djspiewak

Thread Pools

Thread pools on the JVM should usually be divided into the following three categories:

1. CPU-bound
2. Blocking IO
3. Non-blocking IO polling

Each of these categories has a different optimal configuration and usage pattern.

djspiewak

Quick Tips for Fast Code on the JVM

I was talking to a coworker recently about general techniques that almost always form the core of any effort to write very fast, down-to-the-metal hot path code on the JVM, and they pointed out that there really isn't a particularly good place to go for this information. It occurred to me that, really, I had more or less picked up all of it by word of mouth and experience, and there just aren't any good reference sources on the topic. So… here's my word of mouth.

This is by no means a comprehensive gist. It's also important to understand that the techniques that I outline in here are not 100% absolute either. Performance on the JVM is an incredibly complicated subject, and while there are rules that almost always hold true, the "almost" remains very salient. Also, for many or even most applications, there will be other techniques that I'm not mentioning which will have a greater impact. JMH, Java Flight Recorder, and a good profiler are your very best friend! Mea

lihaoyi

Provisional benchmarks of AST-free serialization puts my WIP branch of uPickle about ~40% faster than circe on my current set of ad-hoc benchmarks, if the encoders/decoders are cached (bigger numbers is better)

playJson Read 2761067
playJson Write 3412630
circe Read 6005895
circe Write 5205007
upickleDefault Read 4543628
upickleDefault Write 3814459
upickleLegacy Read 8393416

sir-wabbit

Scalanomicon

the most asInstanceOf per line in Scalazzi-compliant code (efficient Nat and Fin types)

nonEmpty without boolean blindness and older version and another one

Dank Cord

Scala having too many features resulting in unsoundness

Odomontois

def fix[A](f: A => A): A = f(fix(f))

val fib = fix[Int => Int]( recur =>  n =>
        if (n <= 1) 1
        else recur(n - 1) + recur(n - 2))

gvolpe

import cats.Traverse
import cats.effect._
import cats.effect.concurrent.Semaphore
import cats.temp.par._
import cats.syntax.all._

import scala.concurrent.duration._

object Main extends IOApp {
  import ParTask._

fanf

import scalaz.nio._
import scalaz.nio.channels.{AsynchronousServerSocketChannel, AsynchronousSocketChannel}
import scalaz.zio.console._
import scalaz.zio._


object TestSocket extends App {

  override def run(args: List[String]): ZIO[Environment, Nothing, Int] = {
    theSocket.foldM(

LukaJCB

Uniting the bifunctor and monofunctor hierarchies

With the rise of so-called bifunctor IO types, such as ZIO, questions have naturally arisen of how one could leverage the cats-effect type classes to make use of this new power. So far suggestions have mostly focused on duplicating the existing hierarchy into two distinct branches, one parameterized over F[_] and another parameterized over F[_, _]. To me this is not a great situation, as now library maintainers would have to write code for both of these hierarchies or choose one and leave the other one in the dust.

Instead we should find a way to unite the two shapes under a single hierarchy. This is a draft on how to enable this unification using polymorphic function types in Dotty.

melvic-ybanez

What I Didn't Know about Functional Programming until 2020

1. Programming using a series of transformations and aggregations, something I've been doing for years, is known as programming in the map/reduce style.
2. The more abstract the type is, the greater its cardinality, and the smaller the set of operations it supports. So make use of universal quantifiers, particularly by implementing fully parametric functions. They guide you on how to implement their term-level definitions by narrowing down the number of possible implementations. In other words, the type system of Scala (or Haskell, for that matter) is not only great for capturing compile-time errors, but is also capable of leading you to the correct solution.
3. You can encode union types by combining different Scala features such as type constructors, subtyping and implicits, and by taking advantage of the Curry-Howard Isomorphism and De Morgan's Laws for neg