scala - 使用 future 时程序不会终止

Question

我正在尝试对目录中的每个文件同时运行一个函数。可悲的是，每当我使用 Futures 时，我的程序都不想终止(永远运行)。我试过使用 Await.result()结果相同:/
运行代码时它执行得很好，甚至“完成？”被打印，然后它挂起......
继承人我的代码。 (我是 Scala 的新手)

val execService = Executors.newFixedThreadPool(3)
implicit val execContext = ExecutionContext.fromExecutorService(execService)

val futures = for (file <- filesList) yield Future {
   println(file)
   // theFunc(file)
}
val seq = Future.sequence(futures)
seq.onComplete {
   case Success(x) => println("finish?")
   case Failure(e) => println(e)
}

Answer 1

Executors.newFixedThreadPool引擎盖下使用 defaultThreadFactory 创建非守护线程

Returns a default thread factory used to create new threads. This factory creates all new threads used by an Executor in the same ThreadGroup... Each new thread is created as a non-daemon thread

因为这些是非守护线程，所以程序不会终止。另一方面，例如，scala.concurrent.ExecutionContext.Implicits.global创建 daemon线程

val threadFactory = new DefaultThreadFactory(daemonic = true,
                                             maxBlockers = getInt("scala.concurrent.context.maxExtraThreads", "256"),
                                             prefix = "scala-execution-context-global",
                                             uncaught = (thread: Thread, cause: Throwable) => reporter(cause))

我们注意到的地方 daemonic = true ，所以下面的程序会在最后终止

implicit val execContext = scala.concurrent.ExecutionContext.Implicits.global

val futures = for (file <- filesList) yield Future {
   println(file)
   // theFunc(file)
}
...

基于

https://stackoverflow.com/a/16612739/5205022

https://stackoverflow.com/a/28086797/5205022