探索Playframework: 如何正確使用thread pool

在scala的世界, 我們常會用Future來處理某些非同步的工作,
用Future, 必需要透過implict的方式提供execution context, 來執行這些工作.

白話的說就是要指定你的code要在哪個thread pool跑.

使用Playframework, 在比較單純的情況下直接用預設的thread pool就可以了.
然後再透過application.conf設定適當的參數.

import play.api.libs.concurrent.Execution.Implicits._

def someAsyncAction = Action.async {
  import play.api.Play.current
  WS.url("http://www.playframework.com").get().map { response =>
    // This code block is executed in the imported default execution context
    // which happens to be the same thread pool in which the outer block of
    // code in this action will be executed.
    Results.Ok("The response code was " + response.status)
  }
}

play {
  akka {
    akka.loggers = ["akka.event.Logging$DefaultLogger", "akka.event.slf4j.Slf4jLogger"]
    loglevel = WARNING
    actor {
      default-dispatcher = {
        fork-join-executor {
          parallelism-factor = 1.0
          parallelism-max = 24
        }
      }
    }
  }
}

import play.api.libs.concurrent.Execution.Implicits._
先來找找我們用的execution context在哪裡,
defaultContext是ActorSystem的dispatcher
而create ActorSystem用的設定是"play"這個關鍵字下面的所有屬性.
接下來就是看ActorSystem如何設定dispatcher囉~
defaultGlobalDispatcher是用DefaultDispatcherId(即akka.actor.default-dispatcher)抓到設定值

大概是這樣囉!


針對不同類型的工作, 有時候我們會不希望所有事情都塞在預設的thread pool做,
要使用其他的thread pool, 只需要先在application.conf加上一組新的設定.
再用lookup讓Akka能找到它就好.
可以直接在產生Future的時候指定execution context或是直接import讓implicit發生作用

my-context {
  fork-join-executor {
    parallelism-factor = 20.0
    parallelism-max = 200
  }
}

object Contexts {
  implicit val myExecutionContext: ExecutionContext = Akka.system.dispatchers.lookup("my-context")
}

Future {
  // Some blocking or expensive code here
}(Contexts.myExecutionContext)

or

import Contexts.myExecutionContext
Future {
  // Some blocking or expensive code here
}

當然實際上要如何設定thread pool還是要參考測試結果啦!

ref:
- playframework source code (2.3.x)
- akka source code (2.3)
- understanding play thread pools (2.3.5)