duration.Inf))