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Implementing the Pipes and Filters Pattern Using Actors in Akka for Java

27 points by DrLegend 10y ago

mpweiher 10y ago
I've been experimenting with pipe/filter architectures on and off for quite some time and so am very heartened to see renewed interest. In addition, I've heard a lot (mostly good) about Akka but haven't had a chance to actually work with it so this practical example is very welcome. That said, the code I see seems very verbose, particularly the config part, for what amounts to: text-checker | latex2unicode | upload-to-s3 In my own Objective-C based P/F implementation, I currently deal with pipes as arrays of filters, so it would be something like: [MPWPipe pipeWithFilters:@[ textChecker, latex2unicode, upload-to-s3 ]]; In Objective-Smalltalk, I'd think I can do better.
ryteu 10y ago
An overengineered solution for a trivial problem. All you'd need is 3 functions. No reason at all to use Akka.
- meddlepal 10y ago
  If you only see value in solving the problem then yea it's over engineered. If you see value in learning a new technique for solving problems then it's a solid example and write up. Not everything has to be done for the sole purpose of being the best solution.
- manyxcxi 10y ago
  Though it's probably over engineered for this trivial problem, would you, as someone not familiar to Akka or Pipes&Filters want to waste your mental bandwidth on a really complex problem, or get a familiarization with the concepts first?
yummyfajitas 10y ago
This article is pretty silly. Why use Akka for this at all? You don't need an untyped distributed system just to chain functions together. For logically chaining functions together and accumulating errors, use Scalaz's \/: http://eed3si9n.com/learning-scalaz/Either.html http://eed3si9n.com/learning-scalaz/Either.html text >>= (t => if (containsForbiddenWord) { MyError.left[String] } else { t.right[MyError] }) >>= latexToUnicode _ >>= ...etc... Unlike actors, this is deterministic and easily testable code. If you really need to use a fancy concurrent system for this, Akka already has a built in piping/filtering framework called streams: http://doc.akka.io/docs/akka/2.4.16/scala/stream/index.html http://doc.akka.io/docs/akka/2.4.16/scala/stream/index.html Unlike this actor example, streams comes with built in backpressure/concurrency handling. For new code you should probably be using streams rather than akka actors. This article is neat for learning about actors, but you should almost certainly not write production code this way.
- hhandoko 10y ago
  Perhaps there was a constraint to use Java lang and not Scala, thus Scalaz probably can't apply here.
  - yummyfajitas 10y ago
    True, I think of Akka as a Scala library but it works in Java too. But I'm sure Java has some similar deterministic abstraction. I know Java used to just use deterministic functions + exceptions, and that was hardly unreasonable.

27 points by DrLegend 10y ago

I've been experimenting with pipe/filter architectures on and off for quite some time and so am very heartened to see renewed interest. In addition, I've heard a lot (mostly good) about Akka but haven't had a chance to actually work with it so this practical example is very welcome. That said, the code I see seems very verbose, particularly the config part, for what amounts to: text-checker | latex2unicode | upload-to-s3 In my own Objective-C based P/F implementation, I currently deal with pipes as arrays of filters, so it would be something like: [MPWPipe pipeWithFilters:@[ textChecker, latex2unicode, upload-to-s3 ]]; In Objective-Smalltalk, I'd think I can do better.

ryteu 10y ago

An overengineered solution for a trivial problem. All you'd need is 3 functions. No reason at all to use Akka.

meddlepal 10y ago
If you only see value in solving the problem then yea it's over engineered. If you see value in learning a new technique for solving problems then it's a solid example and write up. Not everything has to be done for the sole purpose of being the best solution.
manyxcxi 10y ago
Though it's probably over engineered for this trivial problem, would you, as someone not familiar to Akka or Pipes&Filters want to waste your mental bandwidth on a really complex problem, or get a familiarization with the concepts first?

yummyfajitas 10y ago

This article is pretty silly. Why use Akka for this at all? You don't need an untyped distributed system just to chain functions together. For logically chaining functions together and accumulating errors, use Scalaz's \/: http://eed3si9n.com/learning-scalaz/Either.html http://eed3si9n.com/learning-scalaz/Either.html text >>= (t => if (containsForbiddenWord) { MyError.left[String] } else { t.right[MyError] }) >>= latexToUnicode _ >>= ...etc... Unlike actors, this is deterministic and easily testable code. If you really need to use a fancy concurrent system for this, Akka already has a built in piping/filtering framework called streams: http://doc.akka.io/docs/akka/2.4.16/scala/stream/index.html http://doc.akka.io/docs/akka/2.4.16/scala/stream/index.html Unlike this actor example, streams comes with built in backpressure/concurrency handling. For new code you should probably be using streams rather than akka actors. This article is neat for learning about actors, but you should almost certainly not write production code this way.

hhandoko 10y ago
Perhaps there was a constraint to use Java lang and not Scala, thus Scalaz probably can't apply here.
- yummyfajitas 10y ago
  True, I think of Akka as a Scala library but it works in Java too. But I'm sure Java has some similar deterministic abstraction. I know Java used to just use deterministic functions + exceptions, and that was hardly unreasonable.