Scala 在播放框架关闭期间，如何等待演员停止？

当我关闭播放服务器时，下面的代码抛出一个java.lang.IllegalMonitorStateException异常；它是由onStop方法中的a.wait（1000）调用引起的。有谁能告诉我为什么会出现这种情况，以及如何优雅地等待演员在Play框架内完成关机

import play.api.GlobalSettings
import play.api.libs.concurrent.Akka
import akka.actor.{ Actor, Props }
import play.api.libs.concurrent.Execution.Implicits.defaultContext
import play.api.Play.current
import models.{ TestActor, StartMessage, StopMessage }

object Global extends GlobalSettings {

    override def onStart(application : play.api.Application) {
        val a = Akka.system.actorOf(Props[TestActor], name = "test-actor")
        a ! StartMessage("Start instruction")

    }

    override def onStop(application : play.api.Application) {
        val a = Akka.system.actorSelection("akka://application/user/test-actor")
        a ! StopMessage("Stop instruction")
        a.wait(1000)
        Akka.system.shutdown()
    }
}

更新：

以下是完整的解决方案，回答如下：

import play.api.GlobalSettings
import play.api.libs.concurrent.Akka
import akka.actor.{ Actor, Props }
import play.api.libs.concurrent.Execution.Implicits.defaultContext
import play.api.Play.current
import models.{ TestActor, StartMessage, StopMessage }
import akka.pattern.gracefulStop
import scala.concurrent.Future
import scala.concurrent.duration.FiniteDuration
import scala.concurrent.Await
import com.typesafe.config.impl.ResolveContext
import com.typesafe.config.impl.ResolveContext
import akka.actor.ActorIdentity

object Global extends GlobalSettings {

    override def onStart(application : play.api.Application) {
        val a = Akka.system.actorOf(Props[TestActor], name = "test-actor")
        a ! StartMessage("Start Instruction")
    }

    override def onStop(application : play.api.Application) {
        val a = Akka.system.actorFor("akka://application/user/test-actor")
        a ! StopMessage("Stop Instruction")

        try {
            val stopped : Future[Boolean] = gracefulStop(a, scala.concurrent.duration.Duration(5, "seconds"))
            Await.result(stopped, scala.concurrent.duration.Duration(6, "seconds"))
            // the actor has been stopped
        }
        catch {
            case e : akka.pattern.AskTimeoutException => // the actor wasn't stopped within 5 seconds
        }

        Akka.system.shutdown()
        Akka.system.awaitTermination()
    }
}

“优雅的停止 如果需要等待终止或编写多个参与者的有序终止，gracefulStop非常有用：

import akka.pattern.gracefulStop
import akka.dispatch.Await
import akka.actor.ActorTimeoutException

try {
  val stopped: Future[Boolean] = gracefulStop(actorRef, 5 seconds)(system)
  Await.result(stopped, 6 seconds)
  // the actor has been stopped
} catch {
  case e: ActorTimeoutException ⇒ // the actor wasn't stopped within 5 seconds
}

"

---

另外，在谷歌上搜索“优雅的演员阿克卡”会得到最好的结果。

你可能会发现这篇文章很有用：