如何启用 Source.Queue 背压

Question

我正在使用带有队列的主机级API。

  private val (queueSource, connectionPool) = Source.queue[(HttpRequest, Promise[HttpResponse])](queueSize, OverflowStrategy.backpressure).async
    .viaMat(poolFlow)(Keep.both)
    .toMat(
      Sink.foreach({
        case ((Success(resp), p)) =>
          p.success(resp)
        case ((Failure(e), p)) => p.failure(e)
      })
    )(Keep.left)
    .run()

我有很多请求在连接池中争夺连接，但出现以下错误：

 java.lang.IllegalStateException: You have to wait for previous offer to be resolved to send another request
    at akka.stream.impl.QueueSource$$anon$1.akka$stream$impl$QueueSource$$anon$$bufferElem(QueueSource.scala:84)
    at akka.stream.impl.QueueSource$$anon$1$$anonfun$1.apply(QueueSource.scala:94)
    at akka.stream.impl.QueueSource$$anon$1$$anonfun$1.apply(QueueSource.scala:91)
    at akka.stream.impl.fusing.GraphInterpreter.runAsyncInput(GraphInterpreter.scala:447)
    at akka.stream.impl.fusing.GraphInterpreterShell$AsyncInput.execute(ActorGraphInterpreter.scala:464)
    at akka.stream.impl.fusing.GraphInterpreterShell.processEvent(ActorGraphInterpreter.scala:559)
    at akka.stream.impl.fusing.ActorGraphInterpreter.akka$stream$impl$fusing$ActorGraphInterpreter$$processEvent(ActorGraphInterpreter.scala:741)
    at akka.stream.impl.fusing.ActorGraphInterpreter$$anonfun$receive$1.applyOrElse(ActorGraphInterpreter.scala:756)
    at akka.actor.Actor$class.aroundReceive(Actor.scala:517)
    at akka.stream.impl.fusing.ActorGraphInterpreter.aroundReceive(ActorGraphInterpreter.scala:666)
    at akka.actor.ActorCell.receiveMessage(ActorCell.scala:527)
    at akka.actor.ActorCell.invoke(ActorCell.scala:496)
    at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:257)
    at akka.dispatch.Mailbox.run(Mailbox.scala:224)
    at akka.dispatch.Mailbox.exec(Mailbox.scala:234)
    at akka.dispatch.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)
    at akka.dispatch.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339)
    at akka.dispatch.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)
    at akka.dispatch.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)

我尝试添加 .async 但背压仍然没有启动。上面的错误是什么意思以及如何着手调查问题？

Answer 1

您已经Source使用Source.queue对象方法构造了 a ，因此我认为不可能直接对正在调用的任何功能应用反压queue.offer。但是，您的问题可能可以通过不同的方式解决。

不同的OverflowStrategy

您可以将策略更改为类似OverflowStrategy.dropHead或 的内容OverflowStrategy.dropTail。如果您的queueSize调用率足够大，queue.offer那么这可能会满足您的需求。