Question

在Windows 7上播放2.4。我是Scala / Play框架中的新手，我有如下操作：

def delay = Action.async { request =>
    println(new Date() + "-1-" + Thread.currentThread().getId)
    val delayed = play.api.libs.concurrent.Promise.timeout("Delayed", 10.seconds)
    println(new Date() + "-2-" + Thread.currentThread().getId)
    val result = delayed.map{
        println(new Date() + "-3-" + Thread.currentThread().getId)
        Ok(_)
    }
    println(new Date() + "-4-" + Thread.currentThread().getId)
    result
}

我希望执行顺序应为1,2,4,3。但是输出是1,2,3,4并且都在同一个线程中。然后我改变代码，替换

val result = delayed.map{
    println(new Date() + "-3-" + Thread.currentThread().getId)
    Ok(_)
}

带

val result = delayed.map{ message =>
  println(new Date() + "-3-" + Thread.currentThread().getId)
  Ok(message)
}

然后输出是1,2,4,3，并且3在不同的线程中。

有人可以告诉我原因吗？谢谢！

Answer 1

让我们稍微重构一下代码。第一个：

// The code between the braces here is just a code block. It is
// executed immediately to calculate the value of mappingFunction.
// That is before the assignment to mappingFunction.
val mappingFunction = {
  println(new Date() + "-3-" + Thread.currentThread().getId)
  { message: String => Ok(message) }
}

val result = delayed.map(mappingFunction)

第二个：

// The code between the braces here is the function that will
// be executed when the future is completed. In which thread it
// will be executed depends on the execution context, and is not
// guaranteed to be the one where mappingFunction is defined.
val mappingFunction = { message: String =>
  println(new Date() + "-3-" + Thread.currentThread().getId)
  Ok(message)
}

val result = delayed.map(mappingFunction)

Play框架中有和没有_的奇怪行为

1 个答案: