Mic*_*ael 83 concurrency scala future
假设我有几个期货,需要等到其中任何一个失败或全部成功.
例如:我们有3个期货:f1,f2,f3.
如果f1成功并f2失败,我不等待f3(并将失败返回给客户端).
如果f2失败f1而且f3仍然在运行,我不等待它们(并返回失败)
如果f1成功然后f2成功我会继续等待f3.
你会如何实现它？
cmb*_*ter 79
你可以使用for-comprehension来代替:
val fut1 = Future{...}
val fut2 = Future{...}
val fut3 = Future{...}
val aggFut = for{
f1Result <- fut1
f2Result <- fut2
f3Result <- fut3
} yield (f1Result, f2Result, f3Result)
在这个例子中,期货1,2和3并行开始.然后,在for comprehension中,我们等到结果1然后2然后3可用.如果1或2失败,我们将不再等待3.如果所有3都成功,那么aggFutval将保持一个具有3个时隙的元组,对应于3个期货的结果.
现在如果你需要停止等待的行为,如果说fut2首先失败,事情会变得有点棘手.在上面的例子中,你必须等到fut1完成才能实现fut2失败.要解决这个问题,你可以尝试这样的事情:
val fut1 = Future{Thread.sleep(3000);1}
val fut2 = Promise.failed(new RuntimeException("boo")).future
val fut3 = Future{Thread.sleep(1000);3}
def processFutures(futures:Map[Int,Future[Int]], values:List[Any], prom:Promise[List[Any]]):Future[List[Any]] = {
val fut = if (futures.size == 1) futures.head._2
else Future.firstCompletedOf(futures.values)
fut onComplete{
case Success(value) if (futures.size == 1)=>
prom.success(value :: values)
case Success(value) =>
processFutures(futures - value, value :: values, prom)
case Failure(ex) => prom.failure(ex)
}
prom.future
}
val aggFut = processFutures(Map(1 -> fut1, 2 -> fut2, 3 -> fut3), List(), Promise[List[Any]]())
aggFut onComplete{
case value => println(value)
}
现在这可以正常工作,但问题来自于知道Future从Map成功完成时删除哪些.只要你有一些方法可以将结果与产生该结果的Future进行正确关联,那么这样的事情就可以了.它只是递归地从地图中删除已完成的Futures,然后调用Future.firstCompletedOf剩余的,Futures直到没有剩下的,收集结果.它不漂亮,但如果你真的需要你正在谈论的行为,那么这个,或类似的东西可以工作.
gou*_*ama 32
您可以使用承诺,并向其发送第一个失败或最终完成的聚合成功:
def sequenceOrBailOut[A, M[_] <: TraversableOnce[_]](in: M[Future[A]] with TraversableOnce[Future[A]])(implicit cbf: CanBuildFrom[M[Future[A]], A, M[A]], executor: ExecutionContext): Future[M[A]] = {
val p = Promise[M[A]]()
// the first Future to fail completes the promise
in.foreach(_.onFailure{case i => p.tryFailure(i)})
// if the whole sequence succeeds (i.e. no failures)
// then the promise is completed with the aggregated success
Future.sequence(in).foreach(p trySuccess _)
p.future
}
然后Await,Future如果你想阻止,或者只是map把它变成别的东西,你就可以了.
与理解的区别在于,在这里你得到第一个失败的错误,而对于理解,你得到输入集合的遍历顺序中的第一个错误(即使另一个先失败).例如:
val f1 = Future { Thread.sleep(1000) ; 5 / 0 }
val f2 = Future { 5 }
val f3 = Future { None.get }
Future.sequence(List(f1,f2,f3)).onFailure{case i => println(i)}
// this waits one second, then prints "java.lang.ArithmeticException: / by zero"
// the first to fail in traversal order
和:
val f1 = Future { Thread.sleep(1000) ; 5 / 0 }
val f2 = Future { 5 }
val f3 = Future { None.get }
sequenceOrBailOut(List(f1,f2,f3)).onFailure{case i => println(i)}
// this immediately prints "java.util.NoSuchElementException: None.get"
// the 'actual' first to fail (usually...)
// and it returns early (it does not wait 1 sec)
这是一个不使用actor的解决方案.
import scala.util._
import scala.concurrent._
import java.util.concurrent.atomic.AtomicInteger
// Nondeterministic.
// If any failure, return it immediately, else return the final success.
def allSucceed[T](fs: Future[T]*): Future[T] = {
val remaining = new AtomicInteger(fs.length)
val p = promise[T]
fs foreach {
_ onComplete {
case s @ Success(_) => {
if (remaining.decrementAndGet() == 0) {
// Arbitrarily return the final success
p tryComplete s
}
}
case f @ Failure(_) => {
p tryComplete f
}
}
}
p.future
}
为此我会使用Akka演员.与for-comprehension不同,它会在任何期货失败时立即失败,因此在这个意义上它会更有效率.
class ResultCombiner(futs: Future[_]*) extends Actor {
var origSender: ActorRef = null
var futsRemaining: Set[Future[_]] = futs.toSet
override def receive = {
case () =>
origSender = sender
for(f <- futs)
f.onComplete(result => self ! if(result.isSuccess) f else false)
case false =>
origSender ! SomethingFailed
case f: Future[_] =>
futsRemaining -= f
if(futsRemaining.isEmpty) origSender ! EverythingSucceeded
}
}
sealed trait Result
case object SomethingFailed extends Result
case object EverythingSucceeded extends Result
然后,创建actor,向其发送消息(以便它知道将其回复发送到何处)并等待回复.
val actor = actorSystem.actorOf(Props(new ResultCombiner(f1, f2, f3)))
try {
val f4: Future[Result] = actor ? ()
implicit val timeout = new Timeout(30 seconds) // or whatever
Await.result(f4, timeout.duration).asInstanceOf[Result] match {
case SomethingFailed => println("Oh noes!")
case EverythingSucceeded => println("It all worked!")
}
} finally {
// Avoid memory leaks: destroy the actor
actor ! PoisonPill
}
你可以单独用期货做这件事.这是一个实现.请注意,它不会提前终止执行!在这种情况下,您需要做一些更复杂的事情(并且可能自己实施中断).但是如果你只是不想继续等待一些不起作用的东西,那么关键是要等待第一件事情完成,并在没有任何东西或者遇到异常时停止:
import scala.annotation.tailrec
import scala.util.{Try, Success, Failure}
import scala.concurrent._
import scala.concurrent.duration.Duration
import ExecutionContext.Implicits.global
@tailrec def awaitSuccess[A](fs: Seq[Future[A]], done: Seq[A] = Seq()):
Either[Throwable, Seq[A]] = {
val first = Future.firstCompletedOf(fs)
Await.ready(first, Duration.Inf).value match {
case None => awaitSuccess(fs, done) // Shouldn't happen!
case Some(Failure(e)) => Left(e)
case Some(Success(_)) =>
val (complete, running) = fs.partition(_.isCompleted)
val answers = complete.flatMap(_.value)
answers.find(_.isFailure) match {
case Some(Failure(e)) => Left(e)
case _ =>
if (running.length > 0) awaitSuccess(running, answers.map(_.get) ++: done)
else Right( answers.map(_.get) ++: done )
}
}
}
以下是一切正常的例子:
scala> awaitSuccess(Seq(Future{ println("Hi!") },
Future{ Thread.sleep(1000); println("Fancy meeting you here!") },
Future{ Thread.sleep(2000); println("Bye!") }
))
Hi!
Fancy meeting you here!
Bye!
res1: Either[Throwable,Seq[Unit]] = Right(List((), (), ()))
但是当出现问题时:
scala> awaitSuccess(Seq(Future{ println("Hi!") },
Future{ Thread.sleep(1000); throw new Exception("boo"); () },
Future{ Thread.sleep(2000); println("Bye!") }
))
Hi!
res2: Either[Throwable,Seq[Unit]] = Left(java.lang.Exception: boo)
scala> Bye!
这个问题已经回答了，但是我要发布我的值类解决方案（在2.10中添加了值类），因为这里没有一个。请随时批评。
implicit class Sugar_PimpMyFuture[T](val self: Future[T]) extends AnyVal {
def concurrently = ConcurrentFuture(self)
}
case class ConcurrentFuture[A](future: Future[A]) extends AnyVal {
def map[B](f: Future[A] => Future[B]) : ConcurrentFuture[B] = ConcurrentFuture(f(future))
def flatMap[B](f: Future[A] => ConcurrentFuture[B]) : ConcurrentFuture[B] = concurrentFutureFlatMap(this, f) // work around no nested class in value class
}
def concurrentFutureFlatMap[A,B](outer: ConcurrentFuture[A], f: Future[A] => ConcurrentFuture[B]) : ConcurrentFuture[B] = {
val p = Promise[B]()
val inner = f(outer.future)
inner.future onFailure { case t => p.tryFailure(t) }
outer.future onFailure { case t => p.tryFailure(t) }
inner.future onSuccess { case b => p.trySuccess(b) }
ConcurrentFuture(p.future)
}
ConcurrentFuture是一个无开销的Future包装器，它将默认的Future map / flatMap从do-this-then-to更改为合并，如果有任何失败，则全部失败。用法：
def func1 : Future[Int] = Future { println("f1!");throw new RuntimeException; 1 }
def func2 : Future[String] = Future { Thread.sleep(2000);println("f2!");"f2" }
def func3 : Future[Double] = Future { Thread.sleep(2000);println("f3!");42.0 }
val f : Future[(Int,String,Double)] = {
for {
f1 <- func1.concurrently
f2 <- func2.concurrently
f3 <- func3.concurrently
} yield for {
v1 <- f1
v2 <- f2
v3 <- f3
} yield (v1,v2,v3)
}.future
f.onFailure { case t => println("future failed $t") }
在上面的示例中，f1，f2和f3将同时运行，并且如果任何顺序失败，则元组的将来将立即失败。
小智 5
您可能想查看 Twitter 的 Future API。尤其是 Future.collect 方法。它完全符合您的要求：https : //twitter.github.io/scala_school/finagle.html
源代码 Future.scala 可在此处获得：https : //github.com/twitter/util/blob/master/util-core/src/main/scala/com/twitter/util/Future.scala