Scala 控制台应用程序在等待 Futures 时永远不会退出

Question

每当我运行一个使用 Future 结果的 Scala 进程时（通过 Await、map、onComplete 等），它永远不会退出，迫使我们手动终止进程。无论我使用 extends App 还是仅使用标准 def main(args: Array[String]) 方法，都会发生这种情况。

在我看来，它与 scala 将旋转起来执行的 ThreadPoolExecutor 有关 Future 在函数末尾徘徊，但我似乎无法获取它的句柄以将其关闭。

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))
}

虽然这段代码退出得很好（唯一的变化是 returns 未来的异步版本，然后等待）：

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 客户端来创建 Future。但是，我们在以其他方式执行 Futures 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

您可以映射未来值并在末尾添加 Thread.sleep()。

val result = layersResponse  map { futureValue =>
 Json.parse(layerResponse)
}

Thread.sleep(10000)
println(Json.prettyPrint(result))

Answer 2

我们最终找到了问题所在。 Play wsClient 需要一个演员系统（从 Play 2.5 开始）。我们需要在退出主 class 之前手动终止这个 actor 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()
 }
}

Scala 控制台应用程序在等待 Futures 时永远不会退出

Scala console application never exits when awaiting Futures

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threadpoolexecutor