Akka Sink never closes

Question

I am uploading a single file to an SFTP server using Alpakka but once the file is uploaded and I have gotten the success response the Sink stays open, how do I drain it?

I started off with this:

val sink = Sftp.toPath(path, settings, false)
val source = Source.single(ByteString(data))

source
  .viaMat(KillSwitches.single)(Keep.right)
  .toMat(sink)(Keep.both).run()
  .map(_.wasSuccessful)

But that ends up never leaving the map step. I tried to add a killswitch, but that seems to have had no effect (neither with shutdown or abort):

val sink = Sftp.toPath(path, settings, false)
val source = Source.single(ByteString(data))

val (killswitch, result) = source
  .viaMat(KillSwitches.single)(Keep.right)
  .toMat(sink)(Keep.both).run()

result.map {
  killswitch.shutdown()
  _.wasSuccessful
}

Am I doing something fundamentally wrong? I just want one result.

EDIT The settings sent in to toPath:

SftpSettings(InetAddress.getByName(host))
    .withCredentials(FtpCredentials.create(amexUsername, amexPassword))
    .withStrictHostKeyChecking(false)

Try putting `Await.result(result, Duration.Inf)` at the end to block until flow is completed. You don't need KillSwitch. — expert, Oct 26 '18 at 11:49
I don't see how it would help making it synchronous, but I tried and it works. @expert why does the flow never finish without the Away? — spydon, Oct 26 '18 at 12:01
Aaah I'm so stupid. The output that I expected after the map obviously came way before and garbled into the sftp libraries debug output. What made me think that the map wasn't done was because of the ActorSystem not being terminated so the program didn't terminate. Thank you everybody for your help! — spydon, Oct 26 '18 at 12:23

expert · Accepted Answer · 2018-10-26T12:28:06.393

2

By asking you to put Await.result(result, Duration.Inf) at the end I wanted to check the theory expressed by A. Gregoris. Thus it's either

your app exits before Future completes or
(if you app does't exit) function in which you do this discards result

If your app doesn't exit you can try using result.onComplete to do necessary work.

edited Oct 26 '18 at 12:28

answered Oct 26 '18 at 12:22

expert

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Worth mentioning too that the confusion came from me forgetting to terminate the ActorSystem. – spydon Oct 26 '18 at 12:26
1

Ah yeah, then you can call `system.terminate` in handler of `onComplete` and prevent app from prematurely finishing by waiting on `Await.result(system.whenTerminated, Duration.Inf)` – expert Oct 26 '18 at 12:29

score 1 · Answer 2 · answered Oct 26 '18 at 11:02

1

I cannot see your whole code but it seems to me that in the snippet you posted that result value is a Future that is not completing before the end of your program execution and that is because the code in the map is not being executed either.

answered Oct 26 '18 at 11:02

A. Gregoris

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It is a Future indeed, it's a Future[IOResult]. And the code in the `map` is being executed. – spydon Oct 26 '18 at 11:37
I see that your user is new here, a friendly tip is to use the comment function and not the answer function before you know the answer, otherwise you will likely get down votes. :) – spydon Oct 26 '18 at 11:46

Akka Sink never closes

2 Answers2