On 11/12/2015 06:57 PM, Endre Varga wrote:
Hi Simon,
This documentation section explains this in more detail:
http://doc.akka.io/docs/akka-stream-and-http-experimental/2.0-M1/scala/stream-rate.html
Ok, I didn't come to that point of the documentation so far. I'm going
to have a look, thanks!
Btw, Sink.head actually does not request more than one, however this
is not transitive and cannot be. Grouped cannot possibly know how many
elements a downstream ever needs, so it tries to prefetch and exploit
concurrency.
Why not? Doesn't it have to wait for a demand as all other components
have to do too? I mean Sink.head has a demand of 1, shouldn't grouped
get this demand and then forward a demand of 1*N, where N is the
argument to grouped?
-Endre
On Thu, Nov 12, 2015 at 6:39 PM, Simon Schäfer <[email protected]
<mailto:[email protected]>> wrote:
I just tried the following (on 2.0-M1):
scala> Source(1 to 100).map{i ⇒ println(i);
i}.grouped(10).runWith(Sink.head)
1
2
3
4
5
6
7
8
9
10
11
res10:
scala.concurrent.Future[scala.collection.immutable.Seq[Int]] =
scala.concurrent.impl.Promise$DefaultPromise@2df79942
12
13
14
15
16
scala> 17
18
19
20
21
22
23
24
res10.onComplete(println)
Success(Vector(1, 2, 3, 4, 5, 6, 7, 8, 9, 10))
A similar behavior can be seen for the take function:
scala> Source(1 to 100).map{i ⇒ println(i);
i}.take(10).runWith(Sink.fold(Vector[Int]())(_ :+ _))
...
As one can see, the stream processes more elements than it has to.
It is not a problem for me, but I would like to know if this
behavior is spec'ed anywhere? Shouldn't the stream be able to say,
just by looking at the arguments for grouped, take and the sink,
how many elements should be produced?
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