Scalawags #19

thescalawags's podcast

Five Years of Akka w/ Legendary Viktor Klang

Scalawags, not the podcast you come to for facts

Scalawags, the podcast that brings the Internet to its knees with double-digit live-viewing numbers!

with special guest Viktor Klang, man of Akka

youtube: https://www.youtube.com/watch?v=x9IxmgJNLbg

Intro (0:00)

• Viktor loses up here what he gains down there
• the rapture came and only Daniel was chosen

Akka, the early days (3:50)

• Akka is a big deal
  • http://akka.io
• it's five years old
• Jonas Bonér started it...
  • ...but Viktor made the first pull request
• Lift was the matchmaker
• revealed: contents of that first PR!!
• on GitHub, Akka started the day after Node.JS started
• main inspiration: Erlang
• money quote: "concurrency is just a specialization of distributed computing"
• Akka vs. Scala-standard-library actors
  • Akka resembles Erlang less?

Akka rebooted (13:45)

• why the rewrite for 2.0?
  • supervision!
  • actor systems
  • proper classloader handling
  • internal architectural issues

Akka HTTP and Akka Streams (20:40)

• Akka HTTP is what used to be Spray
  • http://spray.io
• but fused with Akka Streams
  • http://typesafe.com/blog/typesafe-announces-akka-streams
• and providing a Java API
• note it's not actually released yet
  • preview announcement: https://typesafe.com/blog/akka-http-preview
• HTTP "gateway" or "shim" to actors
• Akka HTTP vs. Finagle
• COBOL on Cogs, Akka on Airplanes
  • http://www.coboloncogs.org

Actors and type safety (32:50)

• messages are just Any. will this change? how do you type actors?
• actors and the active object design pattern
  • http://en.wikipedia.org/wiki/Active_object
• the first Akka had typed actors, using AOP
  • later Viktor rewrote it to use JDK proxies
  • but, performance penalty
• Roland Kuhn has used macros to type messages and responses
  • issues: thread-safety of reflection? performance? Java interop?
• research on typed actors at EPFL?
• Marlow and Wadler's paper on typing Erlang:
  • https://synrc.com/publications/cat/Functional%20Languages/Erlang/erlang.pdf
• recent discussions on using marker interfaces to associate message types with actors
• Josh: perhaps actors will stay untyped but we'll build higher-level typed APIs over top of them
  • for example, Akka Streams
  • analogy with type erasure in the VM itself?
• nominal typing leads to chicken-or-egg problems with serialization and class loaders

Akka Streams vs. scalaz-stream (46:25)

• Tim Perrett wants some compare-and-contrast on this
  • https://github.com/scalaz/scalaz-stream
• Dick has struggled with scalaz-stream's handling of large files
  • so e.g. https://github.com/scalaz/scalaz-stream/issues/51 and https://github.com/scalaz/scalaz-stream/issues/136, with prospective fixes happening on https://github.com/scalaz/scalaz-stream/tree/lazy
• scalaz-stream runs on tasks, Akka Streams uses actors
• how is resource cleanup handled?
• Viktor disclaims expertise on scalaz-stream, and says it's "too early" to compare
• for now the Akka Streams API is intentionally small
• an early major concern is proper support for backpressure
  • asynchronous, non-blocking backpressure
  • "every stream X will have at most N items in flight"
• listener question about what problem spaces streams address and how supervision of stream actors works
• mining bitcoins with Akka on Raspberry Pi?!
• is Akka Streams usable from Java?

Akka and Java (58:00)

• are Akka Streams usable from Java?
  • yes. does that constrain the design?
• what proportion of Akka users are using it from Java?
  • a lot. could even be 50/50
• "the best way of gaining traction [...] for any technology, is to be open, and not to be judgmental"
• Akka for Python?
  • https://github.com/jodal/pykka is Akka-inspired
  • something similar for .NET exists?
• what are the implications of Java 8 for Akka?

Listening to users (1:03:35)

• Dick: how do you stay in touch with what users want?
• culture!
• putting a high priority on documentation and helping newcomers
• treat root causes, not just symptoms

Security (1:07:25)

• user question: what about security if some nodes are untrusted?
• no man is an island, but actors are

Monitoring (1:10:30)

• JMX is roundly made fun of
• stack traces >> core dumps
  • async "stack traces" at the JVM level? want.

Wrap-up (1:14:10)

• Viktor's thoughts on life, the universe, and everything
• what is the optimum thread pool size of an unladen African swallow?
• are actors people?
• moving past Akka's notorious TerminatedChildrenDungeon scandal
• behind "the one who walks the bubbles of space-time"
  • aka the Flying Spaghetti Actor
• Captain Deadlock Dreadlock
• try Akka! you have the power.