scala.concurrent.Future
異步執行代碼塊html
import java.time._ import scala.concurrent._ import ExecutionContext.Implicits.global // 全局線程池 Future { Thread.sleep(10000) println(s"This is the future at ${LocalTime.now}") } println(s"This is the present at ${LocalTime.now}")
監聽結果(阻塞)java
import scala.concurrent.duration._ val f = Future { Thread.sleep(10000); 42 } val result = Await.result(f, 10.seconds) //阻塞10s val f = Future { ... } Await.ready(f, 10.seconds) val Some(t): Option[Try[T]] = f.value t match { case Success(v) => println(s"The answer is $v") case Failure(ex) => println(ex.getMessage) }
ready()api
- 到達等待時間無結果時,會拋出異常
TimeoutException
- 任務拋出的異常時,result() 會再次拋出異常, ready() 可獲取結果
回調app
val f = Future { Thread.sleep(10000) if (random() < 0.5) throw new Exception 42 } f.onComplete { case Success(v) => println(s"The answer is $v") case Failure(ex) => println(ex.getMessage) }
問題:1.回調地獄;2.執行順序沒法預知dom
val future1 = Future { getData1() } val future2 = Future { getData2() } future1 onComplete { case Success(n1) => future2 onComplete { case Success(n2) => { val n = n1 + n2 println(s"Result: $n") } case Failure(ex) => ... } case Failure(ex) => ... }
將 Future 看做集合異步
// val 會當即執行,def 調用時執行 val future1 = Future { getData1() } val future2 = Future { getData2() } // 都獲取到結果時,纔會進行計算 val combined = for (n1 <- future1; n2 <- future2) yield n1 + n2
CompletableFuture
相似Future 只讀,在任務完成時隱式設置結果值;Promise 相似,但結果值可顯式設置url
// Future def computeAnswer(arg: String) = Future { val n = workHard(arg) n } // Promise def computeAnswer(arg: String) = { val p = Promise[Int]() Future { val n = workHard(arg) // 顯式設置結果 p.success(n) workOnSomethingElse() } // 當即返回該 Promise 對應的 Future p.future } // 多個任務對應一個 Promise val p = Promise[Int]() Future { var n = workHard(arg) // 若 Promise 未完成則接受結果並返回 true;不然忽略結果並返回 false p.trySuccess(n) } Future { var n = workSmart(arg) p.trySuccess(n) }
fork-join
線程池(默認大小爲核數),適用於計算密集型任務對於阻塞型/IO密集型的任務,可以使用 Java 的 Executors
線程
// 隱式聲明,或者使用 Future.apply 顯式聲明 val pool = Executors.newCachedThreadPool() implicit val ec = ExecutionContext.fromExecutor(pool) val f = Future { val url = ... blocking { val contents = Source.fromURL(url).mkString ... } }