CODEWITHSUNDEEP
javamultithreadingscala
KAs
KAs

Reputation: 1868

Scala Process never end when applying Future and ThreadPools for Multi-threading

Here's the code snippet:

object Test {
  def main(args: Array[String]): Unit = {
    // MARK: parallelization
    val pool = Executors.newFixedThreadPool(3)
    implicit val xc = ExecutionContext.fromExecutorService(pool)
    var taskQueue = new ArrayBuffer[Future[Unit]]()

    for (i <- 0 until 10)  {
      try {
        taskQueue += Future {
          print(s"in_${i}\n")
          Thread.sleep(1000)
        }
      } catch {
        case t: Throwable =>  {
          print(t)
        }
      }
    }

    val importTasks = Future.sequence(taskQueue)
    importTasks.onSuccess { case res => print("finishOnSuccess") }
    Await.result(importTasks, Duration.Inf)
  }
}

it will hang forever after all jobs are executed with the following output:

in_1 in_2 in_0 in_4 in_3 in_5 in_8 in_6 in_7 in_9 finishOnSuccess

I tried to call System.exit(0) at the end of main method but still no use. Any suggestions? Thanks!

Upvotes: 1

Views: 108

Answers (1)

chengpohi
chengpohi

Reputation: 14217

You need to shutdown ExecutorService of pool by pool.shutdown() after Await. Since the newFixedThreadPool is creating non-daemon thread by defaultThreadFactory.

and this Post explain more about Daemon thread and Non-Daemon thread:

What is Daemon thread in Java?

Upvotes: 2

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