Question

我在Scala的Future中尝试一些东西。给定执行上下文execContext，它是一个执行上下文，其下是一个最小线程= 2的动态线程池，最大线程= 2，队列大小= 1，并且中止策略为RejectedExecutionHandler和以下函数，

def getFuture(): Future[Unit] = {
   Future{
        Thread.sleep(1000000000)
   }(execContext)
}

当我在主要方法中使用转换时，

def main(args: Array[String]): Unit = {
   val task1 = getFuture()
   val task2 = getFuture()
   val task3 = getFuture()
   val task4 = try {
      getFuture()
   } catch {
     case e: Exception => e.printStackTrace()
     Future.failed(e)
  }

  val task5 = task4.transform(res => {
         println("Success")
     },
     {
       println("Failed " + Thread.currentThread().getName)
       throw new NullPointerException})(execContext)


  println("Awaiting here")
  Await.result(task5 , Duration.Inf)
}

我在输出控制台上看到以下内容（这是符号输出，并不完全是）：

  1)  java.util.concurrent.RejectedExecutionException: Task scala.concurrent.impl.Future$PromiseCompletingRunnable@5c42d2b7 rejected from java.util.concurrent.ThreadPoolExecutor@625abb97[Running, pool size = 2, active threads = 2, queued tasks = 1, completed tasks = 0]
 2) Prints "Failed main" (Apparently main thread executed that function)
 3) Exception in thread "main" java.lang.NullPointerException (Remember, I am throwing NullPointerException in failure function of transform)

我在这里有两个问题：

1）为什么转换中的失败函数由main执行   线？

2）由于整个execContext已填满，为什么我们没有收到任何rejectedExecutionException？

但是，当我在main中尝试以下代码时，它的工作方式有所不同：

   def main(args: Array[String]): Unit = {
    val task1 = getFuture()
    val task2 = getFuture()
    val task3 = getFuture()
    val task4 = try {
      getFuture()
    } catch {
      case e: Exception => e.printStackTrace()
        Future.failed(e)
    }

     val p = Promise[Unit]()

    task4.onComplete {
      case Success(r) => println("Success")
      case Failure(t) => println("Failure " + Thread.currentThread().getName)
    }(execContext)
    val task5 = p.future
    println("Awaiting here")
    Await.result(task5 , Duration.Inf)
  }

此处，输出为以下类型：

1) java.util.concurrent.RejectedExecutionException: Task scala.concurrent.impl.Future$PromiseCompletingRunnable@40f70521 rejected from java.util.concurrent.ThreadPoolExecutor@774698ab[Running, pool size = 2, active threads = 2, queued tasks = 1, completed tasks = 0]
2) prints "Awaiting here"
3) java.util.concurrent.RejectedExecutionException: Task scala.concurrent.impl.CallbackRunnable@7c541c15 rejected from java.util.concurrent.ThreadPoolExecutor@774698ab[Running, pool size = 2, active threads = 2, queued tasks = 1, completed tasks = 0]
And the program keeps on running forever

有人可以向我解释这两个程序之间的区别吗？从技术上讲，第二代码具有与transform方法几乎相同的实现（“ Try”除外）。但是，它的行为方式仍然不同。

请帮助我理解我，我想念什么？

行为异常的Future.transform

0 个答案: