Orest Ivasiv halyph

Latency numbers every programmer should know

L1 cache reference ......................... 0.5 ns
Branch mispredict ............................ 5 ns
L2 cache reference ........................... 7 ns
Mutex lock/unlock ........................... 25 ns
Main memory reference ...................... 100 ns             
Compress 1K bytes with Zippy ............. 3,000 ns  =   3 µs
Send 2K bytes over 1 Gbps network ....... 20,000 ns  =  20 µs
SSD random read ........................ 150,000 ns  = 150 µs

Read 1 MB sequentially from memory ..... 250,000 ns = 250 µs

Story: Writing Scripts with Go

This is a story about how I tried to use Go for scripting. In this story, I’ll discuss the need for a Go script, how we would expect it to behave and the possible implementations; During the discussion I’ll deep dive to scripts, shells, and shebangs. Finally, we’ll discuss solutions that will make Go scripts work.

Why Go is good for scripting?

While python and bash are popular scripting languages, C, C++ and Java are not used for scripts at all, and some languages are somewhere in between.

Thread Pools

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

CPU-bound
Blocking IO
Non-blocking IO polling

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

Getting Started in Scala

This is my attempt to give Scala newcomers a quick-and-easy rundown to the prerequisite steps they need to a) try Scala, and b) get a standard project up and running on their machine. I'm not going to talk about the language at all; there are plenty of better resources a google search away. This is just focused on the prerequisite tooling and machine setup. I will not be assuming you have any background in JVM languages. So if you're coming from Python, Ruby, JavaScript, Haskell, or anywhere… I hope to present the information you need without assuming anything.

Disclaimer It has been over a decade since I was new to Scala, and when I was new to Scala, I was coming from a Java and Ruby background. This has probably caused me to unknowingly make some assumptions. Please feel free to call me out in comments/tweets!

One assumption I'm knowingly making is that you're on a Unix-like platform. Sorry, Windows users.

Getting the JVM

Applied Functional Programming with Scala - Notes

1. Mastering Functions

A function is a mapping from one set, called a domain, to another set, called the codomain. A function associates every element in the domain with exactly one element in the codomain. In Scala, both domain and codomain are types.

val square : Int => Int = x => x * x

	-- save as HaskellCheatsheet.hs
	module HaskellCheatsheet where
	-- On Windows, I sometimes have to remove the module line above
	-- in order to get GHC to compile the file as an executable instead
	-- of a library.


	-- Single line comment

	{-

	.PHONY: help

	# This is a code for automatic help generator.
	# It supports ANSI colors and categories.
	# To add new item into help output, simply add comments
	# starting with '##'. To add category, use @category.
	GREEN := $(shell tput -Txterm setaf 2)
	WHITE := $(shell tput -Txterm setaf 7)
	YELLOW := $(shell tput -Txterm setaf 3)
	RESET := $(shell tput -Txterm sgr0)


	# Go parameters
	GOCMD=go
	GOBUILD=$(GOCMD) build
	GOCLEAN=$(GOCMD) clean
	GOTEST=$(GOCMD) test
	GOGET=$(GOCMD) get
	BINARY_NAME=mybinary
	BINARY_UNIX=$(BINARY_NAME)_unix

	src=foo.lisp
	obj=$(src:.lisp=.fasl)
	bin=foo

	.SUFFIXES:

	.PHONY: eval
	eval:
	sbcl --noinform --load $(basename $(src)) --eval '(main)' --eval '(exit)' \
	2>/dev/null

	import scala.xml._

	// To convert a Maven pom.xml to build.sbt:
	// 1) Place this code into a file called PomToSbt.scala next to pom.xml
	// 2) Type scala PomtoSbt.scala > build.sbt
	// The dependencies from pom.xml will be extracted and place into a complete build.sbt file
	// Because most pom.xml files only refernence non-Scala dependencies, I did not use %%
	val lines = (XML.load("pom.xml") \\ "dependencies") \ "dependency" map { dependency =>
	val groupId = (dependency \ "groupId").text
	val artifactId = (dependency \ "artifactId").text