Question

我开始我的一天有一个奇怪的问题。真的看不出我的代码有什么问题。按下面的行

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)

并在REPL中执行:paste。我看到一个奇怪的例外

~ > 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>

我确实认为没有Could not initialize class错误的原因。根据我的说法，代码应该打印＆＃34;失败，没有工作＆＃34;

Answer 1

问题是这个

Await.result(consolidated, Duration.Inf)

当您Await Future并且该未来失败时，会抛出它包含的异常。由于REPL的工作原理，有一个未被捕获的异常会导致它的某些机制中断。这似乎是REPL中的一个错误，但似乎还没有报道过。

注意，onComplete不会更改Future的结果。它只是安排在Future完成后要完成的事情。特别是，它不会消耗Future。如果您打算转换Future，您可以执行以下操作：

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))

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

1 个答案: