Scala控制台应用程序在等待Futures时永远不会退出

Question

每当我运行使用Future(通过Await、map、onComplete等)结果的scala进程时，它永远不会退出，迫使我们手动终止该进程。无论我使用extends App还是标准def main(args: Array[String])方法，都会发生这种情况。

在我看来，这与ThreadPoolExecutor有关，scala将旋转执行Future挂在函数的末尾，但我似乎无法得到它的句柄来关闭它。

例如，下面的代码将无法退出:

object ExecuteApi extends App with StrictLogging{
  lazy val config = StratumConfiguration.setupConfiguration()
  lazy val apiEndpoint = config.getProperty("APIEndpoint").split("/").head
  lazy val packetApiPath = "packets/getpackets"
  val resourceNames = sys.env.getOrElse("ResourceNames", "").stripMargin.split("[n\s]+").map(_.trim).filterNot(_.isEmpty)
  val searchBody =
  s"""{
    |  "resourceNames": [
    |    "${(resourceNames).mkString("","")}"
    |  ]
    |}""".stripMargin
    logger.info(searchBody)
    val responseFuture = AmazonAsyncApiGatewayHelper.executeHttpRequest(apiEndpoint, searchBody, Some(packetApiPath), Some("api"))
    val response = Await.result(responseFuture, Duration(25, TimeUnit.SECONDS))
    val layerDefinitions = Json.parse(response)
    println(Json.prettyPrint(layerDefinitions))
}

虽然这段代码很好地退出(唯一的变化是Async版本返回一个future，然后是await):

object ExecuteAPI extends App with StrictLogging{
  lazy val config = Configuration.setupConfiguration()
  lazy val apiEndpoint = config.getProperty("APIEndpoint").split("/").head
  lazy val packetApiPath = "packets/getpackets"
  val resourceNames = sys.env.getOrElse("ResourceNames", "").stripMargin.split("n").map(_.trim).filterNot(_.isEmpty)
  val searchBody =
  s"""{
    |  "resourceNames": [
    |    "${(resourceNames).mkString("","")}"
    |  ]
    |}""".stripMargin
    logger.info(searchBody)
    val layersResponse = AmazonapiGatewayHelper.executeHttpRequest(apiEndpoint, searchBody, Some(packetApiPath), Some("api"))
    val layerDefinitions = Json.parse(layersResponse)
    println(Json.prettyPrint(layerDefinitions))
}

AmazonAsyncApiGatewayHelper中的代码最终通过执行Play库HTTP客户端创建Future。然而，我们在以其他方式执行期货时也看到了这一点:

val request = wsClient.url(fullUrl)
    .withRequestTimeout(readTimeout)
val requestWithHeaders = headers.foldLeft(request) { (r, h) =>
  r.withHeaders(h)
}
val playResponseFuture = requestWithHeaders.post(requestBody)

Answer 1

我们最终发现了这个问题。Play wsClient需要一个actor系统(从Play 2.5开始)。我们需要在退出主类之前手动终止这个参与者系统。退出的代码如下所示:

object ExecuteAPI extends App with StrictLogging{
 try {
  lazy val config = Configuration.setupConfiguration()
  lazy val apiEndpoint = config.getProperty("APIEndpoint").split("/").head
  lazy val packetApiPath = "packets/getpackets"
  val resourceNames = sys.env.getOrElse("ResourceNames", "").stripMargin.split("n").map(_.trim).filterNot(_.isEmpty)
  val searchBody =
  s"""{
    |  "resourceNames": [
    |    "${(resourceNames).mkString("","")}"
    |  ]
    |}""".stripMargin
    logger.info(searchBody)
    val responseFuture = AmazonAsyncApiGatewayHelper.executeHttpRequest(apiEndpoint, searchBody, Some(packetApiPath), Some("api"))
    val response = Await.result(responseFuture, Duration(25, TimeUnit.SECONDS))
    val layerDefinitions = Json.parse(response)
    println(Json.prettyPrint(layerDefinitions))
 } finally {
    AmazonAsyncApiGatewayHelper.client.actorSystem.terminate()
 }
}

Answer 2

您可以映射未来的值并在末尾添加Thread.sleep()。

val result = layersResponse  map { futureValue =>
 Json.parse(layerResponse)
}
Thread.sleep(10000)
println(Json.prettyPrint(result))