scala - 玩转 2.0 Scala 和异步回调

Question

我想对我的数据库进行两次调用，这将需要一段时间才能返回结果，而且我不想阻塞当前线程。我使用 Akka Futures 来包装数据库调用。

我不想等待(阻塞)两个调用返回，而是指定要调用的回调函数，然后可以呈现响应。我怎么做？这是我的 Controller 代码:

def showPie = IsAuthenticated(Roles.validator) { user => implicit request =>
    val eventUid = request.session.get(EventUid).get

    val printed = Akka.future(TicketRepository.getCountForState(eventUid, "Printed"))
    val validated = Akka.future(TicketRepository.getCountForState(eventUid, "Validated"))

    //this would be evil, because it would block: Ok(views.html.pie(printed.await(1000).get, validated.await(1000).get)) 

    //create a promise for all the promised results
    val promise = Promise.sequence(List(printed, validated))

    //this doesnt work, but how can I make it work WITHOUT blocking this thread?
    promise.callWhenResultIsReady(Ok(view.html.pie(promise.get))
}

Answer 1

你很接近。您可以简单地调用 map promise 来处理它。在 Async block 内，它保持非阻塞。 Relevant documentation (参见“AsyncResult”)。

def showPie = IsAuthenticated(Roles.validator) { user => implicit request =>
    val eventUid = request.session.get(EventUid).get

    val printed = Akka.future(TicketRepository.getCountForState(eventUid, "Printed"))
    val validated = Akka.future(TicketRepository.getCountForState(eventUid, "Validated"))

    //create a promise for all the promised results
    val promise = Promise.sequence(List(printed, validated))
    Async {
        promise map { res =>
            Ok("Got it!" + res)
        }
    }
}

编辑:从您下面的评论中，让我们仔细看看 Async block 。 Async 接受一个 Promise，并返回一个 AsyncResult，它是 Result 的子类型( >行动需要)。

    Async {
        // We take the promise, and add something akin to a callback
        //  function with `map`. This new function is called when `promise`
        //  is complete.
        val result = promise map { res => // this is the redeemed promise
          Ok("Got it!" + res)
        }
        result // this is the new promise
    } 

由于 map 函数在 promise 完成时被调用，因此它保持非阻塞。整个 block 快速返回一个 AsyncResult，开始玩吧!以类似的方式管理它，在它完成时返回给客户端(同时释放 Play! 去做其他事情)。