On Wed, Nov 16, 2016 at 2:24 PM, Julian Howarth <[email protected]> wrote:
> > On Wednesday, November 16, 2016 at 11:04:55 AM UTC, √ wrote: >> >> How would auxiliary stages know which index the accumulation started at? >> > > That's where I was hoping an appropriate buffer stage could help, by just > keeping the one that corresponds to the initial packet after the > accumulator has emitted. But if not ... > Seems like a "guesswork stage" :S > > The actual use case is for receiving chunked packets over a TCP stream so > that I could keep track of when the first chunk arrived. I was hoping to > use the built in Framing.lengthField flow, but will just implement it > myself, keeping track of the timestamp. As an aside, is there any general > value in extending that framing flow to allow storing additional state? For > instance, in addition to tracking the timestamp, I am also extracting the > original ip address using proxy protocol. > If you come up with a low-to-no-overhead solution for that which is a drop-in replacement for the current one then I'd really like to have a look at it. :) > > >> >> On Wed, Nov 16, 2016 at 12:02 PM, Julian Howarth <[email protected]> >> wrote: >> >>> Thanks Viktor, >>> >>> But as I said, I don't have access to change the accumulator flow - it's >>> a black box that I otherwise would have to reimplement myself. That's why >>> I'm trying to work around it with the Graph DSL. >>> >>> Julian >>> >>> >>> On Wednesday, November 16, 2016 at 10:05:27 AM UTC, √ wrote: >>>> >>>> val accumulator = >>>> Flow[Int] >>>> .statefulMapConcat { () ⇒ >>>> var total = 0 >>>> var curIdx = 0L >>>> var startIdx = curIdx >>>> i ⇒ { >>>> val newTotal = total + i >>>> if (newTotal >= 10) { >>>> val result = List((newTotal, startIdx)) >>>> curIdx += 1 >>>> startIdx = curIdx >>>> total = 0 >>>> result >>>> } else { >>>> val result = List.empty[(Int, Long)] >>>> curIdx += 1 >>>> total = newTotal >>>> result >>>> } >>>> } >>>> } >>>> >>>> >>>> On Wed, Nov 16, 2016 at 10:18 AM, Julian Howarth <[email protected]> >>>> wrote: >>>> >>>>> I have what seems a very simple problem but cannot come up with a >>>>> solution for it. >>>>> Firstly, I have a flow that does some accumulation, therefore only >>>>> emits after it has received a number of elements. As a simple example: >>>>> >>>>> val accumulator = >>>>> Flow[Int] >>>>> .statefulMapConcat { () ⇒ >>>>> var total = 0 >>>>> i ⇒ { >>>>> val newTotal = total + i >>>>> if (newTotal >= 10) { >>>>> total = 0 >>>>> List(newTotal) >>>>> } >>>>> else { >>>>> total = newTotal >>>>> List() >>>>> } >>>>> } >>>>> } >>>>> >>>>> >>>>> This works as expected: >>>>> >>>>> val result = Source(List(2, 5, 6, 3, 8, 4, 1, 8, 7, 4)) >>>>> .via(accumulator) >>>>> .runWith(Sink.fold(Seq.empty[Int])(_ :+ _)) >>>>> >>>>> result.futureValue shouldBe Seq(13, 11, 13, 11) >>>>> >>>>> >>>>> Now, I want to record the index of the first element which started the >>>>> accumulation. In my actual application this is a java.time.Instant, but >>>>> Long suffices for this example. As a first naive attempt, using the Graph >>>>> DSL: >>>>> >>>>> val flow = >>>>> Flow[(Int, Long)] >>>>> .via(Flow.fromGraph(GraphDSL.create() { implicit builder ⇒ >>>>> import GraphDSL.Implicits._ >>>>> val unzip = builder.add(Unzip[Int, Long]()) >>>>> val acc = builder.add(accumulator) >>>>> val zip = builder.add(Zip[Int, Long]()) >>>>> >>>>> unzip.out0 ~> acc ~> zip.in0 >>>>> unzip.out1 ~> zip.in1 >>>>> >>>>> FlowShape[(Int, Long), (Int, Long)](unzip.in, zip.out) >>>>> })) >>>>> >>>>> val result = Source(List(2, 5, 6, 3, 8, 4, 1, 8, 7, 4)).zipWithIndex >>>>> .via(flow) >>>>> .runWith(Sink.fold(Seq.empty[(Int, Long)])(_ :+ _)) >>>>> >>>>> result.futureValue shouldBe Seq((13, 0), (11, 3), (13, 5), (11, 8)) >>>>> >>>>> >>>>> which times out as no elements flow through. So adding a buffer: >>>>> >>>>> val flow = >>>>> Flow[(Int, Long)] >>>>> .via(Flow.fromGraph(GraphDSL.create() { implicit builder ⇒ >>>>> import GraphDSL.Implicits._ >>>>> val unzip = builder.add(Unzip[Int, Long]()) >>>>> val acc = builder.add(accumulator) >>>>> val zip = builder.add(Zip[Int, Long]()) >>>>> >>>>> val buffer = builder.add(Flow[Long].buffer(1, >>>>> OverflowStrategy.dropTail)) >>>>> >>>>> unzip.out0 ~> acc ~> zip.in0 >>>>> unzip.out1 ~> buffer ~> zip.in1 >>>>> >>>>> FlowShape[(Int, Long), (Int, Long)](unzip.in, zip.out) >>>>> })) >>>>> >>>>> >>>>> and I get output, but not what I need: >>>>> >>>>> List((13,0), (11,2), (13,4), (11,7)) was not equal to List((13,0), >>>>> (11,3), (13,5), (11,8)) >>>>> >>>>> I think I know what is happening - the first Long element is buffered >>>>> in the zip stage and so the element in the buffer is not actually the one >>>>> I >>>>> expect. But I don't know how to get around it. Using conflate ends up with >>>>> exactly the same result >>>>> >>>>> Note that I can't easily rewrite the accumulator stage, if I could I >>>>> would just process the pairs together in a stateful stage. >>>>> >>>>> Thanks, >>>>> >>>>> Julian >>>>> >>>>> -- >>>>> >>>>>>>>>> Read the docs: http://akka.io/docs/ >>>>> >>>>>>>>>> Check the FAQ: http://doc.akka.io/docs/akka/c >>>>> urrent/additional/faq.html >>>>> >>>>>>>>>> Search the archives: https://groups.google.com/grou >>>>> p/akka-user >>>>> --- >>>>> You received this message because you are subscribed to the Google >>>>> Groups "Akka User List" group. >>>>> To unsubscribe from this group and stop receiving emails from it, send >>>>> an email to [email protected]. >>>>> To post to this group, send email to [email protected]. >>>>> Visit this group at https://groups.google.com/group/akka-user. >>>>> For more options, visit https://groups.google.com/d/optout. >>>>> >>>> >>>> >>>> >>>> -- >>>> Cheers, >>>> √ >>>> >>> -- >>> >>>>>>>>>> Read the docs: http://akka.io/docs/ >>> >>>>>>>>>> Check the FAQ: http://doc.akka.io/docs/akka/c >>> urrent/additional/faq.html >>> >>>>>>>>>> Search the archives: https://groups.google.com/grou >>> p/akka-user >>> --- >>> You received this message because you are subscribed to the Google >>> Groups "Akka User List" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to [email protected]. >>> To post to this group, send email to [email protected]. >>> Visit this group at https://groups.google.com/group/akka-user. >>> For more options, visit https://groups.google.com/d/optout. >>> >> >> >> >> -- >> Cheers, >> √ >> > -- > >>>>>>>>>> Read the docs: http://akka.io/docs/ > >>>>>>>>>> Check the FAQ: http://doc.akka.io/docs/akka/c > urrent/additional/faq.html > >>>>>>>>>> Search the archives: https://groups.google.com/group/akka-user > --- > You received this message because you are subscribed to the Google Groups > "Akka User List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at https://groups.google.com/group/akka-user. > For more options, visit https://groups.google.com/d/optout. > -- Cheers, √ -- >>>>>>>>>> Read the docs: http://akka.io/docs/ >>>>>>>>>> Check the FAQ: >>>>>>>>>> http://doc.akka.io/docs/akka/current/additional/faq.html >>>>>>>>>> Search the archives: https://groups.google.com/group/akka-user --- You received this message because you are subscribed to the Google Groups "Akka User List" group. 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