TL;DR In Java, get a library that makes Futures work like Scala’s, and then never use ExecutorService directly. In the beginning, there were Threads. And Java threads were nice and simple. That is, Java threads are simple like some assembly languages are simple: there’s only a few things you can do. Since then, Java and … Read moreAbstractions over Threads in Java and Scala
In Java, an ExecutorService manages a pool of threads that can run tasks. Most ExecutorServices treat all tasks the same. Somebody hands it something to do, the ExecutorService parcels it out to a thread, the thread runs it. Next! A ForkJoinPool is an ExecutorService that recognizes explicit dependencies between tasks. It is designed for the … Read moreForkJoinPool: the Other ExecutorService
TL;DR – when in doubt, stick with scala.concurrent.ExecutionContext.global When you want to run some asynchronous code, choosing a thread pool isn’t any fun. Scala has your back, with its global ExecutionContext. When I try to put some code in a Future without specifying where to run it, Scala tells me what to do: scala> Future(println(“Do something slow”)):14: … Read moreScala: the global ExecutionContext makes your life easier
TL;DR: When you need an ExecutorService, the Executors class has several for you. Sometimes it doesn’t matter which you choose, and other times it matters a LOT. The above flow chart is approximate. If it’s simple parallel computation you’re doing, then a fixed pool with as many threads as CPUs works. If those computations start … Read moreChoosing an ExecutorService
Did you know that a thread can achieve deadlock with itself? It can happen in any thread pool of constrained size. Watch out for… Pool-Induced Deadlock! [1] This is easiest in a pool of size 1. Run a task in the pool, and from there, run a task in the same pool. While the outer … Read moreFun with Pool-Induced Deadlock
Testing is easier when you can see what messages are received by your actors. To do this, add logging to your real code, and then change your configuration. This post shows how to hard-code some debugging configuration for testing purposes. Step 1: put logging into your receive method, by wrapping your existing receive definition in … Read moreTesting akka: turn on debug
Lately, open source is important to me. Today, for instance: it starts with a useful library, complicated by Java threading, confused by a Scala language feature, and ends with happiness and joy because Open Source. I’m using scalaz.concurrent.Task, a monad (LINK) with at least three special powers. First, it use a Future internally, which perform … Read moreJVM Threads, ???, and Open Source
This talk from CodeMesh 2013 talks about iteratees in Scala, among other things. Watch it on InfoQ: When Code Reacts to Data (infoq.com)
In Java, there are primitive types and there are objects. Often we want to work with everything as an object, so those primitives get boxed up into object wrappers.Ruby and Scala say, “That’s silly. Let everything be an object to begin with.” That keeps parameter-passing semantics and comparison and printing operations consistent. Yesterday while writing … Read moreTrains within trains
The first useful bit of functional programming is the map method on List. It gives us a new List, which contains the results of the mapped function applied to each item in the list. We might think of it like this, mapping f over a List of a single item of type A: That’s the … Read moreFrom lists to trains to functors